MP2388 – 1A, 21V, 2MHZ , HIGH-EFFICIENCY, SYNCHRONOUS, STEP-DOWN CONVERTER

MP2388 Rev. 1.0

www.MonolithicPower.com

12

4/15/2016

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Internal Soft Start (SS)

A soft start (SS) is implemented to prevent the

converter output voltage from overshooting

during start-up. When the chip starts up, the

internal circuitry generates a soft-start voltage

that ramps up from 0V. The soft-start period

lasts until the voltage on the soft-start capacitor

exceeds the reference voltage (0.798V). At this

point, the reference voltage takes over. The

soft-start time is internally set to around 1.5ms.

Over-Current Protection (OCP) and Hiccup

The MP2388 uses a cycle-by-cycle over-current

limit when the inductor current peak value

exceeds

the

set

current-limit

threshold.

Meanwhile, the output voltage drops until FB is

below

the

under-voltage

(UV)

threshold,

typically 50% below the reference. Once UV is

triggered, the MP2388 enters hiccup mode to

restart the part periodically. This protection

mode is especially useful when the output is

dead-shorted to ground. The average short-

circuit current is greatly reduced to alleviate

thermal issues and protect the regulator. The

MP2388 exits 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, the entire chip shuts

down. When the temperature is below its lower

threshold (typically 130°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. The UVLO

rising threshold is 2.2V with a hysteresis of

150mV. The bootstrap capacitor voltage is

than 5V, U1 regulates M1 to maintain a 5V BST

voltage across C5.

5

R5

Figure 4: Internal Bootstrap Charging Circuit

Start-Up and Shutdown

appropriate thresholds, the chip starts. The

reference block starts first, generating a stable

reference voltage and current, and then the

internal regulator is enabled. The regulator

provides a stable supply for the remaining

circuitries.

Three events can shut down the chip: EN low,

procedure, the signaling path is first blocked to

internal supply rail are then pulled down. The

floating driver is not subject to this shutdown

command.