MIC2085(2004) データシートの表示（PDF） - Micrel

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MIC2085
(Rev.:2004)

Single Channel Hot Swap Controllers

Micrel 

MIC2085/2086

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

Micrel

to remain off until VIN exceeds 1+ RR21 × 1.24V . The GATE

drive output will be shut down when VIN falls below

1+ RR21 × 1.14V . 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 timer

elapses.

VIN

12V

R1

392kΩ

1%

R2

49.9kΩ

1%

C1

1µF

RSENSE

0.010Ω

1 2% 2

3

4

16

VCC

15

SENSE

4 ON

MIC2085

Q1

IRF7822

(SO-8)

GATE 14

FB 7

R3

R4

10Ω

127kΩ

1%

C2

0.01µF

R5

16.2kΩ

1%

CPOR

3

C3

0.1µF

GND

8

5

/POR

Downstream

Signal

Undervoltage Lockout (Rising) = 11.0V

Undervoltage Lockout (Falling) = 10.1V

Undervoltage (Output) = 11.4V

POR/START-UP Delay = 60ms

Additional pins omitted for clarity.

Figure 7. Higher UVLO Setting

VOUT

12V@4A

CLOAD

220µF

January 2004

19

M0235-121903

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