Datasheet

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L T 1111

1111fd

TYPICAL APPLICATIO

APPLICATIO S

DESCRIPTIO

FEATURES

33 F

SUMIDA

CD54-220M

22µH

LT1111 • TA01

MBRS120T3

100mA

GND SW2

SW1

LIM

LT1111CS8-5

SENSE

3V INPUT

10 F*

*OPTIONAL

Micropower

DC/DC Converter

Adjustable and Fixed 5V, 12V

All Surface Mount 3V to 5V Step-Up Converter

Typical Load Regulation

LOAD CURRENT (mA)

OUTPUT VOLTAGE (V)

50 100 150 200

LT1111 • TA02

25 75 125 175

= 2V 2.2 2.4 2.6 2.8 3V

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Operates at Supply Voltages from 2V to 30V

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Works with Surface Mount Inductors

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72kHz Oscillator

■

Only Three External Components Required

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Step-Up or Step-Down Mode

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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 MiniDIP or SO-8 Package

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

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9V to 5V, 12V to 5V Converters

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Remote Controls

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Peripherals and Add-On Cards

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Battery Backup Supplies

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Uninterruptible 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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Flash Memory VPP Generators

The LT

1111 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 LT1111 functions equally well in step-up, step-

down, or inverting applications.

The LT1111 oscillator is set at 72kHz, optimizing the

device to work with off-the-shelf surface mount inductors.

The device can deliver 5V at 100mA from a 3V input in

step-up mode or 5V at 200mA from a 12V input in step-

down mode.

Switch current limit can be programmed with a single

resistor. An auxiliary open-collector gain block can be

configured as a low-battery detector, linear post regulator,

undervoltage lock-out circuit, or error amplifier.

For input sources of less than 2V use the LT1110.

, LTC and LT are registered trademarks of Linear Technology Corporation

Summary of content (16 pages)

PAGE 1
LT1111 Micropower DC/DC Converter Adjustable and Fixed 5V, 12V U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Operates at Supply Voltages from 2V to 30V Works with Surface Mount Inductors 72kHz Oscillator Only Three External Components Required Step-Up or Step-Down Mode 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 The LT®1111 is a versatile micropower DC/DC converter.
PAGE 2
LT1111 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 (LT1111) ............................. 5.5V Switch Current ....................................................... 1.5A Maximum Power Dissipation ............................ 500mW Operating Temperature Range LT1111C ...........
PAGE 3
LT1111 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.VIN = 3V, Military or Commercial Version SYMBOL PARAMETER CONDITIONS TYP MAX UNITS IFB Feedback Pin Bias Current LT1111, VFB = 0V ● MIN 70 120 nA ISET Set Pin Bias Current VSET = VREF ● 70 300 nA VOL Gain Block Output Low ISINK = 300µA, VSET = 1.00V ● 0.15 0.
PAGE 4
LT1111 U W TYPICAL PERFOR A CE CHARACTERISTICS Oscillator Frequency Oscillator Frequency 90 10 74 9.5 9.0 70 60 8.5 72 ON TIME (µs) 80 71 70 7.0 5.5 67 –25 25 75 0 50 TEMPERATURE (°C) 100 125 3 0 6 5.0 –50 9 12 15 18 21 24 27 30 INPUT VOLTAGE (V) 56 0.8 54 52 50 48 46 44 VIN = 3V 1.2 0.7 0.6 0.5 0.4 0.3 0.2 100 0 –50 125 VIN = 2V 1.0 0.8 VIN = 5V 0.6 0.4 0.2 0.1 42 – 25 50 75 0 25 TEMPERATURE (°C) LT1111 • TPC04 100 0 125 0 0.2 0.4 0.6 0.8 1.0 1.
PAGE 5
LT1111 U W TYPICAL PERFOR A CE CHARACTERISTICS Quiescent Current Quiescent Current 500 400 450 340 320 300 280 260 240 400 SWITCH CURRENT (A) 360 QUIESCENT CURRENT (µA) QUIESCENT CURRENT (µA) 380 350 300 250 200 150 220 200 0 3 6 9 12 15 18 21 24 27 30 INPUT VOLTAGE (V) 100 –50 –25 0 25 50 75 TEMPERATURE (°C) LT1111 • TPC10 100 125 Set Pin Bias Current 80 70 70 BIAS CURRENT (nA) 90 80 BIAS CURRENT (nA) 90 60 50 40 30 10 100 RLIM (Ω) 1000 LT1111 • TPC12 60 50 40 30 20 2
PAGE 6
LT1111 W BLOCK DIAGRA S LT1111 LT1111-5/LT1111-12 SET + SET A2 A2 A0 – V IN I LIM GAIN BLOCK/ ERROR AMP 1.25V REFERENCE – – DRIVER OSCILLATOR DRIVER COMPARATOR SW2 FB SW1 + A1 OSCILLATOR COMPARATOR GND I LIM SW1 + A1 A0 – V IN GAIN BLOCK/ ERROR AMP 1.25V REFERENCE + R1 SW2 R2 220k SENSE LT1111 • BD01 GND LT1111-5: R1 = 73.5k LT1111-12: R1 = 25.5k LT1111 • BD02 U OPERATIO The LT1111 is a gated oscillator switcher.
PAGE 7
LT1111 U W U UO APPLICATI S I FOR ATIO Inductor Selection — General PL / f OSC A DC/DC converter operates by storing energy as magnetic flux in an inductor core, and then switching this energy into the load. Since it is flux, not charge, that is stored, the output voltage can be higher, lower, or opposite in polarity to the input voltage by choosing an appropriate switching topology. To operate as an efficient energy transfer element, the inductor must fulfill three requirements.
PAGE 8
LT1111 U W U UO APPLICATI S I FOR ATIO Picking an inductor value of 47µH with 0.2Ω DCR results in a peak switch current of: I PEAK –1.0 Ω • 7 µs   4.5V  1 – e 47µH  = 623mA . =  1.0Ω    (8) Substituting IPEAK into Equation 4 results in: ( )( 1 E L = 47µH 0.623A 2 ) 2 = 9.1µJ VD = diode drop (0.5V for a 1N5818) IOUT = output current VOUT = output voltage VIN = minimum input voltage VSW is actually a function of switch current which is in turn a function of VIN, L, time, and VOUT.
PAGE 9
LT1111 U W U UO APPLICATI S I FOR ATIO switch closes, current in the inductor builds according to IL  VL 1 – e t = R′   () –R′ t  L    (15) where R′ = 0.65Ω + DCRL VL = VIN – 0.75V As an example, suppose –5V at 50mA is to be generated from a 4.5V to 5.5V input. Recalling Equation (14), PL = (-5V+0.5V)(50mA) = 275mW (16) Energy required from the inductor is: PL 275mW = = 3.8µJ.
PAGE 10
LT1111 W U U UO APPLICATI S I FOR ATIO At the end of the switch ON time the current in L1 is1: Diode Selection Speed, forward drop, and leakage current are the three main considerations in selecting a catch diode for LT1111 converters. General purpose rectifiers such as the 1N4001 are unsuitable for use in any switching regulator application. Although they are rated at 1A, the switching time of a 1N4001 is in the 10µs to 50µs range.
PAGE 11
LT1111 U W U UO APPLICATI S I FOR ATIO When the switch turns off, the SW2 pin falls rapidly and actually goes below ground. D1 turns on when SW2 reaches 0.4V below ground. D1 MUST BE A SCHOTTKY DIODE. The voltage at SW2 must never be allowed to go below –0.5V. A silicon diode such as the 1N4933 will allow SW2 to go to –0.8V, causing potentially destructive power dissipation inside the LT1111. Output voltage is determined by: VOUT  R2 =  1 +  1.
PAGE 12
LT1111 W U U UO APPLICATI S I FOR ATIO D1 L1 VOUT + C1 I LIM + C2 VIN SW1 R1 IL 2N3906 LT1111 A0 GND FB SW2 R2 –VIN SWITCH LT1111 • F08 ON OFF ( ) VOUT = R1 1.25V + 0.6V R2 LT1111 • F09 Figure 9. No Current Limit Causes Large Inductor Current Build-Up Figure 8. Negative-to-Positive Converter PROGRAMMED CURRENT LIMIT Using the ILIM Pin The LT1111 switch can be programmed to turn off at a set switch current, a feature not found on competing devices.
PAGE 13
LT1111 W U U UO APPLICATI S I FOR ATIO Using the Gain Block The gain block (GB) on the LT1111 can be used as an error amplifier, low-battery detector or linear post regulator. The gain block itself is a very simple PNP input op amp with an open collector NPN output. The negative input of the gain block is tied internally to the 1.25V reference. The positive input comes out on the SET pin. Arrangement of the gain block as a low-battery detector is straightforward. Figure 12 shows hookup.
PAGE 14
LT1111 UO TYPICAL APPLICATI S 3V to – 22V LCD Bias Generator L1* 27µH 1N4148 R1 100Ω ILIM 732k 1% V IN SW1 2 × 1.5V CELLS LT1111 3V 0.1µF FB GND SW2 + 4.7µF 39.2k 1% MBRS130T3 MBRS130T3 + 22µF 220k * L1 = SUMIDA CD54-270K FOR 5V INPUT CHANGE R1 TO 47Ω. CONVERTER WILL DELIVER –22V AT 40mA.
PAGE 15
LT1111 U PACKAGE DESCRIPTIO J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic) (Reference LTC DWG # 05-08-1110) 0.300 BSC (0.762 BSC) 0.200 (5.080) MAX CORNER LEADS OPTION (4 PLCS) 0.008 – 0.018 (0.203 – 0.457) 0° – 15° 0.015 – 0.060 (0.381 – 1.524) 0.023 – 0.045 (0.584 – 1.143) HALF LEAD OPTION 0.045 – 0.068 (1.143 – 1.727) FULL LEAD OPTION 0.405 (10.287) MAX 0.005 (0.127) MIN 8 NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE OR TIN PLATE LEADS 0.014 – 0.026 (0.360 – 0.660) 0.100 (2.
PAGE 16
LT1111 UO TYPICAL APPLICATI S High Power, Low Quiescent Current Step-Down Converter 0.22Ω VIN 8V TO 18V MTM20P08 BAT54 2k 51Ω L1* 10µH, 3A MBRD320 5V 500mA + 220µF 2N3904 V IN ILIM SW1 1N4148 LT1111 121k FB GND SW2 40.