MPQ4473

–HIGH-EFFICIENCY, FAST-TRANSIENT, SYNCHRONOUS, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED

MPQ4473 Rev. 1.01

www.MonolithicPower.com

14

5/24/2016

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

© 2016 MPS. All Rights Reserved.

Figure 7 shows an equivalent circuit in PWM

mode with the HS-FET OFF and without an

external ramp circuit. The ESR ripple dominates

calculated as follows:

REF

SLOPE1

ESR V

V

L





(7)

proportional to ESR/L. Theref

ore, it’s necessary

to know the minimum ESR value of the output

capacitors without an external ramp. Also, there

is an inductance limit: a smaller inductance leads

to

increased

stability.

Based

on

bench

30V/ms.

In skip mode, the external ramp does not affect

the downward slope; the downward slope of the

external ramp. Figure 8 shows an equivalent

circuit with the HS-FET OFF and the current

modulator regulating the LS-FET.

Figure 8: Simplified Circuit in Skip Mode











REF

SLOPE2

1

2

OUT

V

V

R

R

C

(8)

To keep the system stable during light loads,

value around 0.4V/ms to 0.8mV/ms. Note that

does not impact the system’s light-load stability.

Soft-Start (SS)

The MPQ4473 employs soft-start (SS) to ensure

smooth output during power-up. When the EN

pin

goes

HIGH,

an

internal-current

source

voltage takes over the REF voltage to the PWM

comparator. The output voltage smoothly ramps

over the PWM comparator. At this point, soft-start

finishes and the MPQ4473 enters steady state.

 

 

 

 

SS

SS

SS

REF

t

ms

I

A

C

nF

VV





(9)

If the output capacitors have large capacitance

values, avoid setting a short SS or risk hitting the

current limit during SS. Select a minimum value

of 4.7nF if the output capacitance value exceeds

330

μF.

Power Good (PGOOD)

The

MPQ4473

has

power-good

(PGOOD)

output. The PGOOD pin is the open drain of a

voltage source) through a resistor (e.g. 100k

Ω).

In the presence of an input voltage, the MOSFET

turns ON so that the PGOOD pin is pulled to

a delay, typically 700

μs).

PGOOD pin is pulled LOW.

Over-Current Protection (OCP) and Short-

Circuit Protection (SCP)

The MPQ4473 has cycle-by-cycle over-current

limit control. The inductor current is monitored

during the ON state. Once the inductor current

exceeds the current limit, the HS-FET turns OFF.

Simultaneously, the OCP timer starts. The OCP

timer is set at 100

μs. Hitting the current limit

every cycle during the 100

μs time frame will

trigger hiccup SCP.

If

a

short

circuit

occurs,

the

MPQ4473

considers this an output dead short and will

trigger hiccup SCP immediately.

Under-Voltage Protection (UVP)

The MPQ4473 monitors the output voltage

through the tap of a resistor divider to the FB pin.

This detects output under-voltage conditions.