APEX MICROTECHNOLOGY CORPORATION • TELEPHONE (520) 690-8600 • FAX (520) 888-3329 • ORDERS (520) 690-8601 • EMAIL prodlit@apexmicrotech.com

5

Switching noise spikes will invariably be found at the I

SENSE pins. The noise spikes could trip the current limit

threshold which is only 100 mV. R

adjusted so as to reduce the switching noise well below 100

mV to prevent false current limiting. The sum of the DC level

plus the noise peak will determine the current limiting value.

As in most switching circuits it may be difficult to determine

the true noise amplitude without careful attention to grounding

of the oscilloscope probe. Use the shortest possible ground

lead for the probe and connect exactly at the GND terminal of

the amplifier. Suggested starting values are C

R

The required value of R

culated by:

R

where R

maximum desired current. In current mode the required value

of each R

divided down by 2 (see Figure B). If R

divide down the sense voltage. The shutdown divider network

will also have an effect on the filtering circuit.

���������

���������

�������

��������

������

��

����������������������������

����������������������

���������

���������

�������

��������

������

��

��

����������������������������

����������������������

SHUTDOWN

The shutdown circuitry makes use of the internal current

limiting circuitry. The two functions may be externally combined

in voltage and current modes as shown below in Figures A

and B. The R

can be considered zero for this application. In Figure A, R

SHDN

and 1K form a voltage divider for the shutdown signal. After a

suitable noise filter is designed for the current limit, adjust the

value of R

at the I LIMIT/SHDN pin when the shutdown signal is high.

Note that C

and the shutdown signal. Shutdown and current limit operate

on each cycle of the internal switching rate. As long as the

shutdown signal is high the output will be disabled.

PROTECTION CIRCUITS

Circuits monitor the temperature and load on each of the

bridge output transistors. On each cycle should any fault condi-

tion be detected all output transistors in the bridge are shut off.

Faults protected against are: shorts across the outputs, shorts

to ground, and over temperature conditions. Should any of

these faults be detected, the output transistors will be latched

off.* In addition there is a built in dead time during which all the

output transistors are off. The dead time removes the possibility

of a momentary conduction path through the upper and lower

transistors of each half bridge during the switching interval.

Noise or flyback may be observed at the outputs during this

time due to the high impedance of the outputs in the off state.

This will vary with the nature of the load.

alternatively, toggle the I

down pulse.

OPERATING

CONSIDERATIONS

SA07

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.

SA07U REV. B DECEMBER 1998 © 1998 Apex Microtechnology Corp.