MP5000S – 12V, 1A-5A PROGRAMMABLE CURRENT LIMIT SWITCH

MP5000S Rev. 1.0

www.MonolithicPower.com

9

4/29/2013

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© 2013 MPS. All Rights Reserved.

OPERATION

The MP5000S is designed to limit the in-rush

current to the load. It offers an integrated solution

to monitor the input voltage, output voltage,

output current and die temperature.

Under Voltage Lock Out Operation

If the supply (input) is below the UVLO threshold,

the output is disabled, and the fault line is driven

low.

When

the

supply

goes

above

the

UVLO

threshold, the output is enabled and the fault line

is released. When the fault line is released it will

be pulled high by a 28uA current source. No

external pull up resistor is required. In addition,

the pull up voltage is limited to 5 volts.

Output Over Voltage Protection

If the input voltage is higher than the OVP

threshold, the output will be clamped at 15V

(typical).

Current Limit

When the part is active, if load reaches trip

current (minimum threshold current triggering

over current protection) or a short is present, the

part switches into to a constant-current (hold

current) mode. Part will be shutdown only if the

over current condition stays long enough to

trigger thermal protection.

EN, the load current should be smaller than hold

current. Otherwise, the part can’t be fully turned

on.

In a typical application using a current limit

resistor of 22Ω, the trip current will be 5A and the

hold current will be 3.7A. If the device is in its

normal operating state and passing 2.0A it will

need to dissipate only 160mw with the very low

on

resistance

of

40

mΩ. For the package

dissipation of 50°C/Watt, the temperature rise will

only be + 8°C. Combined with a 25°C ambient,

this is only 33°C total package temperature.

During a short circuit condition, the device now

has 12V across it and the hold current clamps at

3.7A and therefore must dissipate 44W. At

50°C/watt, if uncontrolled, the temperature would

rise above the MP5000S thermal protection

(+175°C) and shutdown the device to cause the

temperature to drop below a hysteresis level.

Proper heat sink must be used if the device is

intended to supply the hold current and not

shutdown. Without a heat sink, hold current

should be maintained below 250mA at + 25°C

and below 150mA at +85°C to prevent the device

from activating the thermal shutdown feature.

Thermal protection

When thermal protection is triggered, the output

is disabled and the fault line is driven to the

middle level. The thermal fault condition is

latched, and the part will remain latch off state

until restart the power or reset the enable pin.

Enable / Fault Pin

The Enable/Fault Pin is a Bi-Directional three

levels I/O with a weak pull up current (28uA

typical). The three levels are low, mid and high. It

functions to enable/disable the part and to relay

Fault information.

Enable/Fault pin as an input:

1.

Low and mid disable the part.

2.

Low, in addition to disabling the part,

clears the fault flag.

3.

High enables the part (if the fault flag is

clear).

Enable/Fault pin as an output:

1.

The pull up current may (if not over

ridden) allow a “wired nor” pull up to

enable the part.

2.

An under voltage will cause a low on the

Enable/Fault pin, and will clear the fault

flag.

3.

A thermal fault will cause a mid level on

the Enable/Fault pin, and will set the fault

flag.

The Enable/Fault line must be above the mid

level for the output to be turned on.

The fault flag is an internal flip-flop that can be

set or reset under various conditions:

1.

Thermal Shutdown: set fault flag

2.

Under Voltage: reset fault flag