Description
The UC3844 series of control integrated circuits provide the features that are necessary to implement off-line or DC-to-DC fixed-frequency current-mode control schemes, with a minimum number of external components. The internally implemented circuits include an under voltage lockout (UVLO), featuring a start-up current of less than 1 mA, and a precision reference trimmed for accuracy at the error amplifier input. Other internal circuits include logic to ensure latched operation, a pulse-width modulation (PWM) comparator that also provides current-limit control, and a totem-pole output stage that is designed to source or sink high-peak current. The output stage, suitable for driving N-channel MOSFETs, is low when it is in the off state.
The UC3844 family offers a variety of package options, temperature range options, choice of maximum duty cycle, and choice of turn on and turn off thresholds and hysteresis ranges. Devices with higher turn on or turnoff hysteresis are ideal choices for off-line power supplies, while the devices with a narrower hysteresis range are suited for DC-DC applications. The UC184x devices are specified for operation from –55°C to 125°C, the UC284x series is specified for operation from –40°C to 85°C, and the UC384x series is specified for operation from 0°C to 70°C.
Features for the UC3844
- Optimized for off-line and DC-to-DC converters
- Low start-up current (< 1 mA)
- 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
- Up to 500-kHz operation
- Error amplifier with low output resistance
- specified for operation from 0°C to 70°C.
Package includes: 1xUC3844
