MP5003 – 3.3V, 1A-3A PROGRAMMABLE CURRENT LIMIT SWITCH WITH AUTO ENABLE

MP5003 Rev. 0.921

www.MonolithicPower.com

9

2/29/2012

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2012 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)

13

24

50

100

Trip Current

(A)

4

2.5

1.7

1.37

Hold Current

(A)

3.2

1.55

0.77

0.37

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 enter thermal cycling 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 24Ω, the trip current will be 2.5A and

the hold current will be 1.55A. If the device is in

its normal operating state and passing 1.5A it will

need to dissipate only 99mW with the very low on

resistance of 44mΩ. For the package dissipation

of 50°C/Watt, the temperature rise will only be +

5°C. Combined with a 25°C ambient, this is only

30°C total package temperature.

During a short circuit condition, the device now

has 3.3V across it and the hold current clamps at

1.55A and therefore must dissipate 5W. At

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

rise above the thermal protection threshold

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

the temperature to drop.

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 909mA at + 25°C

and below 545mA at +85°C to prevent the device

from activating the thermal shutdown feature.

RISE TIME

The rise time is a function of the capacitor

(Cdv/dt) on the dv/dt pin.

Table 2—Rise Time vs. Cdv/dt

Cdv/dt

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.

U

90%

10%

Rise Time

t

Input

Output

Enable

Figure 2—Rise Time

FAULT AND ENABLE PIN

The Enable/Fault Pin is a Bi-Directional I/O with a

weak pull up current (25uA typical). It functions to

enable/disable the part.

Enable pin as an input:

1. Low disables the part.

2. High enables the part.

Enable 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 pin.

3. A thermal fault will cause a low level on

the enable pin.