MIC2085/MIC2086 Single Channel Hot Swap Controllers - Micrel - #19

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Micrel, Inc. MIC2085/2086 May 2006 19 M9999-050406 (408) 955-1690 Higher UVLO Setting Once a PCB is inserted into a backplane (power supply), the internal UVLO circuit of the MIC2085/86 holds the GATE output charge pump off until VCC exceeds 2.18V. If VCC falls below 2V, the UVLO circuit pulls the GATE output to ground and clears the overvoltage and/or current limit faults. For a higher UVLO threshold, the circuit in Figure 7 can be used to delay the output MOSFET from switching on until the desired input voltage is achieved. The circuit allows the charge pump to remain off until VIN exceeds 1.24V R2 R1 1 × .. .. + . The GATE drive output will be shut down when VIN falls below 1.14V R2 R1 1 × .. .. + . In the example circuit (Figure 7), the rising UVLO threshold is set at approximately 11V and the falling UVLO threshold is established as 10.1V. The circuit consists of an external resistor divider at the ON pin that keeps the GATE output charge pump off until the voltage at the ON pin exceeds its threshold (VON) and after the start-up time relapses. Figure 7. Higher UVLO Setting