LT1073 - Micropower DC/DC Converter Adjustable …

1 LT10731 TYPICAL APPLICATION FEATURESDESCRIPTIONM icropower DC/DC Converter Adjustable and Fixed 5V, 12 VThe LT 1073 is a versatile Micropower DC/DC Converter . The device requires only three external components to deliver a fixed output of 5V or 12V. The very low minimum supply voltage of 1V allows the use of the LT1073 in applications where the primary power source is a single cell. An on-chip auxiliary gain block can function as a low-battery detector or linear current drain of the LT1073 -5 used as shown in the Typical Application circuit below is just 135 A unloaded, making it ideal for applications where long battery life is important. The circuit shown can deliver 5V at 40mA from an input as low as and 5V at 10mA from a 1V device can easily be configured as a step-up or step-down Converter , although for most step-down applications or input sources greater than 3V, the LT1173 is recom-mended.

2 Switch current limiting is user- Adjustable by adding a single external resistor. Unique reverse-battery protection circuitry limits reverse current to safe, non-destructive levels at reverse supply voltages up to nNo Design Required nOperates at Supply Voltages from 1V to 30V nConsumes Only 95 A Supply Current nWorks in Step-Up or Step-Down Mode nOnly Three External Off-the-Shelf Components Required nLow-Battery Detector Comparator On-Chip nUser- Adjustable Current Limit nInternal 1A Power Switch nFixed or Adjustable Output Voltage Versions nSpace-Saving 8-Pin PDIP or SO-8 Package nPagers nCameras nSingle-Cell to 5V Converters nBattery Backup Supplies nLaptop and Palmtop Computers nCellular Telephones nPortable Instruments n4mA to 20mA Loop Powered Instruments nHand-Held Inventory Computers nBattery-Powered , , and Particle DetectorsL, LTC.

3 And LT are registered trademarks of Linear Technology to 5V ConverterSingle Alkaline AA Cell Operating Hours vs DC Load Current+1N58185V40mA100 FSANYO0S-CON1073 CELL*CADDELL-BURNS7300-1282 HOPERATES WITH CELL VOLTAGE 1 VADD 10 F DECOUPLING CAPACITOR IF BATTERY IS MORE THAN 2" AWAY FROM LT1073 *LOAD CURRENT (mA)1 CONTINUOUS OPERATION (HOURS)100010010110100LT1073 TA02L = 180 HL = 82 HLT10732 PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGSS upply Voltage, Step-Up Mode ..15 VSupply Voltage, Step-Down Mode ..36 VSW1 Pin Voltage ..50 VSW2 Pin Voltage .. to VINF eedback Pin Voltage ( LT1073 ) ..5 VSwitch Current .. Power Dissipation ..500mWOperating Temperature Range ..0 C to 70 CStorage Temperature Range .. 65 C to 150 CLead Temperature (Soldering, 10 sec) ..300 C(Note 1)ELECTRICAL CHARACTERISTICSSYMBOLPARAMETERCONDITIONS MINTYPMAXUNITSIQQ uiescent CurrentSwitch Offl95130 AIQQ uiescent Current, Step-Up Mode ConfigurationNo LoadLT1073-5 LT1073 -12135 250 A AVINI nput VoltageStep-Up VStep-Down Model30 VComparator Trip Point VoltageLT1073 (Note 2)l202212222mVVOUTO utput Sense VoltageLT1073-5 (Note 3) LT1073 -12 (Note 3)l VComparator HysteresisLT1073l510mVOutput HysteresisLT1073-5 LT1073 -12l l125 300250 600mV mVfOSCO scillator Frequencyl151923kHzDCDuty CycleFull Load (VFB = VREF)

4 L657280%tONSwitch ON Timel303850 sIFBF eedback Pin Bias CurrentLT1073, VFB = 0Vl1050nAISETSet Pin Bias CurrentVSET = VREFl60120nAVAOAO Output LowIAO = 100 Line Regulation1V VIN VIN 12Vl %VVCESATS witch Saturation Voltage Set-Up ModeVIN = , ISW = 400mA l300400 600mV mVVIN = , ISW = 500mA l400550 750mV mVVIN = 5V, ISW = 1A l7001000 1500mV mVAVA2 Error Amp GainRL = 100k (Note 4)l4001000V/V The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25 C. VIN = unless otherwise VIEWILIMVINSW1SW2FB (SENSE)*SETA0 GNDN8 PACKAGE8-LEAD PDIPS8 PACKAGE8-LEAD PLASTIC SO*FIXED VERSIONS TJMAX = 125 C, JA = 100 C/W (N8) TJMAX = 125 C, JA = 120 C/W (S8)ORDER PART NUMBERLT1073CN8LT1073CN8-5LT1073CN8-12LT 1073CS8LT1073CS8-5LT1073CS8-12S8 PART MARKING107310735107312 Consult factory for parts specified with wider operating temperature CHARACTERISTICSNote 1: Absolute Maximum Ratings are those values beyond which the life of a device may be 2: This specification guarantees that both the high and low trip point of the comparator fall within the 202mV to 222mV 3: This specification guarantees that the output voltage of the fixed versions will always fall within the specified range.

5 The waveform at the SENSE pin will exhibit a sawtooth shape due to the comparator 4: 100k resistor connected between a 5V source and the AO 5: The LT1073 is guaranteed to withstand continuous application of applied to the GND and SW2 pins while VIN, ILIM and SW1 pins are Battery Current(Note 5)750mAILIMC urrent Limit220 Between ILIM and VIN400mACurrent Limit Temperature Coefficient CILEAKS witch OFF Leakage CurrentMeasured at SW1 Pin110 AVSW2 Maximum Excursion Below GNDISW1 10 A, Switch Off 400 350mV The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25 C.

6 VIN = unless otherwise PERFORMANCE CHARACTERISTICSS aturation Voltage Step-Up Mode (SW2 Pin Grounded)Switch ON Voltage Step-Down Mode (SW1 Pin Connected to VIN)Maximum Switch Current vs RLIMFB Pin Bias Current vs TemperatureSET Pin Bias Current vs Temperature Gain Block GainISWITCH (A)0 VCESAT (V) = = = 5 VVIN = 2 VVIN = 1 VVIN = 3 VTEMPERATURE ( C) 50FB BIAS CURRENT (nA)1001073 G04050201816141210864 252575125 ISWITCH (A)0 SWITCH ON VOLTAGE (V) ( C) 50 SET PIN BIAS CURRENT (nA)1001073 G050502001751501251007550250 252575125 RLIM ( )10 SWITCH CURRENT (mA)120011001000900800700600500400300200 10010010001073 G03L = 82 HVIN = 3 VVIN = ( C) 50GB GAIN (V/V)1001073 G06050180016001400120010008006004002000 252575125 VIN = = 100kLT10734 +A1A2 COMPARATORDRIVER212mVREFERENCEOSCILLATOR GAIN BLOCK/ERROR AMPVINSETA0 ILIMSW1Q1SW2 FBGND1073 BD01 +A1A2 COMPARATORDRIVER212mVREFERENCEOSCILLATOR GAIN BLOCK/ERROR AMPVINSETA0 ILIMSW1Q1SW2 GND1073 BD02R1R2940kSENSELT1073-5: R1 = 40kLT1073-12: R2 = PERFORMANCE CHARACTERISTICSS upply Current vs TemperatureRecommended Minimum Inductance ValueGuaranteed Minimum Output Current at 5V vs VINTEMPERATURE ( C) 50 SUPPLY CURRENT ( A)1001073 G070501501401301201101009080706050 252575125 VIN = VOLTAGE (V)MINIMUM INDUCTANCE ( H)1073 = 0 VVIN (V) CURRENT (mA) G09 FOR VIN > A68 RESISTORMUST BE CONNECTED BETWEEN ILIM AND VINPIN FUNCTIONSBLOCK DIAGRAMSILIM (Pin 1): Connect this pin to VIN for normal use.

7 Where lower current limit is desired, connect a resistor between ILIM and VIN. A 220 resistor will limit the switch current to approximately (Pin 2): Input Supply VoltageSW1 (Pin 3): Collector of Power Transistor. For step-up mode connect to inductor/diode. For step-down mode connect to (Pin 4): Emitter of Power Transistor. For step-up mode connect to ground. For step-down mode connect to inductor/diode. This pin must never be allowed to go more than a Schottky diode drop below (Pin 5): (Pin 6): Auxiliary Gain Block (GB) Output. Open col-lector, can sink 100 (Pin 7): GB Input. GB is an op amp with positive input connected to SET pin and negative input connected to 212mV (Pin 8): On the LT1073 ( Adjustable ) this pin goes to the comparator input. On the LT1073 -5 and LT1073 -12, this pin goes to the internal application resistor that sets output and LT1073 -12LT10735 OPERATIONLT1073 The LT1073 is gated oscillator switcher.

8 This type archi-tecture has very low supply current because the switch is cycled only when the feedback pin voltage drops below the reference voltage. Circuit operation can best be understood by referring to the LT1073 Block Diagram. Comparator A1 compares the FB pin voltage with the 212mV reference signal. When FB drops below 212mV, A1 switches on the 19kHz oscillator. The driver amplifier boosts the signal level to drive the output NPN power switch Q1. An adap-tive base drive circuit senses switch current and provides just enough base drive to ensure switch saturation without overdriving the switch, resulting in higher efficiency. The switch cycling action raises the output voltage and FB pin voltage. When the FB voltage is sufficient to trip A1, the oscillator is gated off. A small amount of hysteresis built into A1 ensures loop stability without external frequency compensation.

9 When the comparator is low the oscillator and all high current circuitry is turned off, lowering device quiescent current to just 95 A for the reference, A1 and oscillator is set internally for 38 s ON time and 15 s OFF time, optimizing the device for step-up circuits where VOUT 3 VIN, , to 5V. Other step-up ratios as well as step-down (buck) converters are possible at slight losses in maximum achievable power is a versatile gain block that can serve as a low-battery detector, a linear post-regulator, or drive an undervolt-age lockout circuit. The negative input of A2 is internally connected to the 212mV reference. An external resistor divider from VIN to GND provides the trip point for A2. The AO output can sink 100 A (use a 56k resistor pull-up to 5V). This line can signal a microcontroller that the battery voltage has dropped below the preset resistor connected between the ILIM pin and VIN adjusts maximum switch current.

10 When the switch current exceeds the set value, the switch is turned off. This feature is espe-cially useful when small inductance values are used with high input voltages. If the internal current limit of is desired, ILIM should be tied directly to VIN. Propagation delay through the current-limit circuitry is about 2 step-up mode, SW2 is connected to ground and SW1 drives the inductor. In step-down mode, SW1 is connected to VIN and SW2 drives the inductor. Output voltage is set by the following equation in either step-up or step-down modes where R1 is connected from FB to GND and R2 is connected from VOUT to FB. VOUT=212mV()R2R1+1 LT1073 -5 and LT1073 -12 The LT1073 -5 and LT1073 -12 fixed output voltage versions have the gain-setting resistor on-chip. Only three external components are required to construct a fixed-output con-verter.