MP8861 – 2.85V - 18V, 6A, SYNCHRONOUS, STEP-DOWN CONVERTER

MP8861 Rev. 1.1

www.MonolithicPower.com

24

5/28/2020

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The bit Retry OVP defines the protection mode

when OVP is triggered. When Retry OVP is set

to 1, the part enters auto-recovery when OVP is

removed. When Retry OVP is set to 0, the part

latches off once output OVP occurs, and VIN

OVP is triggered until VIN or EN are toggled.

The bit Hiccup OCP defines the over-current

protection mode. When Hiccup OCP is set to 1,

the part enters hiccup mode when OCP and

UVP are both triggered. When Hiccup OCP is

set to 0, the part enters latch-off when OCP and

UVP are both triggered.

The lowest bit, Mode, is used for selecting

forced PWM or auto-PFM/PWM mode at light

load. When Mode is set to 0, auto-PFM/PWM

mode is enabled at light load. When Mode is

set to 1, forced PWM mode is enabled at light

load.

NAME

BITS

DEFAULT

DESCRIPTION

EN

D[7]

1

I2C controlled turn-on or turn-off of the part. When the external EN is low, the

converter is off and I2C shuts down. When EN is high, the EN bit takes over.

The default EN bit is 1.

GO_BIT

D[6]

0

Switch bit of the I2C writing authority for the output reference command only.

Set GO_BIT = 1 to enable the I2C authority of writing the output reference.

When the command is finished, GO_BIT auto-resets to 0 to prevent false

operation of the Vref scaling.

Voltage scaling examples:

1) Set GO_BIT = 1.

2) Write register 00: set the output reference.

3) Read back the GO_BIT value to see if the output scaling is finished. If

GO_BIT = 0, the voltage scaling is done. Otherwise, Vref is still in

adjustment.

4) Set GO_BIT = 1 if output voltage scaling is needed a second time.

5) Write register 00: set the output reference.

Slew

Rate

D[5:3]

100

The slew rate during the I2C-controlled voltage changing is defined by three

bits. The output voltage changes linearly from the previous voltage to the

new set voltage with a slew rate (see below). This helps reduce the inrush

current, voltage overshoot, and voltage undershoot greatly.

D[5:3]

Slew Rate

D[5:3]

Slew Rate

000

40mV/μs

100

5mV/μs

001

30mV/μs

101

2.5mV/μs

010

20mV/μs

110

1.25mV/μs

011

10mV/μs

111

0.625mV/μs

Retry

OVP

D[2]

1

FB or Vref over-voltage protection mode selection bit. 1 means the part auto-

recovers when OVP is removed. 0 means the part latches off once output

OVP and VIN OVP are both triggered until VIN or EN is power reset.

Hiccup

OCP

D[1]

1

Over-current protection mode selection. 1 means hiccup mode OCP. 0

means latch-off type OCP.

Mode

D[0]

0

Set Mode to 0 to enable PFM mode. Set Mode to 1 to disable auto-

PFM/PWM mode. The default is auto-PFM/PWM mode for light load.