MP5921

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

MP5921 Rev. 1.1

www.MonolithicPower.com

23

5/17/2022

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APPLICATION INFORMATION

Current Limit Resistor (RCS)

The MP5921

’s normal current limit value should

be higher than the normal maximum load

current, allowing the tolerances in the current

sense value. The current limit can be set with

Equation (10):

(A)

10

R

V

I

5

CS

CLREF_NORM

LIMIT



=

(10)

Where VCLREF_NORM is the CLREF voltage when

the power FET works in linear mode, and RCS is

the resistor from CS to ground

(Ω).

If RCS is set to 3kΩ, and VCLREF_NORM is 1.2V, the

desired current limit is around 40A. When

VCLREF_NORM is 0.3V, the desired current limit is

about 10A.

Note that the maximum CS resistor (RCS)

should be set no higher than 3.6

kΩ.

CLREF

CLREF is used to set the current-limit reference

voltage, which can be determined by the hot-

swap controller or a resistor to ground in

standalone operation. A CLREF 10µA current

source sets the pin voltage. Place a 1nF

capacitor from CLREF to ground to smooth the

indicator voltage if the MP5921 is in standalone

mode.

For the current limit at normal operation, the

CLREF voltage can be set from 0.3V to 1.6V to

program the current limit low or high while a

fixed RCS resistor is used.

Current Monitor Set (IMON)

The

MP5921

provides

a power MOSFET

current monitoring function. Place a resistor to

ground to set the gain of the output current.

In a single MP5921 application, the IMON

resistor should be set no lower than the CS

resistor. When the MP5921 is used in a multi-

fuse

parallel

application,

achieve

start-up

current balance per device by connecting IMON

and CS (see Figure 12). The equivalent

average IMON resistor (RIMON_AVG) can be

calculated by RCS/N, where N is the active

parallel number.

MP5921

MP5921

MP5921

IMON

IMON

GND

CS

IMON

RCS

GND

CS

RCS

GND

CS

RCS

N

R

R

CS

IMON_AVG =

RIMON

RIMON

RIMON

RIMON= RCS

Figure 12: Multi-MP5921 IMON and CS

Connection in Parallel Application

Maximum Output Current

The MP5921 drives up to 50A of continuous

current per device at room temperature and can

reach 60A with air flow. The case temperature

rise vs. the output current at different air

conditions is shown in Figure 13.

Figure 13: Output Current De-Rating Curve

No Air Flow

Air Flow = 100 ft/min

Air Flow = 200 ft/min