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

MPQ4462 Rev. 1.11

www.MonolithicPower.com

15

7/17/2013

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• The internal bootstrap circuit’s impedance

may limit the charge to the bootstrap

period. Add an external bootstrap charging

diode if the switching frequency is above

2MHz.

• At

higher

switching

frequencies,

the

capacitor’s

inductive

reactance

(XL

dominates, so that the ESL of the

input/output

capacitor

determines

the

input/output

ripple

voltage

at

higher

switching

frequencies.

Select

a

high-

frequency ceramic capacitor as the input

decoupling capacitor and the output filtering

capacitor for high-frequency operation.

• Layout becomes more important when the

device switches at higher frequencies.

Please refer to the PCB Layout Guide for

more details.

External Bootstrap Diode

Add an external bootstrap diode if the input

voltage is no greater than 5V or if the 5V rail is

available.

This

diode

improves

regulator

efficiency. The bootstrap diode can be a low-

cost one, such as the IN4148 or the BAT54.

SW

BS

5V

Figure 3: External Bootstrap Diode

This diode is also recommended for high-duty-

At no load or light load, the converter may

operate in pulse-skipping mode to maintain

output-voltage regulation. However, pulse-

skipping limits the BST voltage’s charging time.

needs to be higher than 3.3V+3V=6.3V to

maintain the BST voltage at no load or light

load. To meet this requirement, use the EN pin