MP8843 – 6V, 3A, SYNCHRONOUS, STEP-DOWN SWITCHER WITH I

MP8843 Rev. 1.0

www.MonolithicPower.com

16

7/15/2016

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© 2016 MPS. All Rights Reserved.

OPERATION

The MP8843 is a low-voltage, 3A, synchronous,

interface. The MP8843 uses constant-on-time

(COT) control with input voltage feed-forward to

stabilize the switching frequency over the entire

input range. Because it does not require

compensation, it has a simple design procedure.

interface that allows transfers up to 3.4Mbps.

This communication interface can scale the

voltage dynamically with voltage steps as small

as 3.9mV with an output voltage range of 0.6V to

1.1V. The interface can also control the voltage

transition slew rate.

Constant-on-Time (COT) Control

Compared to the fixed-frequency PWM control,

COT control simplifies the control loop and

speeds up the transient response. The MP8843

uses input voltage feed-forward to maintain 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

sw

V

1

Vf





(1)

To prevent inductor current runaway during the

load transient, the MP8843 has a fixed minimum

off time of 90ns. This minimum off time does not

affect steady-state operation in any way.

Light-Load Operation

interface uses power save mode. When the

MODE bit is “0,” the MP8843 enters power save

mode and uses a proprietary control scheme to

save power and improve efficiency. The MP8843

turns off the low-side switch when the inductor

current begins to reverse. Then the MP8843

works in discontinuous conduction mode (DCM).

Enable (EN)

When the input voltage exceeds the under-

voltage lockout (UVLO) threshold (typically

2.35V), the MP8843 can be enabled by pulling

EN above 1.2V. Leave EN floating or pull EN

down to ground to disable the MP8843. There is

an internal 1MΩ resistor from EN to ground.

Soft Start (SS)

The MP8843 has a built-in soft start (SS) that

ramps up the output voltage at a controlled slew

rate to prevent an overshoot at start-up. The

soft-start time is about 1ms, typically, when

Power Good (PG) Indictor

The MP8843 uses an open drain for the power

good (PG) indicator. When PG is able to detect

from the reference, PG is pulled up to VIN by

the external resistor when the OUT voltage is

within 85%~115% of the regulation voltage.

Otherwise, the internal MOSFET pulls PG to

ground. If PG is only able to detect a negative

PG is pulled up to VIN when the OUT voltage is

higher than 115% of regulation voltage. The

200Ω.

Current Limit

The MP8843 has a 4.8A high-side switch

current limit. When the high-side switch reaches

its current limit, the MP8843 turns off the high-

side switch until the low-side current drops to

3.8A. This prevents the inductor current from

continuing to rise and damaging components. If

the over-current status is continuous, the output

voltage falls and may trigger short-circuit

protection.

Short Circuit

The MP8843 monitors the output voltage

through OUT to detect an under-voltage

condition. The MP8843 enters a latch-off

protection mode when an output short occurs.

Only an EN or VIN restart can turn the MP8843

on again.

I

The MP8843 can communicate with the core

interface is shown in Figure 2. The installation

process and usage can be found in the MP8843

software guide.