HI There,
Quick question. If someone is using the LM74502-Q1 as a surge stopper in Section 10.3 (Figure 10-11) of the datasheet, and the VS is clamped at 60V through the Dz and R1, is there still a requirement to have a negative clamping TVS (along with blocking diode) on Vbatt input supply as shown in Figure 10-2?
This is to clamp transients that go below -65V...
Thanks for the sanity check...
Hi,
Yes, you would still need TVS at the input to protect the LM74502-Q1 from negative transients like ISO 7637-2 Pulse 1 which can go as low as -150V.
When ISO 7637-2 Pulse 1 (reverse voltage) is applied at the input, the zener diode Dz will not be able to withstand 150V across it so you need to clamp the voltage at input of LM74502-Q1 to within -60V.
Since you cannot use a single unidirectional TVS at the input ( as it will forward bias and conduct for positive voltage at the input), you will need to add a diode in series connected in reverse orientation as shown below.
