LT1074/LT1076 Step-Down Switching - Analog Devices

1 LT1074/LT10761sn1074 1074fds, LTC and LT are registered trademarks of Linear Technology SUFEATURESDESCRIPTIOUTYPICAL APPLICATIOUStep-Down SwitchingRegulatorThe LT 1074 is a 5A (LT1076 is rated at 2A) monolithicbipolar Switching regulator which requires only a fewexternal parts for normal operation. The power switch , alloscillator and control circuitry, and all current limit com- Buck Converter with Output Voltage Range of 50V Tapped-Inductor Buck Converter with 10A Outputat 5V Positive-to-Negative Converter Negative Boost Converter Multiple Output Buck Converter 5A Onboard switch (LT1074)

2 Operates Up to 60V Input 100kHz Switching Frequency Greatly Improved Dynamic Behavior Available in Low Cost 5 and 7-Lead Packages Only Quiescent Current Programmable Current Limit Micropower Shutdown Modeponents, are included on the chip. The topology is a classicpositive buck configuration but several design innova-tions allow this device to be used as a positive-to-negativeconverter, a negative boost converter, and as a flybackconverter. The switch output is specified to swing 40 Vbelow ground, allowing the LT1074 to drive a tapped-inductor in the buck mode with output currents up to LT1074 uses a true Analog multiplier in the feedbackloop.

3 This makes the device respond nearly instanta-neously to input voltage fluctuations and makes loop gainindependent of input voltage. As a result, dynamic behav-ior of the regulator is significantly improved over pulse by pulse current limiting makes the LT1074nearly bust-proof for output overloads or shorts. The inputvoltage range as a buck converter is 8V to 60V, but a self-boot feature allows input voltages as low as 5V in theinverting and boost LT1074 is available in low cost TO-220 or DD packageswith frequency pre-set at 100kHz and current limit at (LT1076 = ).

4 A 7-pin TO-220 package is also availablewhich allows current limit to be adjusted down to zero. Inaddition, full micropower shutdown can be Application Note 44 for design fixed 5V output, 2A version is also available. See Converter EfficiencyBasic Positive Buck Converter++VSWVINVCGNDFBLT10745V5AC1500 *10V TO 40VC3 200 FL1**50 H (LT1074)100 H (LT1076)USE MBR340 FOR LT1076 COILTRONICS #50-2-52 (LT1074)#100-1-52 (LT1076)PULSE ENGINEERING, INC. #PE-92114 (LT1074) #PE-92102 (LT1076)HURRICANE#HL-AK147QQ (LT1074) #HL-AG210LL (LT1076)RIPPLE CURRENT RATING IOUT/2** LT1074 TA0125 VOUTPUT LOAD CURRENT (A)0 EFFICIENCY (%)607080901234LT1074 TPC275610050L = 50 H TYPE 52 COREDIODE = MBR735V = 5V, V = 15 VOUTINV = 12V, V = 20 VOUTINLT1074LT1074/LT10762sn1074 1074fdsABSOLUTE AXI U RATI GSWWWUPACKAGE/ORDER I FOR ATIOUUW(Note 1)*Assumes package is soldered to IN2 of 1 oz.

5 Copper over internal ground plane or over back side VoltageLT1074/ LT1076 .. 45 VLT1074HV/LT1076HV .. 64 VSwitch Voltage with Respect to Input VoltageLT1074/ LT1076 .. 64 VLT1074HV/LT1076HV .. 75 VSwitch Voltage with Respect to Ground Pin (VSW Negative) LT1074/LT1076 (Note 7) .. 35 VLT1074HV/LT1076HV (Note 7) .. 45 VFeedback Pin Voltage .. 2V, +10 VShutdown Pin Voltage (Not to Exceed VIN) .. 40 VILIM Pin Voltage (Forced) .. Operating Ambient Temperature 0 C to 70 40 C to 85 CMilitary (OBSOLETE) .. 55 C to 125 CMaximum Operating Junction Temperature 0 C to 125 40 C to 125 CMilitary (OBSOLETE).

6 55 C to 150 CMaximum Storage Temperature .. 65 C to 150 CLead Temperature (Soldering, 10 sec) .. 300 CORDER PARTNUMBERORDER PARTNUMBERLT1076: JC = 4 C, JA = 30 C/WLT1076: JC = 4 C, JA = 30 C/WLT1074: JC = C, JA = 50 C/WLT1076: JC = 4 C, JA = 50 C/WLT1074: JC = C, JA = 35 C/WLT1076: JC = 4 C, JA = 35 C/WLT1074: JC = C, JA = 50 C/WLT1076: JC = 4 C, JA = 50 C/WQ PACKAGE5-LEAD PLASTIC DDFRONT VIEWVINVSWGNDVCFB/SENSE54321R PACKAGE7-LEAD PLASTIC DDFRONT VIEWSHDNVCFB/SENSEGNDILIMVSWVIN765432124 13 VCVINVSWCASE IS GNDFBK PACKAGE4-LEAD TO-3 METAL CANBOTTOM VIEWT PACKAGE5-LEAD PLASTIC TO-220 LEADS ARE FORMED STANDARD FORSTRAIGHT LEADS.

7 ORDER FLOW 06 VINVSWGNDVCFBFRONT VIEW54321T7 PACKAGE7-LEAD PLASTIC TO-220 SHDNVCFBGNDILIMVSWVINFRONT VIEW7654321 TAB ISGNDTAB ISGNDTAB ISGNDTAB ISGNDC onsult LTC Marketing for parts specified with wider operating temperature PACKAGEC onsider the T5 Package for Alternate SourceLT1074/LT10763sn1074 1074fdsThe denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25 C. Tj = 25 C, VIN = 25V, unless otherwise On Voltage (Note 2)LT1074 ISW = 1A, Tj 0 = 1A, Tj < 0 = 5A, Tj 0 = 5A, Tj < 0 = = 2A Off LeakageLT1074 VIN 25V, VSW = 05300 AVIN = VMAX, VSW = 0 (Note 8)10500 ALT1076 VIN = 25V, VSW = 0150 AVIN = VMAX, VSW = 0 (Note 8)250 ASupply Current (Note 3)VFB = , VIN 40V < VIN < 60V 912 mAVSHUT = (Device Shutdown) (Note 9) 140300 AMinimum Supply VoltageNormal Mode Mode (Note 4) Current Limit (Note 5)LT1074 ILIM Open = 10k (Note 6) = 7k (Note 6)

8 3 ALT1076 ILIM Open = 10k (Note 6) = 7k (Note 6) Duty Cycle 8590% Switching Frequency90100110kHzTj 125 C 85120kHzTj > 125 C 85125kHzVFB = 0V through 2k (Note 5)20kHzSwitching Frequency Line Regulation8V VIN VMAX (Note 8) Amplifier Voltage Gain (Note 7)1V VC 4V2000V/VError Amplifier Transconductance370050008000 mhoError Amplifier Source and Sink CurrentSource (VFB = 2V)100140225 ASink (VFB = ) Pin Bias CurrentVFB = VREF AReference VoltageVC = 2V Voltage ToleranceVREF (Nominal) = Conditions of Input Voltage, Output 1 , Temperature and Load CurrentReference Voltage Line Regulation8V VIN VMAX (Note 8) Voltage at 0% Duty Temperature 4mV/ CMultiplier Reference Voltage24 VShutdown Pin CurrentVSH = 5V 51020 AVSH VTHRESHOLD ( ) 50 AShutdown ThresholdsSwitch Duty Cycle = 0 Shut Down Resistance Junction to C/WELECTRICAL CHARACTERISTICSLT1074/LT10764sn1074 1074fdsNote 1: Absolute Maximum Ratings are those values beyond which the lifeof a device may be 2.

9 To calculate maximum switch on voltage at currents betweenlow and high conditions, a linear interpolation may be 3: A feedback pin voltage (VFB) of forces the VC pin to its lowclamp level and the switch duty cycle to zero. This approximates the zeroload condition where duty cycle approaches 4: Total voltage from VIN pin to ground pin must be 8V after start-up for proper 5: switch frequency is internally scaled down when the feedback pinvoltage is less than to avoid extremely short switch on times. Duringtesting, VFB is adjusted to give a minimum switch on time of 1 6: ILIM (LT1074), ILIM (LT1076).

10 Note 7: switch to input voltage limitation must also be 8: VMAX = 40V for the LT1074/76 and 60V for the LT1074 9: Does not include switch 1k2kRLIM CHARACTERISTICS6 VREGULATORAND BIAS+ -POWERSHUTDOWN 10 A 320 A + + CURRENTLIMITCOMPC215400+ C1R/SLATCHRRQXYZ+ A1 ERRORAMPFBV100kHzOSCILLATORANALOGMULTIPL IERXYZFREQ SHIFTSYNCG1 PULSE WIDTHCOMPARATOR24V (EQUIVALENT) OUTPUT(V ) SUPPLYSHUTDOWN*I *6V TO ALLCIRCUITRYLIM SW VINCLT1074 BD01100 SWITCHOUTPUT (V ) SW 3V(p-p)LT1076LT1074 *AVAILABLE ON PACKAGES WITH PIN COUNTS GREATER THAN 5.