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

MP5003 Rev. 0.921

www.MonolithicPower.com

11

2/29/2012

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© 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 3―Thermal 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.