MP5077 – 5.5V, 7A, LOW RDSON LOAD SWITCH WITH PROGRAMMABLE CURRENT LIMIT

MP5077 Rev. 1.01

www.MonolithicPower.com

11

6/23/2014

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

© 2014 MPS. All Rights Reserved.

OPERATION

The MP5077 is designed to limit the in-rush

current to the load thereby limiting the

backplane’s voltage drop and the slew rate of

the voltage to the load. It provides an integrated

solution to monitor the input voltage, output

voltage and output current to eliminate the need

for an external current power MOSFET, and

current switch device.

Enable

When input voltage is greater than the under-

voltage lockout threshold (UVLO), typically 0.5V,

MP5077 can be enabled by pulling EN pin to

higher than 1.5V. Pulling down to ground or

floating will disable MP5077.

Current Limit

The MP5077 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:

(1)

S is the current sense ratio of MP5077, and this

values of S please refer the curves in typical

performance characteristics.

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

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 (typical 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

80

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

power FET. If the part is still in short-circuit

condition. MP5077 will reduce the current limit

to 2/3 of pre-set value, and hold it until the part

is so hot and thermal shutdown. After the short-

circuit condition removed, the current limit will

recover to the pre-set value automatically.

Output Discharge

MP5077 has output discharge function. This

function can discharge the Vo by internal pull

shutdown and the load is very light.

Soft-Start

A capacitor connected to the SS pin determines

the soft-start time. There is an internal 9

μA

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 SS

voltage.

The soft-start time can be calculated by below

equation:

(uA)

I

(nF)

C

(V)

V

3

1

(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 Vout rising time will be just

limited by power MOS charge time.