MP2172C – 2A, SYNCHRONOUS STEP-DOWN SWITCHER

MP2172C Rev.1.0

www.MonolithicPower.com

14

4/22/2019

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© 2019 MPS. All Rights Reserved.

OPERATION

The MP2172C uses constant-on-time (COT)

control with input voltage feed-forward to

stabilize the switching frequency over the entire

input range. The part achieves 2A of continuous

output current from a 2.38V to 5.5V input

voltage range with excellent load and line

regulation. The output voltage can be regulated

as low as 0.6V.

Constant-On-Time (COT) Control

Constant-on-time (COT) control offers a simpler

control loop and faster transient response than

fixed-frequency pulse-width modulation (PWM)

control. By using input voltage feed-forward, the

MP2172C

maintains

a

nearly

constant

switching frequency across the input and output

voltage ranges. The switching pulse on time

can be estimated with Equation (1):

OUT

ON

IN

V

t0.91 s

V





(1)

To prevent inductor current runaway during the

load transient, the MP2172C has a fixed

minimum off time of 100ns.

Force PWM Operation

The MP2172C works in continuous current

mode (CCM) to achieve a smaller VO ripple,

load regulation, and load transient in full-load

range.

Enable (EN)

If the input voltage is greater than the under-

voltage lockout (UVLO) threshold (typically

2.3V), the MP2172C can be enabled by pulling

EN higher than 1.2V. Leave EN floating or pull

EN down to ground to disable the MP2172C.

There is an internal 1MΩ resistor from EN to

ground.

When the device is disabled, the MP2172C

enters output discharge mode automatically. Its

internal discharge MOSFET provides a resistive

discharge path for the output capacitor.

Soft Start (SS)

The MP2172C has a built-in soft start that

ramps up the output voltage at a controlled slew

rate to avoid overshooting at start-up. The soft-

start time is typically about 0.5ms.

Current Limit

The MP2172C has a typical minimum 2.8A

high-side switch current limit. When the high-

side switch reaches its current limit, the

MP2172C remains in hiccup mode until the

current drops. This prevents the inductor

current from continuing to rise and damaging

components.

Short Circuit and Recovery

The MP2172C enters short-circuit protection

(SCP) mode when it reaches its current limit,

and attempts to recover with hiccup mode. The

part

disables

the

output

power

stage,

discharges

the

soft-start

capacitor,

and

attempts to soft start again automatically. If the

short-circuit condition remains after the soft

start ends, the MP2172C repeats this cycle until

the short circuit is removed and the output rises

back to the regulation level.

Over-Voltage Protection (OVP)

The MP2172C monitors the feedback voltage to

detect over-voltage. When the feedback voltage

(VFB) exceeds 115% of the target voltage, the

controller enters a dynamic regulation period.

During this period, the low-side MOSFET (LS-

FET) turns on until the low-side current drops to

-1.5A. This discharges the output to keep it

within the normal range. If the over-voltage

condition still remains, the LS-FET turns on

again after a 1µs delay. The MP2172C exits

this regulation period when VFB falls below

105% of the reference voltage. If the dynamic

regulation cannot limit the increasing VOUT, once

the input detects the 6.1V input, over-voltage

protection (OVP) occurs. The MP2172C stops

switching until the input voltage drops below

5.7V, and then the part resumes operation.