UC3173A

Full Bridge Power Amplifier

FEATURES

• Precision Current Control

• ± 500mA Load Current

• Controlled Velocity Head Parking

• Precision Dual Supply Monitor with

Indicator

• Range Control for 4:1 Gain Change

• Compensation Adjust Pin for

Bandwidth Control

• Inhibit Input and UVLO

• 5V or 12V Operation

• 12mA Quiescent Supply Current

• PLCC, SOIC, and Low Profile Quad

Flat Pack Packages

DESCRIPTION

This full bridge power amplifier, rated for continuous output current of

0.55A, is intended for use in demanding servo applications such as head

positioning for high density disk drives. This device includes a precision cur-

rent sense amplifier that senses load current with a single resistor in series

with the load. The UC3173A 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 1.5mA of total supply current.

Auxiliary functions on this device include a dual input undervoltage com-

parator, which can monitor two independent supply voltages and activate

the built in head park function when either is below minimum. The park cir-

cuitry allows a programmable retract voltage to be applied to the load for

limiting maximum head velocity. A separate low side parking drive pin per-

mits a series impedance to be inserted to control maximum retract current.

The parking drive function can be configured to operate with supply volt-

ages 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. Band-

width variations that would otherwise result with the gain change can be

controlled with a compensation adjust pin.

BLOCK DIAGRAM

04/99

UDG-94039