LT1738 Slew Rate Controlled Ultralow Noise DC/DC Controller DESCRIPTIO FEATURES n Greatly Reduced Conducted and Radiated EMI The LT 1738 is a switching regulator controller designed n Low Switching Harmonic Content to lower conducted and radiated electromagnetic interfer- n Independent Control of Output Switch Voltage and ence (EMI). Ultralow noise and EMI are achieved by Current Slew Rates controlling the voltage and current slew rates of an exter- n Greatly Reduced Need for External Filters nal N-channel MOSFET switch. Current and voltage slew n Single N-Channel MOSFET Driver rates can be independently set to optimize harmonic n 20kHz to 250kHz Oscillator Frequency content of the switching waveforms vs efficiency. The n Easily Synchronized to External Clock LT1738 can reduce high frequency harmonic power by as n Regulates Positive and Negative Voltages much as 40dB with only minor losses in efficiency. n Easier Layout Than with Conventional Switchers The LT1738 utilizes a current mode architecture opti- mized for single switch topologies such as boost, flyback U and Cuk. The IC includes gate drive and all necessary APPLICATIO S oscillator, control and protection circuitry. Unique error n Power Supplies for Noise Sensitive Communication amp circuitry can regulate both positive and negative Equipment voltages. The internal oscillator may be synchronized to n EMI Compliant Offline Power Supplies an external clock for more accurate placement of switch- n Precision Instrumentation Systems ing harmonics. n Isolated Supplies for Industrial Automation Protection features include gate drive lockout for low V , IN n Medical Instruments soft-start, output current limit, short-circuit current limit- n Data Acquisition Systems ing, gate drive overvoltage clamp and input supply undervoltage lockout. , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO Ultralow Noise 5V to 12V Converter 12V Output Noise (Bandwidth = 100MHz) MBRD620 22H 10H B A 5V 12V V IN 1A + + 150F 4 150F P3 OSCON OSCON + OPTIONAL 100F 17 3 V GCL IN 5pF POINT A 14 2 400m V P-P SHDN CAP ON SCHEMATIC 5 V5 500m V/DIV 6 SYNC 1.3nF 7 1 C GATE Si9426 T POINT B LT1738 16.9k 8 R ON SCHEMATIC T 50mV/DIV 25k 3.3k 16 4 R CS VSL 25k 3.3k 25m 15 R 20 CSL 22nF PGND 21.5k 12 V 9 C FB 1738 TA01a 5m s/DIV 0.22F SS GND NFB 1.5k 2.5k 13 11 10 1738 TA01 10nF 1738fa 1 U ULT1738 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) TOP VIEW ORDER PART Supply Voltage (V ) ................................................ 20V IN NUMBER Gate Drive Current .....................................Internal Limit GATE 1 20 PGND V5 Current .................................................Internal Limit CAP 2 19 NC GCL 3 18 NC LT1738EG SHDN Pin Voltage .................................................... 20V CS 4 17 V IN LT1738IG Feedback Pin Voltage (Trans. 10ms) ...................... 10V V5 5 16 R VSL Feedback Pin Current............................................ 10mA SYNC 6 15 R CSL Negative Feedback Pin Voltage (Trans. 10ms) ........ 10V C 7 14 SHDN T CS Pin.......................................................................... 5V 8 R 13 SS T GCL Pin ..................................................................... 16V 9 FB 12 V C SS Pin.......................................................................... 3V 10 NFB 11 GND Operating Junction Temperature Range G PACKAGE (Note 3) ............................................ 40 C to 125 C 20-LEAD PLASTIC SSOP Storage Temperature Range ................. 65 C to 150 C T = 150 C, q = 110 C/ W JMAX JA Lead Temperature (Soldering, 10 sec).................. 300 C Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V = 12V, V = 0.9V, V = V , R , R = 16.9k, R = 16.9k and A IN C FB REF VSL CSL T other pins open unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Error Amplifiers V Reference Voltage Measured at Feedback Pin l 1.235 1.250 1.265 V REF I Feedback Input Current V = V l 250 1000 nA FB FB REF FB Reference Voltage Line Regulation 2.7V V 20V l 0.012 0.03 %/V REG IN V Negative Feedback Reference Voltage Measured at Negative Feedback Pin l 2.56 2.50 2.45 V NFR with Feedback Pin Open I Negative Feedback Input Current V = V 37 25 m A NFR NFB NFR NFB Negative Feedback Reference Voltage Line Regulation 2.7V V 20V l 0.009 0.03 %/V REG IN g Error Amplifier Transconductance D I = 50m A 1100 1500 2200 m mho m C l 700 2500 m mho I Error Amp Sink Current V = V + 150mV, V = 0.9V l 120 200 350 m A ESK FB REF C I Error Amp Source Current V = V 150mV, V = 0.9V l 120 200 350 m A ESRC FB REF C V Error Amp Clamp Voltage High Clamp, V = 1V 1.27 V CLH FB V Error Amp Clamp Voltage Low Clamp, V = 1.5V 0.12 V CLL FB A Error Amplifier Voltage Gain 180 250 V/V V FB FB Overvoltage Shutdown Outputs Drivers Disabled 1.47 V OV I Soft-Start Charge Current V = 1V 9.0 12 m A SS SS 1738fa 2 U WWW