MP2172 – 5.5V, 2A, 2.6MHz, SYNCHRONOUS STEP-DOWN SWITCHER

MP2172 Rev. 1.0

www.MonolithicPower.com

13

4/24/2019

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OPERATION

The MP2172 uses constant-on-time (COT)

control with input voltage feed-forward to

stabilize the switching frequency over its entire

input range. The MP2172 achieves up to 2A of

continuous output current from a 2.5V to 5.5V

input voltage 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

(COT) control offers a simpler control loop and

faster transient response. By using input

voltage feed-forward, the MP2172 maintains a

nearly constant switching frequency across the

entire input and output voltage range. The

switching pulse on time can be estimated with

Equation (1):

Ton(µs)=VOUT/VIN×0.33+0.03µs

(1)

Where 0.03µs is the loop delay.

For the specific value of the on time, refer to the

EC table on page 3.

To prevent inductor current runaway during the

load transient, the MP2172 implements a

minimum off time in each cycle. This minimum

off time limit does not affect the operation of the

MP2172 in steady state in any way.

Enable (EN)

When the input voltage exceeds the under-

voltage lockout (UVLO) threshold (typically

2.2V), the MP2172 is enabled by pulling the

enable pin (EN) above 1.2V. Float EN or

connect EN to ground to disable the MP2172.

There is an internal 1MΩ resistor from EN to

ground.

Soft-Start/Soft-Stop

The MP2172 has a built-in soft start that ramps

up the output voltage at a constant slew rate to

avoid overshooting during start-up. The soft-

start time is about 1.3ms, typically. When

disabled, the MP2172 ramps down the internal

reference voltage to allow the load to discharge

the output linearly.

Power Good (PG) Indicator

The MP2172 has an open drain with a 500kΩ

pull-up resistor pin for power good indication

(PG). When FB is within ±10% of the regulation

voltage (0.6V), PG is pulled up to VIN by the

internal resistor. If the FB voltage is outside the

±10% window, PG is pulled to ground by an

internal MOSFET.

Current Limit

The MP2172 has a 4.5A current limit for the

high-side switch (HS-FET). When the HS-FET

reaches its current limit, the MP2172 enters

hiccup mode until the current drops to prevent

the inductor current from building and damaging

the components.

Short Circuit and Recovery

The MP2172 enters short-circuit protection

(SCP) mode when it reaches the current limit

and attempts to recover from the short circuit

with hiccup mode. In SCP, the MP2172

disables the output power stage, discharges a

soft-start capacitor, and then enacts a soft-start

procedure. If the short-circuit condition still

remains after the soft start ends, the MP2172

repeats this operation until the short circuit is

removed and the output rises back to the

regulation level.