Datasheet

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LT1304/LT1304-3.3/LT1304-5

Micropower

DC/DC Converters with

Low-Battery Detector

Active in Shutdown

The LT

1304 is a micropower step-up DC/DC converter

ideal for use in small, low voltage, battery-operated sys-

tems. The devices operate from a wide input supply range

of 1.5V to 8V. The LT1304-3.3 and LT1304-5 generate

regulated outputs of 3.3V and 5V and the adjustable

LT1304 can deliver output voltages up to 25V. Quiescent

current, 120µA in active mode, decreases to just 10µA in

shutdown with the low-battery detector still active. Peak

switch current, internally set at 1A, can be reduced by

adding a single resistor from the I

LIM

pin to ground. The

high speed operation of the LT1304 allows the use of

small, surface-mountable inductors and capacitors. The

LT1304 is available in an 8-lead SO package.

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

APPLICATIONS

■

2-, 3-, or 4-Cell to 5V or 3.3V Step-Up

■

Portable Instruments

■

Bar Code Scanners

■

Palmtop Computers

■

Diagnostic Medical Instrumentation

■

Personal Data Communicators/Computers

■

5V at 200mA from Two Cells

■

10µA Quiescent Current in Shutdown

■

Operates with V

as Low as 1.5V

■

Low-Battery Detector Active in Shutdown

■

Low Switch V

CESAT

: 370mV at 1A Typical

■

120µA Quiescent Current in Active Mode

■

Switching Frequency Up to 300kHz

■

Programmable Peak Current with One Resistor

■

8-Lead SO Package

FEATURES

DESCRIPTION

TYPICAL APPLICATION

Efficiency



LOAD CURRENT (mA)

EFFICIENCY (%)

1304 TA02

0.1 1 10 500100

= 3.3V

= 2.5V

= 1.8V

SHDN GND

SENSELBI

LBOI

LIM

LT1304-5

100k

100µF

*

604k

100µF

2 CELLS

499k

22µH*

D1**

5V

200mA

LBO

LOW WHEN 

BAT

< 2.2V

SUMIDA CD54-220

1N5817

1304 TA01

SHUTDOWN

2-Cell to 5V Step-Up Converter with Low-Battery Detect

Summary of content (16 pages)

PAGE 1
LT1304/LT1304-3.3/LT1304-5 Micropower DC/DC Converters with Low-Battery Detector Active in Shutdown U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT®1304 is a micropower step-up DC/DC converter ideal for use in small, low voltage, battery-operated systems. The devices operate from a wide input supply range of 1.5V to 8V. The LT1304-3.3 and LT1304-5 generate regulated outputs of 3.3V and 5V and the adjustable LT1304 can deliver output voltages up to 25V.
PAGE 2
LT1304/LT1304-3.3/LT1304-5 W U U W W U W ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION VIN Voltage ................................................................ 8V SW Voltage ............................................... – 0.4V to 25V FB Voltage (LT1304) ...................................... VIN + 0.3V Sense Voltage (LT1304-3.3/LT1304-5) ..................... 8V ILIM Voltage .............................................................. 5V SHDN Voltage ....................................
PAGE 3
LT1304/LT1304-3.3/LT1304-5 ELECTRICAL CHARACTERISTICS VIN = 2V, VSHDN = 2V unless otherwise noted. PARAMETER CONDITIONS Switch Saturation Voltage ISW = 1A ISW = 700mA Switch Off, VSW = 5V Switch Leakage MIN TYP MAX UNITS ● 0.37 0.26 0.35 V V ● 0.01 7 µA The ● denotes specifications which apply over the 0°C to 70°C operating temperature range. U W TYPICAL PERFORMANCE CHARACTERISTICS Switch Saturation Voltage Peak Switch Current Limit 500 On- and Off-Times 1.3 8 1.2 7 200 1.
PAGE 4
LT1304/LT1304-3.3/LT1304-5 U W TYPICAL PERFORMANCE CHARACTERISTICS Burst ModeTM Operation Load Transient Response VOUT 100mV/DIV AC COUPLED VSW 5V/DIV VOUT 100mV/DIV AC COUPLED ILOAD 200mA 0 IL 500mA/DIV 100µs/DIV 1304 G07 VIN = 2.5V VOUT = 5V ILOAD = 185mA L = 22µH 20µs/DIV 1304 G08 Burst Mode is a trademark of Linear Technology Corporation. U U U PIN FUNCTIONS LBI (Pin 1): Low-Battery Detector Input. When voltage on this pin is less than 1.17V, detector output is low.
PAGE 5
LT1304/LT1304-3.3/LT1304-5 W BLOCK DIAGRA S VIN + L1 C1 LB0 2 VIN 3 + D1 4 VOUT C2 SW 1.5V UNDERVOLTAGE LOCKOUT 1 36mV LBI + + – – A3 R1 7.2Ω R2 1k A2 1.17V BIAS ~1V OFF R3 8 FB – ENABLE A1 R4 + Q3 1k TIMERS 6µs ON 1.5µs OFF DRIVER 1.24V VREF Q1 ×200 Q2 ×1 SHUTDOWN 7 SHDN 6 ILIM 5 GND 1304 F01 Figure 1. LT1304 Block Diagram. Independent Low-Battery Detector A3 Remains Alive When Device Is in Shutdown LBI LB0 VIN SW 1 2 3 4 1.
PAGE 6
LT1304/LT1304-3.3/LT1304-5 U OPERATIO The LT1304’s operation can best be understood by examining the block diagram in Figure 1. Comparator A1 monitors the output voltage via resistor divider string R3/R4 at the FB pin. When VFB is higher than the 1.24V reference, A2 and the timers are turned off. Only the reference, A1 and A3 consume current, typically 120µA. As VFB drops below 1.24V plus A1’s hysteresis (about 6mV), A1 enables the rest of the circuit.
PAGE 7
LT1304/LT1304-3.3/LT1304-5 U OPERATIO Table 1 lists inductor suppliers along with appropriate part numbers. Table 1. Recommended Inductors VENDOR SERIES PHONE NUMBER Sumida CD54, CD43 (708) 956-0666 Coiltronics CTX20-1 (407) 241-7876 Dale LPT4545 (605) 665-9301 Coilcraft DO3316, DO1608, DO3308 (708) 639-6400 Capacitor Selection Low ESR (Equivalent Series Resistance) capacitors should be used at the output of the LT1304 to minimize output ripple voltage.
PAGE 8
LT1304/LT1304-3.3/LT1304-5 U OPERATIO If the full power capability of the LT1304 is not required, peak switch current can be limited by connecting a resistor RLIM from the ILIM pin to ground. With RLIM = 22k, peak switch current is reduced to approximately 500mA. Smaller power components can then be used. The graph in Figure 6 shows switch current vs RLIM resistor value. VOUT 2V/DIV bypass capacitor is required. If the input supply is close to the IC, a 1µF ceramic capacitor can be used instead.
PAGE 9
LT1304/LT1304-3.3/LT1304-5 U OPERATIO 1000 VLBO 2V/DIV HOURS (H) 100 10 VLBI 200mV/DIV 1304 F08 Figure 8. Low-Battery Detector Transfer Function. Pull-Up R = 22k, VIN = 2V, Sweep Frequency = 10Hz 1 1 10 LOAD CURRENT (mA) 100 200 1304 F10 Figure 10. Battery Life vs Load Current. Dots Specify Actual Measurements How may hours does it work? This is the bottom line question that must be asked of any efficiency study. AA alkaline cells are not perfect power sources.
PAGE 10
LT1304/LT1304-3.3/LT1304-5 U OPERATIO 100 ELECTROCHEMICAL EFFICIENCY (%) Figure 12 shows overall energy conversion efficiency, assuming availability of 6.5WH of battery energy. This efficiency approximates the electrical efficiency at load current levels from 1mA to 10mA, but drops severely at load currents above 10mA (load power above 50mW).
PAGE 11
LT1304/LT1304-3.3/LT1304-5 U TYPICAL APPLICATIONS 2-Cell to 3.3V Converter Efficiency 2-Cell to 3.3V Boost Converter L1* 22µH MBRS130L 90 80 SW 3.3V 300mA SENSE + C1** 100µF EFFICIENCY (%) VIN LT1304-3.3 2 CELLS SHDN ILIM SHUTDOWN + GND C2** 100µF 10V NC 70 60 50 VIN = 3.3V VIN = 2.5V 2.5V VIN = 1.8V 40 *SUMIDA CD54-220 **AVX TPSD107M010R0100 30 0.1 1304 TA05 1 10 100 LOAD CURRENT (mA) 1000 1304 TA06 3.
PAGE 12
LT1304/LT1304-3.3/LT1304-5 U TYPICAL APPLICATIONS 5V to 12V DC/DC Converter L1* 22µH 5V to 12V Converter Efficiency D1† 90 5V 85 VIN + SW LT1304 12V 200mA FB SHDN SHUTDOWN 1.07M 1% GND 124k 1% EFFICIENCY (%) 47µF** + *SUMIDA CD54-220 **AVX TPSD476M016R0150 † MOTOROLA MBRS130L 47µF** 16V 80 75 70 65 1304 TA11 1 10 100 LOAD CURRENT (mA) 300 1304 TA12 Single Li-Ion Cell to 5V Converter with Load Disconnect at VIN < 2.7V 22µH** (2.7V to 4.
PAGE 13
LT1304/LT1304-3.3/LT1304-5 U TYPICAL APPLICATIONS Negative LCD Bias Generator L1* 10µH 1µF CERAMIC ** VIN 1.69M 1% SW –VOUT –14V TO –22V 1mA TO 10mA FB + 2 CELLS LT1304 47µF 90.9k 1% ILIM ** 1M 1% 110k 1% GND 1000pF ** + + 3.
PAGE 14
LT1304/LT1304-3.3/LT1304-5 U TYPICAL APPLICATIONS 2- to 4-Cell to 1kV Step-Up Converter 0.01µF VIN 2V TO 6V 0.01µF 0.01µF 0.01µF 0.01µF T1* 3 + 4 0.01µF 47µF 1 0.01µF 0.01µF AGE 6 MBR0530 VIN ER ANG D R1** 500M VOUT 1kV 250µA ( ) R2 620k LT1304 SHUTDOWN LT H VO G ! HI SW FB 0.1µF 0.01µF VOUT = 1.24V 1+ SHDN ILIM GND * DALE LPE3325-A205 TRANSFORMER MEASURES 6.5mm × 8.2mm × 5.2mm (H) (605) 665-9301 ** IRC CGX-1/2 ALL 0.
PAGE 15
LT1304/LT1304-3.
PAGE 16
LT1304/LT1304-3.3/LT1304-5 U PACKAGE DESCRIPTION Dimension in inches (millimeter) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 2 3 4 0.053 – 0.069 (1.346 – 1.752) 0.004 – 0.010 (0.101 – 0.254) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.