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SA07 Datasheet(PDF) 5 Page - Cirrus Logic |
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SA07 Datasheet(HTML) 5 Page - Cirrus Logic |
5 / 5 page 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 FILTER and CFILTER should be 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 FILTER = .001uF, R FILTER = 5k . The required value of R LIMIT in voltage mode may be cal- culated by: R LIMIT = .1 V / ILIMIT where R LIMIT is the required resistor value, and ILIMIT is the maximum desired current. In current mode the required value of each R LIMIT is 2 times this value since the sense voltage is divided down by 2 (see Figure B). If R SHDN is used it will further 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 LIMIT resistors will normally be very low values and 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 SHDN to give a minimum 110 mV of shutdown signal at the I LIMIT/SHDN pin when the shutdown signal is high. Note that C FILTER will filter both the current limit noise spikes 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. * To restart the SA07 remove the fault and recycle VCC or, alternatively, toggle the I LIMIT/SHDN (PIN16) with a shut 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. |
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