Product description
The UC3843B is a fixed-frequency current-mode PWM controller designed for off-line and DC-to-DC converter applications. Internal blocks include a precision trimmed bandgap voltage reference, error amplifier with 2.5V reference input, PWM comparator with cycle-by-cycle current limiting, oscillator set by an external resistor and capacitor on the RT/CT pin, and a totem-pole output stage capable of directly driving an N-channel MOSFET gate. The output is actively held low during undervoltage lockout. A trimmed oscillator provides precise frequency control and guaranteed operation at 250 kHz. The UC3843B differs from the UC3842B in UVLO thresholds and maximum duty cycle. The UC2843B extends the temperature range to -25°C to +85°C.
- Control mode: peak current mode
- Maximum duty cycle: up to 100%
- UVLO turn-on: 8.4V, turn-off: 7.6V (suitable for DC-DC applications)
- Start-up current: less than 0.5 mA
- Operating supply current: 12 mA typ, 17 mA max
- Oscillator frequency: up to 500 kHz, set by external RT and CT, guaranteed at 250 kHz
- Reference voltage (VREF): 5.0V trimmed (4.90V min, 5.10V max at 25°C)
- Error amplifier reference input: 2.5V, unity gain bandwidth 1 MHz typ
- Current sense maximum input: 1.0V typ
- Output peak current: 1A source and sink
- Supply voltage abs. max: 30V
