MP8652 – 15A, 14V, HIGH FREQUENCY STEP-DOWN WITH SYNCHRONOUS GATE DRIVER

MP8652 Rev. 0.9

www.MonolithicPower.com

8

10/26/2009

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Internal Regulator

Most of the internal circuitries are powered from

the 5V internal regulator. This regulator takes the

VIN input and operates in the full VIN range.

When VIN is greater than 5.0V, the output of the

regulator is in full regulation. When VIN is lower

than 5.0V, the output decreases. Since this

internal regulator provides the bias current for the

bottom gate driver that requires significant

amount of current depending upon the external

MOSFET selection, a 1µF ceramic capacitor for

decoupling purpose is required.

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) is implemented to

protect the chip from operating at insufficient

supply voltage. The MP8652 UVLO comparator

monitors the output voltage of the internal

regulator, VCC. The UVLO rising threshold is

about 4.0V while its falling threshold is a

consistent 3.2V.

Soft-Start

The soft-start is implemented to prevent the

converter output voltage from overshooting

during startup. When the chip starts, the internal

current source (10µA) charges up an external

is lower than the internal reference (REF), SS

overrides REF so the error amplifier uses SS as

the reference. When SS is higher than REF, REF

regains control.

Over-Current-Protection and Latch off

The MP8652 has cycle-by-cycle over current limit.

If the soft start Voltage is greater than 1.2V, and

inductor current exceeds the current limit

threshold, and FB voltage drops below 50% of

reference Voltage, then the MP8652 goes into

latch off until En or IN is recycled. This protection

mode is especially useful when the output is

dead-short to ground.

Thermal Shutdown

Thermal shutdown is implemented to prevent the

chip

from

operating

at

exceedingly

high

temperatures. When the silicon die temperature

is higher than 150

°C, it shuts down the whole

chip. When the temperature is lower than its

lower threshold, typically 140

°C, the chip is

enabled again.

Floating Driver and Bootstrap Charging

The floating power MOSFET driver is powered by

an external bootstrap capacitor. This floating

driver has its own UVLO protection. This UVLO’s

rising threshold is 2.2V with a hysteresis of

150mV. The bootstrap capacitor voltage is

U2 will regulate M3 to maintain a 5V BST voltage

across C4.

--

+

--

+

5V

U2

D1

M3

BST

SW

C4

C2

L1

Figure 3—Internal Bootstrap Charging Circuit

Startup and Shutdown

If both VIN and EN are higher than their

appropriate thresholds, the chip starts. The

reference block starts first, generating stable

reference voltage and currents, and then the

internal regulator is enabled. The regulator

provides

stable

supply

for

the

remaining

circuitries.

Three events can shut down the chip: EN low,

VIN low and thermal shutdown. In the shutdown

procedure, the signaling path is first blocked to

avoid any fault triggering. The COMP voltage and

the internal supply rail are then pulled down. The

floating driver is not subject to this shutdown

command.

Synchin/Synchout Control

The MP8652 has a dedicated synchin control pin

(SYNCIN) that allows MP8652 be synchronized

to external clock ranging from 300KHz up to 1

MHz. the MP8652 also has a synchout pin

(SYNCOUT) generating a 50% duty cycle, 180°

out of phase logic signal. The Synchout signal

can be used to synchronize a slave phase by

connecting the SYNCOUT pin of the master

MP8652 with the SYNCIN pin of the slave

MP8652. The 180° interleaving operation greatly

reduces the requirement of the input decoupling

capacitors.