MP2263

– 30V, 3A, LOW IQ, SYNCHRONOUS, STEP-DOWN CONVERTER

MP2263 Rev. 1.0

www.MonolithicPower.com

13

6/22/2016

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© 2016 MPS. All Rights Reserved.

reference (REF), the error amplifier uses (SS -

control.

ref

Tss(ms) Iss( A)

Css(nF)

1.125 V (V)







(2)

Pre-Bias Start-Up

The MP2263 is designed for monotonic start-up

into pre-biased loads. If the output is pre-biased

to a certain voltage during start-up, the BST

voltage is refreshed and charged. The voltage on

the soft-start capacitor is also charged. If the BST

voltage exceeds its rising threshold voltage, and

the

soft-start

capacitor

voltage

exceeds

normally.

Thermal Shutdown

Thermal shutdown is implemented to prevent the

chip from running away thermally. When the

silicon die temperature is higher than its upper

threshold, the power MOSFETs shut down.

When the temperature is lower than its lower

threshold, thermal shutdown is removed, and the

chip is enabled again.

Current Comparator and Current Limit

The power MOSFET current is sensed accurately

via a current sense MOSFET. This current is fed

to the high-speed current comparator for current-

mode control purposes. The current comparator

uses this sensed current as one of its inputs.

When the HS-FET is turned on, the comparator

is first blanked until the end of the turn-on

transition to avoid noise. The comparator then

the comparator outputs low to turn off the HS-

FET. The maximum current of the internal power

MOSFET is limited cycle-by-cycle internally.

Hiccup Protection

When the output is shorted to ground, causing

the output voltage to drop below 70% of its

nominal output, the IC shuts down momentarily

and begins discharging the soft-start capacitor.

The IC restarts with a full soft start when the soft-

start capacitor is fully discharged. This hiccup

process is repeated until the fault is removed.

Start-Up and Shutdown

If both VIN and EN are higher than their

respective thresholds, the chip starts up. The

reference block starts first, generating stable

reference voltages and currents, and then the

internal regulator is enabled. The regulator

provides a stable supply for the rest of the

circuitries.

When the internal supply rail is up, an internal

timer holds the power MOSFET off for about

50µs to blank the start-up glitches. When the

soft-start block is enabled, the SS output is held

low to ensure that the rest of the circuitries are

ready before slowly ramping up.

Three events can shut down the chip: EN low,

VIN low, and thermal shutdown. In the shutdown

procedure, the signaling path is blocked first to

supply rail are then pulled down. The floating

driver is not subject to this shutdown command,

but its charging path is disabled.

Power Good Output

The MP2263 has an open-drain pin as the power

good indicator (PG). PG can indicate under

voltage (UV) and over voltage (OV). Pull PG up

to VCC through a 100k

Ω resistor. In the UV

internal MOSFET pulls PG down to ground. In