MIC2085 Datasheet, PDF (17/29 Pages) Micrel Semiconductor – Single Channel Hot Swap Controllers

Micrel, Inc.
overvoltage protection circuitry, resistors R2 and R3 in
Figure 5. For input overvoltage protection, the first
consideration is to establish the input voltage level that
indicates an overvoltage triggering a sys-tem (output
voltage) shut down. For this example, the input value for
which a 12V supply will signal an “output shut down” is
13.2V (+10%). Similarly, from the previous example:
1) Choose R3 to satisfy 100µA condition.
R3 ≥ ^{VOV (MIN)} ≥ ^1.19V ≥ 11.9kΩ
100µΑ 100µΑ
R3 is chosen as 13.7kΩ ± 1%.
MIC2085/2086
2) Thus, following the previous example and
substituting R2 and R3 for R5 and R6,
respectively, and 13.2V overvoltage for 11V
output “good”, the same formula yields R2 of
138.3kΩ.The next highest standard 1% value is
140kΩ.
Now, consider the 12.6V maximum input voltage (V_CC
+5%), the higher tolerance for R3 and lower tolerance
for R2, 13.84k and 138.60kΩ, respectively. With a 12.6V
input, the voltage sensed at the OV pin is below V_OV(MIN),
and the MIC2085/86will not indicate an overvoltage
condition until VCC exceeds at least 13.2V.
Figure 5. Undervoltage/Overvoltage Circuit
May 2006
17
M9999-050406
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