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LT1073

APPLICATIO S

DESCRIPTIO

FEATURES

TYPICAL APPLICATION

The 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 post-regulator.

Average current drain of the LT1073-5 used as shown in

the Typical Application circuit below is just 135µA un-

loaded, 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 1.25V and 5V at 10mA from a 1V

input.

The device can easily be configured as a step-up or step-

down converter, although for most step-down applica-

tions or input sources greater than 3V, the LT1173 is

recommended. Switch current limiting is user-adjustable

by adding a single external resistor. Unique reverse-

battery protection circuitry limits reverse current to safe,

nondestructive levels at reverse supply voltages up to

1.6V.

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Pagers

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Cameras

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Single-Cell to 5V Converters

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Battery Backup Supplies

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Laptop and Palmtop Computers

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Cellular Telephones

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Portable Instruments

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4mA to 20mA Loop Powered Instruments

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Hand-Held Inventory Computers

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Battery-Powered α, β, and γ Particle Detectors

, LTC and LT are registered trademarks of Linear Technology Corporation.

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No Design Required

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Operates at Supply Voltages from 1V to 30V

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Consumes Only 95µA Supply Current

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Works in Step-Up or Step-Down Mode

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Only Three External Off-the-Shelf Components

Required

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Low-Battery Detector Comparator On-Chip

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User-Adjustable Current Limit

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Internal 1A Power Switch

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Fixed or Adjustable Output Voltage Versions

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Space-Saving 8-Pin PDIP or SO-8 Package

Micropower

DC/DC Converter

Adjustable and Fixed 5V, 12V

1N5818

40mA

100µF

SANYO

0S-CON

1073 TA01

LT1073-5

LIM

SW1

SENSE

SW2GND

1.5V

AA CELL*

CADDELL-BURNS

7300-12

82µH

OPERATES WITH CELL VOLTAGE ≥1V

ADD 10µF DECOUPLING CAPACITOR IF

BATTERY IS MORE THAN 2" AWAY FROM LT1073

LOAD CURRENT (mA)

CONTINUOUS OPERATION (HOURS)

1000

100

10 100

LT1073 TA02

L = 180µH

L = 82µH

Single-Cell to 5V Converter

Single Alkaline “AA” Cell Operating

Hours vs DC Load Current

Summary of content (16 pages)

PAGE 1
LT1073 Micropower DC/DC Converter Adjustable and Fixed 5V, 12V U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO No Design Required Operates at Supply Voltages from 1V to 30V Consumes Only 95µA Supply Current Works in Step-Up or Step-Down Mode Only Three External Off-the-Shelf Components Required Low-Battery Detector Comparator On-Chip User-Adjustable Current Limit Internal 1A Power Switch Fixed or Adjustable Output Voltage Versions Space-Saving 8-Pin PDIP or SO-8 Package U APPLICATIO S ■ ■ ■ ■ ■ ■ ■ ■ ■ Pag
PAGE 2
LT1073 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage, Step-Up Mode ................................ 15V Supply Voltage, Step-Down Mode ........................... 36V SW1 Pin Voltage ...................................................... 50V SW2 Pin Voltage ........................................... –0.4 to VIN Feedback Pin Voltage (LT1073) ................................. 5V Switch Current ........................................................ 1.
PAGE 3
LT1073 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.5V unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP IREV Reverse Battery Current (Note 5) 750 mA ILIM Current Limit 220Ω Between ILIM and VIN 400 mA Current Limit Temperature Coefficient MAX UNITS –0.
PAGE 4
LT1073 U W TYPICAL PERFOR A CE CHARACTERISTICS Recommended Minimum Inductance Value Supply Current vs Temperature SUPPLY CURRENT (µA) 130 120 110 100 90 80 70 1000 RLIM = 0V 250 OUTPUT CURRENT (mA) 140 300 VIN = 1.5V MINIMUM INDUCTANCE (µH) 150 Guaranteed Minimum Output Current at 5V vs VIN 200 150 100 100 FOR VIN > 1.6V A 68Ω RESISTOR MUST BE CONNECTED BETWEEN ILIM AND VIN 50 60 50 –50 –25 25 0 50 75 100 125 0 1.0 1.5 TEMPERATURE (°C) 2.0 2.5 3.0 3.5 4.0 INPUT VOLTAGE (V) 4.
PAGE 5
LT1073 U OPERATIO LT1073 The LT1073 is gated oscillator switcher. This type architecture 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.
PAGE 6
LT1073 U W U U APPLICATIO S I FOR ATIO Table 1. Component Selection for Step-Up Converters INPUT VOLTAGE (V) BATTERY TYPE OUTPUT VOLTAGE (V) OUTPUT CURRENT (MIN) INDUCTOR VALUE (µH) INDUCTOR PART NUMBER CAPACITOR VALUE (µF) 1.55-1.25 Single Alkaline 3 60mA 82 G GA10-822K, CB 7300-12 150 1.30-1.05 Single Ni-Cad 3 20mA 180 G GA10-183K, CB 7300-16 47 1.55-1.25 Single Alkaline 5 30mA 82 G GA10-822K, CB 7300-12 100 1.30-1.
PAGE 7
LT1073 U W U U APPLICATIO S I FOR ATIO Specifying a proper inductor for an application requires first establishing minimum and maximum input voltage, output voltage and output current. In a step-up converter, the inductive events add to the input voltage to produce the output voltage. Power required from the inductor is determined by: PL = (VOUT + VD – VIN)(IOUT) where VD is the diode drop (0.5V for a 1N5818 Schottky).
PAGE 8
LT1073 U W U U APPLICATIO S I FOR ATIO 50mV/DIV 50mV/DIV 50mV/DIV 20µs/DIV 20µs/DIV Figure 3. Aluminum Figure 4. Tantalum microampere range, a leaky capacitor will noticeably decrease efficiency. In this type application tantalum capacitors are the best choice, with typical leakage currents in the 1µA to 5µA range. Diode Selection Speed, forward drop and leakage current are the three main considerations in selecting a catch diode for LT1073 converters.
PAGE 9
LT1073 U W U U APPLICATIO S I FOR ATIO VOUT  R2 =  1 +  212mV  R1 ( ) Step-Down (Buck Mode) Operation A step-down DC/DC converter converts a higher voltage to a lower voltage. It is short-circuit protected because the VIN R3 220Ω R3 programs switch current limit. This is especially important in applications where the input varies over a wide range. Without R3, the switch stays on for a fixed time each cycle.
PAGE 10
LT1073 U W U U APPLICATIO S I FOR ATIO In Figure 9, the input is negative while the output is positive. In this configuration, the magnitude of the input voltage can be higher or lower than the output voltage. A level shift, provided by the PNP transistor, supplies proper polarity feedback information to the regulator. Using the ILIM Pin The LT1073 switch can be programmed to turn off at a set switch current, a feature not found on competing devices.
PAGE 11
LT1073 U W U U APPLICATIO S I FOR ATIO L1 VOUT 5V VIN R1 VBAT 212mV REF SET R3 680k LT1073 100k – A0 ILIM VIN AO SW1 TO PROCESSOR + FB VBAT + C1 SET GND SW2 R1 V LB ( 212mV –1) R1 = R2 R2 LT1073 R2 GND D1 Table 2. Inductor Manufacturers )( ( 1073 F12 Figure 12. Settling Low Battery Detector Trip Point 1073 F13 VOUT = R2 + 1 212mV R1 VLB = BATTERY TRIP POINT ) Figure 13. Output Ripple Reduction Using Gain Block Table 3.
PAGE 12
LT1073 U TYPICAL APPLICATIO S 1.5V to 12V Step-Up Converter L1† 120µH L1† 68µH 12V OUTPUT 5mA AT VBATTERY = 1V 16mA AT VBATTERY = 1.5V ILIM + SW1 TWO 1.5V CELLS 47µF LT1073-12 † 5V OUTPUT 100mA AT VBATTERY = 2V VIN + SW1 100µF LT1073-5 SENSE SENSE GND 1N5818 100Ω VIN ILIM 1.
PAGE 13
LT1073 U TYPICAL APPLICATIO S 1.5V to 5V Step-Up Converter with Logic Shutdown L1† 82µH 1.5V to 5V Step-Up Converter with Low-Battery Detector L1† 82µH 1N5818 1N5818 5V OUTPUT 5V OUTPUT 909k* ILIM 1.5V CELL + SW1 1.5V CELL 442k* VIN 100µF LT1073 100k ILIM VIN SET SW1 + 100µF LT1073-5 100k* FB GND AO SW2 40.2k* 1N4148 1073 TA11 OPERATE SW2 LO BAT GOES LOW AT VBATTERY = 1.
PAGE 14
LT1073 U TYPICAL APPLICATIO S 1.5V to 5V Low Noise Step-Up Converter 3V to 5V Step-Up Converter with Undervoltage Lockout L1† 68µH 100k 909k* 100Ω 100k 2N3906 3V ILIM VIN AO SW1 SET + 100k* ILIM VIN FB SW1 1.5V 100µF AO SW2 40.3k* * 1% METAL FILM L1 = GOWANDA GA10-682k OR CADDELL-BURNS 7300-11 909k* + SW2 40.2k* * 1% METAL FILM † L1 = GOWANDA GA10-822k OR CADDELL-BURNS 7300-12 1073 TA17 1.
PAGE 15
LT1073 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) ( 0.045 – 0.065 (1.143 – 1.651) 0.130 ± 0.005 (3.302 ± 0.127) 0.065 (1.651) TYP +0.035 0.325 –0.015 +0.889 8.255 –0.381 0.400* (10.160) MAX ) 8 7 6 5 1 2 3 4 0.255 ± 0.015* (6.477 ± 0.381) 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 0.100 (2.54) BSC (0.457 ± 0.
PAGE 16
LT1073 U TYPICAL APPLICATIO S 1.5V Powered Temperature Compensated Crystal Oscillator L1† 820µH 1.5V 30.1k* 27.4k* 150k* + LT1017 150k 1.5V – 6.81K* ILIM VIN FB SW1 1k LT1073 A0 SET LM134-3 SW2 1.5V 1.5V 2N3906 100k 2N3906 1N4148 150k* 73.2k* + + 47µF 100Ω 100k 39.2k* 47µF 10M* 2N3904 OUTPUT 1MHz 0.05ppm/°C 0.02µF * 1% METAL FILM L1 = J.W. MILLER #100267 = AT CUT –35° 20' ANGLE 510pF 2k † 100k 1MHz 560k MV209 510pF 1073 TA23 1.