MP5003 – 3.3V, 1A-3A PROGRAMMABLE CURRENT LIMIT SWITCH WITH AUTO ENABLE
MP5003 Rev. 0.921 www.MonolithicPower.com 11
2/29/2012 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
THERMAL PROTECTION
The MP5003 only considers a thermal overload
to be a fault. Under a fault condition the MP5003
will have two actions:
1) Turn off the output power device.
2) Drive the enable/fault pin to the low level.
The power device will remain off until the die
temperature drops below the hysteresis level.
When the die cools down below the thermal
hysteresis level, the MP5003 will restart in the
start up mode and the fault line will be pulled high
through a 25uA pull up current. If the cause of
the fault has been removed, the output will ramp
up in a controlled fashion with the ramp rate
controlled by the dv/dt function. If the cause of
the fault is still present, the excess power
dissipation will heat up the part. When the die
temperature reaches the thermal shutdown
temperature, the output will be turned off and the
enable/fault pin will be driven to the low level.
This cycle will repeat until the cause of the fault is
removed.
Output Voltage
UVLO Threshold
Input Voltage
Output Short (Cause of Fault)
Die Temperature
Thermal Shutdown Temp
Thermal Hysteresis
Fault/Enable Pin
Output Current
Normal operating current
Current Limit
T0
T1
T4
T2
T3
T5
T6
T7
Figure 3Thermal Protection in Short Condition
The drawing above shows the initial start up
sequence and the occurrence of a short at the
output.
At time T0 the input voltage begins to rise. At T1
the input voltage rises above the UVLO threshold
and the part starts up. The output current ramps
up and settles in at the normal operating current
level until time T2. There is a very small
temperature heating of the die in normal
operation.
At time T2 the output is shorted. This brings the
output very close to ground. The output current
increases to the current limit level and is held
there by the MP5003. Because of the large
current and the large voltage across the power
device, the die will begin to heat up.
At time T3 the die temperature is at the thermal
shutdown level and the part will turn the power
device off. The enable/fault pin is driven to the
low level. Once the power device is off, the die
temperature will begin to drop.
