LT1072

LT1072 1.25A High Efficiency Switching Regulator FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Available in MiniDiP, TO-220, and TO-3 Packages Wide Input Voltage Range 3V to 60V Low Quiescent Current—6mA Internal 1.25A Switch Very Few External Parts Required Self-Protected Against Overloads Operates in Nearly All Switching Topologies Shutdown Mode Draws Only 50µA Supply Current Flyback-Regulated Mode has Fully Floating Outputs Can be Externally Synchronized The LT®1072 is a monolithic high power switching regulator. It 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 LT1072 to be built in a standard 5-pin TO-3 or TO-220 power package as well as the 8-pin miniDlP. This makes it extremely easy to use and provides “bust proof” operation similar to that obtained with 3-pin linear regulators. The LT1072 operates with supply voltages from 3V to 60V, and draws only 6mA quiescent current. It can deliver load power up to 20 watts with no external power devices. By utilizing current-mode switching techniques, it provides excellent AC and DC load and line regulation. The LT1072 has many unique features not found even on the vastly more difficult to use low power control chips presently available. It uses an adaptive anti-sat switch drive to allow very wide ranging load currents with no loss in efficiency. An externally activated shutdown mode reduces total supply current to 50µA typical for standby operation. Totally isolated and regulated outputs can be generated by using the optional “flyback regulation mode” built into the LT1072, without the need for optocouplers or extra transformer windings. APPLICATIO S ■ ■ ■ ■ ■ ■ ■ Logic Supply 5V at 2.5A 5V Logic to ±15V Op Amp Supply Offline Converter up to 50W Battery Upconverter Power lnverter (+ to –) or (– to +) Fully Floating Multiple Outputs Driver for High Current Supplies USER NOTE: This data sheet is only intended to provide specifications, graphs, and a general functional description of the LT1072. Application circuits are included to show the capability of the LT1072. A complete design manual (AN-19) should be obtained to assist in developing new designs. This manual contains a comprehensive discussion of both the LT1070 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 LT1072 by factoring in the lower switch current rating. , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO 5V 220µH** Boost Converter (5V to 12V) 25 Maximum Output Power* VIN VSW POWER (W) 20 BUCK-BOOST VO = 30V BOOST 10 FLYBACK ISOLATED C3 25µF* + – LT1072 10.7k GND VC 1k 1µF FB 12V, 0.25A 15 + – 1.24k + 470µF – 5 BUCK-BOOST VO = 5V 0 0 10 30 20 INPUT VOLTAGE (V) 40 50 *REQUIRED IF INPUT LEADS ≥ 2” **PULSE ENGINEERING 52626 LT1072 • TA01 *ROUGH GUIDE ONLY. BUCK MODE POUT = 1A x VOUT. MINIDIP OUTPUT POWER MAY BE LIMITED BY PACKAGE TEMPERATURE RISE AT HIGH INPUT VOLTAGES OR HIGH DUTY CYCLES LT1072 • TA02 U 1072fc U U 1 LT1072 ABSOLUTE (Note 1) AXI U RATI GS Note 1: Minimum switch “on” time for the LT1072 in current limit is ≈ 0.7µsec. This limits the maximum input voltage during short-circuit to conditions, in the buck and inverting modes only, ≈ 40V. Normal (unshorted) conditions are not affected. If the LT1072 is being operated in the buck or inverting mode at high input voltages and short-circuit conditions are expected, a resistor must be placed in series with the inductor, as follows: The value of the resistor is given by: Supply Voltage LT1072HV (See Note 1) ......................................... 60V LT1072 (See Note 1) ............................................. 40V Switch Output Voltage LT1072HV ............................................................. 75V LT1072 .................................................................. 65V LT1072S8 .............................................................. 60V Feedback Pin Voltage (Transient, 1ms) ................. ±15V Operating Junction Temperature Range LT1072HVM, LT1072M (OBSOLETE) .... –55°C to 150°C LT1072HVC, LT1072C (Oper.)* ............0°C to 100°C LT1072HVC, LT1072C (Sh. Ckt.)* ........0°C to 125°C LT1072HVI ....................................... –40°C to 125°C Storage Temperature Range ............... –65°C to 150°C Lead Temperature (Soldering, 10 sec) ............... 300°C *Includes LT1072S8 PACKAGE/ORDER I FOR ATIO BOTTOM VIEW VSW 1 4 VIN 2 3 VC CASE IS GND FB ORDER PART NUMBER LT1072HVMK LT1072MK LT1072HVCK LT1072CK GND VC FB NC 1 2 3 4 K PACKAGE 4-LEAD TO-3 METAL CAN TJMAX = 150°C, θJC = 8°C/W, θJA = 35°C/W TJMAX = 100°C*, θJC = 8°C/W, θJA = 35°C/W N PACKAGE 8-LEAD PDIP TJMAX = 100°C, θJA = 130°C/W OBSOLETE PACKAGE ORDER PART NUMBER VIN VSW GND FB VC FRONT VIEW 5 4 3 2 1 LT1072CT LT1072HVCT LT1072HVIT T PACKAGE 5-LEAD TO-220 TJMAX = 100°C/W, θJC = 8°C/W, θJA = 50°C/W Consult LTC Marketing for parts specified with wider operating temperature ranges. 1072fc 2 U U W WW U W R= (t) (f) (VIN) – Vf – RL I(LIMIT) t = Minimum “on” time of LT1072 in current limit, ≈ 0.7µs f = Operating frequency (40kHz) Vf = Forward voltage of external catch diode at I(LIMIT) I(LIMIT) = Current limit of LT1072 (2A) RL = Internal series resistance of inductor TOP VIEW 8 7 6 5 TOP VIEW E2 VSW E1 VIN GND VC FB NC 1 2 3 4 8 7 6 5 ORDER PART NUMBER E2 VSW E1 VIN LT1072CN8 LT1072CS8 S8 PART MARKING 1072 S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 100°C, θJA = 130°C/W J PACKAGE 8-LEAD CERAMIC DIP TJMAX = 150°C, θJA = 100°C/W LT1072MJ8 LT1072CJ8 OBSOLETE PACKAGE Consider the S8 or N8 Packages for Alternate Source TOP VIEW NC NC GND VC FB NC NC NC 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 NC NC E2 VSW E1 VIN NC NC ORDER PART NUMBER LT1072CSW SW PACKAGE 16-LEAD PLASTIC SO WIDE TJMAX = 100°C, θJC = 130°C/W LT1072 • POI01 LT1072 ELECTRICAL CHARACTERISTICS SYMBOL VREF IB gm PARAMETER Reference Voltage Feedback Input Current Error Amplifier Transconductance Error Amplifier Source or Sink Current Error Amplifier Clamp Voltage Reference Voltage Line Regulation AV IQ Error Amplifier Voltage Gain Minimum Input Voltage Supply Current Control Pin Threshold Normal/Flyback Threshold on Feedback Pin VFB Flyback Reference Voltage Change in Flyback Reference Voltage Flyback Reference Voltage Line Regulation Flyback Amplifier Transconductance (gm) Flyback Amplifier Source and Sink Current BV Output Switch Breakdown Voltage Output Switch ON Resistance (Note 2) The ● denotes specifications which apply over the full operating temperature range. Unless otherwise specified, VIN = 15V, VC = 0.5V, VFB = VREF, output pin open. CONDITlONS Measured at Feedback Pin VC = 0.8V VFB = VREF ● ● MIN 1.224 1.214 TYP 1.244 1.244 350 MAX 1.264 1.274 750 1100 6000 7000 350 400 2.3 0.52 0.03 UNITS V V nA nA µmho µmho µA µA V V %/V %/V V/V V mA V V V V V V %/V %/V µmho µA µA V V V ∆IC = ±25µA ● 3000 2400 150 120 1.8 0.25 4400 200 VC = 1.5V ● Hi Clamp, VFB = 1V Lo Clamp, VFB = 1.5V 3V ≤ VIN ≤ VMAX VC = 0.8V 0.9V ≤ VC ≤ 1.4V ● ● 0.38 500 800 2.6 6 3.0 9 1.08 1.25 0.54 17.6 18 8.5 0.03 650 70 70 3V ≤ VIN ≤ VMAX, VC = 0.6V Duty Cycle = 0 ● 0.8 0.6 0.4 15 14 4.5 0.9 0.45 16.3 6.8 0.01 lFB = 50µA ● 0.05 ≤ IFB ≤ 1mA lFB = 50µA 3V ≤ VIN ≤ VMAX (Note 4) ∆IC = ±10µA VC = 0.6V Source IFB = 50µA Sink 3V ≤ VIN ≤ VMAX ISW = 1.5mA ISW = 1.25A Duty Cycle = 50% TJ ≥ 25°C Duty Cycle = 50% TJ < 25°C Duty Cycle = 80% (Note 3) LT1072 LT1072HV LT1072S8 ● ● ● ● ● ● 150 15 25 65 75 60 300 32 40 90 90 80 0.6 2 VSAT ILIM 1 3 3.5 2.5 Ω A/V A A A mA/A kHz kHz % µs µA mV mV Control Voltage to Switch Current Transconductance Switch Current Limit ● ● ● 1.25 1.25 1 25 35 33 90 40 92 1.5 100 100 50 150 ∆IIN ∆ISW f DC (max) Supply Current Increase During Switch ON Time Switching Frequency ● 35 45 47 97 250 250 300 Maximum Switch Duty Cycle Flyback Sense Delay Time Shutdown Mode Supply Current Shutdown Mode Threshold Voltage 3V ≤ VIN ≤ VMAX VC = 0.05V 3V ≤ VIN ≤ VMAX ● Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Measured with VC in hi clamp, VFB = 0.8V. Note 3: For duty cycles (DC) between 50% and 80%, minimum guaranteed switch current is given by ILIM = 0.833 (2 – DC). Note 4: VMAX = 55V for LT1072HV to avoid switch breakdown. 1072fc 3 LT1072 TYPICAL PERFOR A CE CHARACTERISTICS Switch Current Limit vs Duty Cycle 4 96 95 SWITCH CURRENT (A) 3 DUTY CYCLE (%) 94 93 92 91 0 0 10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%) LT1072 • TPC01 –55°C 2 125°C 1 25°C TIME (µs) LT1072 • TPC02 Minimum Input Voltage 2.9 SWITCH SATURATION VOLTAGE (V) 1.6 MINIMUM INPUT VOLTAGE (V) 2.8 2.7 2.6 SWITCH CURRENT = 1.25A 100°C 1.0 0.8 0.6 0.4 0.2 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 SWITCH CURRENT (A) 2 25°C –55°C FLYBACK VOLTAGE (V) SWITCH CURRENT = 0A 2.5 2.4 2.3 –75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) LT1072 • TPC04 Line Regulation 5 REFERENCE VOLTAGE CHANGE (mV) 4 REFERENCE VOLTAGE (V) 3 2 1 0 –1 –2 –3 –4 –5 0 10 TJ = – 55°C TJ = 150°C 25 TJ= °C FEEDBACK BIAS CURRENT (nA) 30 40 20 INPUT VOLTAGE (V) 4 UW 50 LT1072 • TPC07 Maximum Duty Cycle 2.2 2.0 1.8 1.6 1.4 1.2 Flyback Blanking Time 90 –75 –50 –25 0 25 50 75 100 125 150 JUNCTION TEMPERATURE (°C) 1.0 –75 –50 –25 0 25 50 75 100 125 150 JUNCTION TEMPERATURE (°C) LT1072 • TPC03 Switch Saturation Voltage 23 22 150°C 1.2 21 20 19 18 17 16 1.4 Isolated Mode Flyback Reference Voltage RFEEDBACK = 500Ω RFEEDBACK = 1kΩ RFEEDBACK = 10kΩ 15 –75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (C°) LT1072 • TPC06 LT1072 • TPC05 Reference Voltage and Switching Frequency vs Temperature 1.250 1.248 1.246 1.244 1.242 REFERENCE VOLTAGE 1.240 1.238 1.236 1.234 –75 –50 –25 37 36 35 34 0 25 50 75 100 125 150 TEMPERATURE (°C) LT1072 • TPC08 Feedback Bias Current vs Temperature 42 800 700 600 500 400 300 200 100 0 –75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) LT1072 • TPC09 SWITCHING FREQUENCY 41 40 FREQUENCY (kHz) 39 38 60 1072fc LT1072 TYPICAL PERFOR A CE CHARACTERISTICS Driver Current* vs Switch Current 80 70 SUPPLY CURRENT (mA) DRIVER CURRENT (mA) 60 50 40 30 20 10 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 SWITCH CURRENT (A) 2 15 14 SUPPLY CURRENT (µA) *AVERAGE LT1072 POWER SUPPLY CURRENT IS FOUND BY MULTIPLYING DRIVER CURRENT BY DUTY CYCLE, THEN ADDING QUIESCENT CURRENT LT1072 • TPC10 Normal/Flyback Mode Threshold on Feedback Pin 500 490 –24 –22 200 180 480 470 460 450 440 430 420 410 400 –50 –25 0 FEEDBACK PIN CURRENT (AT THRESHOLD) FEEDBACK PIN VOLTAGE (AT THRESHOLD) –20 –18 –16 –14 –12 –10 –8 –6 –4 25 50 75 100 125 150 TEMPERATURE (°C) LT1072 • TPC13 TRANSCONDUCTANCE (µmho) FEEDBACK PIN VOLTAGE (mV) SUPPLY CURRENT (µA) Shutdown Thresholds 400 350 VC PIN VOLTAGE (mV) 300 250 200 VOLTAGE 150 100 50 VC VOLTAGE IS REDUCED UNTIL REGULATOR CURRENT DROPS BELOW 300µA –150 –100 –50 CURRENT (OUT OF VC PIN) –400 –350 IDLE SUPPLY CURRENT (mA) –300 –250 –200 VC PIN VOLTAGE (µA) 11 10 9 8 7 6 5 4 3 2 FEEDBACK VOLTAGE (mV) 0 –75 –50 –25 0 0 25 50 75 100 125 150 TEMPERATURE (°C) LT1072 • TPC16 UW Supply Current vs Input Voltage* TJ = 25°C Supply Current vs Supply Voltage (Shutdown Mode) 160 140 120 100 VC = 50mV 80 60 40 20 VC = 0V 0 10 20 40 30 SUPPLY VOLTAGE (V) 50 60 TJ = 25°C NOTE THAT THIS CURRENT DOES NOT 13 INCLUDE DRIVER CURRENT, WHICH IS A FUNCTION OF LOAD CURRENT AND 12 DUTY CYCLE. 90% DUTY CYCLE 11 10 9 8 7 6 5 0 10 0% DUTY CYCLE 30 40 20 INPUT VOLTAGE (V) 50 60 50% DUTY CYCLE 10% DUTY CYCLE 0 *UNDER VERY LOW OUTPUT CURRENT CONDITIONS, DUTY CYCLE FOR MOST CIRCUITS WILL APPROACH 10% OR LESS LT1072 • TPC11 LT1072 • TPC12 Shutdown Mode Supply Current 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0 10 20 30 40 50 60 70 80 90 100 VC PIN VOLTAGE (mV) LT1072 • TPC14 Error Amplifier Transconductance Gm = ∆I (VC PIN) ∆V (FB PIN) FEEDBACK PIN CURRENT (µA) 160 140 120 100 80 60 40 20 0 – 55°C ≤ TJ ≤ 125°C TJ = 150°C 0 –75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (C°) LT1072 • TPC15 Idle Supply Current vs Temperature VC = 0.6V 500 450 400 350 300 250 200 150 100 50 0 0 25 50 75 100 125 150 TEMPERATURE (°C) LT1072 • TPC17 Feedback Pin Clamp Voltage –55°C 25°C 150°C VSUPPLY = 60V VSUPPLY = 3V 1 –75 –50 –25 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 FEEDBACK CURRENT (mA) 1 LT1072 • TPC18 1072fc 5 LT1072 TYPICAL PERFOR A CE CHARACTERISTICS Transconductance of Error Amplifier 7000 6000 θ –30 0 TRANSCONDUCTANCE (µmho) 100 0 –100 –200 VFB = 0.8V (CURRENT OUT OF VC PIN) –300 TJ = 25°C SWITCH CURRENT (µA) 2.5 VC PIN CURRENT (µA) 5000 4000 3000 2000 1000 0 Gm –1000 1k 10k 100k 1M FREQUENCY (Hz) BLOCK DIAGRA SHUTDOWN CIRCUIT CURRENT AMP GAIN ≈6 1.24V REF 0.15V * ALWAYS CONNECT E1 TO GROUND PIN ON MINIDIP AND SURFACE MOUNT PACKAGES. EMITTERS TIED TO GROUND ON TO-3 AND TO-220 PACKAGES GND LT1072 • BD01 6 – + UW LT1072 • TPC19 VC Pin Characteristics 300 200 VFB = 1.5V (CURRENT INTO VC PIN) Switch “Off” Characteristics 1000 900 800 700 600 VSUPPLY = 55V VSUPPLY = 40V VSUPPLY = 15V 500 VSUPPLY = 3V 400 300 200 100 30 60 90 120 150 180 210 10M PHASE (°) –400 0 0.5 2.0 1.5 1.0 VC PIN VOLTAGE (V) 0 0 10 20 30 40 50 60 70 80 90 100 SWITCH VOLTAGE (V) LT1072 • TPC21 LT1072 • TPC20 W VIN 16V SWITCH OUT 2.3V REG FLYBACK ERROR AMP 40kHz OSC LOGIC DRIVER MODE SELECT COMP ANTISAT FB – ERROR AMP VC + 0.16Ω 0.16Ω E1* E2 1072fc LT1072 LT1072 OPERATIO The LT1072 is a current mode switcher. 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 90 phase shift at midfrequencies in the energy storage inductor. This greatly simplifies closed loop frequency compensation under widely varying input voltage or output load conditions. Finally, it allows simple pulseby-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 LT1072. This low-dropout design allows input voltage to vary from 3V to 60V with virtually no change in device performance. A 40kHz oscillator is the basic clock for all internal timing. It turns “on” the output switch via the logic and driver circuitry. Special adaptive antisat 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 turn-off 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 function; when pulled low with an external resistor, it programs the LT1072 to disconnect the main error amplifier output and connects the output of the flyback amplifier to the comparator input. The LT1072 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 U inside the LT1072 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 (VC) 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 0.9V (low output current) and 2.0V (high output current). The error amplifiers are current output (gm) 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 VC pin is pulled to ground through a diode, placing the LT1072 in an idle mode. Pulling the VC pin below 0.15V causes total regulator shutdown, with only 50µA supply current for shutdown circuitry biasing. See AN-19 for full application details. Extra Pins on the MiniDIP and Surface Mount Packages The 8 and 16-pin versions of the LT1072 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 100mA. 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.” Thermal Considerations When Using Small Packages The low supply current and high switch efficiency of the LT1072 allow it to be used without a heat sink in most applications when the TO-220 or TO-3 package is selected. These packages are rated at 50°C/W and 35 °C/W respectively. The small packages, however, are rated at greater than 100°C/W. Care should be taken with these packages to ensure that the worse case input voltage and load current conditions do not cause excessive die temperatures. The following formulas can be used as a 1072fc 7 LT1072 LT1072 OPERATIO rough guide to calculate LT1072 power dissipation. For more details, the reader is referred to Application Note 19 (AN19), “Efficiency Calculations” section. Average supply current (including driver current) is: IIN ≈ 6mA + ISW(0.004 + DC/40) ISW = switch current DC = switch duty cycle Switch power dissipation is given by: PSW = (ISW)2 • RSW • DC RSW = LT1072 switch “on” resistance (1Ω maximum) Total power dissipation is the sum of supply current times input voltage plus switch power: PTOT = (llN)(VIN) + PSW In a typical example, using a boost converter to generate 12V @ 0.12A from a 5V input, duty cycle is approximately 60%, and switch current is about 0.65A, yielding: llN = 6mA + 0.65(0.004 + DC/40) = 18mA PSW = (0.65)2 • 1Ω • (0.6) = 0.25W PTOT = (5V)(0.018A) + 0.25 = 0.34W Temperature rise in a plastic miniDIP would be 130°C/W times 0.34W, or approximately 44°C. The maximum ambient temperature would be limited to 100 ° 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 LT1072 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 non-critical applications with temporary overloads. A second approach is to use the larger TO-220 (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. 8 U The third approach for lower current applications is to leave the second switch emitter 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 I2R switch dissipation under current limit conditions. The fourth approach is to clamp the VC pin to a voltage less than its internal clamp level of 2V. The LT1072 switch current limit is zero at approximately 1V on the VC pin and 2A at 2V on the VC pin. Peak switch current can be externally clamped between these two levels with a diode. See AN-19 for details. LT1072 Synchronizing The LT1072 can be externally synchronized in the frequency range of 48kHz to 70kHz. This is accomplished as shown in the accompanying figures. Synchronizing occurs when the VC 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 1µs. C2 sets the pulse width at ≈ 0.35µs. The effect of a synchronizing pulse on the LT1072 amplifier offset can be calculated from: KT (t )(f ) I + VC q S S C R3 ∆VOS = IC (( ( ( KT = 26mV at 25°C q tS = pulse width fS = pulse frequency IC = LT1072 VC source current (≈ 200µA) VC = LT1072 operating VC voltage (1V to 2V) R3 = resistor used to set mid-frequency “zero” in LT1072 frequency compensation network. With tS = 0.35µs, fS = 50kHz, VC = 1.5V, and R3 = 2KΩ, offset voltage shift is ≈2.2mV. This is not particularly bothersome, but note that high offsets could result if R3 were reduced to a much lower value. Also, the synchronizing transistor must sink higher currents with low values of R3, so larger drives may have to be used. The transistor must be capable of pulling the VC pin to within 200mV of ground to ensure synchronizing. 1072fc LT1072 LT1072 OPERATIO U Synchronizing with MOS Transistor VIN LT1072 GND VC C2 68pF R3 C1 2N2369 R2 2.2k FROM 5V LOGIC GND LT1072 VC C2 200pF R1 3k R3 C1 D1 1N4158 VN2222* R2 2.2k D2 1N4158 FROM 5V LOGIC *SILICONIX OR EQUIVALENT LT1072 • OP01 LT1072 • OP02 Synchronizing with Bipolar Transistor VIN TYPICAL APPLICATIO S Totally Isolated Converter OPTIONAL OUTPUT FILTER L1 10µH VIN 5V C5 25µF* + LT1072 FB 500Ω C2 0.01µF R2 5k *REQUIRED IF INPUT LEADS ≥ 2” N = 0.875 = 7:8 FOR VOUT = 15V U 1:N R4 2.7k C3 0.47µF D1 15V + N N C1 200µF C4 200µF + COM L2 –15V 10µH C5 200µF C6 200µF + + VIN VSW GND VC ≈ 16V VIN 0 tOFF tON SWITCH VOLTAGE VOUT + Vf (Vf = DIODE FORWARD VOLTAGE) 0V N • VIN SECONDARY VOLTAGE LT1072 • TA03 1072fc 9 LT1072 TYPICAL APPLICATIO S Flyback Converter L2 10µH C4 200µF OPTIONAL FILTER VIN 20 TO 30V ** R4 1k C3 0.47µF D2 VIN C4 + 25µF* VSW R1 3.74k 0 IPRI SECONDARY CURRENT N IPRI LT1070 SWITCH CURRENT C2 0.15µF R3 1.5k R2 1.24k 0 IPRI SNUBBER DIODE CURRENT 0 (I ) (LL) t = PRI VSNUB D1 1 N* N* = 1 3 VOUT 5V 1.5A VSNUB CLAMP TURN-ON SPIKE LT1072 0 GND VC FB *REQUIRED IF INPUT LEADS ≥ 2" **OPTIONAL TO REPLACE R4 AND C3 Negative to Positive Buck-Boost Converter L1** 220µH VIN VSW C2 1000µF C4 25µF* OPTIONAL INPUT FILTER L3 VIN –12V + LT1072 GND VC FB R3 2.2k R2 1.24k *REQUIRED IF INPUT LEADS ≥ 2" **PULSE ENGINEERING 52626 LT1072 • TA05 C1 0.22µF 10 U VIN 0V a b VOUT + Vf c + Vf V PRIMARY FLYBACK VOLTAGE = OUT N LT1072 SWITCH VOLTAGE AREA “a” = AREA “b” TO MAINTAIN ZERO DC VOLTS ACROSS PRIMARY + 0V C1 500µF d ∆I IPRI N • VIN SECONDARY VOLTAGE AREA “c” = AREA “d” TO MAINTAIN ZERO DC VOLTS ACROSS SECONDARY PRIMARY CURRENT LT1072 • TA04 External Current Limit L2 OPTIONAL OUTPUT FILTER D1 C3 VIN VSW LT1072 VOUT 12V, 0.5A + – VIN + Q1 R1 11.3k GND VC FB R1 1k Q1 C1 1000pF RS R2 C2 NOTE THAT THE LT1072 GND PIN IS NO LONGER COMMON TO VIN (–) LT1072 • TA06 1072fc LT1072 TYPICAL APPLICATIO S Positive to Negative Buck-Boost Converter D3† 1N4001 R5† 470Ω, 1W C5 100µF* VSW *REQUIRED IF INPUT LEADS ≥ 2" **PULSE ENGINEERING 92113 † C4 5µF + U VIN 10 TO 30V VIN LT1072 R1 10.7k GND VC R3 5k C2 0.1µF FB R2 1.24k D2 1N914 R4 47Ω TO AVOID START-UP PROBLEMS FOR INPUT VOLTAGES BELOW 10V, CONNECT ANODE OF D3 TO VIN, AND REMOVE R5. C1 MAY BE REDUCED FOR LOWER OUTPUT CURRENTS. C1 ≈ (500µF)(IOUT). FOR 5V OUTPUTS, REDUCE R3 TO 1.5k, INCREASE C2 TO 0.3µF, AND REDUCE R6 TO 100Ω + C3 2µF D1 + C1 C† 1000µF R6 470Ω VOUT –12V AT 2A LT1072 • TA07 L1** 200µH External Current Limit VX LT1072 R2 ≈ 2V R1 500Ω D1 GND VC LT1072 • TA08 Voltage Boosted Boost Converter R4 1.5k 1/2W C3 0.68 D2 VIN VIN 15V VSW + LT1072 R1 98k GND VC FB R3 10k C2 0.047µF R2 1.24k TOTAL INDUCTANCE = 8mH 1 INTERLEAVE PRIMARY AND L1 N = 5 SECONDARY FOR LOW LEAKAGE INDUCTANCE D1 VOUT 100V AT 75mA + C1 200µF LT1072 • TA09 1072fc 11 LT1072 TYPICAL APPLICATIO S Driving High Voltage FET (for Offline Applications, See AN-25) G D1 VIN VSW D Q1 OPTIONAL INPUT FILTER L3 VIN –20V *REQUIRED IF INPUT LEADS ≥ 2" **PULSE ENGINEERING 52626 VIN D3 L2 VIN C3 2.2µF C5* 25µF VSW 4µ H OPTIONAL OUTPUT FILTER R1 3.74k GND VC FB R3 470Ω r D1 *REQUIRED IF INPUT LEADS ≥ 2" **PULSE ENGINEERING 52626 LT1072 • TA12 + R2 1.24k 12 U + 10 TO 20V LT1072 GND LT1072 • TA10 Negative Buck Converter D1 VIN C3 25µF* C2 500µF L1** 220µH + R1 4.64k LOAD –5.2V AT 1A Q1 2N3906 VSW + GND LT1072 VC FB C1 R3 R2 1.24k OPTIONAL + OUTPUT FILTER L2 4µH LT1072 • TA11 C4 200µF Positive Buck Converter + LT1072 C5 200µF D2 1N914 L1** 220µH C4 500µF R4 10Ω C1 1µ F C2 1µ F + + 5V, 1A 100mA MINIMUM 1072fc LT1072 TYPICAL APPLICATIO S Negative Boost Regulator D2 VIN R1 27k R0 (MINIMUM LOAD) C4 470µF* + GND VC FB R3 3.3k C2 0.22µF R2 1.24k VIN –15V PACKAGE DESCRIPTIO CORNER LEADS OPTION (4 PLCS) .045 – .068 (1.143 – 1.650) FULL LEAD OPTION .300 BSC (7.62 BSC) .008 – .018 (0.203 – 0.457) NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE OR TIN PLATE LEADS U U VSW LT1072 + C3 10µF + C1 1000µF L1 200µH D1 VOUT –28V AT 0.25A *REQUIRED IF INPUT LEADS ≥ 2" LT1072 • TA13 J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic) (Reference LTC DWG # 05-08-1110) .405 (10.287) MAX 8 7 6 5 .005 (0.127) MIN .023 – .045 (0.584 – 1.143) HALF LEAD OPTION .025 (0.635) RAD TYP 1 2 3 .220 – .310 (5.588 – 7.874) 4 .200 (5.080) MAX .015 – .060 (0.381 – 1.524) 0° – 15° .045 – .065 (1.143 – 1.651) .014 – .026 (0.360 – 0.660) .100 (2.54) BSC .125 3.175 MIN J8 0801 OBSOLETE PACKAGE 1072fc 13 LT1072 PACKAGE DESCRIPTIO U K Package 4-Lead TO-3 Metal Can (Reference LTC DWG # 05-08-1311) 0.320 – 0.350 (8.13 – 8.89) 0.760 – 0.775 (19.30 – 19.69) 0.060 – 0.135 (1.524 – 3.429) 0.420 – 0.480 (10.67 – 12.19) 0.038 – 0.043 (0.965 – 1.09) 1.177 – 1.197 (29.90 – 30.40) 0.655 – 0.675 (16.64 – 19.05) 0.151 – 0.161 (3.84 – 4.09) DIA 2 PLC 0.167 – 0.177 (4.24 – 4.49) R 72° 18° 0.490 – 0.510 (12.45 – 12.95) R 0.470 TP P.C.D. K4(TO-3) 1098 OBSOLETE PACKAGE N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .400* (10.160) MAX 8 7 6 5 .255 ± .015* (6.477 ± 0.381) 1 .300 – .325 (7.620 – 8.255) 2 3 4 .130 ± .005 (3.302 ± 0.127) .045 – .065 (1.143 – 1.651) .008 – .015 (0.203 – 0.381) +.035 .325 –.015 .065 (1.651) TYP .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 (0.457 ± 0.076) N8 1002 ( 8.255 +0.889 –0.381 ) .100 (2.54) BSC INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) NOTE: 1. DIMENSIONS ARE 1072fc 14 LT1072 PACKAGE DESCRIPTIO U S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .045 ±.005 .050 BSC 8 N N .245 MIN .160 ±.005 .228 – .244 (5.791 – 6.197) 1 2 3 N/2 N/2 .150 – .157 (3.810 – 3.988) NOTE 3 .189 – .197 (4.801 – 5.004) NOTE 3 7 6 5 1 2 3 4 .053 – .069 (1.346 – 1.752) 0°– 8° TYP .004 – .010 (0.101 – 0.254) .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .030 ±.005 TYP RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) .014 – .019 (0.355 – 0.483) TYP .050 (1.270) BSC SO8 0502 SW Package 16-Lead Plastic Small Outline (Wide .300 Inch) (Reference LTC DWG # 05-08-1620) .030 ±.005 TYP N .050 BSC .045 ±.005 .398 – .413 (10.109 – 10.490) NOTE 4 16 15 14 13 12 11 10 9 N .420 MIN .325 ±.005 NOTE 3 .394 – .419 (10.007 – 10.643) 1 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT 1 .291 – .299 (7.391 – 7.595) NOTE 4 .010 – .029 × 45° (0.254 – 0.737) 0° – 8° TYP 2 3 4 5 6 7 8 .093 – .104 (2.362 – 2.642) .037 – .045 (0.940 – 1.143) .005 (0.127) RAD MIN .009 – .013 (0.229 – 0.330) NOTE 3 .016 – .050 (0.406 – 1.270) .050 (1.270) BSC .004 – .012 (0.102 – 0.305) NOTE: 1. DIMENSIONS IN .014 – .019 (0.356 – 0.482) TYP S16 (WIDE) 0502 INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS 4. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) 1072fc 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. 15 LT1072 PACKAGE DESCRIPTIO U T Package 5-Lead Plastic TO-220 (Standard) (Reference LTC DWG # 05-08-1421) .147 – .155 (3.734 – 3.937) DIA .230 – .270 (5.842 – 6.858) .460 – .500 (11.684 – 12.700) .570 – .620 (14.478 – 15.748) .330 – .370 (8.382 – 9.398) .700 – .728 (17.78 – 18.491) .620 (15.75) TYP .165 – .180 (4.191 – 4.572) .045 – .055 (1.143 – 1.397) SEATING PLANE .152 – .202 .260 – .320 (3.861 – 5.131) (6.60 – 8.13) .095 – .115 (2.413 – 2.921) .155 – .195* (3.937 – 4.953) .013 – .023 (0.330 – 0.584) BSC .067 (1.70) .028 – .038 (0.711 – 0.965) .135 – .165 (3.429 – 4.191) * MEASURED AT THE SEATING PLANE T5 (TO-220) 0801 .390 – .415 (9.906 – 10.541) RELATED PARTS PART NUMBER LT1070/HV LT1071/HV LT1082 LT1170/HV LT1171/HV LT1172/HV LT1307/LT1307B LT1317/LT1317B LT1370/HV LT1371/HV DESCRIPTION 5A ISW, 40kHz, High Efficiency Switching Regulator 2.5A ISW, 40kHz, High Efficiency Switching Regulator 1A ISW, 60kHz, High Efficiency Switching Regulator 5A ISW, 100kHz, High Efficiency Switching Regulator 2.5A ISW, 100kHz, High Efficiency Switching Regulator 1.25A ISW, 100kHz, High Efficiency Switching Regulator 600mA ISW, 600kHz, High Efficiency Switching Regulator 600mA ISW, 600kHz, High Efficiency Switching Regulator 6A ISW, 500kHz, High Efficiency Switching Regulator 3A ISW, 500kHz, High Efficiency Switching Regulator COMMENTS VIN=3V to 40/60V, VOUT up to 65/75V, IQ=6mA, ISD