LT3498 20mA Driver OLED Driver with Integrated Schottky DESCRIPTION
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LT3498 20mA Driver OLED Driver with Integrated Schottky DESCRIPTION
LT®3498 dual output boost converter featuring 2.3MHz Driver OLED Driver. includes internal power switch Schottky diode each driver. Both converters independently shut down modulated. This highly integrated power solution ideal dual display electronic devices. 2.3MHz step-up converter designed drive white LEDs series from Li-Ion cell. device features unique high side current sense that enables part function "one-wire" current source-one side string returned ground anywhere. Traditional drivers grounded resistor sense current, requiring 2-wire connection string. OLED driver noise boost converter that features novel control technique.* converter controls power delivery varying both peak inductor current switch time. This technique results output voltage ripple, well high efficiency over wide load range. time switch allowed exceed fixed level, guaranteeing switching frequency that stays above audio band.
Lare registered trademarks Linear Technology Corporation. other trademarks property their respective owners. *Patent Pending
Dual Output Boost Dual Display Devices Drives White LEDs OLED/LCD Bias Internal Power Switches Schottky Diodes Independent Dimming Shutdown 200mV High Side Sense Driver Allows "One-Wire Current Source" Wide Input Voltage Range: 2.5V Wide Output Voltage Range: 2.3MHz Frequency Driver OLED Driver Non-Audible Over Entire Load Range Open Protection (27V Maximum CAP1 Pin) OLED Output Disconnect Available 12-Pin Package Tall Solution Height
APPLICATIONS
Cellular Phones PDAs, Handheld Computers Digital Cameras Players Receivers
TYPICAL APPLICATION
Li-Ion White LEDs OLED/LCD Bias
4.7µF 0.47µF
OLED Efficiency
EFFICIENCY
24mA
3.6V VOUT2 LOAD FROM VOUT2
POWER LOSS (mW)
15µH CAP1
15µH CAP2 VOUT2
POWER LOSS FROM VOUT2 CURRENT (mA)
10µF LT3498 LED1 20mA CTRL1 SHUTDOWN DIMMING CONTROL
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GND1
GND2
CTRL2 SHUTDOWN CONTROL
2.21M
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LT3498 ABSOLUTE MAXIMUM RATINGS
(Notes
PACKAGE/ORDER INFORMATION
VIEW LED1 CTRL1 GND1 GND2 CTRL2 CAP1 CAP2 VOUT2
Input Voltage (VIN) .12V CTRL1 CTRL2 Voltage .12V Voltage .2.5V VOUT2 Voltage .32V Voltage .32V CAP1 CAP2 Voltage .32V LED1 Voltage .32V Operating Junction Temperature Range .-40°C 85°C Maximum Junction Temperature 125°C Storage Temperature Range.-65°C 150°C
PACKAGE 12-LEAD (3mm 2mm) PLASTIC TJMAX 125°C, 160°C/W EXPOSED (PIN GND, MUST SOLDERED
ORDER PART NUMBER LT3498EDDB
PART MARKING LCQF
Order Options Tape Reel: Lead Free: #PBF Lead Free Tape Reel: #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult Marketing parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER Minimum Operating Voltage Maximum Operating Voltage Supply Current (LED Off, OLED Off) Supply Current (LED OLED Off) Supply Current (LED Off, OLED Supply Current (LED OLED VCTRL1 Full Current VCTRL2 Full OLED Brightness VCTRL1 VCTRL2 Turn VCTRL1 VCTRL2 Shut Down CTRL1, CTRL2 Bias Current Driver Current Sense Voltage (VCAP VLED) CAP1, LED1 Bias Current VCAP1, VLED1 Common Mode Minimum Voltage Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C, VCTRL1 VCTRL2
CONDITIONS VCTRL1 VCTRL2 VCTRL1 VCTRL2 VCAP1 24V, VLED1 VCTRL1 VCTRL2 VFB2 VCTRL1 VCTRL2 VCAP1 24V, VLED1
UNITS
1.65
2.05
VCAP1 24V, 200mA VCAP1 16V, VLED1
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200mA
LT3498 ELECTRICAL CHARACTERISTICS
PARAMETER Switch Leakage Current CAP1 Overvoltage Protection Schottky Forward Voltage Schottky Reverse Leakage OLED Driver Feedback Voltage Feedback Resistor Minimum Switch Time Minimum Switch Time Maximum Switch Time Switch Current Limit Switch VCESAT Switch Leakage Current Schottky Forward Voltage Schottky Reverse Leakage PMOS Disconnect VCAP2 VOUT2 CTRL2 Offset Maximum Shunt Current ISW2 200mA VSW2 ISCHOTTKY2 100mA VREVERSE2 IOUT2 10mA, VCAP2 VCTRL2 0.5V VFB2 1.3V After Start-Up During Start-Up (Note VFB2 1.5V
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C, VCTRL1 VCTRL2
CONDITIONS VSW1 ISCHOTTKY1 100mA VREVERSE1 VCTRL2 (Note
UNITS
1.18
1.215
1.25
Note Stresses beyond those listed under Absolute Maximum Ratings cause permanent damage device. Exposure Absolute Maximum Rating condition extended periods affect device reliability lifetime. Note LT3498 guaranteed meet performance specifications from 85°C. Specifications over -40°C 85°C junction operating temperature range assured design, characterization correlation with statistical process controls.
Note Internal reference voltage determined finding VFB2 voltage level which causes quiescent current increase 20µA above "Not Switching" level. Note CTRL2 overriding internal reference, start-up mode occurs when VFB2 less then half voltage CTRL2. CTRL2 overriding internal reference, start-up mode occurs when VFB2 less then half voltage internal reference.
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LT3498 TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Current (VCTRL1 VCTRL2
SWITCH SATURATION VOLTAGE (mV) -50°C -50°C SCHOTTKY FORWARD CURRENT (mA)
1635
25°C, unless otherwise specified. Schottky Forward Voltage Drop
125°C -50°C 25°C
Switch Saturation Voltage (VCESAT1)
SHUTDOWN CURRENT (µA)
125°C
25°C
25°C 125°C
SWITCH CURRENT (mA)
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SCHOTTKY FORWARD DROP (mV)
1000
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Sense Voltage (VCAP1 VLED1) VCTRL1
SENSE VOLTAGE (mV) 1000 VCTRL1 (mV) 1500 2000
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Sense Voltage (VCAP1 VLED1) Temperature
Sense Voltage (VCAP1 VLED1) VCAP1
25°C -50°C 125°C SENSE VOLTAGE (mV)
SENSE VOLTAGE (mV)
125°C 25°C
-50°C
TEMPERATURE (°C)
CAP1 VOLTAGE
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Current Limit Temperature
Open Circuit Output Clamp Voltage
-50°C 25°C 150°C INPUT CURRENT (mA)
Input Current Output Open Circuit
CURRENT LIMIT (mA)
OUTPUT CLAMP VOLTAGE
150°C 25°C -50°C
TEMPERATURE (°C)
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LT3498 TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency Temperature
SWITCHING FREQUENCY (MHz) TEMPERATURE (°C) SWITCH SATURATION VOLTAGE (mV) SCHOTTKY FORWARD CURRENT (mA) 125°C -50°C 25°C
25°C, unless otherwise specified. OLED Schottky Forward Voltage Drop
125°C 25°C -50°C 1000 SCHOTTKY FORWARD DROP (mV) 1200
OLED Switch Saturation Voltage (VCESAT2)
SWITCH CURRENT (mA)
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VOUT2 VCTRL2 (VOUT2 16V)
OUTPUT VOLTAGE CHANGE VOUT2 VOLTAGE 1500 1000 CTRL2 VOLTAGE 2000
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VOUT2 Temperature (VOUT2 16V)
VOUT2 VOLTAGE CHANGE TEMPERATURE (°C) -0.5 -1.0 -1.5 -2.0
VOUT2 Load Regulation
LOAD CURRENT (mA)
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OLED Minimum Switching Frequency
SWITCHING FREQUENCY (kHz) TEMPERATURE (°C) SWITCHING FREQUENCY (kHz) 1200 1000
OLED Switching Frequency Load Current
PEAK INDUCTOR CURRENT (mA) LOAD CURRENT (mA)
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Peak Inductor Current
TEMPERATURE (°C)
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LT3498 TYPICAL PERFORMANCE CHARACTERISTICS
Switching Waveforms
10V/DIV VCAP1 5V/DIV VCTRL1 5V/DIV
25°C, unless otherwise specified. OLED Switching Waveforms with Load
VOUT2 10mV/DIV COUPLED
Transient Response
VCAP1 50mV/DIV 100mA/ 500ns/DIV 3.6V FRONT PAGE APPLICATION
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VOLTAGE 10V/DIV
200mA/ 1ms/DIV 3.6V FRONT PAGE APPLICATION
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INDUCTOR CURRENT 50mA/DIV 3.6V VOUT2 5µs/DIV
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OLED Switching Waveforms with Load
VOUT2 10mV/DIV COUPLED VOLTAGE 10V/DIV INDUCTOR CURRENT 200mA/DIV 3.6V VOUT2 2µs/DIV VOUT2 10mV/DIV COUPLED VOLTAGE 10V/DIV INDUCTOR CURRENT 200mA/DIV
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OLED Switching Waveforms with 35mA Load
CAP2 VOLTAGE 5V/DIV VOUT2 VOLTAGE 5V/DIV
OLED Switching Waveforms During Start-Up
3.6V VOUT2
500ns/DIV
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INDUCTOR CURRENT 100mA/DIV 3.6V VOUT2 500µs/DIV
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FUNCTIONS
LED1 (Pin Connection Point Between Anode Highest Sense Resistor. current programmed 200mV ILED1 RSENSE1 CTRL1 (Pin Dimming Shutdown Pin. Connect this below 75mV disable white driver. voltage ramped from 1.5V, current ramps from (ILED1 200mV RSENSE1). GND1, (Pins Ground. directly local ground plane. GND1 GND2 connected internally. CTRL2 (Pin Dimming Shutdown Pin. Connect below 75mV disable noise boost converter. voltage ramped from 1.5V, output ramps programmed output voltage. (Pin Feedback Pin. Reference voltage 1.215V. There internal 182k resistor from GND. achieve desired output voltage, choose RFB2 according following formula: RFB2 OUT2 1.215
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LT3498 FUNCTIONS
VOUT2 (Pin Drain Output Disconnect PMOS. Place bypass capacitor from this GND. Applications Information section. CAP2 (Pin Output OLED Driver. This connected cathode internal Schottky diode. Place bypass capacitor from this GND. (Pin Switch Pin. This collector internal power switch. Minimize metal trace area connected this minimize EMI. (Pin 10): Input Supply Pin. Must locally bypassed. (Pin 11): Switch Pin. Connect inductor white driver this pin. Minimize metal trace area this minimize EMI. CAP1 (Pin 12): Output White Driver. This connected cathode internal Schottky. Connect output capacitor this sense resistor from this LED1 pin. Exposed (Pin 13): Ground. Exposed must soldered PCB.
BLOCK DIAGRAM
10µF 4.7µF 15µF
CAP2 0.47µF
COMPARATOR
DRIVER OVERVOLTAGE PROTECTION
CAP1
START-UP CONTROL
RAMP GENERATOR VOUT2 10µF DISCONNECT CONTROL SHUNT CONTROL RFB2 2.21M DRIVER SWITCH CONTROL 2.3MHz OSCILLATOR RSENSE1
LED1
VREF
182k GND2 CTRL2 CTRL1 GND1
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LT3498 OPERATION-LED DRIVER
portion LT3498 uses constant-frequency, current mode control scheme provide excellent line load regulation. Operation best understood referring Block Diagram. power-up, capacitor CAP1 charged (input supply voltage) through inductor internal Schottky diode. CTRL1 pulled higher than 125mV, bandgap reference, start-up bias oscillator turned start each oscillator cycle, power switch turned voltage proportional switch current added stabilizing ramp resulting into positive terminal comparator, When this voltage exceeds level negative input logic turns power switch. level negative input error amplifier simply amplified version difference between VCAP1 VLED1 voltage bandgap reference. this manner error amplifier, sets correct peak current level inductor keep output regulation. CTRL1 used adjust current. Driver shutdown when CTRL1 pulled lower than 75mV. Minimum Output Current Driver LT3498 drive 4-LED string current, without pulse-skipping, using same external components shown application circuit front page this data sheet. current further reduced, device will begin skipping pulses. This will result some frequency ripple, although average current remains regulated down zero. photo Figure details circuit operation driving four white LEDs load. Peak inductor current less than 60mA regulator operates discontinuous mode, meaning inductor current reaches zero during discharge phase. After inductor current reaches zero, exhibits ringing tank circuit formed inductor combination with switch diode capacitance. This ringing harmful; less spectral energy contained ringing than switch transitions.
50mA/DIV
10V/DIV
4.2V ILED LEDs
200ns/DIV
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Figure Switching Waveforms with Four White LEDs Load
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LT3498 OPERATION-OLED DRIVER
noise boost LT3498 uses novel control scheme provide high efficiency over wide range output current. addition, this technique keeps switching frequency above audio band over load conditions. operation part better understood referring Block Diagram. part senses output voltage monitoring voltage pin. user sets desired output voltage choosing value external topside feedback resistor. part incorporates precision 182k bottom-side feedback resistor. Assuming that output voltage adjustment used (CTRL2 tied 1.5V, greater), internal reference (VREF 1.215V) sets voltage which will servo during regulation. Switch Control block senses output amplifier adjusts switching frequency, well other parameters achieve regulation. During start-up circuit, special precautions taken ensure that inductor current remains under control. Because switching frequency never allowed fall below approximately 50kHz, minimum load must present prevent output voltage from drifting high. This minimum load automatically generated within part Shunt Control block. level this current adaptable, removing itself when needed improve efficiency higher load levels. low-noise boost LT3498 also integrated Schottky diode PMOS output disconnect switch. PMOS switch turned when part enabled. When part shutdown, PMOS switch turns off, allowing VOUT2 node ground. This type disconnect function often required power supplies.
APPLICATIONS INFORMATION- DRIVER
Inductor Selection 15µH inductor recommended most applications driver LT3498. Although small size high efficiency major concerns, inductor should have core losses 2.3MHz (copper wire resistance). Some small inductors this category listed Table efficiency comparison different inductors shown Figure
Table Recommended Inductors
(µH) 0.58 0.764 0.80 0.86 CURRENT RATING (mA)
EFFICIENCY CURRENT (mA)
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15uH Murata LQH32CN150K53 15uH Murata LQH2MCN150K02 15uH Cooper SD3110-150 15uH Toko D312C 15uH Coilcraft DO3314-153ML
PART LQH32CN150K53 LQH2MCN150K02 LQH32CN100K53 LQH2MCN100K02 SD3110-150 1001AS-150M (TYPE D312C) D03314-153ML
VENDOR Murata www.murata.com
Figure Efficiency Comparison Different Inductors
Capacitor Selection small size ceramic capacitors makes them ideal LT3498 driver applications. only types, because they retain their capacitance over wider temperature ranges than other types, such Z5U. 4.7µF input capacitor output capacitor sufficient most applications.
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Cooper www.cooperet.com Toko www.toko.com Coilcraft www.coilcraft.com
LT3498 APPLICATIONS INFORMATION- DRIVER
Table Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden Murata (800) 368-2496 www.t-yuden.com (803) 448-9411 www.avxcorp.com (714) 852-2001 www.murata.com
Inrush Current LT3498 Driver built-in Schottky diode. When supply voltage applied pin, inrush current flows through inductor Schottky diode charges CAP1 voltage. Schottky diode Driver LT3498 sustain maximum current inductors, which usually case this application, peak inrush current simplified follows:
Overvoltage Protection driver LT3498 internal open-circuit protection circuit. cases output open circuit, when LEDs disconnected from circuit LEDs fail open-circuit, VCAP1 clamped (typ). driver will then switch very frequency minimize input current. VCAP1 input current during output open-circuit shown Typical Performance Characteristics. Figure shows transient response when LEDs disconnected.
200mA/DIV
where inductance, inductor output capacitance. Table gives inrush peak currents some component selections.
Table Inrush Peak Currents
0.58 0.739 (µH) COUT (µF) 0.828 0.682 0.794 0.803
VCAP1 10V/DIV
LEDs DISCONNECTED THIS POINT 500µs/DIV 3.6V FRONT PAGE APPLICATION CIRCUIT
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Figure Transient Response with LEDs Disconnected From Output
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LT3498 APPLICATIONS INFORMATION- DRIVER
Programming Current feedback resistor (RSENSE1) sense voltage (VCAP1 VLED1) control current. CTRL1 controls sense reference voltage shown Typical Performance Characteristics. CTRL1 higher than 1.5V, sense reference 200mV, which results full current. have accurate current, precision resistors preferred recommended). formula table RSENSE selection shown below. 200mV RSENSE1 ILED
Table RSENSE1 Value Selection 200mV Sense
ILED (mA) RSENSE1 13.3
current ILED ILED 200mV when VCTRL1 1.5V RSENSE1 VCTRL1 when VCTRL1 1.25V 6.25 RSENSE1
Feedback voltage variation versus control voltage given Typical Performance Characteristics. Using Filtered Signal filtered signal used control brightness string. signal filtered (Figure network CTRL1 pin. corner frequency should much lower than frequency signal. needs much smaller than internal impedance CTRL1 which (typ).
Dimming Control There three different types dimming control circuits. current modulating CTRL1 with voltage, filtered signal directly with signal. Using Voltage some applications, preferred method brightness control variable voltage adjust current. CTRL1 voltage modulated dimming string. voltage CTRL1 increases from 1.5V, current increases from ILED. CTRL1 voltage increases beyond 1.5V, effect current.
Figure Dimming Control Using Filtered Signal
100k 0.1µF LT3498 CTRL1
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10kHz
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LT3498 APPLICATIONS INFORMATION- DRIVER
Direct Dimming Changing forward current flowing LEDs only changes intensity LEDs, also changes color. chromaticity LEDs changes with change forward current. Many applications cannot tolerate shift color LEDs. Controlling intensity LEDs with direct signal allows dimming LEDs without changing color. addition, direct dimming offers wider dimming range user. Dimming LEDs signal essentially involves turning LEDs frequency. typical human limit frames second. increasing frequency ~80Hz higher, will interpret that pulsed light source continuously Additionally, modulating duty cycle (amount "on-time"), intensity LEDs controlled. color LEDs remains unchanged this scheme since current value either zero constant value. Figure shows Li-Ion powered driver four white LEDs. Direct dimming method requires external NMOS tied between cathode lowest string ground shown Figure simple logic level Si2304 MOSFET used since source connected ground. signal applied CTRL1 LT3498 gate MOSFET.
15µH CAP1 COUT1 Si2304BDS 100k FREQ
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signal should traverse between ensure proper turn-on -off driver NMOS transistor When signal goes high, LEDs connected ground current ILED 200mV RSENSE1 flows through LEDs. When signal goes low, LEDs disconnected turn off. MOSFET ensures that LEDs quickly turn without discharging output capacitor which turn allows LEDs turn faster. Figure shows dimming waveforms circuit Figure
ILED 20mA/DIV
200mA/DIV 5V/DIV 2ms/DIV
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LEDs
Figure Direct Dimming Waveforms
3.4V LEDs 100Hz
EFFICIENCY
RSENSE1
CAP2 VOUT2 LT3498
LED1 CTRL1 GND1
GND2
CTRL2
CURRENT (mA)
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Figure Dimming Efficiency
Figure Li-Ion Four White LEDs with Direct Dimming
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LT3498 APPLICATIONS INFORMATION- DRIVER
time takes current reach programmed value sets achievable dimming range given frequency. example, settling time current Figure approximately 40µs input voltage. achievable dimming range this application 100Hz frequency determined using following method. Example: 100Hz, SETTLE PERIOD Range PERIOD SETTLE Cycle SETTLE PERIOD Duty Cycle Range 100Hz calculations show that 100Hz signal dimming range 250:1. addition, minimum duty cycle 0.4% ensures that current enough time settle final value. Figure shows dimming range achievable three different frequencies with settling time 40µs.
10000 FREQ Si2304BDS 100k
dimming range further extended changing amplitude signal. height signal sets commanded sense voltage across sense resistor through CTRL1 pin. this manner both analog dimming direct dimming extend dimming range given application. color LEDs longer remains constant because forward current changes with height CTRL1 signal. four application described above, LEDs dimmed first, modulating duty cycle signal. Once minimum duty cycle reached, height signal decreased below 1.5V down 125mV. both techniques together allows average current four application varied from 20mA down less than 20µA. Figure shows application dimming using both analog dimming dimming. potentiometer must added ensure that gate NMOS receives logic-level signal, while CTRL1 signal adjusted lower amplitudes.
RSENSE1 15µH CAP1 COUT1
CAP2 VOUT2 LT3498
LED1 CTRL1 GND1
GND2
CTRL2
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DIMMING RANGE
1000
PULSING VISIBLE
Figure Li-Ion Four White LEDs with Both Dimming Analog Dimming
1000 FREQUENCY (Hz) 10000
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Figure Dimming Ratio Freqeuncy
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LT3498 APPLICATIONS INFORMATION- OLED DRIVER
Inductor Selection Several recommended inductors that work well with OLED driver LT3498 listed Table although there many other manufacturers devices that used. Consult each manufacturer more detailed information their entire selection related parts. Many different sizes shapes available. equations recommendations next sections find correct inductance value your design.
Table Recommended Inductors
(µH) 0.58 0.505 0.764 CURRENT RATING (mA) VENDOR Murata www.murata.com
Capacitor Selection small size ceramic capacitors makes them suitable most OLED Driver applications. types recommended because they retain their capacitance over wider voltage temperature ranges than other types such Z5U. 4.7µF input capacitor 10µF output capacitor sufficient most applications OLED Driver. Always capacitor with sufficient voltage rating. Many capacitors rated 10µF, particularly 0805 0603 case sizes, have greatly reduced capacitance when bias voltages applied. sure check actual capacitance desired output voltage. Generally 1206 size capacitor will adequate. 0.47µF capacitor placed node recommended filter inductor current while larger 10µF placed VOUT node will give excellent transient response stability. Table shows list several capacitor manufacturers. Consult manufacturers more detailed information their entire selection related parts.
Table Recommended Ceramic Capacitor Manufacturers
MANUFACTURER Taiyo Yuden Murata Kemet PHONE 408-573-4150 843-448-9411 814-237-1431 408-986-0424 www.t-yuden.com www.avxcorp.com www.murata.com www.kemet.com
PART LQH32CN100K53 LQH2MCN100K02 LQH32CN150K53 LQH2MCN150K02 SD3110-100 SD3110-150
Cooper www.cooperet.com
Inductor Selection-Boost Regulator formula below calculates appropriate inductor value used noise boost regulator LT3498 least provides good starting point). This value provides good tradeoff inductor size system performance. Pick standard inductor close this value. larger value used slightly increase available output current, limit around twice value calculated below, large inductance will decrease output voltage ripple without providing much additional output current. smaller value used (especially systems with output voltages greater than 12V) give smaller physical size. Inductance calculated VOUT VIN(MIN) where VOUT2 desired output voltage VIN(MIN) minimum input voltage. Generally, 10µH 15µH inductor good choice.
Setting Output Voltage Auxiliary Reference Input OLED driver LT3498 equipped with both internal 1.215V reference auxiliary reference input. This allows user select between using built-in reference, supplying external reference voltage. voltage CTRL2 adjusted while chip operating alter output voltage LT3498 purposes such display dimming contrast adjustment. internal 1.215V reference, CTRL2 must held higher than 1.5V. When CTRL2 held between 1.5V OLED driver will regulate output such that voltage nearly equal CTRL2 voltage. CTRL2 voltages close 1.215V,
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LT3498 APPLICATIONS INFORMATION- OLED DRIVER
soft transition occurs between CTRL2 internal reference. Figure shows this behavior.
1.500 1.250 VOLTAGE 1.000 0.750 0.500 0.250
Choosing Feedback Node single feedback resistor connected VOUT2 CAP2 (see Figure 11). Regulating VOUT2 eliminates output offset resulting from voltage drop across output disconnect PMOS. Regulating CAP2 does compensate voltage drop across output disconnect, resulting output voltage VOUT2 that slightly lower than voltage resistor divider. Under most conditions, advised that feedback resistor tied VOUT2 pin. Connecting Load CAP2 Node
CTRL2 VOLTAGE
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Figure CTRL2 Transfer Curve
maximum output voltage, select values RFB2 according following equation: RFB2 OUT2 1.215 When CTRL2 used override internal reference, output voltage lowered from maximum value down nearly input voltage level. voltage source driving CTRL2 located distance LT3498, small 0.1µF capacitor needed bypass locally.
CAP1 CAP2 VOUT2
efficiency converter improved connecting load CAP2 instead VOUT2 pin. power loss PMOS disconnect circuit then made negligible. connecting feedback resistor VOUT2 pin, quiescent current will consumed feedback resistor string during shutdown since PMOS transistor will open (see Figure 12). disadvantage this method that CAP2 node cannot ground during shutdown, will limited around diode drop below Loads connected part should only sink current. Never force external power supplies onto CAP2 VOUT2 pins. larger value output capacitor should placed node which load connected.
CAP1
CAP2
VOUT2
ILOAD
LT3498 LED1 CTRL1 GND1 GND2 CTRL2
RFB2
LT3498 LED1 CTRL1 GND1 GND2 CTRL2
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RFB2
Figure Improved Efficiency
CAP1 CAP2 VOUT2 LT3498 LED1 CTRL1 GND1 GND2 CTRL2
RFB2
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Figure Feedback Connection Using CAP2 VOUT2
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LT3498 APPLICATIONS INFORMATION- OLED DRIVER
Maximum Output Load Current maximum output current particular LT3498 circuit function several circuit variables. following method helpful predicting maximum load current given circuit: Step Calculate peak inductor current: ILIMIT amps Step Calculate nominal output current: IOUT(NOM) IIN( AVG) 0.75 VOUT amps
Step Derate output current: IOUT IOUT(NOM) amps output voltages output current capability will increased. When using output disconnect (load current taken from VOUT2), these higher currents will cause drop PMOS switch higher resulting reduced output current capability than those predicted preceding equations. Inrush Current When stepped from ground operating voltage while output capacitor discharged, higher level inrush current will flow through inductor integrated Schottky diode into output capacitor. Conditions that increase inrush current include larger more abrupt voltage step VIN, larger output capacitor tied CAP2 pin, inductor with saturation current. While internal diode designed handle such events, inrush current should allowed exceed circuits that output capacitor values within recommended range have input voltages less than inrush current remains low, posing hazard device. cases where there large steps (more than and/or large capacitor used CAP2 pin, inrush current should measured ensure safe operation.
where ILIMIT 0.3A OLED driver. inductance value Henrys input voltage boost circuit. Step Calculate inductor ripple current: IRIPPLE
(VOUT2 VIN)
amps
where VOUT2 desired output voltage. inductor ripple current less then peak current, then circuit will only operate discontinuous conduction mode. inductor value should increased that IRIPPLE IPK. application circuit designed operate only discontinuous mode, output current capability will reduced. Step Calculate average input current: IIN( AVG) IRIPPLE amps
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LT3498 APPLICATIONS INFORMATION- OLED DRIVER
Board Layout Considerations with switching regulators, careful attention must paid board layout component placement. prevent electromagnetic interference (EMI) problems, proper layout high frequency switching paths essential. Minimize length area traces connected switching node pins (SW1 SW2). Keep sense voltage pins (CAP1 LED1) away from switching node. connection feedback resistor RFB2 should tied directly from VOUT2 kept short possible, ensuring clean, noise-free connection. Place COUT1 COUT2 next CAP1 CAP2 pins respectively. Always ground plane ender switching regulator minimize interplane coupling. Recommended component placement shown Figure
LED1
RSENSE1
CAP1
CTRL1 CTRL2 RFB2 VOUT2 VIAS GROUND PLANE REQUIRED IMPROVE THERMAL PERFORMANCE VIAS VOUT2 CAP2
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VOUT2
Figure Recommended Board Layout
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LT3498 TYPICAL APPLICATIONS
Li-Ion White LEDs OLED/LCD Bias
4.7µF 10µH
0.47µF
10µH
24mA CAP2 VOUT2 10µF
CAP1 20mA LED1 RSENSE1 CTRL1 SHUTDOWN DIMMING CONTROL
LT3498 GND1
GND2
CTRL2 SHUTDOWN CONTROL
RFB2 2.21M
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CIN, WITH SUFFICIENT VOLTAGE RATING TAIYO YUDEN GMK212BJ105KG TAIYO YUDEN TMK316BJ106ML MURATA LQH32CN100K53
Efficiency 3.6V, LEDs
EFFICIENCY CURRENT (mA)
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LT3498 TYPICAL APPLICATIONS
Li-Ion White LEDs OLED/LCD Bias
4.7µF 10µH
0.47µF
10µH
24mA CAP2 VOUT2 10µF
CAP1
LT3498
RSENSE1
LED1
CTRL1 SHUTDOWN DIMMING CONTROL
GND1
GND2
CTRL2 SHUTDOWN CONTROL
RFB2 2.21M
20mA
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CIN, WITH SUFFICIENT VOLTAGE RATING TAIYO YUDEN GMK212BJ105KG TAIYO YUDEN TMK316BJ106ML MURATA LQH32CN100K53
Efficiency 3.6V, LEDs
EFFICIENCY CURRENT (mA)
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LT3498 TYPICAL APPLICATIONS
Li-Ion Three White LEDs OLED/LCD Bias
4.7µF 10µH
0.47µF
15µH
24mA CAP2 VOUT2 10µF
CAP1
LT3498
RSENSE1
LED1
CTRL1 SHUTDOWN DIMMING CONTROL
GND1
GND2
CTRL2 SHUTDOWN CONTROL
RFB2 2.21M
20mA
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CIN, WITH SUFFICIENT VOLTAGE RATING TAIYO YUDEN GMK212BJ105KG TAIYO YUDEN TMK316BJ106ML MURATA LQH32CN150K53 MURATA LQH32CN100K53
Efficiency 3.6V, LEDs
EFFICIENCY
CURRENT (mA)
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LT3498 TYPICAL APPLICATIONS
Li-Ion Four White LEDs OLED/LCD Bias
4.7µF 10µH
0.47µF
15µH
24mA CAP2 VOUT2 10µF
CAP1
LT3498
RSENSE1
LED1
CTRL1 SHUTDOWN DIMMING CONTROL
GND1
GND2
CTRL2 SHUTDOWN CONTROL
RFB2 2.21M
20mA
3498 TA05
CIN, WITH SUFFICIENT VOLTAGE RATING TAIYO YUDEN GMK212BJ105KG TAIYO YUDEN TMK316BJ106ML MURATA LQH32CN150K53 MURATA LQH32CN100K53
Efficiency 3.6V, LEDs
EFFICIENCY
CURRENT (mA)
3498 TA05b
3498f
LT3498 TYPICAL APPLICATIONS
Li-Ion White LEDs OLED/LCD Bias
RSENSE1 4.7µF 10µH 0.47µF
15µH
24mA CAP2 VOUT2 10µF
CAP1 LED1 20mA CTRL1
LT3498 GND1
GND2
CTRL2
RFB2 2.21M
SHUTDOWN DIMMING CONTROL
SHUTDOWN CONTROL
3498 TA06
CIN, WITH SUFFICIENT VOLTAGE RATING TAIYO YUDEN GMK212BJ105KG TAIYO YUDEN TMK316BJ106ML CENTRAL SEMICONDUCTOR CMDSH-3 MURATA LQH32CN150K53 MURATA LQH32CN100K53
Efficiency, 3.6V, LEDs
EFFICIENCY EFFICIENCY CURRENT (mA)
3498 TA06b
OLED Efficiency Power Loss 3.6V, VOUT2
POWER LOSS (mW)
LOAD CURRENT (mA) LOAD FROM VOUT2 LOAD FROM CAP2 POWER LOSS FROM VOUT2 POWER LOSS FROM CAP2
3498 TA06c
3498f
LT3498 PACKAGE DESCRIPTION
Package 12-Lead Plastic (3mm 2mm) (Reference 05-08-1723
0.64 ±0.05 SIDES) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 0.25 0.05 0.45 2.39 ±0.05 SIDES) RECOMMENDED SOLDER PITCH DIMENSIONS APPLY SOLDER MASK AREAS THAT SOLDERED 3.00 ±0.10 SIDES) 0.05 0.115 0.40 0.10
MARK (SEE NOTE
2.00 ±0.10 SIDES) 0.64 0.10 SIDES) 0.23 0.05 2.39 ±0.10 SIDES) BOTTOM VIEW-EXPOSED
0.20 0.25 CHAMFER
(DDB12) 0106
0.200
0.75 ±0.05
0.45
0.05
NOTE: DRAWING JEDEC PACKAGE OUTLINE DRAWING SCALE DIMENSIONS MILLIMETERS DIMENSIONS EXPOSED BOTTOM PACKAGE INCLUDE MOLD FLASH. MOLD FLASH, PRESENT, SHALL EXCEED 0.15mm SIDE EXPOSED SHALL SOLDER PLATED SHADED AREA ONLY REFERENCE LOCATION BOTTOM PACKAGE
3498f
Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
LT3498 TYPICAL APPLICATION
Output Voltage Ripple Load Current
VOUT2 PEAK-TO-PEAK RIPPLE (mV)
VOUT
LOAD CURRENT (mA)
3498 TA06d
RFB2 VALUE REQUIRED 3.57 3.40 3.24 3.09 2.94 2.80 2.67 2.49 2.37 2.21 2.05
MAXIMUM OUTPUT CURRENT INPUT (mA) 12.5 13.4 14.4 15.6 16.8 18.1 19.6 21.2 22.5 24.2
RELATED PARTS
PART NUMBER LT1932 LT1937 LT3463/ LT3463A LT3465/ LT3465A LT3466/ LT3466-1 LT3471 LT3473/ LT3473A LT3491 LT3494/ LT3494A LT3497 LT3591 DESCRIPTION Constant-Current, 1.2MHz, High Efficiency White Boost Regulator Constant-Current, 1.2MHz, High Efficiency White Boost Regulator Dual Output, Boost/Inverter, 250mA ISW, Constant Off-Time, High Efficiency Step-Up DC/DC Converter with Integrated Schottky Diodes COMMENTS 10V; VOUT(MAX) 34V; 1.2mA; <1µA; ThinSOTPackage 2.5V 10V; VOUT(MAX) 34V; 1.9µA; <1µA; ThinSOT SC70 Packages 2.3V 15V; VOUT(MAX) ±40V; 40µA; <1µA; DFN-10 Package
Constant-Current, 1.2/2.7MHz, High Efficiency White 2.3V 16V; VOUT(MAX) 40V; 40µA; <1µA; Boost Regulator with Integrated Schottky Diode DFN-10 Package Dual Constant-Current, 2MHz, High Efficiency White Boost Regulator with Integrated Schottky Diode Dual Output, Boost/Inverter, 1.3A ISW, 1.2MHZ, High Efficiency Boost-Inverting DC/DC Converter 2.3V 16V; VOUT(MAX) 40V; 65µA; <1µA; DFN-8 Package 2.4V 16V; VOUT(MAX) ±40V; 2.5µA; <1µA; DFN-10 Package
40V, 1.2MHz Micropower Noise Boost Converter 2.2V 16V; VOUT(MAX) 36V; 150µA; <1µA; DFN-12 Package with Output Disconnect Constant-Current, 2.3MHz, High Efficiency White Boost Regulator with Integrated Schottky Diode 40V, 180mA/350mA Micropower Noise Boost Converter with Output Disconnect Dual 2.3MHz, Full Function Driver with Integrated Schottky Diode 250:1 True Color PWMDimming Constant-Current, 1MHz, High Efficiency White Boost Regulator with Integrated Schottky Diode 80:1 True Color Dimming 2.5V 12V; VOUT(MAX) 27V; 12.6µA; <8µA; DFN-6 SC70 Packages 2.3V 16V; VOUT(MAX) 40V; 65µA; <1µA; DFN-8 Package 2.5V 10V; VOUT(MAX) 32V; 6mA; <12µA; DFN-10 Package 2.5V 12V; VOUT(MAX) 40V; 4mA; <9µA; DFN-8 Package
ThinSot True Color trademarks Linear Technology Corporation
3498f
Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
0507 PRINTED
1630 McCarthy Blvd., Milpitas, 95035-7417
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2007
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