LT1173 Micropower DC/DC Converter Adjustable and Fixed 5V, 12V FEATURES DESCRIPTIOU n Operates at Supply Voltages From 2.0V to 30V The LT1173 is a versatile micropower DC-DC converter. n Consumes Only 110m A Supply Current The device requires only three external components to n Works in Step-Up or Step-Down Mode deliver a fixed output of 5V or 12V. Supply voltage ranges n Only Three External Components Required from 2.0V to 12V in step-up mode and to 30V in step-down n Low Battery Detector Comparator On-Chip mode. The LT1173 functions equally well in step-up, step- n User-Adjustable Current Limit down or inverting applications. n Internal 1A Power Switch The LT1173 consumes just 110m A supply current at n Fixed or Adjustable Output Voltage Versions standby, making it ideal for applications where low quies- n Space Saving 8-Pin MiniDIP or SO8 Package cent current is important. The device can deliver 5V at APPLICATIOUS 80mA from a 3V input in step-up mode or 5V at 200mA from a 12V input in step-down mode. n Flash Memory Vpp Generators Switch current limit can be programmed with a single n 3V to 5V, 5V to 12V Converters resistor. An auxiliary gain block can be configured as a low n 9V to 5V, 12V to 5V Converters battery detector, linear post regulator, under voltage lock- n LCD Bias Generators out circuit or error amplifier. n Peripherals and Add-On Cards n Battery Backup Supplies For input sources of less than 2V, use the LT1073. n Laptop and Palmtop Computers n Cellular Telephones n Portable Instruments and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation. TYPICAL APPLICATIOUS Logic Controlled Flash Memory VPP Generator VPP Output L1*(cid:13) (cid:13) 100m H 1N5818 12V(cid:13) 5VI N 100mA 47W VOUT 5V/DIV ILIM VIN + SW1 1.07M†+ SANYO(cid:13) 0V 10 m F LT1173 OS-CON(cid:13) 100 m F FB PROGRAM GND SW2 124k† 5V/DIV 5ms/DIV 1173 TA02 1N4148 PROGRAM LT1173 • TA01 *L1 = GOWANDA GA20-103K(cid:13) EFFICIENCY = 81% (cid:9)(cid:9)(cid:9)(cid:9)(cid:9)(cid:9)(cid:9)(cid:9)(cid:9)(cid:9)COILTRONICS CTX100-4 † = 1% METAL FILM NO OVERSHOOT 1

LT1173 ABSOLUTE WAXIWUW RATIUGS PACKAGE/ORDER IUFORWATIOU Supply Voltage (V )................................................ 36V IN TOP VIEW ORDER PART SW1 Pin Voltage (V ).......................................... 50V SW1 SW2 Pin Voltage (V ).............................–0.5V to V ILIM(cid:13) 1(cid:13) 8(cid:13) FB (SENSE)*(cid:13) NUMBER SW2 IN Feedback Pin Voltage (LT1173)................................. 5V VIN(cid:13) 2(cid:13) 7(cid:13) SET(cid:13) LT1173CN8 SW1(cid:13) 3(cid:13) 6(cid:13) AO(cid:13) Sense Pin Voltage (LT1173, -5, -12) ....................... 36V LT1173CN8-5 SW2 4 5(cid:13) GND Maximum Power Dissipation.............................500mW LT1173CN8-12 (cid:13) Maximum Switch Current....................................... 1.5A N8 PACKAGE(cid:13) 8-LEAD PLASTIC DIP(cid:13) Operating Temperature Range.....................0(cid:176) C to 70(cid:176) C *FIXED VERSIONS Storage Temperature Range..................–65(cid:176) C to 150(cid:176) C TJMAX = 90(cid:176)C, q JA = 130(cid:176)C/W Lead Temperature, (Soldering, 10 sec.)................300(cid:176) C TOP VIEW LT1173CS8 ILIM(cid:13) 1(cid:13) 8(cid:13) FB (SENSE)*(cid:13) LT1173CS8-5 Consult factory for Industrial and Military grade parts VIN(cid:13) 2(cid:13) 7(cid:13) SET(cid:13) LT1173CS8-12 SW1(cid:13) 3(cid:13) 6(cid:13) AO(cid:13) S8 PART MARKING SW2 4 5 GND 1173 S8 PACKAGE(cid:13) 8-LEAD PLASTIC SOIC(cid:13) 11735 *FIXED VERSIONS 117312 TJMAX = 90(cid:176)C, q JA = 150(cid:176)C/W ELECTRICAL CHARACTERISTICS T = 25(cid:176) C, V = 3V, unless otherwise noted. A IN SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS I Quiescent Current Switch Off l 110 150 m A Q I Quiescent Current, Boost No Load LT1173-5 135 m A Q Mode Configuration LT1173-12 250 m A V Input Voltage Step-Up Mode l 2.0 12.6 V IN Step-Down Mode l 30 V Comparator Trip Point Voltage LT1173 (Note 1) l 1.20 1.245 1.30 V V Output Sense Voltage LT1173-5 (Note 2) l 4.75 5.00 5.25 V OUT LT1173-12 (Note 2) l 11.4 12.0 12.6 V Comparator Hysteresis LT1173 l 5 10 mV Output Hysteresis LT1173-5 l 20 40 mV LT1173-12 l 50 100 mV f Oscillator Frequency l 18 23 30 kHz OSC Duty Cycle Full Load l 43 51 59 % t Switch ON Time I tied to V l 17 22 32 m s ON LIM IN Feedback Pin Bias Current LT1173, V = 0V l 10 50 nA FB Set Pin Bias Current V = V l 20 100 nA SET REF V Gain Block Output Low I = 100m A, V = 1.00V l 0.15 0.4 V OL SINK SET Reference Line Regulation 2.0V £ V £ 5V l 0.2 0.4 %/V IN 5V £ V £ 30V l 0.02 0.075 %/V IN V SW Voltage, Step-Up Mode V = 3.0V, I = 650mA l 0.5 0.65 V SAT SAT IN SW V = 5.0V, I = 1A 0.8 1.0 V IN SW l 1.4 V 2

LT1173 ELECTRICAL CHARACTERISTICS T = 25(cid:176) C, V = 3V, unless otherwise noted. A IN SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V SW Voltage, Step-Down Mode V = 12V, I = 650mA 1.1 1.5 V SAT SAT IN SW l 1.7 V A Gain Block Gain R = 100kW (Note 3) l 400 1000 V/V V L Current Limit 220W to I to V 400 mA LIM IN Current Limit Temperature Coeff. l –0.3 %/(cid:176) C Switch OFF Leakage Current Measured at SW1 Pin 1 10 m A V Maximum Excursion Below GND I £ 10m A, Switch Off –400 –350 mV SW2 SW1 The l denotes the specifications which apply over the full operating Note 2: The output voltage waveform will exhibit a sawtooth shape due to temperature range. the comparator hysteresis. The output voltage on the fixed output versions Note 1: This specification guarantees that both the high and low trip points will always be within the specified range. of the comparator fall within the 1.20V to 1.30V range. Note 3: 100kW resistor connected between a 5V source and the AO pin. TYPICAL PERFORWAUCE CHARACTERISTICS Switch ON Voltage Saturation Voltage Step-Up Mode Step-Down Mode Maximum Switch Current vs (SW2 Pin Grounded) (SW1 Pin Connected to V ) R Step-Up Mode IN LIM 1.2 1.4 1200 1100 2V £ VIN £ 5V 1.0 1.3 1000 V (V)CESAT 000...468 VI N =V 2I N . 0=V 3.0V VI N = 5.0V SWITCH ON VOLTAGE (V) 0111....9012 SWITCH CURRENT (mA)489765000000000000 0.2 300 0.8 200 0 0.7 100 0 0.2 0.4 0.6 0.8 1.0 1.2 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 10 100 1000 IS W I T C H (A) I S W I T C H (A) R L I M (W(cid:13) ) LT1173 • TPC01 LT1173 • TPC02 LT1173 • TPC03 Maximum Switch Current vs Set Pin Bias Current vs Feedback Pin Bias Current vs R Step-Down Mode Temperature Temperature LIM 1000 20 18 VOUT = 5V 900 WITCH CURRENT (mA)487653000000000000 LV I=N 2=5 01m2VH(cid:13)VL I=N 5=0 02m4VH(cid:13) PIN BIAS CURRENT (nA) 1105 VI N = 3V mCK PIN BIAS CURRENT ( A) 111246 VI N = 3V S200 SET DBA 10 E E 100 F 0 5 8 100 1000 –50 –25 0 25 50 75 100 125 –50 –25 0 25 50 75 100 125 R L I M (W(cid:13) ) TEMPERATURE (°C) TEMPERATURE (°C) LT1173 • TPC09 LT1173 •TPC04 LT1173 •TPC05 3

LT1173 TYPICAL PERFORWAUCE CHARACTERISTICS Quiescent Current vs Temperature Supply Current vs Switch Current Oscillator Frequency 120 50 26.0 25.5 VI N = 3V 40 A) 25.0 m mI ( A)IN110100 PLY CURRENT ( 2300 VI N = 5V VI N = 2V F (kHz)OSC222344...550 P U S 23.0 10 22.5 90 0 22.0 –50 –25 0 25 50 75 100 125 0 200 400 600 800 1000 0 5 10 15 20 25 30 TEMPERATURE (°C) SWITCH CURRENT (mA) VIN(V) LT1173 •TPC06 LT1173 •TPC07 LT1173 • TPC08 PIU FUUCTIOUS I (Pin 1): Connect this pin to V for normal use. Where GND (Pin 5): Ground. LIM IN lower current limit is desired, connect a resistor between AO (Pin 6): Auxiliary Gain Block (GB) output. Open collec- ILIM and VIN. A 220W resistor will limit the switch current tor, can sink 100m A. to approximately 400mA. SET (Pin 7): GB input. GB is an op amp with positive input V (Pin 2): Input supply voltage. IN connected to SET pin and negative input connected to SW1 (Pin 3):Collector of power transistor. For step-up 1.245V reference. mode connect to inductor/diode. For step-down mode FB/SENSE (Pin 8): On the LT1173 (adjustable) this pin connect to V . IN goes to the comparator input. On the LT1173-5 and SW2 (Pin 4): Emitter of power transistor. For step-up LT1173-12, this pin goes to the internal application resis- mode connect to ground. For step-down mode connect to tor that sets output voltage. inductor/diode. This pin must never be allowed to go more than a Schottky diode drop below ground. BLOCK DIAGRAWS LT1173 LT1173-5, -12 SET SET A2 AO A2 AO VIN VIN GAIN BLOCK/ GAIN BLOCK/ ERROR AMP ILIM SW1 ERROR AMP ILIM SW1 1.245V REFERENCE 1.245V A1 OSCILLATOR REFERENCE A1 OSCILLATOR DRIVER COMPARATOR DRIVER R2 SW2 GND COMPARATOR SW2 R1 753k W LT1173-5:R1 = 250kW FB GND SENSE LT1173-12:R1 = 87.4kW LT1173 • BD01 LT1173 • BD02 4

LT1173 LT1173 OPERATIOU The LT1173 is a gated oscillator switcher. This type archi- A2 is a versatile gain block that can serve as a low battery tecture has very low supply current because the switch is detector, a linear post regulator, or drive an under voltage cycled only when the feedback pin voltage drops below the lockout circuit. The negative input of A2 is internally reference voltage. Circuit operation can best be under- connected to the 1.245V reference. A resistor divider from stood by referring to the LT1173 block diagram. Compara- V to GND, with the mid-point connected to the SET pin IN tor A1 compares the feedback pin voltage with the 1.245V provides the trip voltage in a low battery detector applica- reference voltage. When feedback drops below 1.245V,A1 tion. The gain block output (AO) can sink 100m A (use a 47k switches on the 24kHz oscillator. The driver amplifier resistor pull-up to +5V). This line can signal a microcon- boosts the signal level to drive the output NPN power troller that the battery voltage has dropped below the switch. An adaptive base drive circuit senses switch preset level. current and provides just enough base drive to ensure A resistor connected between the I pin and V sets switch saturation without overdriving the switch, resulting LIM IN maximum switch current. When the switch current ex- in higher efficiency. The switch cycling action raises the ceeds the set value, the switch cycle is prematurely output voltage and feedback pin voltage. When the feed- terminated. If current limit is not used, I should be tied back voltage is sufficient to trip A1, the oscillator is gated LIM directly to V . Propagation delay through the current limit off. A small amount of hysteresis built into A1 ensures loop IN circuitry is approximately 2m s. stability without external frequency compensation. When the comparator is low the oscillator and all high current In step-up mode the switch emitter (SW2) is connected to circuitry is turned off, lowering device quiescent current ground and the switch collector (SW1) drives the induc- to just 110m A, for the reference, A1 and A2. tor; in step-down mode the collector is connected to V IN and the emitter drives the inductor. The oscillator is set internally for 23m s ON time and 19m s OFF time, optimizing the device for circuits where VOUT The LT1173-5 and LT1173-12 are functionally identical to and VIN differ by roughly a factor of 2. Examples include a the LT1173. The -5 and -12 versions have on-chip voltage 3V to 5V step-up converter or a 9V to 5V step-down setting resistors for fixed 5V or 12V outputs. Pin 8 on the converter. fixed versions should be connected to the output. No external resistors are needed. APPLICATIOUS IUFORWATIOU Measuring Input Current at Zero or Light Load Obtaining meaningful numbers for quiescent current and approach is required to measure the 100m A off-state and efficiency at low output current involves understanding 500mA on-state currents of the circuit. how the LT1173 operates. At very low or zero load current, Quiescent current can be accurately measured using the the device is idling for seconds at a time. When the output circuit in Figure 1. V is set to the input voltage of the voltage falls enough to trip the comparator, the power SET LT1173. The circuit must be “booted” by shorting V2 to switch comes on for a few cycles until the output voltage V . After the LT1173 output voltage has settled, discon- rises sufficiently to overcome the comparator hysteresis. SET nect the short. Input voltage is V2, and average input When the power switch is on, inductor current builds up current can be calculated by this formula: to hundreds of milliamperes. Ordinary digital multimeters are not capable of measuring average current because of (cid:86)(cid:50)- (cid:86)(cid:49) ( ) (cid:73) = (cid:48)(cid:49) bandwidth and dynamic range limitations. A different (cid:73)(cid:78) (cid:49)(cid:48)(cid:48)W 5

LT1173 APPLICATIOUS IUFORWATIOU 1MW the inductive events add to the input voltage to produce the output voltage. Power required from the inductor is deter- +12V 1m F* mined by – 100W LT1173 P = (V + V – V ) (I ) (02) LTC1050 L OUT D IN OUT V1 V2 CIRCUIT + + 1000m F where V is the diode drop (0.5V for a 1N5818 Schottky). D Energy required by the inductor per cycle must be equal or VSET *NON-POLARIZED greater than LT1173 • TA06 Figure 1. Test Circuit Measures No Load Quiescent Current of (cid:80) ( ) (cid:76) LT1073 Converter (cid:48)(cid:51) (cid:70) (cid:79)(cid:83)(cid:67) Inductor Selection in order for the converter to regulate the output. A DC-DC converter operates by storing energy as mag- When the switch is closed, current in the inductor builds netic flux in an inductor core, and then switching this according to energy into the load. Since it is flux, not charge, that is stored, the output voltage can be higher, lower, or oppo- ( ) (cid:86) (cid:230) (cid:177)(cid:82)(cid:169)(cid:116)(cid:246) ( ) site in polarity to the input voltage by choosing an (cid:73)(cid:76) (cid:116) = (cid:73)(cid:78) (cid:231) (cid:49)(cid:177) (cid:101) (cid:76) (cid:247) (cid:48)(cid:52) (cid:82)(cid:169) Ł ł appropriate switching topology. To operate as an efficient energy transfer element, the inductor must fulfill three where R' is the sum of the switch equivalent resistance requirements. First, the inductance must be low enough (0.8W typical at 25(cid:176) C) and the inductor DC resistance. for the inductor to store adequate energy under the worst When the drop across the switch is small compared to V , IN case condition of minimum input voltage and switch ON the simple lossless equation time. The inductance must also be high enough so that ( ) (cid:86) ( ) maximum current ratings of the LT1173 and inductor are (cid:73) (cid:116) = (cid:73)(cid:78) (cid:116) (cid:48)(cid:53) (cid:76) not exceeded at the other worst case condition of maxi- (cid:76) mum input voltage and ON time. Additionally, the inductor can be used. These equations assume that at t = 0, core must be able to store the required flux; i.e., it must not inductor current is zero. This situation is called “discon- saturate. At power levels generally encountered with tinuous mode operation” in switching regulator parlance. LT1173 based designs, small axial leaded units with Setting “t” to the switch ON time from the LT1173 speci- saturation current ratings in the 300mA to 1A range fication table (typically 23m s) will yield i for a specific PEAK (depending on application) are adequate. Lastly, the in- “L” and V . Once i is known, energy in the inductor at IN PEAK ductor must have sufficiently low DC resistance so that the end of the switch ON time can be calculated as excessive power is not lost as heat in the windings. An additional consideration is Electro-Magnetic Interference (cid:49) ( ) (cid:69) = (cid:76)(cid:105)(cid:50) (cid:48)(cid:54) (EMI). Toroid and pot core type inductors are recom- (cid:76) (cid:50) (cid:80)(cid:69)(cid:65)(cid:75) mended in applications where EMI must be kept to a E must be greater than P /F for the converter to deliver minimum; for example, where there are sensitive analog L L OSC the required power. For best efficiency i should be circuitry or transducers nearby. Rod core types are a less PEAK kept to 1A or less. Higher switch currents will cause expensive choice where EMI is not a problem. excessive drop across the switch resulting in reduced Specifying a proper inductor for an application requires efficiency. In general, switch current should be held to as first establishing minimum and maximum input voltage, low a value as possible in order to keep switch, diode and output voltage, and output current. In a step-up converter, inductor losses at a minimum. 6

LT1173 APPLICATIOUS IUFORWATIOU As an example, suppose 9V at 50mA is to be generated In the negative-to-positive case, the switch saturates and from a 3V input. Recalling Equation 02, the 0.8W switch ON resistance value given for Equation 04 can be used. In both cases inductor design proceeds from P = (9V + 0.5V – 3V) (50mA) = 325mW. (07) L Equation 03. Energy required from the inductor is The step-down case is different than the preceeding three (cid:80) (cid:51)(cid:50)(cid:53)(cid:109)(cid:87) ( ) in that the inductor current flows through the load in a (cid:76) = =(cid:49)(cid:51)(cid:46)(cid:53)m (cid:74)(cid:46) (cid:48)(cid:56) step-down topology (Figure 6). Current through the switch (cid:70) (cid:50)(cid:52)(cid:107)(cid:72)(cid:122) (cid:79)(cid:83)(cid:67) should be limited to ~650mA in step-down mode. This can Picking an inductor value of 100m H with 0.2W DCR results be accomplished by using the I pin. With input voltages LIM in a peak switch current of in the range of 12V to 25V, a 5V output at 300mA can be generated with a 220m H inductor and 100W resistor in (cid:51)(cid:86) (cid:230) (cid:177)(cid:49)W •(cid:50)(cid:51)m (cid:115)(cid:246) ( ) series with the I pin. With a 20V to 30V input range, a (cid:105)(cid:80)(cid:69)(cid:65)(cid:75) = (cid:49)W Ł(cid:231) (cid:49)(cid:177)(cid:101) (cid:49)(cid:48)(cid:48)m (cid:72) ł(cid:247) =(cid:54)(cid:49)(cid:54)(cid:109)(cid:65)(cid:46) (cid:48)(cid:57) 470m H inductorL IsMhould be used along with the 100W resistor. Substituting i into Equation 04 results in PEAK Capacitor Selection (cid:49)( )( )(cid:50) ( ) (cid:69) = (cid:49)(cid:48)(cid:48)m (cid:72) (cid:48)(cid:46)(cid:54)(cid:49)(cid:54)(cid:65) =(cid:49)(cid:57)(cid:46)m(cid:48) (cid:74)(cid:46) (cid:49)(cid:48) Selecting the right output capacitor is almost as important (cid:76) (cid:50) as selecting the right inductor. A poor choice for a filter Since 19m J > 13.5m J the 100m H inductor will work. This capacitor can result in poor efficiency and/or high output trial-and-error approach can be used to select the opti- ripple. Ordinary aluminum electrolytics, while inexpensive mum inductor. Keep in mind the switch current maximum and readily available, may have unacceptably poor equiva- rating of 1.5A. If the calculated peak current exceeds this, lent series resistance (ESR) and ESL (inductance). There consider using the LT1073. The 70% duty cycle of the are low-ESR aluminum capacitors on the market specifi- LT1073 allows more energy per cycle to be stored in the cally designed for switch mode DC-DC converters which inductor, resulting in more output power. work much better than general-purpose units. Tantalum capacitors provide still better performance at more ex- An inductor’s energy storage capability is proportional to pense. We recommend OS-CON capacitors from Sanyo its physical size. If the size of the inductor is too large for Corporation (San Diego, CA). These units are physically a particular application, considerable size reduction is quite small and have extremely low ESR. To illustrate, possible by using the LT1111. This device is pin compat- Figures 2, 3, and 4 show the output voltage of an LT1173 ible with the LT1173 but has a 72kHz oscillator, thereby based converter with three 100m F capacitors. The peak reducing inductor and capacitor size requirements by a switch current is 500mA in all cases. Figure 2 shows a factor of three. Sprague 501D, 25V aluminum capacitor. V jumps by OUT For both positive-to-negative (Figure 7) and negative-to- over 120mV when the switch turns off, followed by a drop in voltage as the inductor dumps into the capacitor. This positive configurations (Figure 8), all the output power works out to be an ESR of over 240mW . Figure 3 shows the must be generated by the inductor. In these cases same circuit, but with a Sprague 150D, 20V tantalum P = ( (cid:231) V (cid:231) + V ) (I ). (11) L OUT D OUT capacitor replacing the aluminum unit. Output jump is now about 35mV, corresponding to an ESR of 70mW . In the positive-to-negative case, switch drop can be mod- eled as a 0.75V voltage source in series with a 0.65W Figure 4 shows the circuit with a 16V OS-CON unit. ESR is now only 20mW . resistor so that V = V – 0.75V – I (0.65W ). (12) L IN L 7

LT1173 APPLICATIOUS IUFORWATIOU V V V DI DI DI V/ V/ V/ m m m 0 0 0 5 5 5 5m s/DIV 5m s/DIV 5m s/DIV LT1173 • TA07 LT1173 • TA08 LT1173 • TA09 Figure 2. Aluminum Figure 3. Tantalum Figure 4. OS-CON In very low power applications where every microampere Step-Up (Boost Mode) Operation is important, leakage current of the capacitor must be A step-up DC-DC converter delivers an output voltage considered. The OS-CON units do have leakage current in higher than the input voltage. Step-up converters are not the 5m A to 10m A range. If the load is also in the microam- short circuit protected since there is a DC path from input pere range, a leaky capacitor will noticeably decrease to output. efficiency. In this type application tantalum capacitors are the best choice, with typical leakage currents in the 1m A to The usual step-up configuration for the LT1173 is shown 5m A range. in Figure 5. The LT1173 first pulls SW1 low causing V – IN V to appear across L1. A current then builds up in L1. CESAT Diode Selection At the end of the switch ON time the current in L1 is1: Speed, forward drop, and leakage current are the three (cid:86) ( ) main considerations in selecting a catch diode for LT1173 (cid:105) = (cid:73)(cid:78)(cid:116) (cid:49)(cid:51) (cid:80)(cid:69)(cid:65)(cid:75) (cid:79)(cid:78) (cid:76) converters. General purpose rectifiers such as the 1N4001 L1 D1 are unsuitable for use in any switching regulator applica- VIN VOUT tion. Although they are rated at 1A, the switching time of R3* a 1N4001 is in the 10m s-50m s range. At best, efficiency will be severely compromised when these diodes are used; at ILIM VIN R2 SW1 worst, the circuit may not work at all. Most LT1173 circuits + LT1173 FB C1 will be well served by a 1N5818 Schottky diode. The combination of 500mV forward drop at 1A current, fast GND SW2 turn ON and turn OFF time, and 4m A to 10m A leakage R1 current fit nicely with LT1173 requirements. At peak switch currents of 100mA or less, a 1N4148 signal diode * = OPTIONAL LT1173 • TA10 may be used. This diode has leakage current in the 1nA- Figure 5. Step-Up Mode Hookup. 5nA range at 25(cid:176) C and lower cost than a 1N5818. (You can Refer to Table 1 for Component Values also use them to get your circuit up and running, but beware of destroying the diode at 1A switch currents.) In Immediately after switch turn off, the SW1 voltage pin situations where the load is intermittent and the LT1173 is starts to rise because current cannot instantaneously stop flowing in L1. When the voltage reaches V + V , the idling most of the time, battery life can sometimes be OUT D extended by using a silicon diode such as the 1N4933, inductor current flows through D1 into C1, increasing which can handle 1A but has leakage current of less than VOUT. This action is repeated as needed by the LT1173 to 1m A. Efficiency will decrease somewhat compared to a 1N5818 while delivering power, but the lower idle current Note 1: This simple expression neglects the effect of switch and coil may be more important. resistance. This is taken into account in the “Inductor Selection” section. 8

LT1173 APPLICATIOUS IUFORWATIOU keep V at the internal reference voltage of 1.245V. R1 R3 programs switch current limit. This is especially im- FB and R2 set the output voltage according to the formula portant in applications where the input varies over a wide range. Without R3, the switch stays on for a fixed time (cid:230) (cid:82)(cid:50)(cid:246) ( ) ( ) each cycle. Under certain conditions the current in L1 can (cid:86) =(cid:231) (cid:49)+ (cid:247) (cid:49)(cid:46)(cid:50)(cid:52)(cid:53)(cid:86) (cid:46) (cid:49)(cid:52) (cid:79)(cid:85)(cid:84) Ł (cid:82)(cid:49)ł build up to excessive levels, exceeding the switch rating and/or saturating the inductor. The 100W resistor pro- grams the switch to turn off when the current reaches Step-Down (Buck Mode) Operation approximately 800mA. When using the LT1173 in step- A step-down DC-DC converter converts a higher voltage down mode, output voltage should be limited to 6.2V or to a lower voltage. The usual hookup for an LT1173 based less. Higher output voltages can be accommodated by step-down converter is shown in Figure 6. inserting a 1N5818 diode in series with the SW2 pin (anode connected to SW2). VIN R3(cid:13) 100W Inverting Configurations + ILIM VIN SW1 The LT1173 can be configured as a positive-to-negative C2 FB converter (Figure 7), or a negative-to-positive converter LT1173 L1 (Figure 8). In Figure 7, the arrangement is very similar to SW2 VOUT a step-down, except that the high side of the feedback is GND R2 D1(cid:13) + referred to ground. This level shifts the output negative. 1N5818 C1 R1 As in the step-down mode, D1 must be a Schottky diode, and ‰ V ‰ should be less than 6.2V. More nega- OUT tive output voltages can be accomodated as in the prior LT1173 • TA11 Figure 6. Step-Down Mode Hookup section. When the switch turns on, SW2 pulls up to VIN – VSW. This +VIN puts a voltage across L1 equal to V – V – V , IN SW OUT R3 causing a current to build up in L1. At the end of the switch + ON time, the current in L1 is equal to ILIM VIN SW1 C2 FB (cid:86) - (cid:86) - (cid:86) ( ) LT1173 (cid:105) = (cid:73)(cid:78) (cid:83)(cid:87) (cid:79)(cid:85)(cid:84) (cid:116) (cid:46) (cid:49)(cid:53) L1 (cid:80)(cid:69)(cid:65)(cid:75) (cid:79)(cid:78) SW2 (cid:76) GND R1 D1(cid:13) + When the switch turns off, the SW2 pin falls rapidly and 1N5818 C1 R2 actually goes below ground. D1 turns on when SW2 –VOUT reaches 0.4V below ground. D1 MUST BE A SCHOTTKY LT1173 • F07 DIODE. The voltage at SW2 must never be allowed to go Figure 7. Positive-to-Negative Converter below –0.5V. A silicon diode such as the 1N4933 will allow SW2 to go to –0.8V, causing potentially destructive power In Figure 8, the input is negative while the output is dissipation inside the LT1173. Output voltage is deter- positive. In this configuration, the magnitude of the input mined by voltage can be higher or lower than the output voltage. A level shift, provided by the PNP transistor, supplies proper (cid:230) (cid:82)(cid:50)(cid:246) ( ) ( ) polarity feedback information to the regulator. (cid:86) =(cid:231) (cid:49)+ (cid:247) (cid:49)(cid:46)(cid:50)(cid:52)(cid:53)(cid:86) (cid:46) (cid:49)(cid:54) (cid:79)(cid:85)(cid:84) Ł (cid:82)(cid:49)ł 9

LT1173 APPLICATIOUS IUFORWATIOU L1 D1 +VOUT + R1 C1 IL ILIM VIN 2N3906 SW1 + C2 LT1173 ON AO FB SWITCH GND SW2 OFF R2 ( R 1 (cid:13)) LT1173 • TA14 V = 1.245V + 0.6V OUT R2 Figure 9. No Current Limit Causes Large Inductor –VIN LT1173 • TA13 Current Build-Up Figure 8. Negative-to-Positive Converter Using the I Pin PROGRAMMED CURRENT LIMIT LIM The LT1173 switch can be programmed to turn off at a set IL switch current, a feature not found on competing devices. This enables the input to vary over a wide range without ON SWITCH exceeding the maximum switch rating or saturating the OFF inductor. Consider the case where analysis shows the LT1173 • TA15 Figure 10. Current Limit Keeps Inductor Current Under Control LT1173 must operate at an 800mA peak switch current with a 2.0V input. If V rises to 4V, the peak switch current Figure 11 details current limit circuitry. Sense transistor IN will rise to 1.6A, exceeding the maximum switch current Q1, whose base and emitter are paralleled with power rating. With the proper resistor selected (see the “Maxi- switch Q2, is ratioed such that approximately 0.5% of Q2’s mum SwitchCurrent vs R ” characteristic), the switch collector current flows in Q1’s collector. This current is LIM current will be limited to 800mA, even if the input voltage passed through internal 80W resistor R1 and out through increases. the I pin. The value of the external resistor connected LIM between I and V sets the current limit. When suffi- Another situation where the I feature is useful occurs LIM IN LIM cient switch current flows to develop a V across R1 + when the device goes into continuous mode operation. BE R , Q3 turns on and injects current into the oscillator, This occurs in step-up mode when LIM turning off the switch. Delay through this circuitry is (cid:86)(cid:79)(cid:85)(cid:84) + (cid:86)(cid:68)(cid:73)(cid:79)(cid:68)(cid:69) < (cid:49) (cid:46) ((cid:49)(cid:55)) aapccpuroraxtiem afoter lys w2mitcsh. TOhNe ctuimrreesn t letrsips pthoainnt 4bmecso. mReess ilsetsosr (cid:86) - (cid:86) (cid:49)- (cid:68)(cid:67) (cid:73)(cid:78) (cid:83)(cid:87) values programming switch ON time for 2m s or less will When the input and output voltages satisfy this relation- cause spurious response in the switch circuitry although ship, inductor current does not go to zero during the the device will still maintain output regulation. switch OFF time. When the switch turns on again, the current ramp starts from the non-zero current level in the RLIM(cid:13) ILIM (EXTERNAL) inductor just prior to switch turn on. As shown in Figure VIN R1(cid:13) 80W (cid:13) 9, the inductor current increases to a high level before the (INTERNAL) Q3 comparator turns off the oscillator. This high current can SW1 cause excessive output ripple and requires oversizing the DRIVER Q1 output capacitor and inductor. With the I feature, OSCILLATOR Q2 LIM however, the switch current turns off at a programmed SW2 level as shown in Figure 10, keeping output ripple to a LT1173 • TA28 Figure 11. LT1173 Current Limit Circuitry minimum. 10

LT1173 APPLICATIOUS IUFORWATIOU Using the Gain Block +5V The gain block (GB) on the LT1173 can be used as an error VIN amplifier, low battery detector or linear post regulator. The LT1173(cid:13) 100k R1 gain block itself is a very simple PNP input op amp with an 1.245V(cid:13) – REF open collector NPN output. The negative input of the gain VBAT AO TO (cid:13) PROCESSOR block is tied internally to the 1.245V reference. The posi- SET + tive input comes out on the SET pin. Arrangement of the gain block as a low battery detector is R2 GND R3 straightforward. Figure 12 shows hookup. R1 and R2 need only be low enough in value so that the bias current of the SET input does not cause large errors. 100kW for R2 is R1 = VLB – 1.245V(cid:13) 11.7m A adequate. R3 can be added to introduce a small amount of VLB= BATTERY TRIP POINT R2= 100kW hysteresis. This will cause the gain block to “snap” when R3= 4.7MW LT1173 • TA16 the trip point is reached. Values in the 1M-10M range are Figure 12. Setting Low Battery Detector Trip Point optimal. The addition of R3 will change the trip point, however. Table 1. Component Selection for Common Converters INPUT OUTPUT OUTPUT CIRCUIT INDUCTOR INDUCTOR CAPACITOR VOLTAGE VOLTAGE CURRENT (MIN) FIGURE VALUE PART NUMBER VALUE NOTES 2.0-3.1 5 90mA 5 47m H G GA10-472K, C CTX50-1 100m F * 2.0-3.1 5 10mA 5 220m H G GA10-223K, C CTX 22m F 2.0-3.1 12 50mA 5 47m H G GA10-472K, C CTX50-1 47m F * 2.0-3.1 12 10mA 5 150m H G GA10-153K 22m F 5 12 90mA 5 120m H G GA10-123K 100m F 5 12 30mA 5 150m H G GA10-153K 47m F ** 5 15 50mA 5 120m H G GA10-123K C CTX100-4 47m F 5 30 25mA 5 100m H G GA10-103K, C CTX100-4 10m F, 50V 6.5-9.5 5 50mA 6 47m H G GA10-472K, C CTX50-1 100m F ** 12-20 5 300mA 6 220m H G GA20-223K 220m F ** 20-30 5 300mA 6 470m H G GA20-473K 470m F ** 5 –5 75mA 7 100m H G GA10-103K, C CTX100-4 100m F ** 12 –5 250mA 7 470m H G GA40-473K 220m F ** –5 5 150mA 8 100m H G GA10-103K, C CTX100-4 220m F –5 12 75mA 8 100m H G GA10-103K, C CTX100-4 47m F G = Gowanda C = Coiltronics * Add 68W from I to V LIM IN ** Add 100W from I to V LIM IN 11

LT1173 APPLICATIOUS IUFORWATIOU Table 2. Inductor Manufacturers Table 3. Capacitor Manufacturers MANUFACTURER PART NUMBERS MANUFACTURER PART NUMBERS Gowanda Electronics Corporation GA10 Series Sanyo Video Components OS-CON Series 1 Industrial Place GA40 Series 2001 Sanyo Avenue Gowanda, NY 14070 San Diego, CA 92173 716-532-2234 619-661-6835 Caddell-Burns 7300 Series Nichicon America Corporation PL Series 258 East Second Street 6860 Series 927 East State Parkway Mineola, NY 11501 Schaumberg, IL 60173 516-746-2310 708-843-7500 Coiltronics International Custom Toroids Sprague Electric Company 150D Solid Tantalums 984 S.W. 13th Court Surface Mount Lower Main Street 550D Tantalex Pompano Beach, FL 33069 Sanford, ME 04073 305-781-8900 207-324-4140 Renco Electronics Incorporated RL1283 60 Jefryn Boulevard, East RL1284 Deer Park, NY 11729 800-645-5828 TYPICAL APPLICATIOUS 3V to –22V LCD Bias Generator L1*(cid:13) 100m H 1N4148 R1(cid:13) 2.21M(cid:13) 100W 1% ILIM VIN SW1 2 X 1.5V(cid:13) 3V LT1173 CELLS FB GND SW2 + 4.7m F 0.1m F 118k(cid:13) 1% 1N5818 1N5818 + 22m F 220k * L1 = GOWANDA GA10-103K(cid:13) COILTRONICS CTX100-4(cid:13) –22V OUTPUT(cid:13) FOR 5V INPUT CHANGE R1 TO 47W .(cid:13) 7mA AT 2.0V INPUT(cid:13) CONVERTER WILL DELIVER –22V AT 40mA. 70% EFFICIENCY LT1173 • TA19 12

LT1173 TYPICAL APPLICATIOUS 3V to 5V Step-Up Converter 9V to 5V Step-Down Converter L1*(cid:13) 100 m H 100W ILIM VSINW1 ILIM VIN SW1 9V(cid:13) LT1173-5 BATTERY 2 X 1.5V(cid:13) LT1173-5 1N5818 SENSE CELLS 5V OUTPUT(cid:13) SENSE 150mA AT 3V INPUT(cid:13) GND SW2 L1*(cid:13) 60mA AT 2V INPUT 47m H 5V OUTPUT(cid:13) GND SW2 + 150mA AT 9V INPUT(cid:13) 100 m F + 50mA AT 6.5V INPUT 1N5818 100 m F * L1 = GOWANDA GA10-472K(cid:13) * L1 = GOWANDA GA10-103K(cid:13) COILTRONICS CTX50-1(cid:13) COILTRONICS CTX100-1 (SURFACE MOUNT) LT1173 • TA17 FOR HIGHER OUTPUT CURRENTS SEE LT1073 DATASHEET LT1173 • TA18 +5V to –5V Converter +20V to 5V Step-Down Converter +VIN(cid:13) +VIN(cid:13) 5V INPUT 12V-28V 100W 100W ILIM VIN ILIM VIN + SW1 SW1 22m F LT1173-5 LT1173-5 SENSE SENSE GND SW2 L1*(cid:13) GND SW2 L1*(cid:13) 100m H 220m H 5V OUTPUT(cid:13) 300mA + + 1N5818 100 m F 1N5818 100 m F –5V OUTPUT(cid:13) 75mA * L1 = GOWANDA GA10-103K(cid:13) COILTRONICS CTX100-1 LT1173 • TA20 * L1 = GOWANDA GA20-223K LT1173 • TA21 Telecom Supply L1*(cid:13) 500m H MUR110 44mH ~ + +5V(cid:13) + 100mA 48V DC 4170m0VF(cid:13) 3.6MW 220m F(cid:13)+ 390kW 10V ~ – 44mH 10k VN2222 2N5400 10nF 12V *L1 = CTX110077 IRF530 IQ = 120m A 100W 1N4148 15V ILIM VIN + SW1 10m F(cid:13) 1N965B 16V LT1173 FB GND SW2 110kW LT1173 • TA22 13

LT1173 TYPICAL APPLICATIOUS “5 to 5” Step-Up or Step-Down Converter L1*(cid:13) 100m H 1N5818 SI9405DY +5V(cid:13) OUTPUT 56W 1 2 470k 75k ILIM VIN 3 SW1 4 X NICAD(cid:13) + + OR(cid:13) 470m F 7 SET LT1173 AO 6 470m F ALKALINE(cid:13) CELLS 8 FB + GND SW2 470m F 240W 5 4 24k *L1 = COILTRONICS CTX100-4(cid:13) VIN = 2.6V TO 7.2V GOWANDA GA20-103K VOUT = 5V AT 100mA LT1173 • TA23 2V to 5V at 300mA Step-Up Converter with Under Voltage Lockout L1*(cid:13) 20m H, 5A 1N5820 47k 100k 220 100k ILIM VIN 100 2N3906 AO SW1 2N4403 2.2M LT1173 2 X NICAD +5V OUTPUT(cid:13) 301k† 300mA(cid:13) SET FB LOCKOUT AT(cid:13) GND SW2 5W 1.85V INPUT + 100m F(cid:13) MJE200 OS-CON 100k 100k† 47W *L1 = COILTRONICS CTX-20-5-52 †1% METAL FILM LT1173 • TA24 14

LT1173 TYPICAL APPLICATIOUS Voltage Controlled Positive-to-Negative Converter L1*(cid:13) VIN(cid:13) 0.22 MJE210 50m H, 2.5A 5V-12V + 1N5818 1N5820 100m F 220 –VOUT = –5.13 • VC(cid:13) 2W MAXIMUM OUTPUT VIN ILIM 150 SW1 VIN 200k 39k LT1173 – VC (0V TO 5V) FB LT1006 GND SW2 + * L1 = GOWANDA GT10-101 LT1173 • TA25 High Power, Low Quiescent Current Step-Down Converter L1*(cid:13) VIN(cid:13) 0.22W MTM20P08 25m H, 2A 5V(cid:13) 7V-24V 500mA 18V(cid:13) + 1N5818 1W 2k 51W 1N5820 470m F 2N3904 100W(cid:13) VIN ILIM 1/2W SW1 1N4148 LT1173 121k FB GND SW2 40.2k * L1 = GOWANDA GT10-100 EFFICIENCY ‡ 80% FOR 10mA £ ILOAD £ 500mA(cid:13) STANDBY IQ £ 150m A OPERATE STANDBY LT1173 • TA26 2 Cell Powered Neon Light Flasher 0.02m F L1*(cid:13) 470m H 1N4148 1N4148 1N4148 95V REGULATED ILIM VIN SW1 0.02m F 0.02m F 3V LT1173 100M FB GND SW2 0.68m F(cid:13) NE-2(cid:13) 1.3M BLINKS AT(cid:13) 200V 3.3M 0.5Hz *TOKO 262LYF-0100K LT1173 • TA27 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. 15 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.

LT1173 PACKAGE DESCRIPTIOU Dimensions in inches (milimeters) unless otherwise noted. N8 Package 8-Lead Plastic DIP 0.400*(cid:13) (10.160)(cid:13) MAX 8 7 6 5 0.255 ± 0.015*(cid:13) (6.477 ± 0.381)(cid:13) (cid:13) 1 2 3 4 0.300 – 0.325(cid:13) 0.045 – 0.065(cid:13) 0.130 ± 0.005(cid:13) (7.620 – 8.255) (1.143 – 1.651) (3.302 ± 0.127) 0.065(cid:13) (1.651)(cid:13) 0.009 – 0.015(cid:13) TYP (0.229 – 0.381) 0.125(cid:13) (3.175)(cid:13) 0.015(cid:13) (0.325–+00..002155)(cid:13) (01..014453 ±± 00..031851(cid:13)) MI(cid:13)N(cid:13) (0M.3I8N0)(cid:13) +0.635(cid:13) 8.255 –0.381 0.100 ± 0.010(cid:13) 0.018 ± 0.003(cid:13) (2.540 ± 0.254) (0.457 ± 0.076) N8 0694 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.(cid:13) MOLD FLASH OR PROTURSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm). S8 Package 8-Lead Plastic SOIC 0.189 – 0.197*(cid:13) (4.801 – 5.004) 8 7 6 5 0.228 – 0.244(cid:13) 0.150 – 0.157*(cid:13) (5.791 – 6.197) (3.810 – 3.988) 1 2 3 4 0.010 – 0.020(cid:13)· 45(cid:176) 0.053 – 0.069(cid:13) (0.254 – 0.508) (1.346 – 1.752) 0.004 – 0.010(cid:13) 0.008 – 0.010(cid:13) (0.203 – 0.254) 0°– 8° TYP (0.101 – 0.254) 0.016 – 0.050(cid:13) 0.014 – 0.019(cid:13) 0.050(cid:13) 0.406 – 1.270 (0.355 – 0.483) (1.270)(cid:13) BSC SO8 0294 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.(cid:13) (cid:9)(cid:9)MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm). 16 Linear Technology Corporation LT/GP 0894 2K REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 l F AX: (408) 434-0507 l TELEX: 499-3977 ª LINEAR TECHNOLOGY CORPORATION 1994