MP5002 – 3.3V, 1A-3A PROGRAMMABLE CURRENT LIMIT SWITCH
MP5002 Rev. 0.93 www.MonolithicPower.com 9
10/15/2010 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 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
(V
IN
=3.3V)
Current Limit
Resistor (Ω)
13 24 50 100
Trip Current (A)
3.90 2.50 1.70 1.37
Hold Current (A)
2.99 1.55 0.74 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 be shutdown only if the
overcurrent condition stays long enough to
trigger thermal protection.
However, when the part is powered up by V
CC
or
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 24, 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 44m. 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
* Notes: Rise Time = K
RT
*(50pF+C
dv/dt
), K
RT
=22E6
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 three
level 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 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 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, and will clear the fault flag.
3. A thermal fault will cause a mid level on
the enable pin, and will set the fault flag.
The Enable/Fault line must be above the mid
level for the output to be turned on.
