Topic: Avalon Overclocking Thread - Share Your Results and Tips for others - page 3. (Read 11007 times)

The range of short circuit current thresholds that can be expected is shown in Equation 2 and Equation 3.

I SCP(max)=V ILIM(max)/RDS(on)min

I SCP(min)=V ILIM(min)/RDS(on)max

where
•
•
•
ISCP is the short circuit current
VILIM is the short circuit threshold for the low-side MOSFET
RDS(on) is the channel resistance of the low-side MOSFET
(3)
Note that due to blanking time considerations, overcurrent threshold accuracy may fall off for duty cycle greater
than 75% with the TPS40192, or 88% with the TPS40193. The reason for this is that the over current comparator
will have only a very short time to sample the SW pin voltage under these conditions and may not have time to
respond to voltages very near the threshold.
The short circuit protection threshold for the high-side MOSFET is fixed at 550 mV typical, 400 mV minimum.
This threshold is in place to provide a maximum current output using pulse by pulse current limit in the case of a
fault. The pulse will be terminated when the voltage drop acros the high side FET exceeds the short circuit
threshold. The maximum amount of current that can be specified to be sourced from a converter is found by
Equation 4.

I OUT(max)=V ILIM(min)/RDS(on)max

where
•
•
•
IOUT(max) is the maximum current that the converter is specified to source
VILIMH(min) is the short circuit threshold for the high-side MOSFET (400 mV)
RDS(on)max is the maximum resistance of the high-side MOSFET
(4)
If the required current from the converter is greater than the calculated IOUT(max) , a lower resistance high-side
MOSFET must be chosen. Both the high side and low side thresholds use temperature compensation to
approximate the change in resistance for a typical power MOSFET. This will help couneract shifts in overcurrent
thresholds as temperature increases. For this to be effective, the MOSFETs and the device must be well coupled
thermally.