Datasheet

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LT1107

1107fa

FEATURES

APPLICATIO S

DESCRIPTIO

TYPICAL APPLICATIO

Micropower

DC/DC Converter

Adjustable and Fixed 5V, 12V

Efficiency

■

Operates at Supply Voltages from 2V to 30V

■

Consumes Only 320µA Supply Current

■

Works in Step-Up or Step-Down Mode

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Only Three External Components Required

■

Low-Battery Detector Comparator On-Chip

■

User Adjustable Current Limit

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Internal 1A Power Switch

■

Fixed or Adjustable Output Voltage Versions

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Space Saving 8-Pin MiniDIP or SO-8 Package

The LT

1107 is a versatile micropower DC/DC converter.

The device requires only three external components to

deliver a fixed output of 5V or 12V. Supply voltage ranges

from 2V to 12V in step-up mode and to 30V in step-down

mode. The LT1107 functions equally well in step-up, step-

down, or inverting applications.

The LT1107 is pin-for-pin compatible with the

LT1111, but

has a duty cycle of 70%, resulting in increased output

current in many applications. The LT1107 can deliver

150mA at 5V from a 2AA cell input and 5V at 300mA from

24V in step-down mode. Quiescent current is just 320µA,

making the LT1107 ideal for power-conscious battery-

operated systems. The 63kHz oscillator is optimized to

work with surface mount inductors and capacitors.

Switch current limit can be programmed with a single

resistor. An auxiliary gain block can be configured as a

low-battery detector, linear post regulator, undervoltage

lock-out circuit, or error amplifier.

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Palmtop Computers

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3V to 5V, 5V to 12V Converters

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24V to 5V, 12V to 5V Converters

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LCD Bias Generators

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Peripherals and Add-On Cards

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Battery Backup Supplies

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Cellular Telephones

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Portable Instruments

LOAD CURRENT (mA)

EFFICIENCY (%)

10 100 400

1107 TA02

= 3V

= 2.5V

= 2V

150mA

MBRS120T3

L1*

33µH

47Ω

2 × AA

ALKALINE

CELLS

100µF

SUMIDA CD54-330K

COILCRAFT DT3316-473

LIM

SENSE

SW1

SW2GND

47µF

LT1107-5

1107 TA01

Palmtop Computer Logic Supply

, LTC and LT are registered trademarks of Linear Technology Corporation

Summary of content (16 pages)

PAGE 1
LT1107 Micropower DC/DC Converter Adjustable and Fixed 5V, 12V U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Operates at Supply Voltages from 2V to 30V Consumes Only 320µA Supply Current Works in Step-Up or Step-Down Mode Only Three External 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 MiniDIP or SO-8 Package U APPLICATIO S ■ ■ ■ ■ ■ ■ ■ Palmtop Computers 3V to 5V, 5V to 12V C
PAGE 2
LT1107 W W W AXI U U ABSOLUTE RATI GS (Note 1) Supply Voltage (VIN) ............................................... 36V SW1 Pin Voltage (VSW1) ......................................... 50V SW2 Pin Voltage (VSW2) ............................ – 0.5V to VIN Feedback Pin Voltage (LT1107) ................................ 5V Sense Pin Voltage (LT1107-5, LT1107-12) ............ 36V Maximum Power Dissipation ............................ 500mW Set Pin Voltage ..................................................
PAGE 3
LT1107 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, VIN = 3V, military or commercial version, TA = 25°C, unless otherwise noted. SYMBOL VOL AV PARAMETER CONDITIONS TYP MAX UNITS Feedback Pin Bias Current LT1107, VFB = 0V ● MIN 70 120 nA Set Pin Bias Current VSET = VREF ● 70 300 nA Gain Block Output Low ISINK = 300µA, VSET = 1V ● 0.15 0.4 Reference Line Regulation 5V ≤ VIN ≤ 30V ● 0.02 0.
PAGE 4
LT1107 U W TYPICAL PERFOR A CE CHARACTERISTICS Saturation Voltage, Step-Up Mode (SW2 Pin Grounded) Switch ON Voltage, Step-Down Mode (SW1 Pin Connected to VIN) 1.2 SWITCH ON VOLTAGE (V) SATURATION VOLTAGE (V) VIN = 3V 0.8 VIN = 2V VIN = 5V 0.6 0.4 0.2 SWITCH CURRENT (A) 1.3 1.0 0 1.2 1.1 1.0 0.9 0.8 0 0.2 0.4 0.6 0.8 SWITCH CURRENT (A) 1.0 0.7 1.2 0 0.1 0.3 0.4 0.5 0.6 SWITCH CURRENT (A) 0.2 1107 G01 0.7 Quiescent Current 0.
PAGE 5
LT1107 U W TYPICAL PERFOR A CE CHARACTERISTICS 100 100 90 90 70 60 50 –55°C ≤ TA ≤ 125°C 40 30 70 0°C ≤ TA ≤ 70°C 60 80 70 60 50 TA = 25°C 40 –55°C ≤ TA ≤ 125°C 5 6 7 8 9 10 11 12 13 14 ON TIME (µs) 6 7 8 9 35 –55 –35 –15 1107 G13 LT1107-12 Output Voltage 5.3 LT1107 Feedback Voltage 1.30 12.20 1.29 OUTPUT VOLTAGE (V) 5.0 4.9 4.8 TRIP POINT VOLTAGE (V) 12.15 5.2 5.1 12.10 12.05 12.00 11.95 11.90 11.80 –55 –35 –15 1.28 1.27 1.26 1.25 1.24 1.23 1.22 11.
PAGE 6
LT1107 W BLOCK DIAGRA S LT1107 LT1107-5/LT1107-12 SET SET A2 A2 AO VIN GAIN BLOCK/ ERROR AMP ILIM GAIN BLOCK/ ERROR AMP SW1 ILIM SW1 1.25V REFERENCE 1.25V REFERENCE A1 A1 OSCILLATOR FB OSCILLATOR DRIVER DRIVER COMPARATOR COMPARATOR GND AO VIN SW2 1107 BD01 R1 GND R2 220k SW2 SENSE LT1107-5: R1 = 73.5k LT1107-12: R1 = 25.5k 1107 BD02 U OPERATIO The LT1107 is a gated oscillator switcher.
PAGE 7
LT1107 U W U UO APPLICATI S I FOR ATIO Inductor Selection –– Step-Up Converter In a step-up, or boost converter (Figure 1), power generated by the inductor makes up the difference between input and output. Power required from the inductor is determined by: ( ) PL =  VOUT + V D − VIN(MIN)  IOUT   (1) where VD is the diode drop (0.5V for a 1N5818 Schottky).
PAGE 8
LT1107 U W U UO APPLICATI S I FOR ATIO where DC = duty cycle (0.50 in step-down mode) VSW = switch drop in step-down mode VD = diode drop (0.5V for a 1N5818) IOUT = output current VOUT = output voltage VIN = minimum input voltage In this mode the switch is arranged in common collector or step-down mode. The switch drop can be modeled as a 0.75V source in series with a 0.65Ω resistor.
PAGE 9
LT1107 W U U UO APPLICATI S I FOR ATIO The usual step-up configuration for the LT1107 is shown in Figure 1. The LT1107 first pulls SW1 low causing VIN – VCESAT to appear across L1. A current then builds up in L1. At the end of the switch ON time the current in L1 is1: VIN + C2 R3 100Ω ILIM VIN SW1 FB LT1107 V IPEAK = IN t ON L (20) L1 VOUT SW2 GND D1 1N5818 D1 L1 R2 + C1 VOUT VIN R1 R3 R2 VIN ILIM 1107 F02 + SW1 Figure 2.
PAGE 10
LT1107 W U U UO APPLICATI S I FOR ATIO VOUTshould be less than 6.2V. More negative output voltages can be accommodated as in the prior section. In Figure 4, 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.
PAGE 11
LT1107 U W U UO APPLICATI S I FOR ATIO IL ON SWITCH OFF 1107 F05 Figure 5. No Current Limit Causes Large Inductor Current Build-Up IL SWITCH PROGRAMMED CURRENT LIMIT ON OFF 1107 F06 Figure 6.
PAGE 12
LT1107 U W U UO APPLICATI S I FOR ATIO Figure 7 details current limit circuitry. Sense transistor A1, whose base and emitter are paralleled with power switch Q2, is ratioed such that approximately 0.5% of Q2’s collector current flows in Q1’s collector. This current is passed through internal 80Ω resistor R1 and out through the ILIM pin. The value of the external resistor connected between ILIM and VIN sets the current limit.
PAGE 13
LT1107 U PACKAGE DESCRIPTIO J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic) (Reference LTC DWG # 05-08-1110) CORNER LEADS OPTION (4 PLCS) 0.023 – 0.045 (0.584 – 1.143) HALF LEAD OPTION 0.045 – 0.068 (1.143 – 1.727) FULL LEAD OPTION 0.005 (0.127) MIN 0.405 (10.287) MAX 8 7 6 5 0.025 (0.635) RAD TYP 0.220 – 0.310 (5.588 – 7.874) 1 0.300 BSC (0.762 BSC) 2 3 4 0.200 (5.080) MAX 0.015 – 0.060 (0.381 – 1.524) 0.008 – 0.018 (0.203 – 0.
PAGE 14
LT1107 U PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .400* (10.160) MAX 8 7 6 5 1 2 3 4 .255 ± .015* (6.477 ± 0.381) .300 – .325 (7.620 – 8.255) .009 – .015 (0.229 – 0.381) ( +.035 .325 –.015 8.255 +0.889 –0.381 ) .045 – .065 (1.143 – 1.651) .130 ± .005 (3.302 ± 0.127) .065 (1.651) TYP .100 (2.54) BSC .125 (3.175) .020 MIN (0.508) MIN .018 ± .003 (0.457 ± 0.076) N8 0502 NOTE: 1.
PAGE 15
LT1107 U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 7 6 5 N N .245 MIN .160 ±.005 1 .030 ±.005 TYP .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 2 3 4 .053 – .069 (1.346 – 1.752) .004 – .010 (0.101 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.
PAGE 16
LT1107 UO TYPICAL APPLICATI 24V-to-5V Step-Down Converter 24VIN 220Ω VIN ILIM SW1 + 22µF LT1107-5 SENSE GND SW2 150µH* + 1N5818 5V 300mA 330µF 1107 TA03 *COILTRONICS CTX150-4 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1070/LT1070HV 5A ISW, 40kHz, High Efficiency Switching Regulator VIN = 3V to 40V/60V, VOUT = 65V/75V, IQ = 6mA, ISD = <50µA, Can be Used for Buck, Boost, Inverting Applications, TO220-5 Packages LT1071/LT1071HV 2.