MP2313 – 24V, 1A SYNC STEP DOWN CONVERTER

MP2313 Rev. 1.0

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12

9/1/2014

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Figure 3: 6.5V Zener Diode Connection

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) is implemented

to protect the chip from operating at insufficient

supply voltage. The MP2313 UVLO comparator

monitors the output voltage of the internal

regulator, VCC. The UVLO rising threshold is

about 3.9V while its falling threshold is

consistent 3.25V.

Internal Soft-Start

The soft start is implemented to prevent the

converter output voltage from overshooting

during start up. When the chip starts, the

internal circuitry generates a soft-start voltage

(SS) ramping up from 0V. The soft-start period

lasts until the voltage on the soft-start capacitor

exceeds the reference voltage of 0.8V. At this

point the reference voltage takes over. The soft-

start time is internally set to be around 1.5ms.

Over-Current-Protection and Hiccup

The MP2313 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 50% below the reference. Once a UV

is triggered, the MP2313 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

MP2313 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 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. This

UVLO’s rising threshold is 2.2V with a

hysteresis of 150mV. The bootstrap capacitor

voltage is regulated internally by VIN through

D1, R5, C5, L1 and C2 (Figure 4). If (VIN-VSW)

is more than 5V, U2 will regulate M3 to maintain

a 5V BST voltage across C5.

Figure 4: Internal Bootstrap Charging Circuit

Startup and Shutdown

appropriate thresholds, the chip starts. The

reference block starts first, generating stable

reference voltage and currents, and then the

internal regulator is enabled. The regulator

provides stable supply for the remaining

circuitries.

Three events can shut down the chip: EN low,

VIN low and thermal shutdown. In the shutdown

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.