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4

OPERATING

CONSIDERATIONS

SA50CE

GENERAL

Please read Application Note 30 on "PWM Basics". Refer

to Application Note 1 "General Operating Considerations" for

helpful information regarding power supplies, heat sinking

and mounting. Visit www.apexmicrotech.com for design tools

that help automate pwm filter design and heat sink selection.

The "Application Notes" and "Technical Seminar" sections

contain a wealth of information on specific types of applica-

tions. Information on package outlines, heat sinks, mounting

hardware and other accessories are located in the "Packages

and Accessories" section. Evaluation Kits are available for most

Apex product models, consult the "Evaluation Kit" section for

details. For the most current version of all Apex product data

sheets, visit www.apexmicrotech.com.

PIN DESCRIPTION

V

drivers for the lowside and highside MOSFETS. The

supplies for the highside drivers are derived from this

voltage.

V

obtain the output current from this supply pin. Proper

by-passing to GND with sufficient capacitance to sup-

press any voltage transients, and to ensure removing

any drooping during switching, should be done as close

to the pins on the hybrid as possible.

AOUT - is the output pin for one half of the bridge. Increas-

ing the input voltage causes increasing duty cycle at

this output.

B OUT - is the output pin for the other half of the bridge.

Decreasing the input voltage causes increasing duty

cycles at this point.

RSENSEA - This is the connection for the bottom of the A

half bridge. This can have a sense resistor connected

to the V

be connected directly to ground. The maximum voltage

on this pin is ±2 volts with respect to GND.

GND - is the return connection for the input logic and V

RSENSEB - This is the connection for the bottom of the B

half bridge. This can have a sense resistor connection

to the V

be connected directly to ground. The maximum voltage

on this pin is ±2 volts with respect to GND.

INPUT - is an analog input for controlling the PWM pulse width

of the bridge. A voltage higher than V

greater than 50% duty cycle pulses out of A OUT. A

voltage lower than V

duty cycle pulses out of B OUT.

TYPICAL SYSTEM OPERATION

This is a diagram of a typical application of the SA50CE.

The design Vcc voltage is +12 volts. V

with a good low ESR ceramic capacitor. A higher ESR bulk

capacitor, such as a tantalum electrolytic, may be used ex-

ternally in parallel. The analog input can be an analog speed

control voltage from a potentiometer, other analog circuitry or

by microprocessor and a D/A converter. This analog input gets

pulled by the current control circuitry in the proper direction to

reduce the current flow in the bridge if it gets too high. The gain

of the current control amplifier will have to be set to obtain the

proper amount of current limiting required by the system.

Current sensing is done in this case by a 0.1Ω sense resistor

to sense the current from both legs of the bridge separately. It

is important to make the high current traces as big as possible

to keep inductance down. The storage capacitor connected to

the V

the high energy pulse without the voltage sagging too far. A

low ESR capacitor will be required. Mount capacitor as close

to the hybrid as possible. The connection between GND and

the V

sense resistor signal is common mode filtered as necessary

to feed the limiting circuitry. This application will allow full four

quadrant torque control for a closed loop servo system.

A snubber network is usually required, due to the inductance

in the power loop. It is important to design the snubber network

to suppress any positive spikes above +V

below –2V with respect to pin 7 (GND).

This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifications are subject to change without notice.

SA50CEU REV A FEBRUARY 2007 © 2007 Apex Microtechnology Corp.