MP2276

– 16V, 8A, HIGH EFFICIENCY, SYNC, STEP-DOWN CONVERTER

MP2276 Rev.1.0

www.MonolithicPower.com

16

3/22/2017

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© 2017 MPS. All Rights Reserved.

Output Voltage External Reference

SS/TRK can be used as an analog input pin to

accept an external reference. When an external

voltage signal is connected to SS/TRK, it acts

as a reference for the MP2276 output voltage.

voltage signal exactly. The soft-start settings

are ignored. The SS/TRK input signal can be in

the range of 0.3V to 1.4V. During the initial

start-up, SS/TRK must first reach 800mV or

above to ensure proper operation. Afterward,

SS/TRK can be any value between 0.3V and

1.4V. If the external reference is added before

start-up, it should be no more than 1.2V to

avoid triggering under-voltage protection (UVP).

Pre-Bias Start-Up

The MP2276 is designed for monotonic start-up

into pre-biased loads. If the output is pre-biased

to a certain voltage during start-up, the IC

disables switching for both the high-side and

low-side switches until the internal soft-start

voltage exceeds the sensed output voltage at

FB.

Output Voltage Discharge

When the MP2276 is disabled through EN, the

output voltage discharge mode is enabled. Both

the HS-FET and the LS-FET are latched off. A

discharge MOSFET connected between SW

and GND is turned on to discharge the output

voltage. The typical switch on resistance of this

MOSFET is about 8

off.

Current Sense and Over-Current Protection

(OCP)

The MP2276 features an on-die current sense

and

programmable

positive

current

limit

threshold. The current limit is active when the

MP2276 is enabled. During the LS-FET on

state, the SW current (inductor current) is

sensed and mirrored to ILIM with the ratio of

the SW cycle-by-cycle current. The HS-FET is

the

internal

over-current

protection

(OCP)

state to limit the SW ripple valley current cycle-

by-cycle.

Calculate the current limit threshold setting from

OCP

ILIM

IN

O

O

CS

LIM

IN

s

V

R

( )

(V

V ) V

1

G

(I

)

V

2 L f













(4)

the desired output current limit (A).

During an over-current condition, the average

inductor current is less than the output load

current, and the output capacitor must supply

the extra current. Eventually, the output voltage

drops. Once the output voltage drops to the

under-voltage protection (UVP) threshold, the

MP2276 enters hiccup mode to restart the part

periodically. If the MP2276 detects an over-

current condition for 31 consecutive cycles,

even if the output voltage is above the UVP

level, it enters hiccup mode. The average short-

circuit current is reduced greatly to alleviate the

thermal issue and protect the regulator. The

MP2276 exits hiccup mode once the under-

voltage (UV) condition is removed.

Negative Inductor Current Limit

When LS-FET detects a -4A current, the

MP2276 turns off the LS-FET for 80ns to limit

the negative current.

Under -Voltage Protection (UVP)

The MP2276 monitors the output voltage by

connecting FB to the tap of a resistor divider to

(UVP) is triggered. The MP2276 enters hiccup

protection mode to restart the part periodically.

Output Sinking Mode (OSM)

The MP2276 uses output sinking mode (OSM)

to regulate the output voltage to the targeted

below the OVP threshold, OSM is triggered.

During OSM operation, the LS-FET remains on

until it reaches the -4A negative current limit.

After hitting -4A, the LS-FET is turned off

momentarily for 80ns and is then turned on

again. The MP2276 continues this operation

does,

the

MP2276

exits

OSM

after

15

consecutive cycles of forced CCM.