LT1777 Low Noise Step-Down Switching Regulator FEATURES DESCRIPTIO n The LT 1777 is a Buck (step-down) regulator designed for Programmable dI/dt Limit n noise sensitive applications. It contains a dI/dt limiting Internally Limited dV/dt n circuit programmed via a small external inductor in the High Input Voltage: 48V Max n switching path. Internal circuitry also generates controlled 700mA Peak Switch Rating n dV/dt ramp rates. True Current Mode Control n 100kHz Fixed Operating Frequency The monolithic die includes all oscillator, control and n Synchronizable to 250kHz protection circuitry. The part can accept operating input n Low Supply Current in Shutdown: 30m A voltages as high as 48V, and contains an output switch n Low Thermal Resistance 16-Pin SO Package rated at 700mA peak current. Current mode control offers excellent dynamic input supply rejection and short-circuit U protection. The internal control circuitry is normally pow- APPLICATIO S ered via the V pin, thereby minimizing power drawn CC n Automotive Cellular and GPS Receivers directly from the V supply (see Applications Informa- IN n Telecom Power Supplies tion). The fused-lead SO16 package and 100kHz switch- n Industrial Instrument Power Supplies ing frequency allow for minimal PC board area requirements. , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO Low Noise 5V Step-Down Supply V Switching Waveforms SW V IN 10 24V + 39F V IN 63V 3 4 SHDN V CC 100pF V SW LT1777 1H* 220H V VOLTAGE OUT 12 6 SYNC V 5V 10V/DIV SW 14 5 400mA + V V C D 100F 36.5k 13 10V MBRS1100 1% FB 100pF 12k SGND V SW 2200pF 7 CURRENT 12.1k 200mA/DIV 1% *PROGRAMS dI/dT 1777 TA01 1777 TA02 500ns/DIV 1 U ULT1777 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage ....................................................... 48V ORDER PART TOP VIEW NUMBER Switch Voltage (V V ) (Note 4) ...................... 51V IN SW GND* 1 16 GND* SHDN, SYNC Pin Voltage.......................................... 7V NC 2 15 NC LT1777CS V Pin Voltage ...................................................... 30V CC SHDN 3 14 V C LT1777IS FB Pin Voltage ........................................................ 3.0V V 4 13 FB CC Operating Junction Temperature Range V 5 12 SYNC D V 6 11 NC LT1777C ............................................... 0 C to 125 C SW SGND 7 10 V LT1777I ........................................... 40 C to 125 C IN *FOUR CORNER PINS ARE GND* 8 9 GND* Storage Temperature Range ................ 65 C to 150 C FUSED TO INTERNAL DIE ATTACH PADDLE FOR HEAT Lead Temperature (Soldering, 10 sec)................. 300 C S PACKAGE SINKING. CONNECT THESE 16-LEAD PLASTIC SO FOUR PINS TO EXPANDED PC LANDS FOR PROPER HEAT T = 125 C, q = 50 C/W* JMAX JA SINKING. Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS The l denotes specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. J V = 24V, V Open, V = 5V, V = 1.4V unless otherwise noted. IN SW CC C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Power Supplies V Minimum Input Voltage 6.7 7.0 V IN(MIN) l 7.4 V I V Supply Current V = 0V 620 800 m A VIN IN C l 900 m A I V Supply Current V = 0V 2.5 3.5 mA VCC CC C l 4.5 mA V V Dropout Voltage (Note 2) l 2.8 3.1 V VCC CC Shutdown Mode I V = 0V 30 50 m A VIN SHDN l 75 m A Feedback Amplifier V Reference Voltage 1.225 1.240 1.255 V REF l 1.215 1.265 V I FB Pin Input Bias Current 600 1500 nA IN g Feedback Amplifier Transconductance D I = 10m A 400 650 1000 m mho m C l 200 1500 m mho I , I Feedback Amplifier Source or Sink Current 60 100 170 m A SRC SNK l 45 220 m A V Feedback Amplifier Clamp Voltage 2.0 V CL Reference Voltage Line Regulation 12V V 48V l 0.01 %/V IN Voltage Gain 200 600 V/V 2 U WU U WWW