MP5921

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

MP5921 Rev. 1.1

www.MonolithicPower.com

19

5/17/2022

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© 2022 MPS. All Rights Reserved.

The approximate soft-start time is then 1.5ms,

which is the minimum output voltage soft-start

time.

ON/PD Control

ON/PD can be used for on/off control of the

power FET and the pull-down mode of the

output voltage. When ON/PD is used for on/off

control, the power FET is turned on if the

ON/PD voltage is higher than 1.4V. Once the

ON/PD voltage is lower than 1.2V, the power

FET is turned off. If ON/PD is used for VOUT

pull-down mode, the ON/PD voltage must be

clamped at around 1V for more than 80µs. The

MP5921 recognizes 0.8V < ON/PD < 1.2V as a

special state that requires VOUT to be pulled

down.

If ON/PD is used to turn on the power FET,

there is a fixed 1.3ms insertion delay after

VDD3 and VIN pass the UVLO threshold. All

fault

functionality

is

operative

during

the

insertion delay, so the GOK signal is pulled high

if no fault is detected or remains low if a fault is

detected. The power FET remains off until the

insertion delay time ends. At the end of the

insertion delay, ON/PD behaves normally to

turn on the power FET if no fault occurs. The

detail logic is shown in Figure 7 when GOK is

pulled up to the VDD3 voltage.

VIN/

VDD33

ON/PD

ON

SWITCH

GOK

OFF

>1.4 V

Insertion delay

Insertion delay

ON

Figure 7: Power FET On/Off Control when No

Fault Occurs

Once the ON/PD voltage is pulled above 1.4V

and the insertion delay ends, the internal 12μA

current source charges the power FET’s gate.

Once the gate voltage reaches its threshold

(VGSTH), the output voltage rises. The output

voltage rises following the CLREF-controlled

current limit or SS slew rate and output

capacitor.

If the MP5921 works in standalone mode, a

capacitor on ON/PD can be used for automatic

start-up by the internal 4.2µA pull-up current

source. Once the ON/PD voltage reaches its

turn-on threshold, the power FET gate is

charged by the internal 12µA charge pump.

When the ON/PD voltage is set to around 1V,

the MP5921 works in pull-down mode (see

Figure 8). In pull-down mode, when the power

FET is turned off, an integrated 500Ω pull-down

resistor attached to the output discharges the

output voltage after a fixed delay time (2.1ms).

If the ON/PD signal is pulled low directly, pull-

down mode is disabled, and the Intelli-Fuse

output

voltage

is

discharged

through

the

external load.

ON/PD

>1.4 V

Around 1 V

80µs

Internal PD

Enable

PD delay

SWITCH

<0.8 V

1.2 V

0.8 V

FET on

FET off

VOUT

t

Figure 8: VOUT PD Mode

If the MP5921 is controlled by the hot-swap

controller, to achieve power FET on/off control

and VOUT PD mode control, the ON/PD can be

connected as shown in Figure 9. Pull ON/PD up

to VDD3 through a resistor divider (RPD and RON)

from the controller. If ON/PD is set to around 1V

when the hot-swap controller outputs low to turn

off the power FET. RPD can be calculated with

Equation (4):

( )

( )











=

ON

ON

PD

R

N

4.2

μ

-

1

R

2

R

(4)

Where N is the active parallel number. Choose

RON to be 10kΩ. For example, if N is 2, then RPD

can be set to around 22

kΩ.