MIC2582 datasheet(13/32 Pages) MICROCHIP

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2021 Microchip Technology Inc.

DS20006573A-page 13

MIC2582/3

4.0

FUNCTIONAL DESCRIPTION

4.1

Hot Swap Insertion

When circuit boards are inserted into live system

backplanes and supply voltages, high inrush currents

can result due to the charging of bulk capacitance that

resides across the supply pins of the circuit board. This

inrush current, although transient in nature, may be

high enough to cause permanent damage to on board

components or may cause the system’s supply

voltages to go out of regulation during the transient

period which may result in system failures. The

MIC2582 and MIC2583 act as a controller for external

N-channel MOSFET devices in which the gate drive is

controlled to provide inrush current-limiting and output

voltage slew rate control during hot plug insertions.

4.2

Power Supply

VCC is the supply input to the MIC2582/83 controller

with a voltage range of 2.3V to 13.2V. The VCC input

can withstand transient spikes up to 20V. In order to

ensure stability of the supply voltage, a minimum

0.47 µF capacitor from VCC to ground is

recommended. Alternatively, a low-pass filter, shown in

the Typical Application Circuit, can be used to eliminate

high frequency oscillations as well as help suppress

transient spikes.

Also, due to the existence of an undetermined amount

of parasitic inductance in the absence of bulk

capacitance along the supply path, placing a Zener

diode at the VCC side of the controller to ground in order

to provide external supply transient protection is

strongly recommended for relatively high current

applications (≥3A). See the Typical Application Circuit.

4.3

Start-Up Cycle

Referring to Figure 1-3: When the VCC input voltage is

first applied, it raises above the UVLO threshold

voltage (VUV, (1) in Figure 1-3). A minimum of 20 μs

later, ((2) in Figure 1-3), the voltage on the ON pin can

be taken above the ON pin threshold (VON). At that

time, the CPOR current source (ICPOR), is turned on,

and the voltage at the CPOR pin starts to rise. See

Table 4-2 for some typical supply start-up delays using

several standard value capacitors. When the CPOR

voltage reaches the start threshold voltage (VSTART, (3)

in Figure 1-3), two things happen:

1. The external power FET driver charge pump is

turned on, and the output voltage starts to rise.

2. The capacitor on the CPOR pin is discharged to

ground.

The voltage on the feedback (FB) pin tracks the VOUT,

output voltage through the feedback divider resistors

(R1 and R2 in Figure 1-4). When the output voltage

rises, and the FB voltage reaches the FB threshold

voltage (VFB), the current source into the CPOR pin is

again turned on, and the voltage at the CPOR pin starts

to rise. When the CPOR voltage reaches the threshold

voltage (VTH, (4) in Figure 1-3), the /POR pin goes high

impedance, and is allowed to be pulled up by the

external pull-up resistor on the /POR pin. This indicates

that the output power is good.

In the MIC2583, when the FB threshold voltage (VFB) is

reached, the Power Good (PWRGD) pin goes open

circuit, high impedance, and is allowed to be pulled up

by the external pull-up resistor on the PWRGD pin. The

non-delayed power good feature is only available on

the MIC2583.

Active current regulation is employed to limit the inrush

current transient response during start-up by regulating

the load current at the programmed current-limit value

(See the Current Limiting and Dual-Level Circuit

Breaking section). The following equation is used to

determine the nominal current-limit value:

EQUATION 4-1:

There are two basic start-up modes for the

MIC2582/83: Start-up dominated by load capacitance

or Start-up dominated by total gate capacitance. The

magnitude of the inrush current delivered to the load

will determine the dominant mode. If the inrush current

is greater than the programmed current limit (ILIM), then

load capacitance is dominant. Otherwise, gate

capacitance is dominant. The expected inrush current

is calculated using the following equation:

EQUATION 4-2:

ILIM

VTRIPSLOW

RSENSE

-----------------------------

50mV

RSENSE

-------------------

Where:

VTRIPSLOW = The current limit slow trip threshold

found in the Electrical Characteristics table.

RSENSE = The selected value that will set the desired

current limit.

Inrush IGATE

CLOAD

CGATE

------------------





17A

CLOAD

CGATE

------------------



Where:

IGATE = The GATE pin pull-up current.

CLOAD = The load capacitance.

CGATE = The total GATE capacitance (CISS of the

external MOSFET and any external capacitor

connected from the MIC2582/83 GATE pin to

ground.)

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