MP5000 – 12V, 1A-5A PROGRAMMABLE CURRENT LIMIT SWITCH

MP5000 Rev. 1.41

www.MonolithicPower.com

9

9/6/2013

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© 2013 MPS. All Rights Reserved.

CURRENT LIMIT

The desired current limit is a function of the

external current limit resistor.

Table 1

—Current Limit vs. Current Limit Resistor

Current Limit Resistor (

Ω)

22

50

100

Trip Current (A)

5

2.7

2.3

Hold Current (A)

3.7

1.63

1.1

When the part is active, if load reaches trip

current (minimum threshold current triggering

overcurrent protection) or a short is present, the

part switches into to a constant-current (hold

current) mode. Part will be shutdown only if the

overcurrent 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 176mW with the very low

on

resistance

of

44

mΩ. For the package

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

only be + 9°C. Combined with a 25°C ambient,

this is only 34°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

MP5000

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.

RISE TIME

The rise time is a function of the capacitor

(Cdvdt) on the dv/dt pin.

Table 2

—Rise Time vs. Cdv/dt

Cdvdt

none

50pF

500pF

1nF

Rise Time

(TYPICAL)

(ms)

1.1

2.2

12.3

23.5

The “rise time” is measured by from 10% to 90%

of output voltage.

Figure 2

—Rise Time

ENABLE / FAULT PIN

The Enable/Fault Pin is a Bi-Directional three

levels I/O with a weak pull up current (25uA

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.