I have two questions related to Fig. 21 in LM74700-Q1 datasheet.
1. The recommended TVS+ is SMBJ58A, with the breakdown voltage of 64.4-V (minimum), 67.8 (typical). It it were connected to the ground alone, it meets the requirements that "the breakdown voltage of the TVS+ should be higher than 48-V jump start voltage, less than the absolute maximum ratings of anode and enable pin of LM74700-Q1 (65 V) and should withstand 65-V suppressed load dump." However, there is a TVS- in series with the TVS+ and the TVS- has a forward voltage drop of 3.5-V or 5-V. Thus, the TVS+ will start to break down when the battery voltage at 64.4-V +3.5V, or 67.9-V. it seems to me that the recommendation shown in Fig. 21 won't protect LM74700-Q1 and other downstream devices. I am wondering whether it is an incorrect recommendation, and TVS+ should be changed to SMBJ52A?
2. In this design, The breakdown voltage of the TVS+ is recommended to be less than the maximum voltage of downstream devices such as LM74700-Q1. However, in page 2 of TI application report SLVA930 attached, it said, "For the most reliable operation, the maximum V_CLAMP of a TVS diode should be below the absolute maximum rating of the downstream device. Any condition violating the absolute maximum ratings results in a risk of damaging the component." I am wondering whether the breakdown voltage or the clamp voltage of a TVS should be below the absolute maximum rating of the downstream device.
Could you please answer the above two questions/comments?