MP8714 – 17V, 10A, SYNCHRONOUS, STEP-DOWN CONVERTER

MP8714 Rev.1.0

www.MonolithicPower.com

14

12/27/2016

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Output Over-Voltage Protection (OVP)

The MP8714 monitors both FB and VOUT to

detect an over-voltage event. When the

feedback voltage rises higher than 120% of the

internal reference voltage, the controller enters

linear discharge mode. During this period, a

35Ω resistor connected between VOUT and

ground discharges the output and keeps it

within the normal range. Once the output

voltage falls below 105% of the reference, the

controller exits linear discharge mode.

Over-Current Protection (OCP) and Hiccup

The MP8714 has a cycle-by-cycle over-current

limit. When the inductor current peak value

exceeds the set current limit threshold, the HS-

FET turns off, and the LS-FET turns on and

remains on until the inductor current falls below

the internal valley current limit threshold. The

valley current limit circuit is employed to

decrease the operation frequency after the

peak current limit threshold is triggered.

below

the

under-voltage

(UV)

threshold

(typically 30% below the reference). Once UV is

triggered, the MP8714 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 reduced greatly to alleviate

thermal issues and protect the regulator. The

MP8714 exits hiccup mode once the over-

current condition is removed.

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the silicon die temperature exceeds

160°C, the entire chip shuts down. When the

temperature is below its lower threshold

(typically 140°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 2.2V with a

hysteresis of 150mV. The bootstrap capacitor

voltage is regulated internally by VIN through

D1, M1, C5, L1, and C2 (see Figure 5). If VIN -

5V BST voltage across C5.

Figure 5: Internal Bootstrap Charging Circuit

Start-Up and Shutdown

If both VIN and EN/SYNC exceed their

respective thresholds, the chip starts up. The

reference block starts first, generating stable

reference voltage and currents, 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/SYNC low, VIN low, and thermal shutdown.

In the shutdown procedure, the signaling path is

and the internal supply rail are then pulled

down. The floating driver is not subject to this

shutdown command.