MPM3686 – 18V 20A STEP-DOWN POWER MODULE

MPM3686 Rev. 1.02

www.MonolithicPower.com

15

10/13/2016

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Low-Side Negative Current Limit

: If the sensed

LS-FET negative current exceeds the negative

current limit, the LS-FET turns off immediately

and stays OFF for the remainder of the OFF

period. In this situation, both MOSFETs are OFF

until the end of a fixed interval. The HS-FET body

diode conducts the inductor current for the fixed

time.

Over -Voltage Protection (OVP)

The MPM3686 monitors the output voltage using

the FB pin connected to the tap of a resistor

divider to detect over-voltage. It provides non-

latch OVP mode.

If the FB voltage exceeds the nominal REF

voltage but remains lower than 120% of the REF

voltage (0.611V), both MOSFETs are off.

If the FB voltage exceeds 120% of the REF

voltage but remains below 130%, the LS-FET

turns on while the HS-FET remains off. The LS-

FET remains on until the FB voltage drops below

110% of the REF voltage or the low-side

negative current limit is hit.

If the FB voltage exceeds 130% of the REF

voltage, it enters a non-latch mode. The LS-FET

remains on until the FB voltage drops below

110% of the REF voltage, and the MPM3686

initiates a new SS to rise back to regulation level

and operates normally again.

UVLO protection

The MPM3686 has under-voltage lock-out

protection (UVLO). When the VCC voltage

exceeds

the

UVLO

rising

threshold,

the

MPM3686 powers up. It shuts off when the VCC

voltage falls below the UVLO falling threshold

voltage. This is non-latch protection. The

MPM3686 is disabled when the VCC voltage falls

below 3.3 V. If an application requires a higher

UVLO threshold, use the two external resistors

connected to the EN pin as shown in Figure 9 to

adjust the startup input voltage. For best results,

use the enable resistors to set the input voltage

hysteresis to account for any input supply

variations.

EN Comparator

IN

EN

Figure 7—Adjustable UVLO Threshold

Thermal Shutdown

The MPM3686 has thermal shutdown. The IC

internally monitors the junction temperature. If

the junction temperature exceeds the threshold

value (minimum 150ºC), the converter shuts off.

This is a non-latch protection. There is about

25ºC hysteresis. Once the junction temperature

drops to about 125ºC, it initiates a soft startup.