MPQ4462 datasheet(11/20 Pages) MPS

11 / 20 page

MPQ4462 – 3.5A, 4MHz, 36V, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED

MPQ4462 Rev. 1.11

www.MonolithicPower.com

7/17/2013

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

If VIN is sufficiently higher than VSW, the

bootstrap capacitor charges. When the power

MOSFET is ON, VIN≈VSW so the bootstrap

capacitor cannot charge. When the external

diode is ON, the VIN−VSW is at its maximum for

optimal charging. When there is no current in

the inductor, VSW=VOUT so VIN−VOUT charges the

bootstrap capacitor.

At higher duty cycles, the bootstrap-charging

period is shorter so the bootstrap capacitor may

not charge sufficiently. If the internal circuit

does not have sufficient voltage and the

bootstrap capacitor is not charged, an external

circuit can ensure the bootstrap voltage is in the

normal operational region.

The floating driver’s DC quiescent current

~20µA. Select a bleeding current at the SW

node meets the following criterion:

)

(

Current Comparator and Current Limit

A current-sense MOSFET accurately senses

the power-MOSFET current. The sense value is

compared to VCOMP by a high-speed current

comparator. When the power MOSFET turns on,

the comparator is first blanked till the end of the

turn-on transition. When the sensed current

exceeds VCOMP, the comparator output is low,

turning off the power MOSFET. The cycle-by-

cycle maximum current of the internal power

MOSFET is internally limited.

Startup and Shutdown

If both VIN and VEN exceed their respective

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 a stable supply

for the remaining circuits.

While the internal supply rail is up, an internal

timer holds the power MOSFET OFF for about

50µs to blank the startup noise. When the

internal soft-start block is enabled, it first holds

VSS low before slowly ramping up.

Three events can shut down the chip: VEN LOW,

VIN LOW, and thermal shutdown. For shutdown,

the power MOSFET turn off to avoid triggering

any faults. VCOMP and the internal supply rail are

then pulled down.

Programmable Oscillator

An external resistor (RFREQ) from the FREQ pin

to ground sets the MPQ4462 oscillating

frequency.

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