MP8712 – 18V, 12A, SYNCHRONOUS STEP-DOWN CONVERTER

MP8712 Rev. 1.2

MonolithicPower.com

17

3/19/2021

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Power Good (PG)

Power good (PG) indicates whether the output

voltage is in the normal range compared to the

internal reference voltage. PG is an open-drain

structure. An external pull-up supply is needed.

During power-up, the PG output is pulled low.

This indicates to the system to remain off and

keep the load on the output to a minimum. This

helps reduce inrush current at start-up.

When the output voltage is between 90% and

115% of the nominal voltage and the soft start

is finished, the PG signal is pulled high. When

the output voltage is lower than 85% after the

soft start finishes, the PG signal remains low.

When the output voltage is higher than 115% of

the nominal voltage, PG is switched low. The

PG signal rises high again after the output

voltage drops below 105% of the nominal

voltage.

PG uses a deglitch time whenever VOUT

crosses the UV/OV rising and falling threshold.

The PG output is pulled low immediately when

either EN UVLO, input UVLO, OCP, or OTP is

triggered.

Input Over-Voltage Protection (VIN OVP)

The MP8712 monitors VIN to detect an input

over-voltage (OV) event. This function is only

active when the output is in OV. When the

output is in an over-voltage protection (OVP)

state, output discharge is enabled, charging the

input voltage high. When the input voltage

exceeds the input OVP threshold, both the HS-

FET and LS-FET stop switching.

Output Over-Voltage Protection (OVP)

The MP8712 monitors FB to detect an over-

voltage event. When the FB voltage becomes

higher than 125% of the internal reference

voltage,

the

controller

enters

dynamic

regulation mode, and the input voltage may be

charged up during this time. When input OVP is

triggered, the IC stops switching. Once the

input voltage drops below the VIN OVP

recovery threshold, the IC begins switching.

OVP auto-retry mode occurs only if the soft

start finishes.

Dynamic regulation mode is defined as turning

on the low side until the low-side negative

current limit is triggered, and then the body

diode of the HS-FET freewheels the current.

The output power charges to the input, which

may trigger a VIN OVP function. In VIN OVP,

neither the HS-FET or LS-FET turn on and stop

charging VIN to a higher voltage. If the output is

still over-voltage and the input voltage has

dropped below the VIN OVP threshold, repeat

dynamic regulation mode. If the output voltage

is lower than 110% of the internal reference

voltage, then output OVP is exited.

Output Absolute Over-Voltage Protection

(OVP_ABS)

The MP8712 monitors VOUT to detect absolute

over-voltage protection. When VOUT is larger

than 6.5V, the controller enters dynamic

regulation mode. Absolute OVP can work once

both the input voltage and EN are higher than

their rising thresholds. Therefore, this function

can work even in a soft-start period.

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 less than 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 2.4V with a

hysteresis of 150mV. The bootstrap capacitor

voltage is regulated internally by VIN through

D1, M1, C4, L1, and C2 (see Figure 4). If VBST -

VSW exceeds 3.3V, U1 regulates M1 to maintain

a 3.3V BST voltage across C4.

Figure 4: Internal Bootstrap Charging Circuit