CSD18509Q5B: CSD18509Q5B Body diode specification

Hi James,
Thanks for your promoting TI FETs at your customer. The current ratings for the body diode are the same as the drain-source ratings of the FET since they are physically the same current path thru the device. However, please note that the forward voltage drop of the body diode is usually much greater than the IDS x rds(on) and the power dissipated (IDS x VF) will be much higher for the same drain-source current. Ultimately, it is the thermal limitation of the package. The datasheet specs 3.1W dissipation for 40degC/W typical thermal impedance which gives a 124degC rise above ambient (25degC) for TJ ~ 150degC. Using the typical VF = 0.8V, the continuous forward current = 3.1W/0.8V = 3.88A @ Tamb = 25degC. This would need to be derated at elevated ambient temperature and the customer will also want to derate TJmax to a value < 150degC for reliability.

Similarly, the maximum forward surge or pulsed current is specified the same as the FET. Again, they will have to keep the TJ < TJmax (150degC). The customer can use the transient thermal impedance curve in the datasheet to determine the peak current for a given pulse width to keep TJ < TJmax.

Please note, this is NOT an automotive qualified part. TI does not make any automotive qualified FETs.

Hi James,
We don't include the first 2 parameters in the datasheet but I can give you an estimate using the maximum continuous power dissipation (195W) @ TC = 25degC from page 1 and max VF (1V) from the Electrical Characteristics on page 3. The maximum continuous diode forward current: IS = 195W/1V = 195A. For the pulsed current, we use the transient thermal impedance for 1% duty cycle and 10ms pulse to estimate the power dissipation of the device @ TC = 25degC as follows: (150degC - 25degC)/(0.53 x 0.8W/degC) = 294W. Then: ISpulse = 294W/1V = 294A.