MP5991

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

MP5991 Rev. 1.0

MonolithicPower.com

24

4/27/2022

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© 2022 MPS. All Rights Reserved.

If VOCREF is below VOCREF_CLAMP, then the current-

limit reference voltage is determined by VOCREF.

If VOCREF exceeds VOCREF_CLAMP, then the current-

limit

reference

voltage

is

determined

by

VOCREF_CLAMP.

The desired ILIMIT is a function of RCS, the

current-sense gain (gCS) and VOCREF. ILIMIT can

be calculated with Equation (8):



OCREF

LIMIT

CS

CS

V

I

=

gR

(8)

ILIMIT can exceed the maximum load current

(ILOAD_MAX) during normal operation to allow for

tolerances in the current-sense value.

Over-Current

Protection

(OCP)

during

Start-Up

Once VCS exceeds VOCREF during soft start,

VGATE is regulated to maintain a constant IFET. If

VOUT is below (1/8 x VIN), and IFET is regulated

by VSS_CLAMP for 2.1ms, then the MOSFET

latches off, and GOK is pulled low (see Figure

12).

t

VGS

VOUT

VGOK

VON

VCS

>1.4V

2.1ms

VGS_TH

VOUT < 1/8 x VIN

Figure 12: Failed Start-Up with Output Hard

Short

OCP during Normal Operation

If VOUT exceeds 80% of VIN, then VOCREF_CLAMP is

pulled to 2V, and VGATE is close to the internal

charge pump voltage (VCP). Once soft start is

complete, the MP5991 begins normal operation.

Once VCS (configured via an external resistor)

exceeds VOCREF, the internal circuitry regulates

VGATE to maintain a constant current on the

MOSFET. To limit IOUT, the MOSFET’s VGS is

regulated between 3.3V and 1V. The response

time is about 14µs. IOUT may have a small

overshoot during this response time.

If IOUT exceeds ILIMIT, then the internal fault timer

(220µs) starts. If IOUT drops below ILIMIT within

the fault timer period, then the device resumes

normal operation. If IOUT exceeds ILIMIT for 220µs,

then the MOSFET latches off, and GOK is

pulled low.

If an OC fault occurs, then the GOK and SS

pins are pulled low, and FLT_TYPE outputs

1.2V to indicate an OC fault.

In latch-off mode, cycle the power on VIN,

VDD33, or ON to reset FLT_TYPE to 0.1V. This

initiates a soft start, and then MOSFET turns on.

In hiccup mode, the device attempts to initiate a

new soft start automatically, and GOK is pulled

high after a retry delay time (tRETRY). FLT_TYPE

continues to indicate an OC fault during tRETRY.

FLT_TYPE is reset to 0.1V after tRETRY.

Short-Circuit Current Limit (SCREF)

If ILOAD increases rapidly due to a short circuit,

the current may exceed ILIMIT significantly before

the hot-swap control loop can respond. Once

the Intelli-Fuse current reaches the short-circuit

current limit (ILIMIT_SC), a fast turn-off circuit in

the Intelli-Fuse is enabled to turn the MOSFET

off. The total short-circuit response time is

about 200ns. If IFET exceeds ILIMIT_SC, GOK is

pulled low.

To determine ILIMIT_SC, the MP5991 samples the

SCREF voltage (VSCREF) once the ON voltage

(VON) exceeds its rising threshold during the

tON_DELAY (see Figure 13).

VIN

VDD33

VSCREF

VON

VSS

tON_DELAY

VSCREF is sampled and ILIMIT_SC

is held during the tON_DELAY.

Figure 13: SCREF Voltage Sampling to

Determine the Short-Circuit Current Limit

ILIMIT_SC is held once tON_DELAY is finished.

Changing VSCREF after tON_DELAY does not affect