LM2612 Sub-miniature, Programmable, Step-Down DC-DC Converter Ultra Lo
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LM2612 Sub-miniature, Programmable, Step-Down DC-DC Converter Ultra Low-Voltage Circuits
LM2612 Sub-miniature, Programmable, Step-Down DC-DC Converter Ultra Low-Voltage Circuits
LM2612 step-down DC-DC converter optimized powering ultra-low voltage circuits from single Lithium-Ion cell. provides 400mA (300mA grade), over input voltage range 2.8V 5.5V. programmable output voltages 1.05V, 1.3V, 1.5V 1.8V allow adjustment voltage options without board redesign, well dynamic voltage switching reduced power consumption. device offers superior features performance mobile phones similar portable applications with complex power management systems. Pin-selectable low-noise low-current modes offer improved system control. During full-power operation, fixed-frequency mode reduces interference data acquisition applications minimizing noise harmonics sensitive sampling frequencies. SYNC input allows synchronizing switching frequency range 500kHz 1MHz avoid noise from intermodulation with system frequencies. Internal synchronous rectification provides high efficiency (91% typ. 1.8VOUT). Hysteretic mode reduces quiescent current (typ.) during system standby extended battery life. Shutdown turns device reduces battery consumption 0.1µA (typ.). LM2612 available micro package. This package uses National's chip-scale micro technology offers smallest possible size. high switching frequency (600kHz) allows tiny surface-mount components. Only three small external surface-mount components, inductor ceramic capacitors required. selectable output voltage eliminates need bulky external feedback resistors associated output ripple scaling mode.
Features
Operates from single LiION cell programmable output voltage (1.05V, 1.3V, 1.5V 1.8V), without external feedback resistors output voltage precision 400mA maximum load capability (300mA grade) Sub-miniature 10-pin micro package Only three tiny surface-mount external components required Uses small ceramic capacitors. mode output voltage ripple (2mV typ) Internal synchronous rectification high efficiency (91% 2.8VIN, 1.8VOUT) quiescent current (PFM mode) 0.1µA shutdown current 600kHz switching frequency reduces interference component size SYNC input frequency synchronization from 500kHz 1MHz Internal soft start Current overload protection external compensation required
Applications
Mobile Phones Hand-Held Radios Personal Digital Assistants Hand-Held Portable Instruments Battery Powered Devices
Typical Application Circuit
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2000 National Semiconductor Corporation
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LM2612
Connection Diagrams
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VIEW
BOTTOM VIEW
Ordering Information
Order Number LM2612ABP LM2612BBP LM2612ABPX LM2612BBPX 10-bump Wafer Level Chip Scale (micro SMD) BPA10VWB Package Type Package Drawing Supplied Units, Tape Reel Units, Tape Reel 3000 Units, Tape Reel 3000 Units, Tape Reel
Description
Number Name VID1 VID0 SYNC/MODE Function Feedback Analog Input. Connect output output filter capacitor (Figure Output Voltage Control Inputs. output voltage using these digital inputs connecting them SGND (see Table output defaults 1.5V these pins unconnected. Synchronization Input. this digital input frequency selection modulation control. Set: SYNC/MODE high low-noise 600kHz mode SYNC/MODE low-current mode SYNC/MODE 500kHz 1MHz external clock synchronization external clock mode. Synchronization Operating Modes Device Information section. Enable Input. this digital input high normal operation. shutdown, low. system processor should during power-up other supply voltage conditions. (See Shutdown Mode Device Information section.) Power Ground Switching Node connection internal PFET switch NFET synchronous rectifier. Connect inductor with saturation current rating that exceeds 850mA Switch Peak Current Limit specification LM2612 (Figure Power Supply Input internal PFET switch. Connect input filter capacitor (Figure Analog Supply Input. board layout optimum, optional 0.1µF ceramic capacitor suggested (Figure Analog Control Ground
PGND
PVIN SGND
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LM2612
Absolute Maximum Ratings (Note
Military/Aerospace specified devices required, please contact National Semiconductor Sales Office/ Distributors availability specifications. PVIN, VDD, SGND PGND SGND SYNC/MODE, VID0, VID1 SGND -0.2V -0.2V +0.2V -0.2V (GND -0.2V) (VDD +0.2V)
Storage Temperature Range Lead temperature (Soldering, sec.) Junction Temperature (Note Minimum Rating Human body model, 100pF, Thermal Resistance (JA)
-45°C +150°C 260°C -25°C 125°C
2.5kV 170°C/W
Electrical Characteristics
Specifications with standard typeface 25°C, those bold face type apply over full Operating Temperature Range -25°C +85°C). Unless otherwise specified, PVIN SYNC 3.6V, VID0 VID1 Symbol Parameter Input Voltage Range (Note Feedback Voltage (Note Comparator Hysteresis Voltage (Note Shutdown Supply Current Bias Current into (VOUT 1.5V) Conditions PVIN VID1 VIN, VID0 VID0 VIN, VID1 VID0 VIN, VID1 VID0 VID1 VID0 VID1 VHYST Mode (SYNC No-Load, mode (SYNC/MODE No-Load, mode (SYNC/MODE VIN) Pin-Pin Resistance Pin-Pin Resistance Resistance Temperature Coefficient Switch Peak Current Limit (Note Positive Going Threshold Voltage Negative Going Threshold Voltage SYNC/MODE Positive Going Threshold Voltage SYNC/MODE Negative Going Threshold Voltage VID0, VID1 Positive Going Threshold Voltage VID0, VID1 Negative Going Threshold Voltage VID1, VID0 Pull Down Current SYNC/MODE Clock Frequency Range (Note VID1, VID0 3.6V LM2612ABP LM2612BBP 3.6V 3.6V 1.70 2.54 2.00 0.95 0.92 0.83 2.85 1.00 1.274 1.470 1.764 1.05 1.30 1.50 1.10 1.326 1.530 1.836 Units
ISHDN RDSON RDSON RDSON Ilim VEN_H VEN_L VSYNC_H VSYNC_L VID_H VID_L IVID fsync
1000
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LM2612
Electrical Characteristics
(Continued)
Specifications with standard typeface 25°C, those bold face type apply over full Operating Temperature Range -25°C +85°C). Unless otherwise specified, PVIN SYNC 3.6V, VID0 VID1 Symbol FOSC Parameter Internal Oscillator Frequency Conditions LM2612ABP, Mode (SYNC VIN) LM2612BBP, Mode (SYNC VIN) Tmin Minimum ON-Time Switch Mode Load Transient Response Mode Line Transient Response Mode Circuit Figure IOUT 20mA 200mA Step Circuit Figure 3.0V 3.6V Step Units
Note Absolute maximum ratings indicate limits beyond which damage device occur. Operating Ratings conditions under which operation device guaranteed. guaranteed performance limits associated test conditions, Electrical Characteristics table. Note mode, Thermal shutdown will occur junction temperature exceeds 150°C maximum junction temperature device. Note LM2612 designed applications where turn-on after power-up controlled system processor. Thus, should kept shutdown holding until input voltage exceeds 2.8V. Although LM2612 typically exhibits good behavior when enabled input voltages, this guaranteed. Note feedback voltage trimmed 1.5V output setting. other output voltages result from selection internal DAC's divider ratios. precision feedback voltages except 1.05V setting, which Contact Portable Power Applications group National Semiconductor, trimming other voltages desired. Note hysteresis voltage minimum voltage swing that causes internal feedback control circuitry turn internal PFET switch then off, during mode. Note Current limit built-in, fixed, adjustable. current limit reached while output pulled below about 0.7V, internal PFET switch turns allow inductor current diminish. Note SYNC driven with external clock switching between GND. When external clock present SYNC, forced mode external clock frequency. LM2612 synchronizes rising edge external clock
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LM2612
Typical Operating Characteristics
unless otherwise noted. Quiescent Supply Current Temperature
LM2612ABP, Circuit Figure 3.6V, 25°C,
Quiescent Supply Current Supply Voltage
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Shutdown Quiescent Current Temperature
Output Voltage Temperature (PWM Mode)
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Output Voltage Temperature (PFM Mode)
Output Voltage Supply Voltage (VOUT 1.8V, Mode)
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LM2612
Typical Operating Characteristics
unless otherwise noted. (Continued) Output Voltage Supply Voltage (VOUT 1.8V, Mode)
LM2612ABP, Circuit Figure 3.6V, 25°C,
Output Voltage Supply Voltage (VOUT 1.5V, Mode)
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Output Voltage Supply Voltage (VOUT 1.5V, Mode)
Output Voltage Supply Voltage (VOUT 1.3V, Mode)
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LM2612
Typical Operating Characteristics
unless otherwise noted. (Continued) Output Voltage Supply Voltage (VOUT 1.3V, Mode)
LM2612ABP, Circuit Figure 3.6V, 25°C,
Output Voltage Supply Voltage (VOUT 1.05V, Mode)
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Output Voltage Supply Voltage (VOUT 1.05V, Mode)
Output Voltage Output Current (VOUT 1.8V, Mode)
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LM2612
Typical Operating Characteristics
unless otherwise noted. (Continued) Output Voltage Output Current (VOUT 1.8V, Mode)
LM2612ABP, Circuit Figure 3.6V, 25°C,
Output Voltage Output Current (VOUT 1.5V, Mode)
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Output Voltage Output Current (VOUT 1.5V, Modee)
Output Voltage Output Current (VOUT 1.3V, Mode)
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LM2612
Typical Operating Characteristics
unless otherwise noted. (Continued) Output Voltage Output Current (VOUT 1.3V, Mode)
LM2612ABP, Circuit Figure 3.6V, 25°C,
Output Voltage Output Current (VOUT 1.05V, Mode, With Diode)
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Output Voltage Output Current (VOUT 1.05V, Mode, With Diode)
Efficiency Output Current (VOUT 1.8V, Mode, With Diode)
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LM2612
Typical Operating Characteristics
unless otherwise noted. (Continued) Efficiency Output Current (VOUT 1.8V, Mode, With Diode)
LM2612ABP, Circuit Figure 3.6V, 25°C,
Efficiency Output Current (VOUT 1.5V, Mode, With Diode)
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Efficiency Output Current (VOUT 1.5V, Mode, With Diode)
Efficiency Output Current (VOUT 1.3V, Mode, With Diode)
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LM2612
Typical Operating Characteristics
unless otherwise noted. (Continued) Efficiency Output Current (VOUT 1.3V, Mode)
LM2612ABP, Circuit Figure 3.6V, 25°C,
Efficiency Output Current (VOUT 1.05V, Mode)
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Efficiency Output Current (VOUT 1.05V, Mode, With Diode)
Efficiency Output Current (VOUT 1.8V, Mode,No Diode)
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LM2612
Typical Operating Characteristics
unless otherwise noted. (Continued) Efficiency Output Current (VOUT 1.8V, Mode, Diode)
LM2612ABP, Circuit Figure 3.6V, 25°C,
Maximum Output Current Supply Voltage (PWM Mode)
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Maximum Output Current Supply Voltage (PFM Mode)
Switching Frquency Temperature (PWM Mode)
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LM2612
Typical Operating Characteristics
unless otherwise noted. (Continued) Load Transient Response (PWM Mode)
LM2612ABP, Circuit Figure 3.6V, 25°C,
Load Transient Response (PFM Mode)
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INDUCTOR CURRENT, 500mA/div PIN, 5V/div VOUT, 50mV/div, COUPLED LOAD, 20mA 200mA, 200mA/div
INDUCTOR CURRENT, 500mA/div PIN, 5V/div VOUT, 50mV/div, COUPLED LOAD, 10mA 100mA, 100mA/div
Shutdown Response (PWM Mode)
Shutdown Response (PFM Mode)
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INDUCTOR CURRENT, 500mA/div PIN, 2V/div VOUT, 1V/div 5V/div
INDUCTOR CURRENT, 500mA/div PIN, 2V/div VOUT, 1V/div 5V/div
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LM2612
Typical Operating Characteristics
unless otherwise noted. (Continued) Response
LM2612ABP, Circuit Figure 3.6V, 25°C,
Line Transient Response (PWM Mode)
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INDUCTOR CURRENT, 500mA/div PIN, 2V/div VOUT, 50mV/div, COUPLED SYNC/MODE, 5V/div
SUPPLY VOLTAGE, 500mV/div, COUPLED PIN, 5V/div VOUT, 10mV/div, COUPLED
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LM2612
Device Information
LM2612 simple, step-down DC-DC converter optimized powering low-voltage CPUs DSPs cell phones, portable communicators, handheld instruments similar battery powered devices. designed powering 1.05V, 1.3V, 1.5V 1.8V logic circuits from single LiION battery cell. based current-mode switching buck architecture with synchronous rectification high efficiency. designed maximum load capability 400mA (300mA grade). Maximum load range vary from this depending input voltage, output voltage, SYNC frequency inductor chosen (see Maximum Load Input Voltage Typical Operating Characteristics.) device three pin-selectable operating modes required cell phones other sophisticated portable devices with complex power management needs. Such applications typically spend small portion their time operating full power. During full power, synchronized fixed-frequency operation offers high efficiency while minimizing interference sensitive data acquisition circuits. remainder their time, these applications operate low-current standby mode shutdown conserve battery power. During standby, operation hysteretic mode reduces quiescent current maximize battery life. Shutdown turns device reduces battery consumption 0.1µA (typ.). LM2612 offers superior performance features. mode output voltage precision Efficiency typically 100mA load with 1.8V output, 2.8V input.
mode quiescent current 150µA typ. SYNC/MODE allows synchronization mode external clock between 500kHz 1MHz minimizing interference with sensitive data acquisition circuits. output voltage selectable 1.05V, 1.3V, 1.5V 1.8V eliminate external feedback resistors. Additional features include soft-start, shutdown, current overload protection thermal overload protection. LM2612 constructed using chip-scale 10-pin micro package. This package offers smallest possible size space-critical applications such cell phones, where board area important design consideration. high switching frequency (600kHz) reduces sizes external components. shown Figure only three external power components required implementation. Board area required implementation only 0.12 (77.4mm2). micro-SMD package does allow smallest size also requires additional design considerations implementation. (See micro Package Assembly Applications Information section). fine bump-pitch requires careful board design precision assembly equipment. this package best suited opaque-case applications, where edges subject high-intensity ambient infra-red light. Also, system processor should during power-up other supply voltage conditions. (See Shutdown Mode Device Information section).
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FIGURE Typical Operating Circuit
Circuit Operation
Referring Figure Figure Figure LM2612 operates follows: During first part each switching cycle, control block LM2612 turns internal PFET switch. This allows current flow from input through inductor output filter capacitor load. inductor limits current ramp with slope (VIN -VOUT)/L, storing energy magnetic field. During second part each cycle, controller turns PFET switch off, blocking current flow from input, then turns NFET synchronous rectifier response, inductor's magnetic field collapses, generating voltage that forces current from ground through synchronous rectifier
output filter capacitor load. stored energy transferred back into circuit depleted, inductor current ramps down with slope VOUT/L. inductor current reaches zero before next cycle, synchronous rectifier turned prevent current reversal. output filter stores charge when inductor current high, releases when low, smoothing voltage across load. output voltage regulated modulating PFET switch on-time control average current sent load. effect identical sending duty-cycle modulated rectangular wave formed switch synchronous rectifier low-pass filter created inductor output filter capacitor. output voltage equal average voltage pin.
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LM2612
Circuit Operation
(Continued)
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FIGURE Simplified Functional Diagram
Operation
LM2612 current-mode operation connecting SYNC/MODE VIN. While (Pulse Width Modulation) mode, output voltage regulated switching constant frequency then modulating energy cycle control power load. Energy cycle modulating PFET switch on-time pulse-width control peak inductor current. This done comparing ramp from current-sense amplifier with error signal from voltage-feedback error amplifier. beginning each cycle, clock turns PFET switch, causing inductor current ramp When current sense signal ramps past error amplifier Mode Switching Waveform
signal, comparator turns PFET switch turns NFET synchronous rectifier, ending first part cycle. increase load pulls output voltage down, error amplifier output increases, which allows inductor current ramp higher before comparator turns PFET. This increases average current sent output adjusts increase load. Before going comparator, current sense signal summed with slope compensation ramp from oscillator stability current feedback loop. During second part cycle, zero crossing detector turns NFET synchronous rectifier inductor current ramps zero.
Mode Switching Waveform
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INDUCTOR CURRENT, 500mA/div PIN, 2V/div VOUT, 10mV/div, COUPLED
INDUCTOR CURRENT, 500mA/div PIN, 2V/div VOUT, 50mV/div, COUPLED
FIGURE Typical Circuit Waveforms Mode Mode
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LM2612
Operation
Connecting SYNC/MODE SGND sets LM2612 hysteretic operation. While (Pulse Frequency Modulation) mode, output voltage regulated switching with discrete energy cycle then modulating cycle rate, frequency, control power load. This done using error comparator sense output voltage. device waits load discharges output filter capacitor, until output voltage drops below lower threshold error-comparator. Then device initiates cycle turning PFET switch. This allows current flow from input, through inductor output, charging output filter capacitor. PFET turned when output voltage rises above regulation threshold error comparator. Thus, output voltage ripple mode proportional hysteresis error comparator inductor current. mode, device only switches needed service load. This lowers current consumption reducing power consumed during switching action circuit, transition losses internal MOSFETs, gate drive currents, eddy current losses inductor, etc. also improves light-load voltage regulation. During second part cycle, intrinsic body diode NFET synchronous rectifier conducts until inductor current ramps zero.
SYNC/MODE input also used frequency synchronization. synchronize LM2612 external clock, supply digital signal SYNC/MODE with voltage swing exceeding 0.4V 1.3V. During synchronization, LM2612 initiates cycles rising edge clock. When synchronized external clock, operates mode. device synchronize duty-cycle clock over frequencies from 500kHz 1MHz. following waveform duty-cycle guidelines when applying external clock SYNC/MODE pin. Each clock cycle should have high periods between 1.3µs 200ns duty cycle between 70%. total clock period should less. Clock under/ overshoot should less than 100mV below above VDD. When applying noisy clock signals, especially sharp edged signals from long cable during evaluation, terminate cable characteristic impedance; filter SYNC pin, necessary, soften slew rate over/undershoot. Note that sharp edged signals from pulse function generator develop under/overshoot high improperly terminated cable.
Overvoltage Protection
LM2612 over-voltage comparator that prevents output voltage from rising high when device left mode under low-load conditions. When output voltage rises 30mV over regulation threshold, comparator inhibits operation skip pulses until output voltage returns regulation threshold. over voltage protection, output voltage ripple increase slightly.
Synchronization Operating Mode Selection
LM2612 designed digital control operating modes switching frequency system controller. This prevents spurious switchover, from low-noise mode between transmission intervals mobile phone applications, that occur other products. also allows synchronization external clock prevent beating effects with sensitive data acquisition frequencies. SYNC/MODE digital input used select operating mode. Setting SYNC/MODE high (above 1.3V) selects 600kHz current-mode operation. mode optimized low-noise, high-power operation when load active. Setting SYNC/MODE (below 0.4V) selects hysteretic voltage-mode operation. mode optimized reducing power consumption extending battery life when load low-power standby mode. mode, quiescent current into 150uA typ. contrast, mode VDD-pin quiescent current 555µA typ. operation intended with loads above more, when noise operation desired. Below approximately 50mA, operation should used allow precise regulation, reduced current consumption. LM2612 over-voltage feature that prevents output voltage from rising high, when device left mode under low-load conditions. Overvoltage Protection, more information. Select modes with SYNC/MODE using signal with slew rate faster than 5V/ms. comparator, Schmitt trigger logic gate drive SYNC/MODE pin. leave floating allow linger between thresholds. These measures will prevent output voltage errors response indeterminate logic state. LM2612 switches each rising edge SYNC. Ensure minimum load keep output voltage regulation when switching modes frequently.
Shutdown Mode
Setting digital input 1.7V) places LM2612 0.1uA (typ) shutdown mode. During shutdown, PFET switch, NFET synchronous rectifier, reference, control bias LM2612 turned off. Setting high 2.85V) enables normal operation. While turning soft start activated. should turn LM2612 during power-up undervoltage conditions when supply less than 2.8V minimum operating voltage. LM2612 designed compact portable applications such mobile phones. such applications, power supply sequencing determined system controller. Although LM2612 typically well behaved input voltages, this guaranteed.
Internal Synchronous Rectification
While mode, LM2612 uses internal NFET synchronous rectifier reduce rectifier forward voltage drop associated power loss. Synchronous rectification provides significant improvement efficiency whenever output voltage relatively compared voltage drop across ordinary rectifier diode. Under moderate heavy loads, internal NFET synchronous rectifier turned during inductor current down slope second part each cycle. synchronous rectifier turned prior next cycle, when inductor current ramps zero light loads. NFET designed conduct through it's intrinsic body diode during transient intervals before turns eliminating need external diode. reduce quiescent current during mode, synchronous rectification disabled NFET conducts through it's
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LM2612
Internal Synchronous Rectification
(Continued) body diode during second part each cycle. With very short duty cycles, under high input-output voltage differentials light loads mode, there insufficient time synchronous rectifier activate. body diode NFET also used under these conditions. increase efficiency short duty-cycle conditions, place external Schottky diode from PGND Contact portable power applications group National Semiconductor, interested device with synchronous rectification mode.
Thermal Overload Protection
LM2612 thermal overload protection function that operates protect itself from short-term misuse overload conditions. When junction temperature exceeds about 155°C, device initiates soft-start cycle which completed after temperature drops below 130°C. Prolonged operation thermal overload conditions damage device considered practice.
Application Information
Setting Output Voltage LM2612 features pin-selectable output voltage eliminate need external feedback resistors. Select output voltage 1.05V, 1.3V, 1.5V 1.8V configuring VID0 VID1 pins, directed Table TABLE VID0 VID1 Output Voltage Selection Settings VOUT 1.05 Logic Level VID0 N.C. VID1 N.C.
Current Limiting
current limit feature allows LM2612 protect itself external components during overload conditions. Current limiting implemented using internal comparator that trips 850mA max, (980mA grade devices). mode, cycle-by-cycle current limiting normally used. excessive load pulls output voltage down approximately 0.7V, then device switches timed current limit mode. timed current limit mode internal P-FET switch turned after current comparator trips beginning next cycle inhibited 2.5µs force instantaneous inductor current ramp down safe value. mode also uses timed current limit operation. Timed current limit prevents loss current control seen some products when output voltage pulled serious overload conditions.
Selectable Output Voltage
LM2612 features pin-selectable output voltage eliminate need external feedback resistors. output 1.05V, 1.3V, 1.5V 1.8V configuring VID0 VID1 pins. Setting Output Voltage Application Information section further details.
Soft-Start
LM2612 soft start reduce current inrush during power-up startup. This reduces stress LM2612 external components. also reduces startup transients power source. Soft start implemented ramping internal reference LM2612 gradually increase output voltage. reference ramps about 400µs. When powering mode, soft start take additional 200us allow time error amplifier compensation network charge.
VID0 VID1 digital inputs. They high connecting connecting SGND. Optionally, VID0 VID1 driven digital gates providing over 1.2V input high less than 0.4V ensure valid logic levels. VID0 VID1 inputs each have internal pull-down that pulls them default 1.5V output, when left unconnected. Leaving these pins open acceptable, setting pins high recommended. Inductor Selection 10µH inductor with saturation current rating over 850mA (980mA grade) recommended most applications. inductor 1.8V applications. inductor's resistance should less than good efficiency. Table lists suggested inductors suppliers.
TABLE Suggested Inductors Their Suppliers Low- Cost DO1608C-103 UP1B-100 UP0.4CB-100 ELL6PM100M CDRH5D18-100 Low- Noise DT1608C-103 Vendor Coilcraft Coiltronics Panasonic Sumida Phone 847-639-6400 561-241-7876 714-373-7366 847-956-0666 847-639-1469 561-241-9339 714-373-7323 847-956-0702
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LM2612
Application Information
(Continued)
low-cost applications, unshielded bobbin inductor suggested. noise critical applications, toroidal shielded-bobbin inductor should used. good practice
board with overlapping footprints both types design flexibility. This allows substitution low-noise toroidal inductor, event that noise from low-cost bobbin models unacceptable.
TABLE Suggested Capacitors Their Suppliers Model LMK432BJ226MM JMK325BJ226MM ECJ4YB0J226M EMK325BJ106MN C3216X5R0J106M ECJ4YB1A106K Type Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Vendor Taiyo-Yuden Taiyo-Yuden Panasonic Taiyo-Yuden Panasonic 714-373-7366 847-925-0888 847-803-6100 714-373-7366 714-373-7323 847-925-0899 847-803-6296 714-373-7323 Phone 847-925-0888 847-925-0899
22µF (Output Filter Capacitor)
10µF (Input Filter Capacitor)
Capacitor Selection 10µF ceramic input filter capacitor 22uF ceramic output filter capacitor recommended most applications. These provide optimal balance between small size, cost, reliability performance cell phones similar applications. Table lists suggested capacitors suppliers. 10µF ceramic capacitor used output filter capacitor smaller size, applications where worst-case transient load step less than 200mA. 10µF output capacitor trades smaller size increase output voltage ripple, undershoot during line load transient response. input filter capacitor supplies current PFET switch LM2612 first part each cycle reduces voltage ripple imposed input power source. output filter capacitor smoothes current flow from inductor load, helps maintain steady output voltage during transient load changes reduces output voltage ripple. These capacitors must selected with sufficient capacitance sufficiently perform these functions. ESR, equivalent series resistance, filter capacitors major factor voltage ripple. contribution from voltage ripple around 75-95% most types electrolytic capacitors, less ceramic capacitors. remainder ripple from charge storage capacitance. Since other capacitor types, such tantalum aluminum electrolytic, incurs significant penalty size, cost performance, their with LM2612 been evaluated. such capacitors desired, low-ESR types, evaluate output voltage ripple check stability evaluating transient load steps mode. Load steps should exhibit damped critically damped response with chatter little oscillatory ringing. Since characteristics some electrolytic capacitors change significantly over temperature, stability should evaluated over temperature. electrolytic capacitors used, select filter capacitors with sufficient current ratings DC-DC converter circuit, ensure safe operation long component life. LM2612 typical application circuit, current ratings should exceed 380mA 70mA input output filter capacitors, respectively. Select input filter capacitor with surge current rating sufficient
power-up surge from input power source. power-up surge current approximately capacitor's value (µF) times voltage rise rate (V/µs). Diode Selection optional Schottky diode Figure added increase efficiency mode light-load mode. This desired applications where increased efficiency improving operational battery life takes precedence over increased system size associated with Schottky diode. Typically, external schottky diode increases mode efficiency from 72.7% 85.0% load, VOUT 1.8V, 3.6V). efficiency curves Typical Operating Characteristics. Schottky diode with current rating higher than 850mA, such MBRM140T3. device rated more reduces diode reverse leakage high temperature applications. Thermal Design LM2612 thermal overload protection feature which activates when junction temperature exceeds around 155°C, until device cools 130°C. However, running device this continually damage device poor practice. Sufficient thermal design should done keep device below specified 125°C maximum operating junction temperature. Micro Package Assembly micro package requires specialized board layout, precision mounting careful reflow techniques, detailed National Semiconductor Application Note AN-1112. Refer section Surface Mount Technology (SMT) Assembly Considerations. best results assembly, alignment ordinals board should used facilitate placement device. Since micro packaging technology, layouts assembly means must thoroughly tested prior production. particular, proper placement, solder reflow resistance thermal cycling must verified. 10-Bump package used LM2612 170micron solder balls requires 6.7mil (6.7/1000 in.) pads mounting circuit board. trace each should enter with entry angle prevent debris from being caught deep corners. Initially, trace each should wide, section long longer, thermal relief. Then each trace should neck optimal
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LM2612
Application Information
(Continued)
width over span mils more, that taper extends beyond edge package. important criterion symmetry. This ensures solder bumps LM2612 re-flow evenly that device solders level board. particular, special attention must paid pads bumps 6-9. Because PVIN PGND typically connected large copper planes, inadequate thermal reliefs result late inadequate reflow these bumps. style used with micro package must NSMD (non-solder mask defined) type. This means that solder-mask opening larger than size 9.7mils LM2612. This prevents that otherwise forms solder-mask overlap. This hold device surface board interfere with mounting. Applications Note AN-1112 specific instructions. micro package optimized smallest possible size applications with infra-red opaque cases. Because micro package lacks plastic encapsulation characteristic larger devices, vulnerable light. Back-side metalization and/or epoxy coating, along with front-side shading printed circuit board, reduce this sensitivity. However, package exposed edges. particular, micro devices sensitive light Infrared range shining package's exposed edges. power-up LM2612 while subjecting high intensity infrared light, otherwise degraded, unpredictable erratic operation result. Examples light sources with high infrared content include halogen lamps. Package circuit case opaque infrared light. Board Layout Considerations board layout important part DC-DC converter design. Poor board layout disrupt performance DC-DC converter surrounding circuitry contributing EMI, ground bounce, resistive voltage loss traces. These send erroneous signals DC-DC converter resulting poor regulation instability. Poor layout also result reflow problems leading poor solder joints between Micro package board pads. Poor solder joints result erratic degraded performance. Good layout LM2612 implemented following simple design rules: Place LM2612 6.7mil (6.7/1000 in.) pads. thermal relief, connect each with 6mil wide trace, 6mils long longer. Then incrementally increase each trace optimal width over span 11mil more, that taper extends beyond edge package. important criterion symmetry ensure solder bumps LM2612 re-flow evenly (see Micro Package Assembly Use).
Place LM2612, inductor filter capacitors close together make traces short. traces between these components carry relatively high switching currents antennas. Following this rule reduces radiated noise. Place capacitors inductor within 0.2in (5mm) LM2612.
Arrange components that switching current loops curl same direction. During first part each cycle, current flows from input filter capacitor, through LM2612 inductor output filter capacitor back through ground, forming current loop. second part each cycle, current pulled from ground, through LM2612 inductor, output filter capacitor then back through ground, forming second current loop. Routing these loops current curls same direction prevents magnetic field reversal between part-cycles reduces radiated noise. Connect ground pins LM2612 filter capacitors together using generous component-side copper fill pseudo-ground plane. Then, connect this ground-plane used) with several vias. This reduces ground-plane noise preventing switching currents from circulating through ground plane. also reduces ground bounce LM2612 giving low-impedance ground connection. wide traces between power components power connections DC-DC converter circuit. This reduces voltage errors caused resistive losses across traces. Route noise sensitive traces, such voltage feedback path, away from noisy traces between power components. voltage feedback trace must remain close LM2612 circuit should direct should routed away from noisy components. This reduces radiated onto DC-DC converter's voltage feedback trace. Place noise sensitive circuitry, such radio blocks, away from DC-DC converter, CMOS digital blocks other noisy circuitry. Interference with noise-sensitive circuitry system reduced through distance. mobile phones, example, common practice place DC-DC converter corner board, arrange CMOS digital circuitry around (since this also generates noise), then place sensitive preamplifiers stages diagonally opposing corner. Often, sensitive circuitry shielded with metal power post-regulated reduce conducted noise, using low-dropout linear regulators, such LP2966.
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LM2612
Physical Dimensions
inches (millimeters) unless otherwise noted
NOTES: UNLESS OTHERWISE SPECIFIED EPOXY COATING 63Sn/37Pb EUTECTIC BUMP RECOMMEND NON-SOLDER MASK DEFINED LANDING PAD. ESTABLISHED LOWER LEFT CORNER WITH RESPECT TEXT ORIENTATION. REMAINING PINS NUMBERED COUNTER CLOCKWISE. DRAWING NUMBER REPRESENTS PACKAGE SIZE VARIATION WHERE PACKAGE WIDTH, PACKAGE LENGTH PACKAGE HEIGHT. 6.NO JEDEC REGISTRATION SEPT. 2000. 10-Bump micro Package Package Number BPA10 dimensions given: 1.996 0.030mm 2.504 0.030mm 0.850 0.1mm
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LM2612 Sub-miniature, Programmable, Step-Down DC-DC Converter Ultra Low-Voltage Circuits
Notes
LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT GENERAL COUNSEL NATIONAL SEMICONDUCTOR CORPORATION. used herein: Life support devices systems devices systems which, intended surgical implant into body, support sustain life, whose failure perform when properly used accordance with instructions provided labeling, reasonably expected result significant injury user.
National Semiconductor Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com www.national.com National Semiconductor Europe Fax: 180-530 Email: europe.support@nsc.com Deutsch Tel: 9508 6208 English Tel: 2171 Tel: 8790
critical component component life support device system whose failure perform reasonably expected cause failure life support device system, affect safety effectiveness.
National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: ap.support@nsc.com
National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507
National does assume responsibility circuitry described, circuit patent licenses implied National reserves right time without notice change said circuitry specifications.
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