MIC2582 datasheet(17/32 Pages) MICROCHIP

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2021 Microchip Technology Inc.

DS20006573A-page 17

MIC2582/3

voltage exceeds its threshold (VON) of 1.24V and the

MIC2582/83 initiates a start-up cycle. In Figure 5-1, the

connection sense consisting of a discrete logic-level

MOSFET and a few resistors allows for interrupt control

from the processor or other signal controller to shut off

the output of the MIC2582/83. R4 pulls the GATE of Q2

to VIN and the ON pin is held low until the connectors

are fully mated.

Once the connectors fully mate, a logic LOW at the

/ON_OFF signal turns Q2 off and allows the ON pin to

pull up above its threshold and initiate a start-up cycle.

Applying a logic HIGH at the /ON_OFF signal will turn

Q2 on and short the ON pin of the MIC2582/83 to

ground which turns off the GATE output charge pump.

5.3

Higher UVLO Setting

Once a PCB is inserted into a backplane (power

supply), the internal UVLO circuit of the MIC2582/83

holds the GATE output charge pump off until VCC

exceeds 2.2V. If VCC falls below 2.1V, the UVLO circuit

pulls the GATE output to ground and clears the

overvoltage and/or current limit faults. A typical 12V

application, for example, should implement a higher

UVLO than the internal 2.1V threshold of MIC2582 to

avoid delivering power to downstream modules/loads

while the input is below tolerance. For a higher UVLO

threshold, the circuit in Figure 5-2 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 + R1/R2) x

1.24V. The GATE drive output will be shut down when

VIN falls below (1 + R1/R2) x 1.19V. In the example

circuit (Figure 5-2), the rising UVLO threshold is set at

approximately 9.5V and the falling UVLO threshold is

established as 9.1V. 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.

5.4

5V Switch with 3.3V Supply

Generation

The MIC2582/83 can be configured to switch a primary

supply while generating a secondary regulated voltage

rail. The circuit in Figure 5-3 enables the MIC2582 to

switch a 5V supply while also providing a 3.3V low

dropout regulated supply with only a few added

external components. Upon enabling the MIC2582, the

GATE output voltage increases and thus the 3.3V

supply also begins to ramp. As the 3.3V output supply

crosses 3.3V, the FB pin threshold is also exceeded

which triggers the power-on reset comparator. The

/POR pin goes HIGH, turning on transistor Q3, which

lowers the voltage on the gate of MOSFET Q2. The

result is a regulated 3.3V supply with the gate feedback

loop of Q2 compensated by capacitor C3 and resistors

R4 and R5. For MOSFET Q2, special consideration

must be given to the power dissipation capability of the

selected MOSFET as 1.5V to 2V will drop across the

device during normal operation in this application.

Therefore, the device is susceptible to overheating

dependent upon the current requirements for the

regulated output. In this example, the power dissipated

by Q2 is approximately 1W. However, a substantial

amount of power will be generated with higher current

requirements and/or conditions. As a general guideline,

expect the ambient temperature within the power

supply box to exceed the maximum operating ambient

temperature of the system environment by

approximately 20°C. Given the MOSFET’s Rθ(JA) and

the expected power dissipated by the MOSFET, an

approximation for the junction temperature at which the

device will operate is obtained as follows:

EQUATION 5-4:

FIGURE 5-2:

Higher UVLO Setting.

PD RJA







Where:

TA = TA(MAXOP) + 20°C.

SENSE

VCC

GATE

GND

Undervoltage Lockout Threshold (rising) = 9.5V

Undervoltage Lockout Threshold (falling) = 9.1V

Undervoltage (Output) = 11.4V

Additional pins omitted for clarity.

IRF7822

(SOIC-8)

16.2k

332k

49.9k

MIC2582

μF

(18V)

0.01

μF

C LOAD

220

μF

133k

V OUT

12V@4A

V IN

12V

R SENSE

0.010

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