MP5921

– 16V, 50A, 1mΩ RDS(ON), HOT-SWAP INTELLI-FUSE SOLUTION

MP5921 Rev. 1.1

www.MonolithicPower.com

17

5/17/2022

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2022 MPS. All Rights Reserved.

t

VGS

VOUT

GOK

ON/PD

VCS

e.g., 300 mV

>1.4 V

Maximum SS time 270 ms

VGS_TH

VCLREF_SS

Thermal

shut down

Figure 3: Failed Start-Up within 270ms

Current Limit at Normal Operation

When the output voltage has ramped up close

to VIN, and VOUT is higher than 80%VIN, the

internal current limit reference clamp voltage is

released to 1.6V, and the power FET gate

voltage is close to the internal charge pump

voltage. Once the MP5921 detects that the

start-up has finished, the part works in normal

operation.

During normal operation, once VCS (which is

programmed by an external resistor) exceeds

the normal CLREF threshold, the internal circuit

regulates the gate voltage to hold the power

FET constant. To limit the current, the gate to

the source voltage needs to be regulated from

3.3V to around 1V. The typical response time is

about 14µs. The output current may have a

small overshoot during this time period.

When the current limit is triggered, the internal

fault timer starts. If the output current falls

below the current limit threshold before the end

of the 180µs fault time-out period, the MP5921

resumes normal operation. Otherwise, if the

current limit duration exceeds the fault time-out

period, the power FET is latched off and GOK is

pulled low.

The desired current limit at normal operation is

a function of the CS external resistor (RCS).

The MP5921 current limit value can be higher

than

the

normal

maximum

load

current,

allowing tolerances in the current sense value.

The current limit can be set using Equation (2):

CS

CS

CLREF_NORM

LIMIT

R

g

V

I



=

(2)

Where VCLREF_NORM is the CLREF voltage in

normal operation, and gCS is 10µA/A, which is

the current sense gain when the power FET is

fully on. The FET works in the linear region.

Short-Circuit Protection (SCP)

If the load current increases rapidly due to a

short circuit, the current may exceed the current

limit threshold significantly before the hot-swap

control loop can respond. If the Intelli-Fuse

current reaches 100A, a fast turn-off circuit in

the Intelli-Fuse is activated to turn off the power

FET. The total short-circuit response time is

about 200ns. The GOK signal is pulled low

when the power FET current reaches 100A

current limit and asserts low.

Power-Up Sequence

For hot-swap applications, while the input

voltage rises immediately, the power FET gate

voltage should always be pulled low during the

VIN plug-in with high dV/dt.

There are two operation modes for the MP5921:

controlled

by

a

hot-swap

controller

or

standalone.

If MP5921 is controlled by a hot-swap controller,

the power FET remains off until the ON/PD

signal is pulled high. When the ON/PD signal

becomes high and the insertion delay time ends,

the power FET is charged up by the internal

12

μA charge pump. Once the MP5921 power

FET voltage (VGS) reaches its threshold (VGSTH),

the output voltage rises (see Figure 4). The

maximum VCS is clamped to VCLREF_SS if the load

current is high.

If the ON/PD signal stays high from the hot-

swap controller, the MP5921 can also be turned

on or off through the input voltage.