LT1738 Slew Rate Controlled Ultralow Noise DC/DC Controller UFEATURESDESCRIPTIO ■ Greatly Reduced Conducted and Radiated EMI The LT®1738 is a switching regulator controller designed ■ Low Switching Harmonic Content to lower conducted and radiated electromagnetic interfer- ■ 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- ■ Greatly Reduced Need for External Filters nal N-channel MOSFET switch. Current and voltage slew ■ Single N-Channel MOSFET Driver rates can be independently set to optimize harmonic ■ 20kHz to 250kHz Oscillator Frequency content of the switching waveforms vs efficiency. The ■ Easily Synchronized to External Clock LT1738 can reduce high frequency harmonic power by as ■ Regulates Positive and Negative Voltages much as 40dB with only minor losses in efficiency. ■ 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 ■ Power Supplies for Noise Sensitive Communication amp circuitry can regulate both positive and negative Equipment voltages. The internal oscillator may be synchronized to ■ EMI Compliant Offline Power Supplies an external clock for more accurate placement of switch- ■ Precision Instrumentation Systems ing harmonics. ■ Isolated Supplies for Industrial Automation Protection features include gate drive lockout for low V ■ IN, Medical Instruments soft-start, output current limit, short-circuit current limit- ■ Data Acquisition Systems ing, gate drive overvoltage clamp and input supply undervoltage lockout. , LTC and LT are registered trademarks of Linear Technology Corporation. UTYPICAL APPLICATIOUltralow Noise 5V to 12V Converter12V Output Noise MBRD620 (Bandwidth = 100MHz) 22µH 10 B µH 5V A 12V VIN + + 150 1A 4 µF × 150µF P3 OSCON OSCON + 100µF 17 3 OPTIONAL VIN GCL 5pF POINT A 14 2 400µV SHDN CAP P-P ON SCHEMATIC 5 V5 500µV/DIV 6 SYNC 1.3nF 7 1 C GATE T Si9426 LT1738 POINT B 16.9k 8 RT ON SCHEMATIC 25k 3.3k 50mV/DIV 16 4 RVSL CS 25k 3.3k 15 25mΩ RCSL 20 22nF PGND 12 21.5k VC 9 FB 0.22µF 5µs/DIV 1738 TA01a SS GND NFB 1.5k 2.5k 13 11 10 1738 TA01 10nF 1738fa 1
