LT1110-12

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The LT1110 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 1.0V allows the use of the LT1110 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. The 70kHz oscillator allows the use of surface mount inductors and capacitors in many applications. Quiescent current is just 300µA, making the device ideal in remote or battery powered applications where current consumption must be kept to a minimum. The 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 LT1111 is recommended. 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 1.6V. SFEATURE n Operates at Supply Voltages From 1.0V to 30V n Works in Step-Up or Step-Down Mode n Only Three External Off-the-Shelf Components Required n Low-Battery Detector Comparator On-Chip n User-Adjustable Current Limit n Internal 1A Power Switch n Fixed or Adjustable Output Voltage Versions n Space-Saving 8-Pin MiniDIP or S8 Package USA OPPLICATI n Pagers n Cameras n Single-Cell to 5V Converters n Battery Backup Supplies n Laptop and Palmtop Computers n Cellular Telephones n Portable Instruments n Laser Diode Drivers n Hand-Held Inventory Computers Micropower DC-DC Converter Adjustable and Fixed 5V, 12V LOAD CURRENT (mA) EFFICIENCY (%) 10 20 30 40 LT1110 • TA02 51 5 2 5 3 5 VIN = 1.50V VIN = 1.25V VIN = 1.00V UA OPPLICATITYPICAL Efficiency All Surface Mount Single Cell to 5V Converter LT1110 • TA01 +GND SW2 SENSE SW1 LIMI INV LT1110-51.5V AA CELL* *ADD 10 F DECOUPLING CAPACITOR IF BATTERY IS MORE THAN 2" AWAY FROM LT1110. µ 15µF TANTALUM MBRS120T3 SUMIDA CD54-470K 47µH OPERATES WITH CELL VOLTAGE 1.0V≥

WU UPACKAGE/ORDER I FOR ATIOA UGWA WU WARBSOLUTEX I T I S ORDER PART NUMBER LT1110CN8 LT1110CN8-5 LT1110CN8-12 1110 11105 11012 Consult factory for Industrial and Military grade parts. TJMAX = 90°C, θJA = 150°C/W TOP VIEW ILIM VIN SW1 SW2 FB (SENSE)* SET GND N8 PACKAGE 8-LEAD PLASTIC DIP *FIXED VERSIONS TJMAX = 90°C, θJA = 130°C/W TOP VIEW FB (SENSE)* SET GND I LIM VIN SW1 SW2 S8 PACKAGE 8-LEAD PLASTIC SOIC *FIXED VERSIONS SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS IQ Quiescent Current Switch Off l 300 µA VIN Input Voltage Step-Up Mode l 1.15 12.6 V 1.0 12.6 V Step-Down Mode l 30 V Comparator Trip Point Voltage LT1110 (Note 1) l 210 220 230 mV VOUT Output Sense Voltage LT1110-5 (Note 2) l 4.75 5.00 5.25 V LT1110-12 (Note 2) l 11.4 12.00 12.6 V Comparator Hysteresis LT1110 l 48 m V Output Hysteresis LT1110-5 l 90 180 mV LT1110-12 l 200 400 mV fOSC Oscillator Frequency l 52 70 90 kHz DC Duty Cycle Full Load (V FB < VREF) l 62 69 78 % tON Switch ON Time l 7.5 10 12.5 µs IFB Feedback Pin Bias Current LT1110, V FB = 0V l 70 150 nA ISET Set Pin Bias Current V SET = VREF l 100 300 nA VAO AO Output Low I AO = –300µA, VSET = 150mV l 0.15 0.4 V Reference Line Regulation 1.0V ≤ VIN ≤ 1.5V l 0.35 1.0 %/V 1.5V ≤ VIN ≤ 12V l 0.05 0.1 %/V ELECTRICAL C CHARA TERISTICS TA = 25°C, VIN = 1.5V, unless otherwise noted. S8 PART MARKING LT1110CS8 LT1110CS8-5 LT1110CS8-12

VCESAT Switch Saturation Voltage V IN = 1.5V, ISW = 400mA 300 400 mV Step-Up Mode l 600 mV VIN = 1.5V, ISW = 500mA 400 550 mV l 750 mV VIN = 5V, ISW = 1A 700 1000 mV AV A2 Error Amp Gain R L = 100kΩ (Note 3) l 1000 5000 V/V IREV Reverse Battery Current (Note 4) 750 mA ILIM Current Limit 220 Ω Between ILIM and VIN 400 mA Current Limit Temperature – 0.3 %/ °C Coefficient ILEAK Switch OFF Leakage Current Measured at SW1 Pin 1 10 µA VSW2 Maximum Excursion Below GND I SW1 ≤ 10µA, Switch Off – 400 – 350 mV ELECTRICAL C CHARA TERISTICS TA = 25°C, VIN = 1.5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Note 3: 100kΩ resistor connected between a 5V source and the AO pin. Note 4: The LT1110 is guaranteed to withstand continuous application of +1.6V applied to the GND and SW2 pins while VIN, ILIM, and SW1 pins are grounded. The l denotes the specifications which apply over the full operating temperature range. Note 1: This specification guarantees that both the high and low trip point of the comparator fall within the 210mV to 230mV range. Note 2: This specification guarantees that the output voltage of the fixed versions will always fall within the specified range. The waveform at the sense pin will exhibit a sawtooth shape due to the comparator hysteresis. CCHARA TERISTICSUWATYPICALP E RFOR CE Oscillator Frequency Oscillator Frequency Switch On Time INPUT VOLTAGE (V) FREQUENCY (KHz)66 36 91 2 LT1110 • TPC02 15 18 21 24 27 30 TEMPERATURE (°C) ON TIME (µs) –50 –25 0 25 LT1110 • TPC03 50 75 100 TEMPERATURE (°C) –50 OSCILLATOR FREQUENCY (KHz)50 100 –25 0 25 50 LT1110 • TPC01 75 100

ISWITCH (A) ON VOLTAGE (V) 0 0.2 0.4 0.6 LT1110 • TPC07 0.8 1.0 1.4 1.2 1.0 0.8 0.6 0.4 0.2 VIN = 12V CCHARA TERISTICSUWATYPICALP E RFOR CE Saturation Voltage Duty Cycle Switch Saturation Voltage Step-Up Mode Switch On Voltage Minimum/Maximum Frequency vs Step-Down Mode On Time Quiescent Current Maximum Switch Current vs Maximum Switch Current vs Quiescent Current R LIM Step-Up R LIM Step-Down TEMPERATURE (°C) DUTY CYCLE (%) –50 –25 0 25 LT1110 • TPC04 50 75 100 TEMPERATURE (°C) VCESAT (mV) –50 – 25 0 25 LT1110 • TPC05 50 75 100 500 450 400 350 300 250 200 150 100 VIN = 1.5V ISW = 500mA I (A) V (V) 0.2 0.4 0.6 1.2 1.4 0.2 0.4 0.8 1.2 LT1110 • TPC06 1.0 1.4 1.6 SWITCH CESAT VIN = 1.0V V = 1.2VIN VIN = 1.5V VIN = 5.0V V = 2.0VIN 0.6 1.0 0.8 VIN = 3.0V INPUT VOLTAGE (V) QUIESCENT CURRENT (µA) LT1110 • TPC09 400 380 360 340 320 280 260 240 220 200 300 9 1 21 51 82 12 42 73 0 TEMPERATURE (°C) QUIESCENT CURRENT (µA) –50 LT1110 • TPC10 500 450 400 350 250 –25 150 100 200 300 0 25 50 75 100 RLIM (Ω ) SWITCH CURRENT (A) LT1110 • TPC11 100 1.5 1.3 1.1 0.9 1000 0.7 0.5 0.3 0.1 STEP-UP MODE VIN ≤ 5V RLIM (Ω ) SWITCH CURRENT (A) LT1110 • TPC12 100 1.5 1.3 1.1 0.9 1000 0.7 0.5 0.3 0.1 STEP-DOWN MODE VIN = 12V SWITCH ON TIME (µs) OSCILLATOR FREQUENCY (KHz) 7 9 LT1110 • TPC08 100 0°C ≤ TA ≤ 70°C 8 11 12

CCHARA TERISTICSUWATYPICALP E RFOR CE Set Pin Bias Current FB Pin Bias Current Reference Voltage ILIM (Pin 1): Connect this pin to VIN for normal use. Where lower current limit is desired, connect a resistor between I LIM and VIN. A 220Ω resistor will limit the switch current to approximately 400mA. VIN (Pin 2): Input supply voltage. SW1 (Pin 3): Collector of power transistor. For step-up mode connect to inductor/diode. For step-down mode connect to V IN. SW2 (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 ground. GND (Pin 5): Ground. AO (Pin 6): Auxiliary Gain Block (GB) output. Open collector, can sink 300µA. SET (Pin 7): GB input. GB is an op amp with positive input connected to SET pin and negative input connected to 220mV reference. FB/SENSE (Pin 8): On the LT1110 (adjustable) this pin goes to the comparator input. On the LT1110-5 and LT1110-12, this pin goes to the internal application resistor that sets output voltage. PI UFU UC USOTI TEMPERATURE (°C) BIAS CURRENT (nA) –50 LT1110 • TPC13 160 140 120 100 –25 0 25 50 75 100 TEMPERATURE (°C) VREF (mV) –50 –25 0 25 LT1110 • TPC15 50 75 100 226 224 222 220 218 216 214 212 TEMPERATURE (°C) BIAS CURRENT (nA) –50 120 100 –25 0 25 50 75 100 110 LT1110 • TPC14 LT1110 • BD01 INV GND SET AO GAIN BLOCK/ERROR AMP 220mV REFERENCE DRIVER FB SW1 SW2 LIMI OSCILLATOR COMPARATOR

-LT1110 UOPER OATILT1110 The LT1110 is a 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 LT1110 block diagram above. Comparator A1 compares the FB pin voltage with the 220mV reference signal. When FB drops below 220mV , A1 switches on the 70kHz oscillator. The driver amplifier boosts the signal level to drive the output NPN power switch Q1. An adaptive 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. When the comparator is low the oscillator and all high current circuitry is turned off, lowering device quiescent current to just 300µA for the reference, A1 and A2. The oscillator is set internally for 10µs ON time and 5µs OFF time, optimizing the device for step-up circuits where V OUT ≈ 3VIN, e.g., 1.5V to 5V. Other step-up ratios as well as step-down (buck) converters are possible at slight losses in maximum achievable power output. A2 is a versatile gain block that can serve as a low battery detector, a linear post regulator, or drive an under voltage lockout circuit. The negative input of A2 is internally connected to the 220mV reference. An external resistor divider from V IN to GND provides the trip point for A2. The AO output can sink 300µA (use a 47k resistor pull up to +5V). This line can signal a microcontroller that the battery voltage has dropped below the preset level. To prevent the gain block from operating in its linear region, a 2M Ω resistor can be connected from AO to SET. This provides positive feedback. A resistor connected between the ILIM pin and VIN adjusts maximum switch current. When the switch current ex- ceeds the set value, the switch is turned off. This feature is especially useful when small inductance values are used with high input voltages. If the internal current limit of 1.5A is desired, I LIM should be tied directly to VIN. Propagation delay through the current limit circuitry is about 700ns. In step-up mode, SW2 is connected to ground and SW1 drives the inductor. In step-down mode, SW1 is con- nected 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 V OUT to FB. The LT1110-5 and LT1110-12 fixed output voltage ver- sions have the gain setting resistors on-chip. Only three external components are required to construct a 5V or 12V output converter. 16 µA flows through R1 and R2 in the LT1110-5, and 39µA flows in the LT1110-12. This current represents a load and the converter must cycle from time to time to maintain the proper output voltage. Output ripple, inherently present in gated oscillator designs, will typically run around 90mV for the LT1110-5 and 200mV for the LT1110-12 with the proper inductor/capacitor selection. This output ripple can be reduced considerably by using the gain block amp as a pre-amplifier in front of the FB pin. See the Applications section for details. WIDA G R ABLOCK-5, -12LT1110 LT1110 • BD02 INV GND SET AOA2 220mV REF OSCILLATOR DRIVER SW1 SW2 LIMI 300kΩ SENSE LT1110-5: LT1110-12: R1 = 13.8kΩ R2 = 5.6kΩ GAIN BLOCK/ERROR AMP COMPARATOR UOPER OATI-5, -12 Vm V R ROUT = () + 220 2 1 10 1.( )

Inductor Selection — General A DC-DC converter operates by storing energy as mag- netic 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 oppo- site in polarity to the input voltage by choosing an appro- priate switching topology. To operate as an efficient en- ergy transfer element, the inductor must fulfill three re- quirements. First, the inductance must be low enough for the inductor to store adequate energy under the worst case condition of minimum input voltage and switch ON time. The inductance must also be high enough so maxi- mum current ratings of the LT1110 and inductor are not exceeded at the other worst case condition of maximum input voltage and ON time. Additionally, the inductor core must be able to store the required flux; i.e., it must not saturate. At power levels generally encountered with LT1110 based designs, small surface mount ferrite core units with saturation current ratings in the 300mA to 1A range and DCR less than 0.4Ω (depending on application) are adequate. Lastly, the inductor must have sufficiently low DC resistance so excessive power is not lost as heat in the windings. An additional consideration is Electro- Magnetic Interference (EMI). Toroid and pot core type inductors are recommended in applications where EMI must be kept to a minimum; for example, where there are sensitive analog circuitry or transducers nearby. Rod core types are a less expensive choice where EMI is not a problem. Minimum and maximum input voltage, output voltage and output current must be established before an inductor can be selected. Inductor Selection — Step-Up Converter In a step-up, or boost converter (Figure 4), power gener- ated by the inductor makes up the difference between input and output. Power required from the inductor is determined by PV V V IL OUT D IN MIN OUT=+() ( ) ±( ) 01 where VD is the diode drop (0.5V for a 1N5818 Schottky). USA OPPLICATI WU UI FOR ATIO Energy required by the inductor per cycle must be equal or greater than P f L OSC ()02 in order for the converter to regulate the output. When the switch is closed, current in the inductor builds according to It V R eL IN Rt L() © ±( ) 10 3 where R' is the sum of the switch equivalent resistance (0.8Ω typical at 25 °C) and the inductor DC resistance. When the drop across the switch is small compared to VIN, the simple lossless equation It V L tL IN() = ()04 can be used. These equations assume that at t = 0, inductor current is zero. This situation is called “discon- tinuous mode operation” in switching regulator parlance. Setting “t” to the switch ON time from the LT1110 speci- fication table (typically 10µs) will yield I PEAK for a specific “L” and VIN. Once IPEAK is known, energy in the inductor at the end of the switch ON time can be calculated as EL IL PEAK= 1 2 052 () EL must be greater than PL/fOSC for the converter to deliver the required power. For best efficiency I PEAK should be kept to 1A or less. Higher switch currents will cause excessive drop across the switch resulting in reduced efficiency. In general, switch current should be held to as low a value as possible in order to keep switch, diode and inductor losses at a minimum. As an example, suppose 12V at 120mA is to be generated from a 4.5V to 8V input. Recalling equation (01), P V V V mA mWL =+() ( ) =12 0 5 4 5 120 960 06.± . . ( ) Energy required from the inductor is P f mW kHz JL OSC ==960 70 13 7 07.. ( )µ

USA OPPLICATI WU UI FOR ATIO Picking an inductor value of 47µH with 0.2Ω DCR results in a peak switch current of I V em APEAK s H=− −•45 10 1 862 08 10 1 0 . .( ) W Wm m Substituting IPEAK into Equation 05 results in EH AJL = () ( ) =1 2 47 0 862 17 5 092µµ .. . ( ) Since 17.5µJ > 13.7µJ, the 47µH inductor will work. This trial-and-error approach can be used to select the opti- mum inductor. Keep in mind the switch current maximum rating of 1.5A. If the calculated peak current exceeds this, an external power transistor can be used. A resistor can be added in series with the I LIM pin to invoke switch current limit. The resistor should be picked such that the calculated IPEAK at minimum VIN is equal to the Maximum Switch Current (from Typical Performance Characteristic curves). Then, as V IN increases, switch current is held constant, resulting in increasing efficiency. Inductor Selection — Step-Down Converter The step-down case (Figure 5) differs from the step-up in that the inductor current flows through the load during both the charge and discharge periods of the inductor. Current through the switch should be limited to ~800mA in this mode. Higher current can be obtained by using an external switch (see Figure 6). The I LIM pin is the key to successful operation over varying inputs. After establishing output voltage, output current and input voltage range, peak switch current can be calculated by the formula I I DC VV VV VPEAK OUT OUT D IN SW D = + 2 10± () where DC = duty cycle (0.69) 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 VSW is actually a function of switch current which is in turn a function of VIN, L, time and VOUT. To simplify, 1.5V can be used for VSW as a very conservative value. Once IPEAK is known, inductor value can be derived from L VV V I tIN MIN SW OUT PEAK ON=• ±± ()11 where tON = switch ON time (10µs). Next, the current limit resistor R LIM is selected to give IPEAK from the RLIM Step-Down Mode curve. The addition of this resistor keeps maximum switch current constant as the input voltage is increased. As an example, suppose 5V at 250mA is to be generated from a 9V to 18V input. Recalling Equation (10), I mA mAPEAK = () +  = 2 250 06 9 50 5 91 50 5 498 12. ±. . .( ) Next, inductor value is calculated using Equation (11) L mA sH=• =91 55 Use the next lowest standard value (47µH). Then pick R LIM from the curve. For I PEAK = 500mA, RLIM = 82Ω . Inductor Selection — Positive-to-Negative Converter Figure 7 shows hookup for positive-to-negative conver- sion. All of the output power must come from the inductor. In this case, PV V IL OUT D OUT=+() ( )|| . ( ) 14 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. When the

OUT by only a few millivolts. 1000µF is a good starting value. Figure 13. Output Ripple Reduction Using Gain BlockFigure 12. Setting Low Battery Detector Trip Point Table 2. Capacitor Manufacturers

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Table 3. Transistor Manufacturers Table 1. Inductor Manufacturers

Flash Memory VPP Generator 1.5V Powered Laser Diode Driver 2.2 H LT1110 • TA13 µ 100 F OS-CON µ 1N5818 4.7k 1k* TOSHIBA TOLD-9211 Ω 220Ω 2N3906 22nF 1.5V ADJUST R1 FOR CHANGE IN LASER OUTPUT POWER TOKO 262LYF-0076M 1N4148 GND SW2 SET SW1 LIMI INV FB AO LT1110 LASER DIODE CASE COMMON TO +BATTERY TERMINAL 170mA CURRENT DRAIN FROM 1.5V CELL (50mA DIODE) NO OVERSHOOT MJE210 0.22 F CERAMIC µ 1.5V Powered Laser Diode Driver LT1110 • TA18 GND SW2 SENSE SW1 LIMI INV LT1110CS8-12 *L1= SUMIDA CD105-470M 47µF 20V L1* 47µH VPP 12V 120MA 22µF 10k +5V ±10% MBRS12OT3 MMBT4403 = PROGRAM = SHUTDOWN

0 MMBF170

LT1110 • TA10 GND SW2 SENSE SW1 LIMI INV LT1110-59V *L1 = COILCRAFT 1812LS-473 10µFMBRL120 40mA 220 L1* 47µH LT1110 • TA11 GND SW2 FB SW1 LIMI INV LT11101.5V AA OR AAA CELL = MBRL120 = COILCRAFT 1812LS-823 4.7µF L1* 82µH +5V 3mA 4.7µF +10V 3mA 490k *L1 4.7µF 11k LT1110 • TA09 GND SW2 SENSE SW1 LIMI INV LT1110-5 AA CELL *L1 = COILCRAFT 1812LS-473 10µF MBRL120 L1* 47µH 40mA 220 LT1110 • TA12 GND SW2 SENSE SW1 LIMI INV LT11101.5V AA OR AAA CELL = MBRL120 = COILCRAFT 1812LS-823 4.7µF L1* 82µH +5V 4mA 4.7µF –5V 4mA 4.7µF *L1 USA OPPLICATITYPICAL All Surface Mount 3V to 5V Step-Up Converter All Surface Mount 9V to 5V Step-Down Converter All Surface Mount 1.5V to +10V, +5V Dual Output Step-Up Converter All Surface Mount 1.5V to ± 5V Dual Output Step-Up Converter Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

UPACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. 8-Lead Plastic DIP 8-Lead Plastic SOIC  LINEAR TECHNOLOGY CORPORA TION 1994 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 l FAX: (408) 434-0507 l TELEX: 499-3977 LT/GP 0594 2K REV B • PRINTED IN USA 0.016 – 0.050 0.406 – 1.270 0.010 – 0.020 0°– 8° TYP 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0.014 – 0.019 (0.355 – 0.483) 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 1 2 3 4 0.150 – 0.157* (3.810 – 3.988) 8 7 6 5 0.189 – 0.197* (4.801 – 5.004) 0.228 – 0.244 (5.791 – 6.197) *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm). 0.009 – 0.015 (0.229 – 0.381) 0.300 – 0.320 (7.620 – 8.128) 0.325 +0.025 –0.015 +0.635 –0.3818.255() 0.045 ± 0.015 (1.143 ± 0.381) 0.100 ± 0.010 (2.540 ± 0.254) 0.065 (1.651) TYP 0.045 – 0.065 (1.143 – 1.651) 0.130 ± 0.005 (3.302 ± 0.127) 0.020 (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.076) 0.125 (3.175) MIN 12 3 4 87 6 5 0.250 ± 0.010 (6.350 ± 0.254) 0.400 (10.160) MAX