LT1507 500kHz Monolithic Buck Mode Switching Regulator FEATURES n with all the necessary oscillator, control and logic cir- Constant 500kHz Switching Frequency n cuitry. High switching frequency allows a considerable Uses All Surface Mount Components n reduction in the size of external components. The topology Operates with Inputs as Low as 4V n is current mode for fast transient response and good loop Saturated Switch Design (0.3) n stability. Both fixed output voltage (3.3V) and adjustable Cycle-by-Cycle Current Limiting n parts are available. Easily Synchronizable n Inductor Size as Low as 2H A special high speed bipolar process and new design n Shutdown Current: 20A techniques allow this regulator to achieve high efficiency U at a high switching frequency. Efficiency is maintained APPLICATIONS over a wide output current range by keeping quiescent supply current to 4mA and by utilizing a supply boost n Portable Computers capacitor to allow the NPN power switch to saturate. A n Battery-Powered Systems shutdown signal will reduce supply current to 20A. The n Battery Charger LT1507 can be externally synchronized from 570kHz to n Distributed Power 1MHz with logic level inputs. The LT1507 fits into standard 8-pin SO and PDIP pack- DESCRIPTION ages. Temperature rise is kept to a minimum by the high The LT 1507 is a 500kHz monolithic buck mode switching efficiency design. Full cycle-by-cycle short-circuit protec- regulator, functionally identical to the LT1375 but opti- tion and thermal shutdown are provided. Standard surface mized for lower input voltage applications. It will operate mount external parts are used including the inductor and over a 4V to 15V input range, compared with 5.5V to 25V capacitors. for the LT1375. A 1.5A switch is included on the die along , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATION 5V to 3.3V Volt Down Converter 5V to 3.3V Efficiency 100 D2 V = 5V IN 1N914 V = 3.3V OUT 90 C2 0.1F BOOST OUTPUT 5V V V 3.3V IN SW 80 L1*** 1.25A C3* LT1507-3.3 5H DEFAULT 47F SHDN SENSE (OPEN) 16V 70 = ON TANTALUM GND V C C1** D1 100F 1N5818 C C 10V 60 3.3nF TANTALUM AVX TPSD477M016R0150 OR SPRAGUE 593D EQUIVALENT. * 50 RIPPLE CURRENT RATING 0.6A 0 0.25 0.50 0.75 1.00 1.25 AVX TPSD108M010R0100 OR SPRAGUE 593D EQUIVALENT ** LOAD CURRENT (A) COILTRONICS CTX5-1. SUBSTITUTION UNITS SHOULD BE RATED *** AT 1.25A, USING LOW LOSS CORE MATERIAL LT1507 TA02 SEE BOOST PIN CONSIDERATIONS IN APPLICATIONS INFORMATION SECTION FOR ALTERNATIVE D2 CONNECTION 1 EFFICIENCY (%) + + U ULT1507 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION Input Voltage ........................................................... 16V ORDER PART Boost Pin Voltage .................................................... 25V NUMBER Shutdown Pin Voltage ............................................... 7V TOP VIEW LT1507CN8 FB Pin Voltage (Adjustable Part) ............................. 3.5V BOOST 1 8 V C LT1507CN8-3.3 FB Pin Current (Adjustable Part) ............................. 1mA V 2 7 FB/SENSE IN LT1507CS8 Sense Voltage (Fixed 3.3V Part) ................................ 5V V 3 6 GND SW LT1507CS8-3.3 Sync Pin Voltage ....................................................... 7V SHDN 4 5 SYNC LT1507IN8 Operating Ambient Temperature Range LT1507IN8-3.3 N8 PACKAGE S8 PACKAGE LT1507C .................................................. 0C to 70C 8-LEAD PDIP 8-LEAD PLASTIC SO LT1507IS8 LT1507I .............................................. 40C to 85C LT1507IS8-3.3 Max Operating Junction Temperature................... 125C T = 125C, = 80C/W TO 120C/ W (N) JMAX JA T = 125C, = 120C/W TO 170C/ W (S) S8 PART MARKING JMAX JA Storage Temperature Range ................. 65C to 150C DEPENDING ON PC BOARD LAYOUT Lead Temperature (Soldering, 10 sec).................. 300C 1507 1507I 15073 1507I3 Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS T = 25C, V = 5V, V = 1.5V, boost open, switch open unless otherwise specified. J IN C PARAMETER CONDITIONS MIN TYP MAX UNITS Reference Voltage (Adjustable) 2.39 2.42 2.45 V All Conditions l 2.36 2.48 V Sense Voltage (3.3V) 3.25 3.3 3.35 V All Conditions l 3.23 3.37 V Sense Pin Resistance l 4.0 6.6 9.5 k Reference Voltage Line Regulation 4.3V V 15V l 0.01 0.03 %/V IN FB Input Bias Current l 0.5 2 A Error Amplifier Voltage Gain (Note 8) (Note 1) 150 400 Error Amplifier Transconductance (Note 8) I(V ) = 10A 1500 2000 2700 mho C l 1100 3000 mho V Pin to Switch Current C Transconductance 2 A/V Error Amplifier Source Current V = 2.1V or V = 2.9V l 150 225 320 A FB SENSE Error Amplifier Sink Current V = 2.7V or V = 3.7V 2 mA FB SENSE V Pin Switching Threshold Duty Cycle = 0 0.9 V C V Pin High Clamp V = 2.1V or V = 2.9V 2.1 V C FB SENSE Switch Current Limit V Open, V = 2.1V or V = 2.9V DC 50% l 1.50 2 3 A C FB SENSE V 5V, V = V + 5V DC = 80% l 1.35 3 A IN BOOST IN Switch On Resistance (Note 6) I = 1.5A, V = V + 5V 0.3 0.4 SW BOOST IN l 0.5 Maximum Switch Duty Cycle V = 2.1V or V = 2.9V 90 93 % FB SENSE l 86 93 % 2 U W U U WWW