UC3875

The UC1875 family of integrated circuits implements control of a bridge power stage by phase-shifting the switching of one half-bridge with respect to the other, allowing constant frequency pulse-width modulation in combination with resonant, zero-voltage switching for high efficiency performance at high frequencies. This family of circuits may be configured to provide control in either voltage or current mode operation, with a separate over-current shutdown for fast fault protection.

A programmable time delay is provided to insert a dead-time at the turn-on of each output stage. This delay, providing time to allow the resonant switching action, is independently controllable for each output pair (A-B, C-D).

With the oscillator capable of operation at frequencies in excess of 2MHz, overall switching frequencies to 1MHz are practical. In addition to the standard free running mode, with the CLOCKSYNC pin, the user may configure these devices to accept an external clock synchronization signal, or may lock together up to 5 units with the operational frequency determined by the fastest device.

Protective features include an undervoltage lockout which maintains all outputs in an active-low state until the supply reaches a 10.75V threshold. 1.5V hysteresis is built in for reliable, boot-strapped chip supply. Over-current protection is provided, and will latch the outputs in the OFF state within 70nsec of a fault. The current-fault circuitry implements full-cycle restart operation.

Additional features include an error amplifier with band-width in excess of 7MHz, a 5V reference, provisions for soft-starting, and flexible ramp generation and slope compensation circuitry.

These devices are available in 20-pin DIP, 28-pin "bat-wing" SOIC and 28 lead power PLCC plastic packages for operation over both 0°C to 70°C and –25°C to +85°C temperature ranges; and in hermetically sealed cerdip, and surface mount packages for –55°C to +125°C operation.