MP2482 – 5A, 30V, 420kHZ STEP-DOWN CONVERTER

MP2482 Rev.1.4

www.MonolithicPower.com

8

9/21/2011

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

Preliminary Specifications Subject to Change

© 2011 MPS. All Rights Reserved.

Internal Regulator

Most of the internal circuitries are powered from

the 5V internal regulator. This regulator takes

the VIN input and operates in the full VIN range.

When VIN is greater than 5.0V, the output of

the regulator is in full regulation. When VIN is

lower than 5.0V, the output decreases. Since

this internal regulator provides the bias current

for the bottom gate driver that requires

significant amount of current depending upon

the external MOSFET selection, a 1uF ceramic

capacitor for decoupling purpose is required.

Enable/Synch Control

The MP2482 has a dedicated Enable/Synch

control pin (EN/SYNC). By pulling it high or low,

the IC can be enabled and disabled by EN. Tie

EN to VIN for automatic start up. To disable the

part, EN must be pulled low for at least 5µs.

The MP2482 can be synchronized to external

clock range from 300kHz up to 1.5MHz through

the EN/SYNC pin. The internal clock rising

edge is synchronized to the external clock rising

edge.

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) is implemented

to protect the chip from operating at insufficient

supply voltage. The MP2482 UVLO comparator

monitors the output voltage of the internal

regulator, BYPASS. The UVLO rising threshold

is about 4.0V while its falling threshold is about

3.2V.

Internal Soft-Start

The soft-start is implemented to prevent the

converter output voltage from overshooting

during startup. When the chip starts, the

internal circuitry generates a soft-start voltage

(SS) ramping up from 0V to 1.2V. When it is

lower than the internal reference (REF), SS

overrides REF so the error amplifier uses SS as

the reference. When SS is higher than REF,

REF regains control.

Over-Current-Protection and Hiccup

The MP2482 has cycle-by-cycle over current

limit when the inductor current peak value

exceeds the set current limit threshold.

Meanwhile, output voltage starts to drop until

FB is below the Under-Voltage(UV) threshold,

typically 30% below the reference. Once a UV

is triggered, the MP2482 enters hiccup mode to

periodically restart the part. This protection

mode is especially useful when the output is

dead-short to ground. The average short circuit

current is greatly reduced to alleviate the

thermal issue and to protect the regulator. The

MP2482 exits the hiccup mode once the over

current condition is removed.

Thermal Shutdown

Thermal shutdown is implemented to prevent

the chip from operating at exceedingly high

temperatures. When the silicon die temperature

is higher than 150

°C, it shuts down the whole

chip. When the temperature is lower than its

lower threshold, typically 140

°C, the chip is

enabled again.

Floating Driver and Bootstrap Charging

The floating power MOSFET driver is powered

by an external bootstrap capacitor. This floating

driver has its own UVLO protection. This

UVLO’s rising threshold is 2.2V with a

hysteresis of 150mV. The bootstrap capacitor

voltage is regulated internally (Figure 2). Even

to maintain a 5V BST voltage across C4.

--

+

--

+

5V

U2

D2

M2

BST

SW

C4

C2

L1

Figure 2—Internal Bootstrap Charging Circuit