MP2225 –18V/5A SYNCHRONOUS STEP-DOWN CONVERTER

MP2225 Rev. 1.01

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13

4/13/2016

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To use external clock synchronization, connect

a clock with a frequency range between 200kHz

and 2MHz. The internal clock rising edge will

synchronize with the external clock rising edge.

Meanwhile the width of high level should be

longer than 250ns, and width of low level longer

than 100ns.

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) protects the chip

from operating at insufficient supply voltage.

The MP2225 UVLO comparator monitors the

output voltage of the internal regulator, VCC.

The UVLO rising threshold is about 4.1V while

its falling threshold is 3.4V.

Soft-Start

The soft-start prevents the converter output

voltage from overshooting during startup. When

the chip starts, the internal circuitry generates a

soft-start voltage (SS) that ramps up from 0V to

VCC. When SS is lower than REF, the error

amplifier uses SS as the reference. When SS is

higher than REF, the error amplifier uses REF

as the reference.

The SS time is internally set to 2.4ms.

Over-Current-Protection and Hiccup

The MP2225 has a cycle-by-cycle over-current

limit which can limit the inductor current in case

of output over load or short circuit(SC). If the

over load or SC events last for enough long

time, FB voltage can drop below the Under-

Voltage (UV) threshold—typically 30% of the

reference. Once UV is triggered, the MP2225

enters hiccup mode to periodically restart the

part. 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 to protect the

regulator. The MP2225 exits the hiccup mode

once the over-current condition is removed.

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the temperature of the silicon reaches

temperature is less than its lower threshold,

typically 130°C, the chip is enabled again.

Floating Driver and Bootstrap Charging

An external bootstrap capacitor powers the

floating power MOSFET driver. This floating

driver has its own UVLO protection. This

UVLO’s rising threshold is 2.6V with a

hysteresis of 350mV. The bootstrap capacitor

exceeds 5V, U1 will regulate M1 to maintain a

5V BST voltage across C4.

Figure 4: Internal Bootstrap Charging Circuit

Startup and Shutdown

thresholds, the chip starts. The reference block

starts up first, generating stable reference

voltage, 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

avoid any fault triggering. The COMP voltage

and the internal supply rail are then pulled down.

The floating driver is not subject to this

shutdown command.