TI UC3845D

The UCx84x series control ICs provide the features necessary to implement off-line or DC-DC fixed-frequency current-mode control schemes with a minimum number of external components. Internally implemented circuits include undervoltage lockout (UVLO) — characterized by a startup current of less than 1mA — and a precision reference for trimming accuracy at the error amplifier. Additional internal circuitry includes logic for latched operation, a PWM comparator for current-limit control, and a totem-pole output stage designed to source or sink high peak currents. When in the off state, the output stage — suitable for driving N-channel MOSFETs — is held low.

The UCx84x series offers a variety of package options, temperature range options, maximum duty cycle selections, turn-on and turn-off thresholds, and hysteresis range selections. Devices with higher turn-on or turn-off hysteresis are ideal for off-line power supplies, while devices with a narrower hysteresis range are suited for DC-DC applications. The UC184x devices are specified for an operating temperature range of -55°C to 125°C, the UC284x series is specified for -40°C to 85°C, and the UC384x series is specified for 0°C to 70°C.

• Optimized for off-line and DC-DC converters
• Low startup current (< 1mA)
• Automatic feedforward compensation
• Pulse-by-pulse current limiting
• Enhanced load response characteristics
• Undervoltage lockout with hysteresis
• Double pulse suppression
• High-current totem pole output
• Internally trimmed bandgap reference
• Operating frequency up to 500kHz
• Error amplifier with low output impedance

• Switching regulator with arbitrary polarity
• Transformer-coupled DC-DC converter