MIC2582 datasheet(14/32 Pages) MICROCHIP

14 / 32 page

MIC2582/3

DS20006573A-page 14



2021 Microchip Technology Inc.

4.3.1

LOAD CAPACITANCE-DOMINATED

START-UP

In this case, the load capacitance (CLOAD) is large

enough to cause the inrush current to exceed the

programmed current limit, but is less than the fast-trip

threshold (or the fast-trip threshold is disabled, ‘M’

option). During start-up under this condition, the load

current is regulated at the programmed current-limit

value (ILIM) and held constant until the output voltage

rises to its final value. The output slew rate and

equivalent GATE voltage slew rate is computed by the

following equation:

EQUATION 4-3:

Consequently, the value of CFILTER must be selected to

ensure that the overcurrent response time, tOCSLOW,

exceeds the time needed for the output to reach its final

value. For example, given a MOSFET with an input

capacitance CISS = CGATE = 4700 pF, CLOAD is

2200 µF, and ILIM is set to 6A with a 12V input, then the

load capacitance dominates as determined by the

calculated Inrush > ILIM. Therefore, the output voltage

slew rate determined from Equation 4-3 is:

EQUATION 4-4:

The resulting tOCSLOW needed to achieve a 12V output

is approximately 4.5 ms. (See the Power-on-Reset and

Overcurrent Timer Delays section to calculate

tOCSLOW).

4.3.2

GATE CAPACITANCE-DOMINATED

START-UP

In this case, the value of the load capacitance relative

to the GATE capacitance is small enough such that the

load current during start-up never exceeds the

current-limit threshold as determined by Equation 4-1.

The minimum value of CGATE that will ensure that the

current limit is never exceeded is given by the following

equation:

EQUATION 4-5:

Table 4-1 depicts the output slew rate for various

values of CGATE.

4.4

Current Limiting and Dual-Level

Circuit Breaking

Many applications will require that the inrush and

steady-state supply current be limited at a specific

value in order to protect critical components within the

system. Connecting a sense resistor between the VCC

and SENSE pins sets the nominal current limit value of

the MIC2582/83 and the current limit is calculated

using Equation 4-1.

The MIC2582/83 also features a dual-level circuit

breaker triggered via the 50 mV and 100 mV

current-limit thresholds which are sensed across the

VCC and SENSE pins. The first level of the circuit

breaker functions as follows. For the MIC2583/3R,

once the voltage sensed across these two pins

exceeds 50 mV, the overcurrent timer, its duration set

by capacitor CFILTER, starts to ramp the voltage at

CFILTER using a 6.5 µA constant current source. If the

voltage at CFILTER reaches the overcurrent timer

threshold (VTH) of 1.24V, then CFILTER immediately

returns to ground as the circuit breaker trips and the

GATE output is immediately shut down. The default

overcurrent time period for the MIC2582/83 is 5 µs. For

the second level, if the voltage sensed across VCC and

SENSE exceeds 100 mV at any time, the circuit

breaker trips and the GATE shuts down immediately,

bypassing the overcurrent time period. The

MIC2582-MYM option is equipped with only a single

circuit breaker threshold (50 mV). To disable

current-limit and circuit breaker operation, tie the

SENSE and VCC pins together and the CFILTER

(MIC2583/3R) pin to ground.

dVOUT dt



ILIM

CLOAD

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

Output voltage slew rate:

Where:

ILIM = The programmed current-limit value.

dVOUT dt



2200F

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

2.73V/ms

TABLE 4-1:

OUTPUT SLEW RATE

SELECTION FOR GATE

CAPACITANCE-DOMINATED

START-UP

IGATE = 17 µA

CGATE

dVOUT/dt

0.001 µF

17V/ms

0.01 µF

1.7V/ms

0.1 µF

0.17V/ms

1 µF

0.017V/ms

dVOUT dt



IGATE

CGATE

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