MP2454―36V, 0.6A, STEP-DOWN CONVERTER

MP2454 Rev. 1.01

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13

9/18/2015

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chip shuts down. When the temperature falls

enabled again.

Current Comparator and Current Limit

A current sense MOSFET senses accurately the

power MOSFET current. The sensed current

goes to the high-speed current comparator for

current-mode control. When the power MOSFET

turns on, the comparator is blanked first (until the

end of the turn-on transition) to reduce noise.

Then, the comparator compares the power-

switch current against the reference current set

by the COMP voltage. When the power-switch

current exceeds the reference current, the

comparator outputs low to turn off the power

MOSFET.

The maximum current of the internal power

MOSFET is limited internally cycle-by-cycle. The

current limit is related to the FB voltage and

deceases as Vo decreases, which prevents

inductor current runaway during start-up or an

output short circuit.

Start-Up and Shutdown

thresholds, the chip starts up. The reference

block starts first, generating a stable reference

voltage and stable currents, and then the internal

regulator is enabled. The regulator provides a

stable supply for the rest of the circuit. After this

occurs, the soft-start block starts working and

output ramps up slowly.

low, and thermal shutdown. During shutdown, the

signaling path is blocked initially to avoid

triggering any faults. Then the COMP voltage

and the internal supply rail are pulled down.

Power Good Output

The MP2454 includes an open-drain power good

output that indicates whether the regulator’s

output is within ±10% of its nominal value. When

the output voltage falls outside this range, the

POK output is pulled to ground. It should be

connected to a voltage source of no more than

5V through a resistor (e.g. 100kΩ). There is a

20µs de-glitch time when POK asserts high (if

POKDL is left floating). The de-glitch time can be

programmed by adding a capacitor on POKDL.

To select a capacitor for POKDL, use Equation

(2):

(V)

V

A)

(

I

(ms)

t

(nF)

C

th_POKDL

POKDL

POKDL

DL







(2)

.