MP5092 – DUAL 5.5V, 7.5A LOW RDSON LOAD SWITCH WITH OUTPUT DISCHARGE FUNCTION

MP5092 Rev. 1.0

www.MonolithicPower.com

12

1/8/2015

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OPERATION

The MP5092 is designed to limit the in-rush

current to the load when a circuit card is

inserted into a live backplane power source;

thereby limiting the backplane’s voltage drop

and the slew rate of the voltage to the load.

MP5092 integrated two independent load

switches. Any one channel can work alone.

Each channel can provide 7.5A load capability.

It provides an integrated solution to monitor

output current to eliminate the need for an

external current power MOSFET, and current

sense device.

Enable

When input voltage is greater than the under-

voltage lockout threshold (UVLO), typically 0.5V,

MP5092 can be enabled by pulling EN pin to

higher than 1.5V. Pulling down to ground will

disable MP5092.

The recommend start up sequence is power up

high.

Current Limit

The MP5092 provides a constant current limit

that can be programmed by an external resistor.

Once the device reaches its current limit

threshold, the internal circuit regulates the gate

voltage to hold the current in the power FET

constant. The typical response time is about

20µs and the output current may have a small

overshoot during this time period.

The pre-set current limit value can be

calculated by below equation:

)

(

82000

)

(

Ω

=

LIM

LIM

R

A

I

(1)

ILIM1/2 pin to ground in Figure 4.

If the current limit block starts to regulate the

output current, the power loss on power

MOSFET will cause the IC temperature rise. If

the junction temperature rose to high enough, it

will trigger thermal shutdown. After thermal

shutdown happened, it will disable the output

until the over temperature fault remove. The

Vcc is the bias supply for internal analog circuit.

It is better to have a decouple capacitor to filter

higher than 3V, the Vcc can be directly

Short-Circuit Protection

If the load current increases rapidly due to a

short circuit, the current may exceed the current

limit threshold by a lot before the control loop

can respond. If the current reaches an internal

secondary current limit level (about 13A), a fast

turn-off circuit activates to turn off the power

FET. This limits the peak current through the

switch to limit the input voltage drop. The total

short circuit response time is about 200ns. If

fast off works, it will keep off the power FET for

80us. After that time period, it will re-turn on

power FET..

Output Discharge

MP5092 has output discharge function. This

function can discharge the Vo by internal pull

down resistance when IC disabled and the load

is very light.

Soft-Start

A capacitor connected to the SS pin determines

the soft-start time. There is an internal 9uA

constant current source charge SS cap and

ramps up the voltage on the SS pin. The output

voltage rises at 3 times the slew rate to the SS

voltage.

The soft-start time can be calculated by below

equation:

)

(

)

(

)

(

3

1

)

(

uA

I

nF

C

V

V

ms

T

SS

SS

OUT

SS

⋅

×

=

(2)

The suggestion minimum SS cap should be

bigger than 4.7nF. If the SS pin is floated or SS

cap is too small, the Vo rising time will be just

limited by power MOS charge time.