Typical 24-V battery protection application circuit shown in Figure 10-2 uses two uni-directional TVS diodes to protect from positive and negative transient voltages.

The breakdown voltage of the TVS+ must be higher than 48-V jump start voltage, less than the absolute maximum ratings of source and enable pin of LM74502-Q1 (65 V) and must withstand 65-V suppressed load dump. The breakdown voltage of TVS– must be lower than maximum reverse battery voltage –32 V, so that the TVS– is not damaged due to long time exposure to reverse connected battery.

During ISO 7637-2 pulse 1, the input voltage goes up to –600 V with a generator impedance of 50 Ω. Single bi-directional TVS cannot be used for 24-V battery protection because breakdown voltage for TVS+ ≥ 48 V, maximum negative clamping voltage is ≤ –65 V . Two uni-directional TVS connected back-to-back must be used at the input. For positive side TVS+, TI recommends SMBJ58A with the breakdown voltage of 64.4 V (minimum), 67.8 (typical). For the negative side TVS–, TI recommends SMBJ26A with breakdown voltage close to 32 V (to withstand maximum reverse battery voltage –32 V) and maximum clamping voltage of 42 V.

For 24-V battery protection, TI recommends a 75-V rated MOSFET to be used along with SMBJ26A and SMBJ58A connected back-to-back at the input.