I am currently in the process of designing a PCB with a TPS274160A (the version without the current sense capability) and I have questions regarding the GND network and and the selection of an external TVS diode.
On page 24 of the datasheet, a GND network consisting of a diode in parallel with a resistor is recommended to protect the device against loss of power supply. On page 25, it is mentioned that the diode should have a current rating of >100 mA and the "forward voltage should be less than 0.6 V in any circumstances". I am having trouble determining the maximum current ("circumstances") under which the diode needs to have a voltage of <0.6V, since the mentioned >100 mA is not that precise. In the "Absolute maximum ratings", the current on the GND pin is specified to have a maximum value of -100 to 250 mA. Can I use a diode which has a voltage drop of max. 0.6V at 250 mA? For the reverse voltage rating, I suppose I have to use the maximum clamping voltage, which according to page 7 would be 70V. Is that assumption correct?
The evaluation module TPS274160EVM lists a BAS21-7-F in the BOM, but when I look at the datasheet of this diode, the forward voltage is way higher even at lower currents than the 0.6 V which is recommended. Could you please elaborate a bit more on a proper selection of the diode?
Regarding the resistor which is placed in parallel to the diode, which power dissipation should be expected? The EVM uses a .125W resistor in 0805 package, but would it be possible to use a lower power 0603 resistor?
For additional protection against loss of power supply, I would like to add an additional TVS diode on the outputs of the device. To make sure the external TVS diode only conducts when a loss of power supply occurs, I want to increase its clamping voltage above the internal clamp of the IC. But since I still need to be below the maximum V_DS voltage the MOSFET can endure, I need this value to select a proper diode. Could you provide me this information, since I could not find it in the datasheet? Or would you recommend against an external TVS if a GND network is implemented?
Thanks in advance.