Analog Integrated Circuit Device Data

Freescale Semiconductor

13

34713

FUNCTIONAL DEVICE OPERATION

PROTECTION AND DIAGNOSTIC FEATURES

PROTECTION AND DIAGNOSTIC FEATURES

The 34713 monitors the application for several fault

conditions to protect the load from overstress. The reaction of

the IC to these faults ranges from turning off the outputs to

just alerting the host that something is wrong. In the following

paragraphs, each fault condition is explained:

Output Overvoltage

An overvoltage condition occurs once the output voltage

this case, the power good output signal is pulled high, alerting

the host that a fault is present, but the output will stay active.

To avoid erroneous overvoltage conditions, a 20 µs filter is

implemented. The buck converter will use its feedback loop

to attempt to correct the fault. Once the output voltage falls

cleared and the power good output signal is pulled low, the

device is back in normal operation.

Output Undervoltage

An undervoltage condition occurs once the output voltage

case, the power good output signal is pulled high, alerting the

host that a fault is present, but the output will stay active. To

avoid erroneous undervoltage conditions, a 20 µs filter is

implemented. The buck converter will use its feedback loop

to attempt to correct the fault. Once the output voltage rises

cleared and the power good output signal is pulled low, the

device is back in normal operation.

Output Over Current

This block detects over current in the Power MOSFETs of

the buck converter. It is comprised of a sense MOSFET and

a comparator. The sense MOSFET acts as a current

detecting device by sampling a ratio of the load current. That

sample is compared via the comparator with an internal

reference to determine if the output is in over current or not.

If the peak current in the output inductor reaches the over

operation to limit the current, and a 10 ms over current limit

operation until one of the following occurs:

• The current is reduced back to the normal level before

regained.

which point the device turns off the output and the

power good output signal is pulled high. At the end of a

attempt another soft start cycle.

and turns off the output. The power good output signal

is pulled high.

• The output current keeps increasing until it reaches the

details.

Short Circuit Current Limit

This block uses the same current detection mechanism as

the over current limit detection block. If the load current

the output immediately. This is necessary to prevent damage

in case of a permanent short circuit. Then, at the end of a

another soft start cycle.

Thermal Shutdown

Thermal limit detection block monitors the temperature of

the device and protects against excessive heating. If the

temperature reaches the thermal shutdown threshold

good output signal indicates a fault by pulling high. The

device will stay in this state until the temperature has

decreased by the hysteresis value and then After a time-out

automatically and the output will go through a soft start cycle.

If successful normal operation is regained, the power good

output signal is asserted low to indicate that.