TION EVALUA VAILA High-Efficiency Driver with Boost Converter Fiv
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19-4935; 9/09
TION EVALUA VAILA
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
MAX6948B general-purpose input/output (GPIO) peripheral drives series string white LEDs (WLEDs), contains five general-purpose input/output (GPIO) ports drive additional LEDs. integrated 2MHz boost converter minimizes size cost external components supplies 30mA load current 28V. converter stable under load conditions from includes open-circuit detection prevent damage I2C-programmable 10-bit pulse-width modulation (PWM) signal enables 1024 levels WLED intensity. five GPIO ports function logic inputs, opendrain logic outputs, constant-current sinks combination. Ports withstand 5.5V independent MAX6948B's supply voltage. ports drive additional LEDs 30mA/port, while other three ports drive LEDs 10mA/port. MAX6948B features shutdown standby modes low-power dissipation. constant-current drivers contain programmable outputs allow staggering reduce input peak-current requirements. ports also feature ramp-up ramp-down controls. MAX6948B features single input select from four slave addresses. Programming functionality five GPIO ports identical MAX6946/MAX6947 expanders. MAX6948B available 25-bump (2.31mm 2.31mm) package cell phones, PDAs, other portable consumer electronic applications. MAX6948B operates over -40NC +105NC temperature range.
Features
Step-Up DC-DC Converter with Integrated nMOS Power Switch Built-In 10-Bit Control Improved Efficiency Discharge Path During Period Increased Battery Life Fixed 2MHz Switching Smaller Components Drives Series WLEDs ±8kV Human Body Model (HBM) Protection GPIOs Boost-Converter Output Five Open-Drain GPIOs Capable ConstantCurrent Drive with Individual 8-Bit Intensity Control 2.7V Power-Supply Operation 400kbps, 5.5V Tolerant Interface Four Slave Address Choices Input Clears Serial Interface Exits Shutdown (Reset-Run Option) Small (2.31mm 2.31mm) Package
MAX6948B
Ordering Information
PART MAX6948BGWA+ TEMP RANGE -40NC +105NC PIN-PACKAGE
+Denotes lead(Pb)-free/RoHS-compliant package.
Typical Operating Circuit
2.7V 5.0V 10µH
2.2FF PGND
0.22FF
Applications
Backlighting LCDs Cell Phones PDAs Handheld Games Portable Consumer Electronics
1.7V
MAX6948B
0.1FF COMP 47nF LEDSW
VEXT
NOTE: 0.2V/ILED 0.2V/0.03A 6.7I.
Maxim Integrated Products
pricing, delivery, ordering information, please contact Maxim Direct 1-888-629-4642, visit Maxim's website www.maxim-ic.com.
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
ABSOLUTE MAXIMUM RATINGS
.-0.3V VDD, COMP .-0.3V 0.3V) PGND .-0.3V +0.3V PGND (Note .-0.3V +30V Current into (Note .700mA OUT, LEDSW PGND (Note .-0.3V +30V P0-P4 .-0.3V RST, SDA, SCL, -0.3V (VDD 0.3V) PGND (Note 1).-0.3V +0.3V I.C. .-0.3V +0.3V Current P0-P4 .50mA Current .10mA Total Current.150mA Total PGND Current .150mA Continuous Power Dissipation +70NC) 25-Bump (derate 10.8mW/NC above +70NC) .866mW Junction-to-Ambient Thermal Resistance (BJA) (Note 25-Bump .93NC/W Operating Temperature Range (TMIN TMAX) -40NC +105NC Junction Temperature .+150NC Storage Temperature Range. -65NC +150NC Protection Human Body Model 1.5kI, 100pF) P0-P4, OUT, LEDSW, .Q8kV Other Pins .Q2kV Lead Temperature (soldering, 10s) 25-Bump (Note
Note LEDSW pins have internal clamp diode PGND. Applications that forward bias these diodes should take care exceed power dissipation limits device. Note Package thermal resistances were obtained using method described JEDEC specification JESD51-7, using single-layer board. detailed information package thermal considerations, refer Note Refer Pb-free solder reflow requirement J-STD -020, D.1.
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(Typical Application Circuit, 2.7V 5.0V, 1.7V TMIN TMAX, unless otherwise noted. Typical values 3.3V, 2.5V, +25NC.) (Note PARAMETER Operating Supply Voltage (V+) Operating Supply Voltage (VDD) Output Load External Supply Voltage Port External Supply Voltage Port Voltage (P0, Power-On-Reset Voltage SYMBOL VOUT VEXT VPORT VPOR Boost-converter output P0-P4 high impedance Constant-current Voltage rising Standby mode, boost converter off, VDD, digital inputs Standby mode, GND, fSCL 400kHz, other digital inputs +25NC TMIN TMAX CONDITIONS UNITS
Standby Current
ISTBY
Standby Current Reset (Interface Active)
+25NC
IRST
TMIN TMAX
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
ELECTRICAL CHARACTERISTICS (continued)
(Typical Application Circuit, 2.7V 5.0V, 1.7V TMIN TMAX, unless otherwise noted. Typical values 3.3V, 2.5V, +25NC.) (Note PARAMETER SYMBOL CONDITIONS port 30mA constant current; other ports digital inputs port constant current half-current setting; other ports digital inputs +25NC TMIN TMAX UNITS
MAX6948B
Change Supply Current 30mA Port
DIDD30
+25NC
Change Supply Current 10mA Port
DIDD10
TMIN TMAX
GPIO PORTS (P0-P4) Input High Voltage Input Voltage Input Leakage Current Input Capacitance 30mA Port Sink Constant Current (P0, Port register value 0x02, 3.3V, VEXT VLED 0.5V 1.5V (Note half-current setting, port register value 0x02, 3.3V, VEXT VLED 0.5V 1.5V (Note +25NC TMIN TMAX VIH1 VIL1 Port register value 0x01 Port register value 0x01 ±0.03 (0.7 VDD) (0.3 VDD)
IPORT30
+25NC
10mA Port Sink Constant Current (P2,
IPORT10
TMIN TMAX
0.17 Q0.7
Logic Output Voltage 30mA Port Sink Constant-Current Matching (P0,
VOL1
ISINK 2mA, port register value 0x00 Constant current VPORT 30mA, 3.3V, +25NC (Note VPORT 2.75V Constant current half-current VPORT setting, 3.3V, +25NC (Note current current, port register value changed from 0x01 0x02
DIPORT30
10mA Port Sink Constant-Current Matching (P2,
DIPORT10
Constant-Current Slew Time
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
ELECTRICAL CHARACTERISTICS (continued)
(Typical Application Circuit, 2.7V 5.0V, 1.7V TMIN TMAX, unless otherwise noted. Typical values 3.3V, 2.5V, +25NC.) (Note PARAMETER BOOST CONVERTER Undervoltage Lockout Threshold Undervoltage Lockout Threshold Hysteresis Continuous Output Current Operating Current Current Limit Saturation Voltage Leakage Current Leakage Current Operating Frequency Minimum Duty Cycle Maximum Duty Cycle Amplifier Transconductance Leakage Current 100mV Half-current setting, 3.3V, +25°C Feedback Output Voltage Full-current setting, 3.3V, +25°C Half-current setting Full-current setting Quick-Start Charge Current Quick-Start Time Shutdown Discharge Resistance Output Current Line Regulation Thermal Shutdown Threshold Thermal Shutdown Threshold Hysteresis Overvoltage Threshold Overvoltage Threshold VOV_HYS Hysteresis SERIAL INTERFACE (SDA, SCL, AD0, RST) Input High Voltage Input Voltage Input Leakage Current Output Voltage Input Capacitance VIH2 VIL2 IIN2 VOL2 CIN2 ISINK 0.03 RCOMP 3.0V 5.0V From enable command STOP condition output regulation, CCOMP 0.047FF (Note ILXOFF IOUTOFF fBOOST Continuous conduction mode Discontinuous conduction mode VUVLO VHYS IWLED 100% boost PWM, full-current setting, 6.67I, IWLED VFB/RB boost standby boost 3.3V, +25°C 200mA boost PWM, VOUT 28V, boost converter shutdown ±0.01 VOUT Rising rising falling 0.25 2.65 SYMBOL CONDITIONS UNITS
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
TIMING CHARACTERISTICS
(Typical Application Circuit, 2.7V 5.0V, 1.7V TMIN TMAX, unless otherwise noted. Typical values 3.3V, 2.5V, +25NC.) (Note PARAMETER Internal Boost-Converter Clock Frequency Internal GPIO Clock Frequency Serial-Clock Frequency Free Time Between STOP START Condition Hold Time (Repeated) START Condition Repeated START Condition Setup Time STOP Condition Setup Time Data Hold Time Data Setup Time Clock Period Clock High Period Rise Time Both Signals, Receiving Fall Time Both Signals, Receiving Fall Time Transmitting Pulse Width Spike Suppressed Serial Timeout Capacitive Load Each Line Pulse Width Note Note Note Note Note Note Note SYMBOL fINT_
BOOST
MAX6948B
CONDITIONS
31.25
UNITS
fINT_GPIO fSCL tBUF tHD, tSU, tSU, tHD, tSU, tLOW tHIGH tOUT (Note (Notes (Notes (Notes (Notes (Note
0.1Cb 0.1Cb 0.1Cb
parameters tested +25NC. Specifications over temperature guaranteed design. DIPORT_ specifies current matching between ports single part. Current matching defined percent error individual port from average current maximum value measured minimum value measured. found using equation DIPORT_ (IMMAVG IMEAS)/ IMMAVG where IMMAVG (IMEASMAX IMEASMIN)/2. Guaranteed design. master device must provide hold time least 300ns signal (referred signal) bridge undefined region SCL's falling edge. ISINK 6mA. total capacitance line measured between VDD. Input filters SDA, SCL, inputs suppress noise spikes less than 50ns.
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
Typical Operating Characteristics
3.3V, 2.5V, +25NC, unless otherwise noted.)
EFFICIENCY
FULL-CURRENT LEDs FULL-CURRENT LEDs
MAX6948B toc01
SWITCHING WAVEFORMS
MAX6948B toc02
EFFICIENCY
SOFT-START VOUT (10/1024)
500mV/div
MAX6948B toc03
500mV/div 5V/div VOUT
FULL-CURRENT LEDs
HALF-CURRENT LEDs
HALF-CURRENT LEDs
HALF-CURRENT LEDs 2.70 3.21 3.72 4.23 4.74 5.25
10V/div
5V/div VOUT
SOFT-START VOUT (512/1024)
500mV/div
MAX6948B toc04
SOFT-START VOUT (1024/1024)
500mV/div
MAX6948B toc05
SHUTDOWN RESPONSE (V+, VOUT)
MAX6948B toc06
500mV/div
5V/div VOUT
5V/div VOUT
5V/div VOUT
IWLED 30mA OUTPUT CURRENT
MAX6948B toc07
STANDBY CURRENT IRST
MAX6948B toc08
STANDBY CURRENT (µA)
IWLED (mA)
FULL-CURRENT LEDs
+25NC
STANDBY CURRENT (mA)
+105NC
+25NC, +85NC, +105NC
-40NC
-40NC
+85NC
HALF-CURRENT LEDs 2.70 3.16 3.62 4.08 4.54 5.00
2.70 3.16 3.62 4.08 4.54 5.00
2.70 3.16 3.62 4.08 4.54 5.00
MAX6948B toc09
STANDBY CURRENT ISTBY
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
Typical Operating Characteristics (continued)
3.3V, 2.5V, +25NC, unless otherwise noted.)
SUPPLY CURRENT (BOOST PWM, FULL CURRENT HALF CURRENT)
MAX6948B toc10
MAX6948B
SUPPLY CURRENT (BOOST PWM, FULL CURRENT HALF CURRENT)
MAX6948B toc11
SUPPLY CURRENT (BOOST PWM, FULL CURRENT HALF CURRENT)
SUPPLY CURRENT (mA) -40NC, +25NC, +85NC, +105NC
MAX6948B toc12
-40NC, +25NC, +85NC, +105NC SUPPLY CURRENT (mA) 2.70 3.16 3.62 4.08 4.54
SUPPLY CURRENT (mA) -40NC, +25NC, +85NC, +105NC
5.00
2.70
3.16
3.62
4.08
4.54
5.00
2.70
3.16
3.62
4.08
4.54
5.00
DELTA SUPPLY CURRENT (DIFFERENCE CURRENT FROM PORT
MAX6948B toc13
DELTA SUPPLY CURRENT (DIFFERENCE CURRENT FROM PORT
MAX6948B toc14
OUTPUT SINKING CURRENT VPORT
FULL-CURRENT
MAX6948B toc15
5.70 DELTA SUPPLY CURRENT (mA) 5.65 5.60 5.55 5.50 5.45 5.40 5.35 5.30 2.70 3.16 3.62 4.08 4.54 +25NC, +85NC, +105NC -40NC
5.70 DELTA SUPPLY CURRENT (mA) 5.65 5.60 5.55 5.50 5.45 5.40 5.35 5.30 +25NC, +85NC, +105NC -40NC
OUTPUT SINKING CURRENT (mA)
HALF-CURRENT FULL-CURRENT
HALF-CURRENT
5.00
2.70
3.16
3.62
4.08
4.54
5.00
VPORT
OUTPUT SINKING CURRENT VPORT
MAX6948B toc16
STAGGER PORT WAVEFORMS TIME (50% PWM)
MAX6948B toc17
OUTPUT SINKING CURRENT (mA)
FULL-CURRENT
HALF-CURRENT FULL-CURRENT
BOOST
HALF-CURRENT
1ms/div
VPORT
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
Configuration
VIEW (BUMP BOTTOM)
MAX6948B N.C. LEDSW
I.C. PGND
COMP PGND
(2.31mm 2.31mm)
Description
NAME N.C. I.C. COMP PGND LEDSW Active-Low Reset Input I2C-Compatible, Serial-Clock Input I2C-Compatible, Serial-Data Boost-Converter Supply Voltage Positive Supply Voltage. Bypass with 2.2FF higher value ceramic capacitor. GPIO Port. Open-drain I/O. configured 30mA (max) constant sink current output. Logic Supply Voltage. Bypass with 0.1FF higher value ceramic capacitor. Address Input. selects four device slave addresses (Table 13). GPIO Port. Open-drain I/O. configured 10mA (max) constant sink current output. Ground. Connect PGND. Connection. Internally connected. Internally Connected. Connect I.C. normal operation. Compensation Terminal Boost Converter. capacitor from COMP PGND determines boost-converter stability. GPIO Port. Open-drain I/O. configured 10mA maximum constant sink current output. Load Current-Sense Voltage Feedback Boost Converter. resistor between PGND sets maximum load current. Power Ground. Connect PGND GND. GPIO Port. Open-drain I/O. configured 10mA (max) constant sink current output. Output Voltage Sense Input Boost Converter High-Voltage, Constant-Current Input. Connect LEDSW cathode-end WLED string. Inductor Switch Node FUNCTION GPIO Port. Open-drain I/O. configured 30mA (max) constant sink current output.
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
Functional Block Diagram
MAX6948B
MAX6948B
GATE DRIVE
n-CHANNEL MOSFET
PGND PGND
COMP UVLO THERMAL SHUTDOWN LEDSW
n-CHANNEL MOSFET
125kHz, 31.25kHz OSCILLATOR BANDGAP REFERENCE CURRENT
INTERFACE CONTROL REGISTERS GPIO LOGIC
ENABLE GPIO ENABLE GPIO INPUT
PORT GPIO CONSTANTCURRENT DRIVE
Detailed Description
MAX6948B general-purpose input/output (GPIO) peripheral with integrated boost converter provides boost converter capable driving WLEDs five ports capable driving LEDs powered from alternate power supply such battery. integrated 2MHz boost converter minimizes size cost external components supplies 30mA load current 28V. feedback input error amplifier typical point 0.1V minimize power dissipation. External compensation keeps converter stable under load conditions from 28V. MAX6948B includes overvoltage open-circuit detection prevent damage I2C-programmable 10-bit signal enables 1024 levels WLED intensity. During off-time, internal switch LEDSW disconnects series WLEDs. This limits off-time leakage current minimum, limited only switch internal MAX6948B. Consequently, boost output voltage
remains almost constant during on-/off-time periods. This approach provides advantages minimal WLED color change sharp WLED off, more power efficiency minimal leakage. five GPIO ports function logic inputs, opendrain logic outputs, constant-current sinks combination. Ports withstand 5.5V independent MAX6948B's supply voltage. ports drive additional LEDs 30mA, while other three ports drive LEDs 10mA/port. MAX6948B features shutdown standby modes low-power dissipation. constant-current drivers contain programmable outputs allow staggering reduce input peak current requirements. ports also feature ramp-up ramp-down controls. MAX6948B features single input select from four slave addresses. Programming functionality five GPIO ports identical MAX6946/MAX6947 expanders.
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
MAX6948B contains internal registers (Table Registers 0x00 0x15 control ports P0-P4 remain compatible with MAX6946/MAX6947 port expanders.
Register Description
Register 0x20 0x21 duty cycle integrated boost converter. Register 0x22 conveys boost-converter status.
Table Register Address Autoincrement Address
ADDRESS CODE (hex) 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A AUTO-INCREMENT ADDRESS (hex) 0x01 0x02 0x03 0x04 0x10 0x10 READ/ WRITE REGISTER FUNCTION Reserved Reserved Reserved Reserved Reserved Group control (P0-P4) Group control (P0, Group control (P2, Reserved Port input Reserved Configuration Ramp-down Ramp-up Output current Reserved Global current Boost (MSB) Boost (LSB) Boost status DESCRIPTION Port control settings Port control settings Port control settings Port control settings Port control settings Write: Simultaneously sets settings ports P0-P4 Read: Reads contents address 0x00 Write: Simultaneously sets settings ports Read: Reads contents address 0x00 Write: Simultaneously sets settings ports Read: Reads contents address 0x00 Reads GPIO input values Half-/full-boost current, reset options, stagger, start/stop status, reset run, shutdown setting Port ramp-down hold-off settings Port ramp-up setting Port half-/full-current settings Port maximum current setting Boost circuit setting (MSB) Boost circuit setting (LSB) Boost circuit status standby setting
0x0B
0x10
0x0C 0x0D 0x0E 0x0F 0x10 0x11 0x12 0x13 0x14 0x15 0x20 0x21 0x22
0x10 0x10 0x0E 0x11 0x12 0x13 0x14 0x10 0x21
Read only
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
configuration register select phasing between outputs, monitor fade status, enable hardware startup from shutdown, select shutdown mode (Table
Configuration Register Format (0x10)
Initial Power-Up
power-up, control registers powerup values MAX6948B shutdown mode (Table
MAX6948B
Table Configuration Register Format (0x10)
REGISTER DESCRIPTION Half-/full-boost current Reset/POR option stagger Hold-off status Ramp-down (fade-off) status Ramp-up status Reset-run enable VALUE FUNCTION Half-boost current Full-boost current does change register data resets registers values outputs phase outputs staggered Device hold-off Device hold-off Device fade-off Device fade-off Device ramp-up Device ramp-up Reset disabled Reset enabled Shutdown mode mode DEFAULT VALUE Read only Read only Read only
Table Power-On Reset (POR) Values
ADDRESS CODE (hex) 0x00 0x01 0x02 0x03 0x04 0x10 0x11 0x12 0x13 0x15 0x20 0x21 0x22 READ/ WRITE POWER-UP VALUE (hex) 0xFF 0xFF 0xFF 0xFF 0xFF 0x00 0x00 0x00 0x03 0x07 0x00 0x00 0x01 REGISTER FUNCTION Configuration Ramp-down Ramp-up Output current Global current Boost (MSB) Boost (LSB) Boost status DESCRIPTION Port high impedance Port high impedance Port high impedance Port high impedance Port high impedance Shutdown mode (reset disabled) Port ramp-down hold-off disabled Port ramp-up disabled full current; half current Maximum output current Zero duty cycle Zero duty cycle Boost circuit standby mode
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
Boost Converter
MAX6948B boost converter 10-bit operation using internal 125kHz clock. This yields period 1024/125k 8.192ms. operation allows user adjust intensity lower average current enabling disabling boost converter selectable rate. This rate using boost-converter output registers (Tables duty cycle ranges from 0/1024 intensity off) 1023/1024 (full intensity). Eight bits, which include MSB,
Boost-Converter Output
single register (0x20) allow single write majority intensity level minimize visible flicker during intensity changes. register (0x21) allows very fine adjustments intensity. MAX6948B checks boost converter indicates status boost-converter status register (Table Faults indicated this register include thermal shutdown, overvoltage, current limit. boost converter goes into standby mode whenever boost standby (D0)
Boost-Converter Status Register
Table Boost-Converter Output (MSB) Register Format (0x20)
REGISTER Don't care. DESCRIPTION VALUE FUNCTION Boost-converter output (MSB) Boost-converter output Boost-converter output Boost-converter output Boost-converter output Boost-converter output Boost-converter output Boost-converter output DEFAULT VALUE
Table Boost-Converter Output (LSB) Register Format (0x21)
REGISTER D7-D2 DESCRIPTION Reserved VALUE 000000 Boost-converter output Boost-converter output (LSB) FUNCTION DEFAULT VALUE 000000
Table Boost-Converter Status Register Format (0x22)
REGISTER DESCRIPTION Reserved Schottky open Current limit VALUE Thermal shutdown Schottky diode present Schottky diode open Normal output current Converter output current exceeded current limit Normal operation Device temperature exceeded thermal shutdown threshold Normal operation VOUT exceeded overvoltage limit Boost converter operating according register configuration register Boost converter standby mode Read only FUNCTION DEFAULT VALUE Read only Read only
Overvoltage
Read only
Boost standby
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
boost converter shuts down when configuration register (0x10) when boostconverter status register (0x22) both boost output registers' (0x20, 0x21) values zero, boost converter remains low-current state (standby). Undervoltage Lockout (UVLO) Undervoltage lockout (UVLO) disables boost converter when below 2.4V (max). This resets configuration register puts part into shutdown mode (0x10). Quick Start MAX6948B quick starts charging CCOMP with current source. During this time, internal MOSFET switching minimum duty cycle. Once VCOMP rises above 0.2V, duty cycle increases until output voltage reaches desired regulation level. shutdown mode, COMP pulled with 20kI internal resistor. Overvoltage Protection voltage output terminal rises above 28.5V (min), converter into standby mode. This protects converter from excessive voltage event open-circuit condition. detect boost converter exceeded overvoltage limit, read boost-converter status register (0x22). Once output voltage dropped below overvoltage threshold, read-only (D1) goes zero. boost converter leaves standby mode normal operation resumes. Reading register causes reset. fault still active, will again.
Boost-Converter Shutdown/Standby Modes
Thermal Shutdown Thermal shutdown limits total power dissipation MAX6948B. When junction temperature exceeds 151NC (typ), boost converter ports P0-P4 turn off, allowing part cool. thermal shutdown (D2) boost configuration status register (0x22) high. boost-converter status register (0x22) configuration register (0x10) (reset), device shutdown mode. MAX6948B turns begins quick-start after junction temperature cools 10NC. Reading this register causes reset. fault still active, will again. Current Limit MAX6948B current-limit function monitors inductor current when internal switch node device compares inductor current fixed threshold. When current exceeds threshold, boost-converter status register asserts switch shuts that cycle. Reading this register causes reset. fault still active, will again. boost current, through serial output LEDs, half full scale setting voltage. voltage through configuration register (0x10) (Table voltage settings 100mV 200mV half- full-current mode operation, respectively.
MAX6948B
Boost-Converter Current Settings
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
Ports (P0-P4)
MAX6948B contains five ports (P0-P4). Configure five ports logic inputs, open-drain logic outputs, constant-current sinks combination. Table provides detailed description individual port configuration registers. registers 0x00 0x04 individually assign each port (see Intensity Control Phasing section). registers 0x0A, 0x0B, 0x0C assign same port setting multiple ports (Table When powered off, ports remain high impedance. Figure shows port structure MAX6948B. ports P0-P4 default high impedance power-up, prevent connected ports from drawing current. Ports used inputs load their source signals.
Table Port Registers Format (0x00 0x04, 0x0A, 0x0B, 0x0C)
REGISTER DESCRIPTION Port logic-low. Port still active shutdown mode. Port logic-high. this mode when using GPIO input. Port still active when shutdown mode. Port static constant-current sink. Port high impedance when shutdown mode. Port constant-current sink with 3/256 duty cycle. Port high impedance when shutdown mode. Port constant-current sink with 4/256 duty cycle. Port high impedance when shutdown mode. Port constant-current sink with 5/256 duty cycle. Port high impedance when shutdown mode. REGISTER DATA
Port constant-current sink with 254/256 duty cycle. Port high impedance when shutdown mode. Power-up default setting (port high impedance)
PORT
POSITION 0x00 0x01 POSITION 0x02 0xFF ENABLE 0x00 CLOSE SWITCH: 0x02 0xFE 8-BIT LATCH OUTPUT PORT REGISTER 1-BIT LATCH OUTPUT-CURRENT REGISTER 3-BIT LATCH GLOBAL-CURRENT REGISTER READ PORT COMMAND GENERATOR ENABLE CURRENT 4-BIT
TO/FROM SERIAL INTERFACE
n-CHANNEL MOSFET
Figure Simplified Schematic Ports
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
global-current register sets full (maximum) constant-current sink amount ports configured output (Table Power-up sets global current maximum value. each output port's individual constant-current sink either half scale full scale global current. output-current registers individual currents
Ports Configured Outputs
(Table default, start full current, while half current. each output current individually best suit maximum operating current load, adjust needed double effective intensity control range each output. maximum individual current selection 15mA (half) 30mA (full) ports (half) 10mA (full) ports
MAX6948B
Table Global-Current Register Format (0x15)
REGISTER DATA REGISTER DESCRIPTION 3.75mA full-current value (P0, 1.25mA full-current value (P2, 7.5mA full-current value (P0, 2.5mA full-current value (P2, 11.25mA full-current value (P0, 3.75mA full-current value (P2, 15mA full-current value (P0, full-current value (P2, 18.75mA full-current value (P0, 6.25mA full-current value (P2, 22.5mA full-current value (P0, 7.5mA full-current value (P2, 26.25mA full-current value (P0, 8.75mA full-current value (P2, 30mA full-current value (P0, 10mA full-current value (P2, Power-up default Don't care. RESERVED GLOBAL CURRENT
Table Output-Current Register Format (0x13)
REGISTER DESCRIPTION Reserved VALUE Port half current Port full current Port half current Port full current Port half current Port full current Port half current Port full current Port half current Port full current FUNCTION DEFAULT VALUE
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
MAX6948B uses internal 31.25kHz oscillator generate timing intensity control. period comprises cycles nominal 31.25kHz clock (Figure Each port have individual duty cycle between 3/256 254/256. Table port register settings. Configure timing setting stagger configuration register (Table either with output staggering without. stagger cause outputs using switch same time using timing shown Figure outputs, therefore, draw load current exact same time same setting. This means that example, outputs
Intensity Control Phasing
0x80 (128/256 duty cycle), current draw would zero (all loads off) half time, full (all loads other half. stagger stagger timing five port outputs integrated boost-converter output, distributing port output switching points across period (Figure Staggering reduces di/dt output-switching transient supply reduces peak/mean current requirement. Change stagger-setting during shutdown. Changing stagger during normal operation cause transient flicker PWM-controlled because fundamental timing changes.
OUTPUT REGISTER VALUE 0x00 7.8125ms NOMINAL PERIOD OUTPUT STATIC-LOW LOGIC DRIVE WITH INPUT BUFFER ENABLED (GPI) HIGH-Z HIGH-Z 0x01 0x02 OUTPUT STATIC-HIGH LOGIC DRIVE WITH INPUT BUFFER ENABLED (GPI) OUTPUT STATIC-LOW CONSTANT CURRENT WITH INPUT BUFFER DISABLED (STATIC DRIVE HIGH-Z HIGH-Z 0x03 OUTPUT 3/256 DUTY CONSTANT CURRENT WITH INPUT BUFFER DISABLED (PWM DRIVE) HIGH-Z 0x04 OUTPUT 4/256 DUTY CONSTANT CURRENT WITH INPUT BUFFER DISABLED (PWM DRIVE)
0xFC
OUTPUT 252/256 DUTY CONSTANT CURRENT WITH INPUT BUFFER DISABLED (PWM DRIVE)
HIGH-Z
0xFD
OUTPUT 253/256 DUTY CONSTANT CURRENT WITH INPUT BUFFER DISABLED (PWM DRIVE)
HIGH-Z
0xFE
OUTPUT 254/256 DUTY CONSTANT CURRENT WITH INPUT BUFFER DISABLED (PWM DRIVE)
HIGH-Z HIGH-Z
0xFF
OUTPUT STATIC HIGH IMPEDANCE WITH INPUT BUFFER DISABLED (STATIC DRIVE OFF)
Figure Static Constant-Current Waveforms
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
8.192ms NOMINAL PORT PERIOD NEXT PORT PERIOD NEXT PORT PERIOD
PORT PORTS BOOST PHASE PORT PORTS BOOST PHASE PORT PORTS BOOST PHASE PORT STAGGERED PERIOD PORT STAGGERED PERIOD PORT STAGGERED PERIOD PORT STAGGERED PERIOD PORT STAGGERED PERIOD PORT STAGGERED PERIOD PORT STAGGERED PERIOD PORT STAGGERED PERIOD PORT STAGGERED PERIOD BOOST STAGGERED PERIOD BOOST STAGGERED PERIOD
Figure Staggered Port Boost Waveform
Table Input Ports Register Format (0x0E, Read Only)
REGISTER DESCRIPTION Reserved VALUE Port logic input low, input Port logic input high Port logic input low, input Port logic input high Port logic input low, input Port logic input high Port logic input low, input Port logic input high Port logic input low, input Port logic input high FUNCTION
Configure port logic input writing 0x01 port's output register (Table Reading input port register returns logic levels from ports configured logic input (Table 10). input port register returns logic appropriate position port configured logic input. input ports' registers read only. MAX6948B ignores writes input ports register. Configuring ports logic inputs outputs (all output registers value 0x00 0x01) high impedance (output register value 0xFF) puts device into standby mode. MAX6948B into standby mode lowest supply current consumption.
Ports Configured Inputs
Setting port constant-current output increases operating current (output register value between 0x02 0xFE), even load applied port. MAX6948B enables internal current mirror provide accurate constant-current sink. Enabling internal current mirror increases device's supply current. Each output contains gated mirror, which activates only when required. mode, current mirror turns only duration output's on-time. This means that operating current varies constant-current outputs turned through serial interface, well intensity control.
Standby Mode Operating Current
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
shutdown mode, ports configured constantcurrent outputs (output register value between 0x02 0xFE) switch become high impedance. Shutdown does affect ports configured logic inputs outputs (output registers value 0x00 0x01) (Table This means that ports used GPIOs still operational shutdown mode. MAX6948B into shutdown mode setting (D0) configuration register (0x10) (Table Exit shutdown setting high through serial interface using reset-run option (see Reset-Run Option section). Configure control MAX6948B normally through serial interface shutdown mode. registers accessible shutdown mode. Entering and/or exiting shutdown mode does change register values. Changing port from static logic-low (0x00) static logic-high (0x01) constant-current value (0x02 0xFE) shutdown mode turns that output (logic-high high impedance) like other constant-current outputs shutdown. constant-current output starts just like other constant-current outputs when exiting shutdown. Changing port from constant-current value (0x02 0xFE) static logic-low (0x00) static logic-high (0x01) shutdown causes that output value GPIO output. GPIO output unaffected just like other GPIO output when exiting shutdown. MAX6948B provides controls that allow output currents ramp down into shutdown (ramp-down) ramp again shutdown (ramp-down) (Figures Ramp-down comprises programmable hold-off delay that maintains outputs full current time before programmed ramp-down time. After holdoff delay, output currents ramp down.
Shutdown Mode
ramp-down register sets hold-off ramp-down times allows disabling hold-off ramp-down (zero delay), desired (Table 11). ramp-up register sets ramp-up time allows disabling ramp-up (zero delay), desired (Table 12). configuration register contains three status bits that identify condition MAX6948B, hold-off, ramp-down, ramp-up (Table configuration register also enables disables ramp-up. write command configuration register puts device into shutdown (using hold-off ramp-down settings ramp-down register) read command configuration register determines whether reset enabled restart, whether MAX6948B currently ramp-up rampdown mode. Reset needs used with ramp-up work properly. Ramp-up ramp-down clock timing. internal oscillator always runs during fade sequence, even none ports uses PWM. ramp-up ramp-down circuit operates 3-bit DAC. adjusts internal current reference used constant-current outputs similar manner global-current register (Table MAX6948B scales master-current reference have output constant-current settings adjust same ratio with respect each other. This means LEDs always fade same rate even with different intensity settings. boost circuit does 3-bit DAC. During ramp-down, boost circuit remains programmed output until shuts completely ramp-down period. boost circuit turns completely beginning ramp-up sequence. maximum port output current global-current register (Table also sets point during rampdown that current starts falling, point during ramp-up that current stops rising. Figure shows ramp waveforms that occur with different global-current register settings.
Ramp-Up Ramp-Down Controls
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
ZERO CURRENT RAMP-UP AFTER 1/8s 1/16s FULL CURRENT/ HALF CURRENT EXIT SHUTDOWN COMMAND 1/4s 1/2s
Figure Ramp-Up Behavior
ZERO CURRENT RAMP-DOWN ZERO HOLD-OFF DELAY BEFORE RAMP-DOWN FULL CURRENT/ HALF CURRENT ZERO CURRENT RAMP-DOWN AFTER HOLD-OFF DELAY
1/4s 1/2s 1/8s 1/16s
1/4s 1/2s 1/8s 1/16s
Figure Hold-Off Ramp-Down Behavior
Table Port Ramp-Down Register Format (0x11)
REGISTER DATA REGISTER DESCRIPTION Immediately shuts down after hold-off delay 0.0655s ramp-down from full current after hold-off delay 0.131s ramp-down from full current after hold-off delay 0.262s ramp-down from full current after hold-off delay 0.524s ramp-down from full current after hold-off delay 1.049s ramp-down from full current after hold-off delay 2.097s ramp-down from full current after hold-off delay HOLD-OFF RAMP-DOWN RESERVED
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
Table Port Ramp-Down Register Format (0x11) (continued)
REGISTER DATA REGISTER DESCRIPTION 4.164s ramp-down from full current after ramp-down delay Zero ramp-down delay before fade-off 0.0655s ramp-down delay before fade-off 0.131s ramp-down delay before fade-off 0.262s ramp-down delay before fade-off 0.524s ramp-down delay before fade-off 1.049s ramp-down delay before fade-off 2.097s ramp-down delay before fade-off 4.164s ramp-down delay before fade-off Power-up default Don't care. HOLD-OFF RAMP-DOWN RESERVED
Table Port Ramp-Up Register Format (0x12)
REGISTER DATA REGISTER DESCRIPTION Immediately starts 0.0655s ramp-up full current 0.131s ramp-up full current 0.262s ramp-up full current 0.524s ramp-up full current 1.049s ramp-up full current 2.097s ramp-up full current 4.164s ramp-up full current Power-up default Don't care. RESERVED RAMP-UP
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
Input
active-low input operates reset that voids current transaction involving MAX6948B, forcing device into STOP condition. configuration register (Table configure reset internal registers power-onreset state (Table input overvoltage tolerant 5.5V. MAX6948B ignores activity while remains low. device uses this feature minimize supply current power-critical applications effectively disconnecting MAX6948B from during idle periods. also operates multiplexer, allowing multiple devices same slave address. Drive only MAX6948B input high time multiplexer. MAX6948B features reset-run option. Taking input high brings driver shutdown addition normal function enabling device's interface. MAX6948B features reset-run option enabling bring driver shutdown, addition normal function enabling MAX6948B's interface. This provides alternative method bringing driver shutdown writing configuration register through serial interface. reset-run timing uses internal clock. After enabling reset-run option, MAX6948B uses rising edge RST, followed interface activity MAX6948B periods GPIO clock (32kHz typ) trigger reset-run option. this timeout period elapses without MAX6948B acknowledging transaction, device sets (D0) configuration register brings itself shutdown, activating programmed ramp-up. pulses high less than this timeout period trigger reset run, MAX6948B ignores pulse continues wait suitable trigger. Cancel reset-run trigger transmitting communication MAX6948B before timeout period elapses. trigger cancels when MAX6948B acknowledges transaction requires sending least MAX6948B's slave address. minimum timeout period equal 4ms. minimum clock speed that guarantees successful start data bits bits total) within minimum timeout period 9/4ms equal 2.25kHz. Canceling resetrun trigger clears reset-run (D1) configuration register, disabling reset run. (D0) configuration register remains cleared driver remains shutdown.
MAX6948B
Reset-Run Option
CURRENT CURRENT PORT CURRENT FULL 10mA 30mA
CURRENT CURRENT 10mA 30mA 8.75mA 26.25mA 7.5mA 22.5mA
GLOBAL CURRENT 0x07 GLOBAL CURRENT 0x06 GLOBAL CURRENT 0x05 GLOBAL CURRENT 0x04 GLOBAL CURRENT 0x03 GLOBAL CURRENT 0x02 GLOBAL CURRENT 0x01 GLOBAL CURRENT 0x00
6.25mA 18.75mA
15mA PORT CURRENT HALF
15mA
3.75mA 11.25mA 2.5mA 1.25mA
FULL CURRENT CURRENT CURRENT CURRENT CURRENT CURRENT CURRENT RAMP-DOWN CURRENT ZERO CURRENT
7.5mA 3.75mA
RAMP-UP
ZERO FULL CURRENT CURRENT CURRENT CURRENT CURRENT CURRENT CURRENT CURRENT CURRENT
RAMP-UP
RAMP-DOWN
Figure Output Fade (Global Current 0x07)
Figure Global Current Modifies Ramp-Down Behavior
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
Serial Interface
Figure shows 2-wire serial-interface timing details. MAX6948B operates slave that sends receives data through I2C-compatible 2-wire interface. interface uses serial-data line (SDA) serial-clock line (SCL) achieve bidirectional communication between master(s) slave(s). master (typically microcontroller) initiates data transfers from MAX6948B generates clock that synchronizes data transfer. MAX6948B's line operates both input open-drain output. pullup resistor, typically 4.7kI, required SDA. MAX6948B's line operates only input. pullup resistor required there multiple masters 2-wire interface, master single-master system open-drain output.
Serial Addressing
Each transmission consists START condition (Figure sent master, followed MAX6948B 7-bit slave address plus bit, register address byte, more data bytes, finally STOP condition. Both remain high when interface busy. master signals beginning transmission with START condition transitioning from high while high. When master finished communicating with slave, issues STOP condition transitioning from high while high. then free another transmission. data transferred during each clock pulse (Figure 10). data must remain stable while high.
START STOP Conditions
Transfer
tSU, tHD, tHIGH tSU, tBUF tHD, tSU,
tLOW tHD,STA
REPEATED START CONDITION STOP CONDITION START CONDITION
START CONDITION
Figure 2-Wire Serial-Interface Timing Details
STOP CONDITION
DATA LINE STABLE; CHANGE DATA DATA VALID ALLOWED
START CONDITION
Figure START STOP Conditions
Figure Transfer
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
acknowledge clocked (Figure 11), which recipient uses handshake receipt each byte data. Thus, each byte transferred effectively requires bits. master generates clock pulse, recipient pulls down during acknowledge clock pulse, therefore line stable-low during high period clock pulse. When master transmitting MAX6948B, MAX6948B generates acknowledge because MAX6948B recipient. When MAX6948B transmitting master, master generates acknowledge because master recipient.
Acknowledge
MAX6948B 7-bit long slave address (Figure 12). following 7-bit slave address bit, which write command high read command.
Slave Addresses
MAX6948B
START CONDITION TRANSMITTER RECEIVER
CLOCK PULSE ACKNOWLEDGE
Five bits (A6, A1), MAX6948B slave address always respectively. Slave address bits correspond, matrix Table states device address input AD0, corresponds bit. input connected four signals: GND, VDD, SDA, SCL, giving four possible slave-address pairs, allowing four MAX6948B devices share bus. Because dynamic signals, care must taken ensure that transitions sooner than signals SCL. MAX6948B monitors continuously, waiting START condition followed slave address. When MAX6948B recognizes slave address, acknowledges then ready continued communication.
Figure Acknowledge
Figure Slave Address
Table MAX6948B Slave Address
DEVICE ADDRESS
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
write MAX6948B comprises transmission slave address with zero, followed least byte information. first byte information command byte. command byte determines which register MAX6948B written next byte, received. STOP condition detected after command byte received, MAX6948B takes further action (Figure beyond storing command byte. bytes received after command byte data bytes. first data byte goes into internal register MAX6948B selected command byte (Figure 14). multiple data bytes transmitted before STOP condition detected, these bytes generally stored subsequent MAX6948B internal registers because
Message Format Writing Driver
command-byte address generally autoincrements (Table MAX6948B read using MAX6948B's internally stored command byte address pointer, same stored command byte used address pointer write. pointer generally autoincrements after each data byte read using same rules write (Table Thus, read initiated first configuring MAX6948B's command byte performing write (Figure 13). master read consecutive bytes from MAX6948B, with first data byte being read from register addressed initialized command byte. When performing read-after-write verification, remember reset command byte's address because stored command-byte address generally autoincremented after write (Figure Table
Message Format Reading
COMMAND BYTE STORED RECEIPT STOP CONDITION ACKNOWLEDGE FROM MAX6948B SLAVE ADDRESS
COMMAND BYTE ACKNOWLEDGE FROM MAX6948B
Figure Command Byte Received
ACKNOWLEDGE FROM MAX6948B COMMAND BYTE DATA BYTE INTO MAX6948B REGISTERS ACKNOWLEDGE FROM MAX6948B SLAVE ADDRESS COMMAND BYTE
ACKNOWLEDGE FROM MAX6948B
DATA BYTE BYTE AUTOINCREMENT MEMORY ADDRESS
Figure Command Single Data Byte Received
ACKNOWLEDGE FROM MAX6948B COMMAND BYTE DATA BYTE INTO MAX6948B REGISTERS ACKNOWLEDGE FROM MAX6948B SLAVE ADDRESS COMMAND BYTE DATA BYTE BYTES AUTOINCREMENT MEMORY ADDRESS ACKNOWLEDGE FROM MAX6948B
Figure Data Bytes Received
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
When MAX6948B operated 2-wire interface with multiple masters, master reading MAX6948B uses repeated start between write that sets MAX6948B's address pointer, read(s) that takes data from location(s). This because possible master take over after master MAX6948B's address pointer before master read data. master subsequently resets MAX6948B's address pointer, master read from unexpected location. Address autoincrementing allows MAX6948B configured with fewer transmissions minimizing number times command address needs sent. command address stored MAX6948B generally increments after each data byte written read (Table Autoincrement only works when doing burst read write.
Operation with Multiple Masters
Otherwise, small values discontinuous conduction operation, IPEAK 860mA (typ). Table provides list recommended inductors. typical input capacitor value 2.2FF typical output capacitor 0.22FF. Higher value capacitors reduce input output ripple, expense size higher cost. best operation, ceramic dielectric capacitors. Generally, ceramic capacitors with smaller case sizes have poorer bias characteristics than larger case sizes certain capacitance value. Select capacitor that yields best trade-off between case size bias characteristics.
MAX6948B
Capacitor Selection
Command Address Autoincrementing
Applications Information
MAX6948B optimized 10FH inductor, although larger smaller inductors used. Using smaller inductor results discontinuous-current-mode operation over larger range output power, whereas larger inductor results continuous conduction most operating range. prevent core saturation, ensure that inductor's saturation current rating exceeds peak inductor current application. larger inductor values continuous conduction operation, calculate worstcase peak inductor current with following formula: IPEAK VOUT IOUT(MAX) VIN(MAX) VIN(MIN) 0.5µs
Inductor Selection
high switching frequency MAX6948B demands high-speed rectification diode optimum efficiency. Schottky diode recommended fast recovery time forward-voltage drop. Ensure that diode's average peak current rating exceeds average output current peak inductor current. addition, diode's reverse-breakdown voltage must exceed VOUT. step-up converter uses external compensation network from COMP ensure stability. WLEDs, choose CCOMP COUT/10 optimal transient response. MAX6948B supply (VDD) accepts voltages from 1.7V boost-converter input (V+). determines interface (SDA, SCL), slaveaddress select input (AD0), reset input (RST) logic voltages. five ports P0-P4 overvoltage protected 5.5V independent This allows MAX6948B operate from supply voltage, such 3.3V, while driving some five I/Os inputs from different logic level, such
Diode Selection
Compensation Network Selection
Port Input Interface Logic Voltages
Table Recommended Inductors
VENDOR PART NUMBER TOKO 1069AS-220M TOKO 1098AS-100M (µH) ISAT 0.47 0.75 CASE SIZE (mm)
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
MAX6948B correctly regulates constant-current outputs, provided there minimum voltage drop across port output. This port output voltage difference between load (typically LED) supply load voltage drop (LED forward voltage). supply drops that minimum port output voltage maintained, driver output stages brownout load current falls. minimum port voltage approximately 0.25V 15mA sink current approximately 0.3V 30mA sink current (ports 0.39V sink current approximately 0.4V 10mA sink current (ports P4). Operating LEDs directly from battery supply cause brownouts. example, supply voltage single rechargeable lithium-ion battery with maximum terminal voltage 4.2V charge, 3.4V 3.7V most time, down when discharged. this scenario, supply falls significantly below brownout point when battery end-of-life voltage (3V). Figure shows typical current sink King Bright AA3020ARWC/A white supply voltage varied from 2.5V 5.5V. currents shown ports programmed 10mA 30mA constant current, swept over 2.5V 5.5V supply voltage range. seen that forward voltage falls with current, allowing current fall gracefully, abruptly, brownout. practice, current drops 11mA 12.5mA supply voltage; this
Driving LEDs into Brownout
acceptable performance end-of-life many backlight applications. open-drain output architecture allows ports level translate outputs higher lower voltages than MAX6948B supply (VDD). external pullup resistor output convert high-impedance, logic-high condition positive voltage level. Connect resistor voltage 5.5V. When using pullup constant-current output, select resistor value sink more than hundred logic-low condition. This ensures that current-sink output saturates close GND. interfacing CMOS inputs, pullup resistor value 220kI good starting point. lower resistance improve noise immunity applications where power consumption less critical, where faster rise time needed given capacitive load. stagger option, when selected, applies ports configured constant-current outputs. cycles separated evenly spaced start positions (Figure Optimize phasing when using some ports constant-current outputs allocating ports with most appropriate start positions. general, choose ports that spread start positions evenly possible. This optimally spreads current demand from ports' load supply.
Output-Level Translation
Using Stagger with Fewer Ports
Generating Shutdown/Run Output
VLED VLED SUPPLY
ILED (mA) VLED VLED SUPPLY
ILED VLED SUPPLY
VLED SUPPLY
Figure Brownout
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports
MAX6948B port automatically generate shutdown/run output. shutdown/run output active-low when MAX6948B mode, hold-off, ramp-down, ramp-up, goes high automatically when device finally enters shutdown after rampdown. Programming port's output register value 0x02 puts output into static constant-current mode (Table Program port's output current half current (Table minimize operating current. Connect 220kI pullup resistor this port. mode, output port goes low, approaching port's static constant current saturates trying sink higher current than 220kI pullup resistor source. shutdown mode, output goes high impedance together with other constant-current outputs. This output remains during ramp-up ramp-down sequences because current drawn 220kI pullup resistor much smaller than available output constant current, even lowest fade-current step. MAX6948B drive loads needing more than 30mA, like high-current white LEDs, paralleling outputs. example, consider white that requires 90mA. Drive this using ports P0-P4 connected parallel (shorted together). Configure five ports full current 30mA 10mA) meet 90mA requirement. Control five ports simultaneously with write access using register 0x0C (Table Note that because output ports current limiting, they need switch simultaneously ensure safe current sharing. operates with 2.7V 5.5V power-supply voltage. Bypass with 2.2FF higher ceramic capacitor close possible device. operates with 1.7V power-supply voltage. Bypass with 0.1FF higher ceramic capacitor close possible device. fast switching waveforms high-current paths, careful layout required. Minimize trace lengths between inductor, diode, input capacitor, output capacitor. Minimize trace lengths between input output capacitors MAX6948B terminal, place input output capacitor grounds close together possible. separate power-ground analog-ground copper areas, connect them together outputcapacitor ground. Keep traces short, direct, wide. Keep noisy traces, such node trace, away from sensitive analog circuitry. improved thermal performance, maximize copper area PGND traces. Refer MAX6948B data sheet example layout.
MAX6948B
Power-Supply Considerations
Layout Considerations
Driving Load Currents Higher than 30mA
High-Efficiency Driver with Boost Converter Five Constant-Current GPIO Ports MAX6948B
Chip Information
PROCESS: BiCMOS
Package Information
latest package outline information land patterns, www.maxim-ic.com/packages. Note that "+", "#", package code indicates RoHS status only. Package drawings show different suffix character, drawing pertains package regardless RoHS status.
PACKAGE TYPE PACKAGE CODE B9-7 W252D2+1 DOCUMENT
21-0453
Maxim cannot assume responsibility circuitry other than circuitry entirely embodied Maxim product. circuit patent licenses implied. Maxim reserves right change circuitry specifications without notice time.
Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600 2009 Maxim Integrated Products Maxim registered trademark Maxim Integrated Products, Inc.
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