UC3172A

The UC3172A power amplifier is pin-for-pin compatible with the UC3173A. Improvements have been made to allow more liberal application of the device.

This full bridge power amplifier, rated for continuous output current of 1A, is intended for use in demanding servo applications such as head positioning for high-density disk drives. This device includes a precision current sense amplifier that senses load current with a single resistor in series with the load. The UC3172A is optimized to consume a minimum of supply current, and is designed to operate in both 5V and 12V systems. The power output stages have a low saturation voltage and are protected with current limiting and thermal shutdown. When inhibited the device will draw less than 1.8mA of total supply current.

Auxiliary functions on this device include a dual-input undervoltage comparator, which can monitor two independent supply voltages and activate the builtin head park function when either is below minimum. The park circuitry allows a programmable retract voltage to be applied to the load for limiting maximum head velocity. A separate low-side parking drive pin permits a series impedance to be inserted to control maximum retract current. The parking drive function can be configured to operate with supply voltages as low as 1.2V.

The closed loop transconductance of the configured power amplifier can be switched between a high and low range with a logic input. The 4:1 change in gain can be used to extend the dynamic range of the servo loop. Bandwidth ariations that would otherwise result with the gain change can be controlled with a compensation adjust pin.