MP8845

MP8845 Rev. 1.1

www.MonolithicPower.com

17

2/23/2017

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© 2017 MPS. All Rights Reserved.

OPERATION

The MP8845 is a low-voltage, 5A, synchronous,

step-down converter with a controllable I

interface. The MP8845 applies MPS

’s patented

fixed-frequency hysteretic control to utilize fast

transient response of the hysteretic control and

keep the switching frequency constant. No

compensation is required, which simplifies the

design procedure.

The

MP8845

integrates

an

I

interface that allows transfers up to 3.4Mbps.

This communication interface can be used for

dynamic voltage scaling with voltage steps down

to 3.9mV with the output voltage from 0.6V to

1.1V. The voltage transition slew rate can be

controlled as well.

Fixed-Frequency Hysteretic Control

Compare

to

fixed-frequency

PWM

control,

hysteretic control offers the advantage of a

simpler

control

loop

and

faster

transient

response. By using an internal phase-lock loop,

the MP8845 maintains an optimal constant

switching frequency across the input and output

voltage ranges.

To prevent inductor current runaway during the

load transient, the MP8845 fixes the minimum off

time at 100ns. This minimum off time limit does

not affect operation of the MP8845 in steady

state in any way.

Light-Load Operation

In light load condition, the MP8845 uses a

proprietary control scheme to save power and

improve efficiency. The MP8845 turns off the

low-side switch when the inductor current begins

reversing.

The

MP8845

then

works

in

discontinuous conduction mode (DCM) operation.

Enable (EN)

When the input voltage is greater than the

under-voltage

lockout

threshold

(UVLO)

(typically

2.55V),

the

MP8845

is

enabled

automatically. Pull EN down to ground to disable

the MP8845. There is an internal 1M

Ω resistor

from EN to VIN.

Soft Start (SS)

The MP8845 has a built-in soft start (SS) that

ramps up the output voltage with a controlled

slew rate, avoiding start-up inrush current and

output voltage overshoot. The soft-start time is

about 1.5ms.

Power Good (PG) Indicator

The MP8845 has an open-drain output for the

power good indicator (PG). When the output

voltage is within ±10% of the regulation voltage,

PG is pulled up to VIN by the external resistor.

Current Limit

The MP8845 has a typical 7.5A current limit for

the high-side switch. When the high-side switch

reaches the current limit, the MP8845 expands

the minimum off time until the current drops to

6.5A. Then the high-side switch is turned on for

the next switching cycle. This prevents the

inductor current from continuing to build up and

damaging the components.

Thermal Protection

The MP8845 employs thermal shutdown by

monitoring the junction temperature of the IC

internally. If the junction temperature exceeds

the thermal warning threshold (around 130°C),

OTW is set. If there is no action from the

system, the junction temperature continues

rising until it exceeds the thermal shutdown

threshold

(150°C

typically).

After

thermal

shutdown, a new power start-up cycle is

needed to turn on the MP8845 again.

I

The MP8845 can communicate with the core

with I

control (see Figure 2). The installation process

and usage guidelines can be found in the

MP8845 Software Guide.

I

The I

0xC0H/0xC1H

internally

(see

Table

2).

If

another

slave

address

is

needed,

please

contact the factory.

Table 2: I

Hex

A7

A6

A5

A4

A3

A2

A1

A0

W 0xC0

R 0XC1

1

1

1

1

0

0

0

0

0

0

0

0

0

0

R/

W

Address

0x60