FEATRES Wide Input Voltage Range: 3V to 6V Low Quiescent Current: 6mA Internal 5A Switch (2.5A for LT1171, 1.25A for LT1172) Shutdown Mode Draws Only 5µA Supply Current Very Few External Parts Required Self-Protected Against Overloads Operates in Nearly All Switching Topologies Flyback-Regulated Mode Has Fully Floating Outputs Comes in Standard 5-Pin Packages LT1172 Available in 8-Pin MiniDIP and Surface Mount Packages Can Be Externally Synchronized APPLICATIO S Logic Supply 5V at 1A 5V Logic to ±15V Op Amp Supply Battery pconverter Power Inverter ( to ) or ( to ) Fully Floating Multiple Outputs SER NOTE: This data sheet is only intended to provide specifications, graphs, and a general functional description of the LT117/LT1171/LT1172. Application circuits are included to show the capability of the LT117/LT1171/LT1172. A complete design manual (AN19) should be obtained to assist in developing new designs. This manual contains a comprehensive discussion of both the LT17 and the external components used with it, as well as complete formulas for calculating the values of these components. The manual can also be used for the LT117/LT1171/LT1172 by factoring in the higher frequency. A CAD design program called SwitcherCAD TM is also available. LT117/LT1171/LT1172 1kHz, 5A, 2.5A and 1.25A High Efficiency Switching Regulators DESCRIPTIO The LT 117/LT1171/LT1172 are monolithic high power switching regulators. They can be operated in all standard switching configurations including buck, boost, flyback, forward, inverting and Cuk. A high current, high efficiency switch is included on the die along with all oscillator, control and protection circuitry. Integration of all functions allows the LT117/LT1171/LT1172 to be built in a standard 5-pin TO-3 or TO-22 power package as well as the 8-pin packages (LT1172). This makes them extremely easy to use and provides bust proof operation similar to that obtained with 3-pin linear regulators. The LT117/LT1171/LT1172 operate with supply voltages from 3V to 6V, and draw only 6mA quiescent current. They can deliver load power up to 1W with no external power devices. By utilizing current-mode switching techniques, they provide excellent AC and DC load and line regulation. The LT117/LT1171/LT1172 have many unique features not found even on the vastly more difficult to use low power control chips presently available. They use adaptive antisat switch drive to allow very wide ranging load currents with no loss in efficiency. An externally activated shutdown mode reduces total supply current to 5µA typically for standby operation., LTC and LT are registered trademarks of Linear Technology Corporation. SwitcherCAD is a trademark of Linear Technology Corporation. TYPICAL APPLICATIO C3* 1µF Boost Converter (5V to 12V) 5V LT117 L1** 5µH 1k 1µF MB3 1µF *REQIRED IF INPT LEADS 2" ** COILTRONICS 5-2-52 PLSE ENGINEERING 92114 L2 1µH C3 1µF OTPT FILTER 1.7k 1% 1.24k 1% 117/1/2 TA1 12V 1A POWER (W) ** 1 8 6 4 2 Maximum Output Power* LT117 BOOST FLYBACK 1 2 3 4 5 INPT VOLTAGE (V) BCK-BOOST V O = 3V BCK-BOOST V O = 5V * ROGH GIDE ONLY. BCK MODE P OT = (5A)(V OT ) SPECIAL TOPOLOGIES DELIVER MORE POWER. ** DIVIDE VERTICAL POWER SCALE BY TWO FOR LT1171, BY FOR FOR LT1172. LT117/1/2 TA2 1
LT117/LT1171/LT1172 ABSOLTE AXI RATI GS W W W Supply Voltage LT117/71/72HV (Note 2)... 6V LT117/71/72 (Note 2)... 4V Switch Output Voltage LT117/71/72HV... 75V LT117/71/72... 65V LT1172S8... 6V Feedback Pin Voltage (Transient, 1ms)... ±15V Storage Temperature Range... 65 C to 15 C Lead Temperature (Soldering, 1 sec)... 3 C (Note 1) Operating Junction Temperature Range LT117/71/72M... 55 C to 15 C LT117/71/72HVC, LT117/71/72C (Oper.)... C to 1 C LT117/71/72HVC LT117/71/72C (Sh. Ckt.)... C to 125 C LT117/71/72HVI, LT117/71/72I (Oper.)... 4 C to 1 C LT117/71/72HVI, LT117/71/72I (Sh. Ckt.)... 4 C to 125 C C I W PACKAGE/ORDER I FOR ATIO 1 2 3 NC* 4 J8 PACKAGE 8-LEAD CERDIP T JMAX = 15 C, θ JA = 1 C/W (J) T JMAX = 1 C, θ JA = 1 C/W (N) T JMAX = 1 C, θ JA = 12 C/W to 15 C/W depending on board layout (S) 1172 T JMAX θ JC θ JA LT117MK 15 C 2 C/W 35 C/W LT117CK 1 C 2 C/W 35 C/W LT1171MK 15 C 4 C/W 35 C/W LT1171CK 1 C 4 C/W 35 C/W LT1172MK 15 C 8 C/W 35 C/W LT1172CK 15 C 8 C/W 35 C/W Based on continuous operation. T JMAX = 125 C for intermittent fault conditions. T JMAX = 1 C, θ JA = * C/W TOP VIEW S8 PACKAGE 8-LEAD PLASTIC SO 8 E2 7 6 E1 5 N8 PACKAGE 8-LEAD PDIP * Do not connect Pin 4 of the LT1172 DIP or SO to external circuitry. This pin may be active in future revisions. FRONT VIEW Q PACKAGE 5-LEAD DD BOTTOM VIEW 1 4 2 3 K PACKAGE 4-LEAD TO-3 METAL CAN 5 4 3 2 1 CASE IS *θ will vary from approximately 25 C/W with 2.8 sq. in. of 1oz. copper to 45 C/W with.2 sq. in. of 1oz. copper. Somewhat lower values can be obtained with additional copper layers in multilayer boards. LT117CQ LT117IQ LT1171CQ LT1171IQ ORDER PART NMBER LT1172MJ8 LT1172CJ8 LT1172CN8 LT1172IN8 LT1172CS8 LT1172IS8 S8 PART MARKING 1172I ORDER PART NMBER LT117MK LT117CK LT1171MK LT1171CK LT1172MK LT1172CK ORDER PART NMBER LT1171HVCQ LT1172CQ LT1172HVIQ NC 1 NC 2 3 4 5 NC 6 NC 7 NC 8 TOP VIEW 16 NC 15 NC 14 E2 13 12 E1 11 1 NC 9 NC SW PACKAGE 16-LEAD PLASTIC SO WIDE T JMAX = 1 C, θ JA = 15 C/W Based on continuous operation. T JMAX = 125 C for intermittent fault conditions. FRONT VIEW 5 4 3 2 1 T PACKAGE 5-LEAD PLASTIC TO-22 T JMAX θ JC θ JA LT117CT/LT117HVCT 1 C 2 C/W 75 C/W LT1171CT/LT1171HVCT 1 C 4 C/W 75 C/W LT1172CT/LT1172HVCT 1 C 8 C/W 75 C/W Based on continuous operation. T JMAX = 125 C for intermittent fault conditions. ORDER PART NMBER LT1172CSW ORDER PART NMBER LT117CT LT117IT LT117HVCT LT117HVIT LT1171CT LT1171IT LT1171HVCT LT1172CT LT1172HVCT 2
LT117/LT1171/LT1172 ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = 25 C. = 15V, =.5V, V = V REF, output pin open, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX NITS V REF Reference Voltage Measured at Feedback Pin 1.224 1.244 1.264 V =.8V 1.214 1.244 1.274 V I B Feedback Input Current V = V REF 35 75 na 11 na g m Error Amplifier I C = ±25µA 3 44 6 µmho Transconductance 24 7 µmho Error Amplifier Source or = 1.5V 15 2 35 µa Sink Current 12 4 µa Error Amplifier Clamp Hi Clamp, V = 1V 1.8 2.3 V Voltage Lo Clamp, V = 1.5V.25.38.52 V Reference Voltage Line 3V V MAX.3 %/V Regulation =.8V A V Error Amplifier Voltage Gain.9V 1.4V 5 8 V/V Minimum Input Voltage (Note 5) 2.6 3. V I Q Supply Current 3V V MAX, =.6V 6 9 ma Control Pin Threshold Duty Cycle =.8.9 1.8 V.6 1.25 V Normal/Flyback Threshold.4.45.54 V on Feedback Pin V Flyback Reference Voltage I = 5µA 15. 16.3 17.6 V (Note 5) 14. 18. V Change in Flyback Reference.5 I 1mA 4.5 6.8 9 V Voltage Flyback Reference Voltage I = 5µA.1.3 %/V Line Regulation (Note 5) 7V V MAX Flyback Amplifier I C = ±1µA 15 3 65 µmho Transconductance (g m ) Flyback Amplifier Source =.6V Source 15 32 7 µa and Sink Current I = 5µA Sink 25 4 7 µa BV Output Switch Breakdown 3V V MAX, LT117/LT1171/LT1172 65 9 V Voltage I SW = 1.5mA LT117HV/LT1171HV/LT1172HV 75 9 V LT1172S8 6 8 V V SAT Output Switch LT117.15.24 Ω On Resistance (Note 3) LT1171.3.5 Ω LT1172.6 1. Ω Control Voltage to Switch LT117 8 A/V Current Transconductance LT1171 4 A/V LT1172 2 A/V I LIM Switch Current Limit (LT117) Duty Cycle = 5% T J 25 C 5 1 A Duty Cycle = 5% T J < 25 C 5 11 A Duty Cycle = 8% (Note 4) 4 1 A (LT1171) Duty Cycle = 5% T J 25 C 2.5 5. A Duty Cycle = 5% T J < 25 C 2.5 5.5 A Duty Cycle = 8% (Note 4) 2. 5. A (LT1172) Duty Cycle = 5% T J 25 C 1.25 3. A Duty Cycle = 5% T J < 25 C 1.25 3.5 A Duty Cycle = 8% (Note 4) 1. 2.5 A 3
LT117/LT1171/LT1172 ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = 25 C. = 15V, =.5V, V = V REF, output pin open, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX NITS I IN Supply Current Increase 25 35 ma/a I SW During Switch On-Time f Switching Frequency 88 1 112 khz 85 115 khz DC MAX Maximum Switch Duty Cycle 85 92 97 % Shutdown Mode 3V V MAX 1 25 µa Supply Current =.5V Shutdown Mode 3V V MAX 1 15 25 mv Threshold Voltage 5 3 mv Flyback Sense Delay Time (Note 5) 1.5 µs Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: Minimum effective switch on time for the LT117/71/72 (in current limit only) is.6µs. This limits the maximum safe input voltage during an output shorted condition. Buck mode and inverting mode input voltage during an output shorted condition is limited to: (max, output shorted) = 15V buck and inverting mode R = Inductor DC resistance (R)(I L ) Vf (t)(f) I L = 1A for LT117, 5A for LT1171, and 2.5A for LT1172 Vf = Output catch diode forward voltage at I L t =.6µs, f = 1kHz switching frequency Maximum input voltage can be increased by increasing R or Vf. External current limiting such as that shown in AN19, Figure 39, will provide protection up to the full supply voltage rating. in Figure 39 should be reduced to 2pF. Transformer designs will tolerate much higher input voltages because leakage inductance limits rate of rise of current in the switch. These designs must be evaluated individually to assure that current limit is well controlled up to maximum input voltage. Boost mode designs are never protected against output shorts because the external catch diode and inductor connect input to output. Note 3: Measured with in hi clamp, V =.8V. I SW = 4A for LT117, 2A for LT1171, and 1A for LT1172. Note 4: For duty cycles (DC) between 5% and 8%, minimum guaranteed switch current is given by I LIM = 3.33 (2 DC) for the LT117, I LIM = 1.67 (2 DC) for the LT1171, and I LIM =.833 (2 DC) for the LT1172. Note 5: Minimum input voltage for isolated flyback mode is 7V. V MAX = 55V for HV grade in fully isolated mode to avoid switch breakdown. TYPICAL PERFOR A CE CHARACTERISTICS W 16 Switch Current Limit vs Duty Cycle* 2.9 Minimum Input Voltage 1.6 Switch Saturation Voltage SWITCH CRRENT (A) 12 8 4 55 C 125 C 25 C * DIVIDE VERTICAL SCALE BY TWO FOR LT1171, BY FOR FOR LT1172. 1 2 3 4 5 6 7 8 9 1 DTY CYCLE (%) 117/1/2 G1 MINIMM INPT VOLTAGE (V) SWITCH CRRENT = I MAX 2.8 2.7 2.6 SWITCH CRRENT = A 2.5 2.4 2.3 75 5 25 25 5 75 1 125 15 TEMPERATRE ( C) 117/1/2 G2 SWITCH SATRATION VOLTAGE (V) 1.4 1.2 1..8.6.4.2 1 C 15 C 55 C 1 2 3 4 5 6 7 SWITCH CRRENT (A)* 25 C * DIVIDE CRRENT BY TWO FOR LT1171, BY FOR FOR LT1172. 8 117/1/2 G3 4
LT117/LT1171/LT1172 TYPICAL PERFOR A CE CHARACTERISTICS W 5 Line Regulation 1.25 Reference Voltage vs Temperature 8 Feedback Bias Current vs Temperature REFERENCE VOLTAGE CHANGE (mv) 4 3 2 1 1 2 3 4 T J = 55 C T J = 15 C T J = 25 C REFERENCE VOLTAGE (V) 1.248 1.246 1.244 1.242 1.24 1.238 1.236 FEEDBACK BIAS CRRENT (na) 7 6 5 4 3 2 1 5 1 2 3 4 INPT VOLTAGE (V) 5 6 117/1/2 G4 1.234 75 5 25 25 5 75 1 125 15 TEMPERATRE ( C) 117/1/2 G5 75 5 25 25 5 75 1 125 15 TEMPERATRE ( C) 117/1/2 G6 SPPLY CRRENT (µa) 16 14 12 1 8 6 4 2 Supply Current vs Supply Voltage (Shutdown Mode) T J = 25 C = 5mV = V 1 2 3 4 SPPLY VOLTAGE (V) 5 6 117/1/2 G7 DRIVER CRRENT (ma) 16 14 12 1 8 6 4 2 Driver Current* vs Switch Current T J = 55 C 1 2 3 SWITCH CRRENT (A) T J = 25 C 4 5 117/1/2 G8 * AVERAGE LT117 POWER SPPLY CRRENT IS FOND BY MLTIPLYING DRIVER CRRENT BY DTY CYCLE, THEN ADDING QIESCENT CRRENT. SPPLY CRRENT (ma) 15 14 13 12 11 1 9 8 7 6 5 Supply Current vs Input Voltage* T J = 25 C NOTE THAT THIS CRRENT DOES NOT INCLDE DRIVER CRRENT, WHICH IS A FNCTION OF LOAD CRRENT AND DTY CYCLE. 1 2 3 4 INPT VOLTAGE (V) 9% DTY CYCLE 5% DTY CYCLE 1% DTY CYCLE % DTY CYCLE 5 6 117/1/2 G9 * NDER VERY LOW OTPT CRRENT CONDITIONS, DTY CYCLE FOR MOST CIRCITS WILL APPROACH 1% OR LESS. SPPLY CRRENT (µa) Shutdown Mode Supply Current 2 18 16 14 12 T J = 15 C 1 8 6 55 C T J 125 C 4 2 1 2 3 4 5 6 7 8 9 1 PIN VOLTAGE (mv) 117/1/2 G1 TRANSCONDCTANCE (µmho) Error Amplifier Transconductance 5 45 g m = I ( PIN) V ( PIN) 4 35 3 25 2 15 1 5 75 5 25 25 5 75 1 125 15 TEMPERATRE ( C) 117/1/2 G11 PIN CRRENT (µa) 3 2 1 1 2 3 Pin Characteristics V = 1.5V (CRRENT INTO PIN) T J = 25 C V =.8V (CRRENT OT OF PIN) 4.5 1. 1.5 2. 2.5 PIN VOLTAGE (V) 117/1/2 G12 5
LT117/LT1171/LT1172 TYPICAL PERFOR A CE CHARACTERISTICS W Idle Supply Current vs Temperature Feedback Pin Clamp Voltage Switch Off Characteristics 11 1 =.6V 5 45 1 9 IDLE SPPLY CRRENT (ma) 9 8 7 6 5 4 3 V SPPLY = 6V V SPPLY = 3V FEEDBACK VOLTAGE (mv) 4 35 3 25 2 15 1 55 C 25 C 15 C SWITCH CRRENT (µa) 8 7 6 5 4 3 2 V SPPLY = 3V V SPPLY = 15V V SPPLY = 4V V SPPLY = 55V 2 5 1 1 75 5 25 25 5 75 1 125 15 TEMPERATRE ( C) 117/1/2 G13.1.2.3.4.5.6.7.8.9 1. FEEDBACK CRRENT (ma) 117/1/2 G14 1 2 3 4 5 6 7 8 9 1 SWITCH VOLTAGE (V) 117/1/2 G15 4 Shutdown Thresholds 4 2.2 Flyback Blanking Time 23 Isolated Mode Flyback Reference Voltage VC PIN VOLTAGE (mv) 35 3 25 2 15 CRRENT (OT OF PIN) VOLTAGE 1 1 VOLTAGE IS REDCED NTIL 5 REGLATOR CRRENT DROPS BELOW 3µA 5 75 5 25 25 5 75 1 125 15 TEMPERATRE ( C) 117/1/2 G16 35 3 25 2 15 PIN CRRENT (µa) TIME (µs) 2. 1.8 1.6 1.4 1.2 1. 75 5 25 25 5 75 1 125 15 JNCTION TEMPERATRE ( C) 117/1/2 G17 FLYBACK VOLTAGE (V) 22 21 2 19 18 17 16 R = 5Ω R = 1k R = 1k 15 75 5 25 25 5 75 1 125 15 TEMPERATRE ( C) 117/1/2 G18 TRANSCONDCTANCE (µmho) 7 6 5 4 3 2 1 1 1k Transconductance of Error Amplifier 1k 1k 1M FREQENCY (Hz) θ g m 117/1/2 G19 3 3 6 9 12 15 18 21 1M PHASE (DEG) FEEDBACK PIN VOLTAGE (mv) 5 49 48 47 46 45 44 43 42 41 Normal/Flyback Mode Threshold on Feedback Pin FEEDBACK PIN VOLTAGE (AT THRESHOLD) FEEDBACK PIN CRRENT (AT THRESHOLD) 4 4 5 25 25 5 75 1 125 15 TEMPERATRE ( C) 117/1/2 G2 24 22 2 18 16 14 12 1 8 6 FEEDBACK PIN CRRENT (µa) 6
OPERATIO LT117/LT1171/LT1172 BLOCK DIAGRA W 16V SWITCH OT 2.3V REG FLYBACK ERROR AMP LT1172 1kHz OSC LOGIC DRIVER 5A, 75V SWITCH MODE SELECT ANTI- SAT COMP ERROR AMP 1.24V REF SHTDOWN CIRCIT.15V CRRENT AMP GAIN 6.2Ω (.4Ω LT1171) (.16Ω LT1172).16 Ω (LT117 AND LT1171 ONLY) E1 ALWAYS CONNECT E1 TO THE GROND PIN ON MINIDIP, 8- AND 16-PIN SRFACE MONT PACKAGES. E1 AND E2 INTERNALLY TIED TO GROND ON TO-3 AND TO-22 PACKAGES. E2 117/1/2 BD The LT117/LT1171/LT1172 are current mode switchers. This means that switch duty cycle is directly controlled by switch current rather than by output voltage. Referring to the block diagram, the switch is turned on at the start of each oscillator cycle. It is turned off when switch current reaches a predetermined level. Control of output voltage is obtained by using the output of a voltage sensing error amplifier to set current trip level. This technique has several advantages. First, it has immediate response to input voltage variations, unlike ordinary switchers which have notoriously poor line transient response. Second, it reduces the 9 phase shift at midfrequencies in the energy storage inductor. This greatly simplifies closedloop frequency compensation under widely varying input voltage or output load conditions. Finally, it allows simple pulse-by-pulse current limiting to provide maximum switch protection under output overload or short conditions. A low dropout internal regulator provides a 2.3V supply for all internal circuitry on the LT117/LT1171/LT1172. This low dropout design allows input voltage to vary from 3V to 6V with virtually no change in device performance. A 1kHz oscillator is the basic clock for all internal timing. It turns on the output switch via the logic and driver circuitry. Special adaptive anti-sat circuitry detects onset of saturation in the power switch and adjusts driver current instantaneously to limit switch saturation. This minimizes driver dissipation and provides very rapid turnoff of the switch. A 1.2V bandgap reference biases the positive input of the error amplifier. The negative input is brought out for output voltage sensing. This feedback pin has a second 7
OPERATIO LT117/LT1171/LT1172 function; when pulled low with an external resistor, it programs the LT117/LT1171/LT1172 to disconnect the main error amplifier output and connects the output of the flyback amplifier to the comparator input. The LT117/ LT1171/LT1172 will then regulate the value of the flyback pulse with respect to the supply voltage.* This flyback pulse is directly proportional to output voltage in the traditional transformer coupled flyback topology regulator. By regulating the amplitude of the flyback pulse, the output voltage can be regulated with no direct connection between input and output. The output is fully floating up to the breakdown voltage of the transformer windings. Multiple floating outputs are easily obtained with additional windings. A special delay network inside the LT117/ LT1171/LT1172 ignores the leakage inductance spike at the leading edge of the flyback pulse to improve output regulation. The error signal developed at the comparator input is brought out externally. This pin ( ) has four different functions. It is used for frequency compensation, current limit adjustment, soft starting, and total regulator shutdown. During normal regulator operation this pin sits at a voltage between.9v (low output current) and 2.V (high output current). The error amplifiers are current output (g m ) types, so this voltage can be externally clamped for adjusting current limit. Likewise, a capacitor coupled external clamp will provide soft start. Switch duty cycle goes to zero if the pin is pulled to ground through a diode, placing the LT117/LT1171/LT1172 in an idle mode. Pulling the pin below.15v causes total regulator shutdown, with only 5µA supply current for shutdown circuitry biasing. See AN19 for full application details. Extra Pins on the MiniDIP and Surface Mount Packages The 8- and 16-pin versions of the LT1172 have the emitters of the power transistor brought out separately from the ground pin. This eliminates errors due to ground pin voltage drops and allows the user to reduce switch current limit 2:1 by leaving the second emitter (E2) disconnected. The first emitter (E1) should always be connected to the ground pin. Note that switch on resistance doubles when E2 is left open, so efficiency will suffer somewhat when switch currents exceed 3mA. Also, note that chip dissipation will actually increase with E2 open during normal load operation, even though dissipation in current limit mode will decrease. See Thermal Considerations next. Thermal Considerations When sing the MiniDIP and SW Packages The low supply current and high switch efficiency of the LT1172 allow it to be used without a heat sink in most applications when the TO-22 or TO-3 package is selected. These packages are rated at 5 C/W and 35 C/W respectively. The minidips, however, are rated at 1 C/W in ceramic (J) and 13 C/W in plastic (N). Care should be taken for minidip applications to ensure that the worst case input voltage and load current conditions do not cause excessive die temperatures. The following formulas can be used as a rough guide to calculate LT1172 power dissipation. For more details, the reader is referred to Application Note 19 (AN19), Efficiency Calculations section. Average supply current (including driver current) is: I IN 6mA I SW (.4 DC/4) I SW = switch current DC = switch duty cycle Switch power dissipation is given by: P SW = (I SW ) 2 (R SW )(DC) R SW = LT1172 switch on resistance (1Ω maximum) Total power dissipation is the sum of supply current times input voltage plus switch power: P D(TOT) = (I IN )( ) P SW In a typical example, using a boost converter to generate 12V at.12a from a 5V input, duty cycle is approximately 6%, and switch current is about.65a, yielding: I IN = 6mA.65(.4 DC/4) = 18mA P SW = (.65) 2 (1Ω)(.6) =.25W P D(TOT) = (5V)(.18A).25 =.34W *See note under block diagram. 8
OPERATIO LT117/LT1171/LT1172 Temperature rise in a plastic minidip would be 13 C/W times.34w, or approximately 44 C. The maximum ambient temperature would be limited to 1 C (commercial temperature limit) minus 44 C, or 56 C. In most applications, full load current is used to calculate die temperature. However, if overload conditions must also be accounted for, four approaches are possible. First, if loss of regulated output is acceptable under overload conditions, the internal thermal limit of the LT1172 will protect the die in most applications by shutting off switch current. Thermal limit is not a tested parameter, however, and should be considered only for noncritical applications with temporary overloads. A second approach is to use the larger TO-22 (T) or TO-3 (K) package which, even without a heat sink, may limit die temperatures to safe levels under overload conditions. In critical situations, heat sinking of these packages is required; especially if overload conditions must be tolerated for extended periods of time. The third approach for lower current applications is to leave the second switch emitter (minidip only) open. This increases switch on resistance by 2:1, but reduces switch current limit by 2:1 also, resulting in a net 2:1 reduction in I 2 R switch dissipation under current limit conditions. The fourth approach is to clamp the pin to a voltage less than its internal clamp level of 2V. The LT1172 switch current limit is zero at approximately 1V on the pin and 2A at 2V on the pin. Peak switch current can be externally clamped between these two levels with a diode. See AN19 for details. Synchronizing with Bipolar Transistor LT117/LT1171/LT1172 Synchronizing The LT117/LT1171/LT1172 can be externally synchronized in the frequency range of 12kHz to 16kHz. This is accomplished as shown in the accompanying figures. Synchronizing occurs when the pin is pulled to ground with an external transistor. To avoid disturbing the DC characteristics of the internal error amplifier, the width of the synchronizing pulse should be under.3µs. sets the pulse width at.2µs. The effect of a synchronizing pulse on the LT117/LT1171/LT1172 amplifier offset can be calculated from: ( )( ) KT V t f I C S S q C VOS = IC KT = 26mV at 25 C q t S = pulse width f S = pulse frequency I C = source current ( 2µA) = operating voltage (1V to 2V) = resistor used to set mid-frequency zero in frequency compensation network. With t S =.2µs, f S = 15kHz, = 1.5V, and = 2k, offset voltage shift is 3.8mV. This is not particularly bothersome, but note that high offsets could result if were reduced to a much lower value. Also, the synchronizing transistor must sink higher currents with low values of, so larger drives may have to be used. The transistor must be capable of pulling the pin to within 2mV of ground to ensure synchronizing. Synchronizing with MOS Transistor LT117 LT117 2N2369 39pF 2.2k 3k FROM 5V LOGIC VN2222* 1N4158 2.2k 1pF 1N4158 FROM 5V LOGIC 117/1/2 OP1 * SILICONIX OR EQIVALENT 117/1/2 OP2 9
LT117/LT1171/LT1172 TYPICAL APPLICATIO S Flyback Converter L2 5µH OPTIONAL FILTER V SNB CLAMP TRN-ON SPIKE C4* 1µF 2V TO 3V LT117 D3 25V 1W M1 N* = 1/3 1 N* C4 1µF 2µF V OT 5V 6A 3.74k V V a c I b d V OT V f I PRI N I PRI /N V PRIMARY FLYBACK VOLTAGE = OT Vf N LT117 SWITCH VOLTAGE AREA a = AREA b TO MAINTAIN ZERO DC VOLTS ACROSS PRIMARY SECONDARY VOLTAGE AREA c = AREA d TO MAINTAIN ZERO DC VOLTS ACROSS SECONDARY PRIMARY CRRENT 1.5k.15µF 1.24k I PRI I PRI SECONDARY CRRENT LT117 SWITCH CRRENT *REQIRED IF INPT LEADS 2" t = (I PRI)(L L ) V SNB SNBBER DIODE CRRENT 117/1/2 TA3 LCD Contrast Supply OPTIONAL SHTDOWN E2 VN2222 E1 5V* L1** 5µH LT1172 C4.47µF 1k 15k V BAT * 3V TO 2V 2k 1N914 C3.47µF 1µF TANTALM D3 V OT 1V TO 26V *** 2µF TANTALM, D3 = ER82.4 6mA SCHOTTKY. OTHER FAST SWITCHING TYPES MAY BE SED. * AND BATTERY MAY BE TIED TOGETHER. MAXIMM VALE FOR V BAT IS EQAL TO THE NEGATIVE OTPT 1V. WITH HIGHER BATTERY VOLTAGES, HIGHEST EFFICIENCY IS OBTAINED BY RNNING THE LT1172 PIN FROM 5V. SHTTING OFF THE 5V SPPLY WILL ATOMATICALLY TRN OFF THE LT1172. EFFICIENCY IS ABOT 8% AT I OT = 25mA.,, ARE MADE LARGE TO MINIMIZE BATTERY DRAIN IN SHTDOWN, WHICH IS APPROXIMATELY V BAT /( ). ** FOR HIGH EFFICIENCY, L1 SHOLD BE MADE ON A FERRITE OR MOLYPERMALLOY CORE. PEAK INDCTOR CRRENTS ARE ABOT 6mA AT P OT =.7Ω. INDCTOR SERIES RESISTANCE SHOLD BE LESS THAN.4Ω FOR HIGH EFFICIENCY. *** OTPT RIPPLE IS ABOT 2mV P-P TO 4mV P-P WITH = 2µF TANTALM. IF LOWER RIPPLE IS DESIRED, INCREASE, OR ADD A 1Ω, 1µF TANTALM OTPT FILTER. 117/1/2 TA4 1
LT117/LT1171/LT1172 TYPICAL APPLICATIO S (Note that maximum output currents are divided by 2 for LT1171, by 4 for LT1172.) Driving High Voltage FET (for Off-Line Applications, See AN25) External Current Limit 1V TO 2V LT117 G D Q1 5Ω V X 2V LT117 117/1/2 TA5 117/1/2 TA6 Negative-to-Positive Buck-Boost Converter External Current Limit OPTIONAL INPT FILTER L3 C4* 1µF 2V REQIRED IF INPT LEADS 2" LT117 L1** 5µH 2.2k.22µF 1.24k L2 OPTIONAL OTPT FILTER 1µF * ** PLSE ENGINEERING 92114, COILTRONICS 5-2-52 THIS CIRCIT IS OFTEN SED TO CONVERT 48V TO 5V. TO GARANTEE FLL SHORT-CIRCIT PROTECTION, THE CRRENT LIMIT CIRCIT SHOWN IN AN19, FIGRE 39, SHOLD BE ADDED WITH REDCED TO 2pF. Q1 C3 V OT 12V 2A 11.3k 117/1/2 TA7 Q1 1k 1pF R S NOTE THAT THE LT117 PIN IS NO LONGER COMMON TO. LT117 117/1/2 TA8 Negative Buck Converter * REQIRED IF INPT LEADS 2" ** PLSE ENGINEERING 92114 COILTRONICS 5-2-52 C3* 1µF LT117 L1** 5µH 1µF Q1 2N396 4.64k R4 12k LOAD 5.2V 4.5A OPTIONAL INPT FILTER L3 OPTIONAL OTPT FILTER C4 2µF 2V 1.24k L2 4µH 117/1/2 TA9 11
LT117/LT1171/LT1172 TYPICAL APPLICATIO S Positive-to-Negative Buck-Boost Converter D3 1N41 C4 1µF LT117 R5 47Ω, 1W 5k.1µF 1.7k 1.24k L1** 5µH 1V TO 3V C5 1µF* 1N914 C3 2µF R4 47Ω * REQIRED IF INPT LEADS 2" ** PLSE ENGINEERING 92114, COILTRONICS 5-2-52 TO AVOID STARTP PROBLEMS FOR INPT VOLTAGES BELOW 1V, CONNECT ANODE OF D3 TO, AND REMOVE R5. MAY BE REDCED FOR LOWER OTPT CRRENTS. (5µF)(I OT ). FOR 5V OTPTS, REDCE TO 1.5k, INCREASE TO.3µF, AND REDCE R6 TO 1Ω. 1µF R6 47Ω V OT 12V 2A 117/1/2 TA1 High Efficiency Constant Current Charger INPT VOLTAGE > V BAT 2V < 35V 2µF 35V 1N5819 2.2µF 35V TANTALM LT1171 VC C3.47µF 1k C4.1µF V LT16 V 25k R4 1k I CHRG = * L2 REDCES RIPPLE CRRENT INTO THE BATTERY BY ABOT 2:1. IT MAY BE OMITTED IF DESIRED. L1 1µH, 1A 1.244V R4 R5 L2* 1µH, 1A = 1A AS SHOWN RN = V SHTDOWN = 5V R6 78k R7 22k 2N394 R8 1k MB4 R5.5Ω 1A C4 2µF 25V BATTERY 2V TO 25V 117/1/2 TA11 INPT VOLTAGE 4.5V TO 2V Backlight CCFL Supply (see AN45 for details) L2*** 1k 1N5818 L1** 3µH A 33pF 3kV LAMP Q1* 1µF TANT E2 E1 LT1172 2µF C6 1 µ F.2µF Q2* B 1N914 1k 1N914 56Ω 5k INTENSITY ADJST * Q1,Q2 = BCP56 OR MPS65/561 COILTRONICS CTX3-4 117/1/2 TA12 ** *** SMIDA 6345-2 OR COILTRONICS 1192-1 A MODIFICATION WILL ALLOW OPERATION DOWN TO 4.5V. CONSLT FACTORY. 12
LT117/LT1171/LT1172 TYPICAL APPLICATIO S Positive Buck Converter C3 2.2µF C5* 1µF D3 LT117 47Ω 1µF r * REQIRED IF INPT LEADS 2" ** PLSE ENGINEERING 92114 COILTRONICS 5-2-52 3.74k 1.24k 1µF 1N914 L1** 5µH C4 1µF L2 4µH OPTIONAL OTPT FILTER C5 2µF R4 1Ω 5V, 4.5A 1mA MINIMM 117/1/2 TA13 Negative Boost Regulator C4* 47µF 15V L1 5µH LT117 * REQIRED IF INPT LEADS 2" 3.3k.22µF 27k 1.24k C3 1µF 1µF V OT 28V, 1A R O (MINIMM LOAD) 117/1/2 TA14 Driving High Voltage NPN ** * Q1 LT117 * SETS I B (ON) ** SETS I B (OFF) 117/1/2 TA15 13
LT117/LT1171/LT1172 TYPICAL APPLICATIO S Forward Converter R4 D3 T1 1 M N L1 25µH 2µF 3.74k V OT 5V, 6A 2V TO 3V LT117 D4 C3 Q1 R6 33Ω C4 R5 1Ω 1.24k 117/1/2 TA16 High Efficiency 5V Buck Converter 33µF 35V C6.2µF C4.1µF MB3p 68Ω LT117 C5.3µF DIODE C3 4.7µF TANT V 1N4148 L1 5µH *.13Ω 1µH 3A 1µF 16V 39µF 16V OPTIONAL OTPT FILTER V OT 5V 3A** MODE LOGIC 22pF <.3V = NORMAL MODE >2.5V = SHTDOWN OPEN = BRST MODE MODE LT1432 V LIM V OT * IS MADE FROM PC BOARD COPPER TRACES. ** MAXIMM CRRENT IS DETERMINED BY THE CHOICE OF LT17 FAMILY. SEE APPLICATION SECTION. 117/1/2 TA17 14
LT117/LT1171/LT1172 PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. J8 Package 8-Lead CERDIP (Narrow.3, Hermetic) (LTC DWG # 5-8-111).45.68 (1.143 1.727) FLL LEAD OPTION.3 BSC (.762 BSC) CORNER LEADS OPTION (4 PLCS).23.45 (.584 1.143) HALF LEAD OPTION.5 (.127) MIN.25 (.635) RAD TYP.45 (1.287) MAX 8 7 6 5 1 2 3 4.22.31 (5.588 7.874).2 (5.8) MAX.15.6 (.381 1.524).8.18 (.23.457) 15 NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE OR TIN PLATE LEADS.45.65 (1.143 1.651).14.26 (.36.66).1 (2.54) BSC.125 3.175 MIN J8 1298 15
LT117/LT1171/LT1172 PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. K Package 4-Lead TO-3 Metal Can (LTC DWG # 5-8-1311).32.35 (8.13 8.89).76.775 (19.3 19.69).6.135 (1.524 3.429) 1.177 1.197 (29.9 3.4).47 TP P.C.D..655.675 (16.64 19.5).151.161 (3.84 4.9) DIA 2 PLC.42.48 (1.67 12.19).167.177 (4.24 4.49) R.38.43 (.965 1.9) 18 72.49.51 (12.45 12.95) R K4(TO-3) 198 N8 Package 8-Lead PDIP (Narrow.3) (LTC DWG # 5-8-151).4* (1.16) MAX 8 7 6 5.255 ±.15* (6.477 ±.381) 1 2 3 4.3.325 (7.62 8.255).45.65 (1.143 1.651).13 ±.5 (3.32 ±.127).9.15 (.229.381).325.35.15.889 8.255.381 ( ).65 (1.651) TYP.1 (2.54) BSC *THESE DIMENSIONS DO NOT INCLDE MOLD FLASH OR PROTRSIONS. MOLD FLASH OR PROTRSIONS SHALL NOT EXCEED.1 INCH (.254mm).125 (3.175) MIN.18 ±.3 (.457 ±.76).2 (.58) MIN N8 198 16
LT117/LT1171/LT1172 PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. Q Package 5-Lead Plastic DD Pak (LTC DWG # 5-8-1461).256 (6.52).6 (1.524).6 (1.524) TYP.39.415 (9.96 1.541) 15 TYP.165.18 (4.191 4.572).45.55 (1.143 1.397).6 (1.524).183 (4.648).33.37 (8.382 9.398).59 (1.499) TYP.4.8.4 (.12.23.12).3 (7.62).75 (1.95) BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK.143.12.2 ( 3.632.35.58).67 (1.7).28.38 BSC (.711.965).13.23 (.33.584).95.115 (2.413 2.921).5 ±.12 (1.27 ±.35) Q(DD5) 198 S8 Package 8-Lead Plastic Small Outline (Narrow.15) (LTC DWG # 5-8-161).189.197* (4.81 5.4) 8 7 6 5.228.244 (5.791 6.197).15.157** (3.81 3.988) 1 2 3 4.8.1 (.23.254).1.2 (.254.58) 45 8 TYP.53.69 (1.346 1.752).4.1 (.11.254).16.5 (.46 1.27) * DIMENSION DOES NOT INCLDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED.6" (.152mm) PER SIDE ** DIMENSION DOES NOT INCLDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED.1" (.254mm) PER SIDE.14.19 (.355.483) TYP.5 (1.27) BSC SO8 1298 17
LT117/LT1171/LT1172 PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. SW Package 16-Lead Plastic Small Outline (Wide.3) (LTC DWG # 5-8-162).398.413* (1.19 1.49) 16 15 14 13 12 11 1 9 NOTE 1.394.419 (1.7 1.643).291.299** (7.391 7.595).1.29 45 (.254.737).93.14 (2.362 2.642) 1 2 3 4 5 6 7 8.37.45 (.94 1.143) 8 TYP.9.13 (.229.33).5 (1.27) BSC.14.19 (.356.482) TYP NOTE 1.16.5 (.46 1.27) NOTE: 1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANFACTRING OPTIONS. THE PART MAY BE SPPLIED WITH OR WITHOT ANY OF THE OPTIONS * DIMENSION DOES NOT INCLDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED.6" (.152mm) PER SIDE ** DIMENSION DOES NOT INCLDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED.1" (.254mm) PER SIDE.4.12 (.12.35) S16 (WIDE) 198 18
LT117/LT1171/LT1172 PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. T Package 5-Lead Plastic TO-22 (Standard) (LTC DWG # 5-8-1421).39.415 (9.96 1.541).147.155 (3.734 3.937) DIA.165.18 (4.191 4.572).45.55 (1.143 1.397).23.27 (5.842 6.858).46.5 (11.684 12.7).33.37 (8.382 9.398).57.62 (14.478 15.748).62 (15.75) TYP.7.728 (17.78 18.491) SEATING PLANE.152.22 (3.861 5.131).26.32 (6.6 8.13).95.115 (2.413 2.921).155.195* (3.937 4.953) BSC.67 (1.7).28.38 (.711.965).135.165 (3.429 4.191).13.23 (.33.584) * MEASRED AT THE SEATING PLANE T5 (TO-22) 399 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 19
LT117/LT1171/LT1172 TYPICAL APPLICATIO Positive Current Boosted Buck Converter 28V 47Ω 2W C3.47µF R6 47Ω C6.2µF 1: N C5* 1µF LT117 68Ω.33µF R7 1k C4.1µF 6 4 2pF 7 LM38 1.24k 8 2 3 R4 1.24k N.25 R5 5k 5k 5µF V OT 5V, 1A * REQIRED IF INPT LEADS 2" 117/1/2 TA18 RELATED PARTS PART NMBER DESCRIPTION COMMENTS LT17/LT171/LT172 5A/2.5A/1.25A High Efficiency Switching Regulators 4kHz, to 6V, to 75V LT174/LT176 5.5A/2A Step-Down Switching Regulators 1kHz, Also for Positive-to-Negative Conversion LT182 1A, High Voltage, High Efficiency Switching Regulator to 75V, to 1V, Telecom LT1268/LT1268B 7.5A, 15kHz Switching Regulators to 3V, to 6V LT1269/LT1271 4A High Efficiency Switching Regulators 1kHz/6kHz, to 3V, to 6V LT127/LT127A 8A and 1A High Efficiency Switching Regulators 6kHz, to 3V, to 6V LT137 5kHz High Efficiency 6A Switching Regulator High Power Boost, Flyback, SEPIC LT1371 5kHz High Efficiency 3A Switching Regulator Good for Boost, Flyback, Inverting, SEPIC LT1372/LT1377 5kHz and 1MHz High Efficiency 1.5A Switching Regulators Directly Regulates ±V OT LT1373 25kHz Low Supply Current High Efficiency 1.5A Switching Regulator Low 1mA Quiescent Current LT1374 4A, 5kHz Step-Down Switching Regulator Synchronizable, to 25V LT1375/LT1376 1.5A, 5kHz Step-Down Switching Regulators p to 1.25A Out from an SO-8 LT1425 Isolated Flyback Switching Regulator 6W Output, ±5% Regulation, No Optocoupler Needed LT157 5kHz Monolithic Buck Mode Switching Regulator 1.5A Switch, Good for 5V to 3.3V LT1533 ltralow Noise 1A Switching Regulator Push-Pull, <1µV P-P Output Noise 2 Linear Technology Corporation 163 McCarthy Blvd., Milpitas, CA 9535-7417 (48) 432-19 FAX: (48) 434-57 TELEX: 499-3977 www.linear-tech.com 11712fe LT/TP 1299 2K REV E PRINTED IN SA LINEAR TECHNOLOGY CORPORATION 1991