MP1601A – 1A, SYNCHRONOUS, STEP-DOWN CONVERTER IN A SOT563

MP1601A Rev. 1.0

www.MonolithicPower.com

13

9/2/2016

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© 2016 MPS. All Rights Reserved.

OPERATION

The MP1601A uses constant on-time control

with input voltage feed-forward to stabilize the

switching frequency over the full input range. It

achieves 1A of continuous output current from a

2.3V 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

Compared

to

fixed-frequency

pulse-width

modulation (PWM) control, constant-on-time

control (COT) offers a simpler control loop and a

faster transient response. By using input voltage

feed-forward, the MP1601A 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

T

0.454 s

V







(1)

To prevent inductor current runaway during the

load transient, the MP1601A uses a fixed

minimum off time of 60ns.

Enable (EN)

When the input voltage is greater than the under-

voltage lockout (UVLO) threshold (typically 2V),

the MP1601A can be enabled by pulling EN

higher than 1.2V. Floating EN or pulling it down

to ground disables the MP1601A. There is an

internal 1M

Ω resistor from EN to ground.

When the device is disabled, the MP1601A goes

into output discharge mode automatically. Its

internal discharge MOSFET provides a resistive

discharge path for the output capacitor.

Soft Start (SS)

The MP1601A has a built-in soft start (SS) that

ramps up the output voltage at a controlled slew

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

start time is about 0.5ms, typically.

Current Limit

The MP1601A has a 2A, high-side, switch

current limit, typically. When the high-side switch

reaches its current limit, the MP1601A 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 MP1601A enters short-circuit protection

(SCP) mode when it reaches the current limit

and attempts to recover with hiccup mode. In this

process, the MP1601A disables the output

power stage, discharges the soft-start capacitor,

and then attempts to soft start automatically. If

the short-circuit condition remains after the soft

start ends, the MP1601A repeats this cycle until

the short circuit disappears and the output rises

back to regulation levels.