Method 1: Blocking diode connected with V_S. Both the device and load are protected when in reverse polarity. The blocking diode does not allow any of the current to flow during reverse battery condition.

Figure 8-12 Reverse Protection With Blocking Diode

Method 2 (GND network protection): Only the high-side device is protected under this connection. The load reverse current is limited by the impedance of the load. When reverse polarity happens, the continuous reverse current through the power FET must not make the heat build up be greater than the absolute maximum junction temperature. This can be calculated using the R_ON(REV) value and the R_θJA specification. In the reverse battery condition, the FET must turn on to lower the power dissipation. This action is achieved through the path from EN to system ground where the positive voltage is being applied. No matter what types of connection are between the device GND and the board GND, if a GND voltage shift happens, verify that the following proper connections for the normal operation:

• Connect the current limit programmable resistor to the device GND.

Figure 8-13 Reverse Protection With GND Network

• Recommendation – resistor and diode in parallel: A peak negative spike can occur when the inductive load is switching off, which can damage the HSS or the diode. So, TI recommends a resistor in parallel with the diode when driving an inductive load. The recommended selection are a 1kΩ resistor in parallel with an I_F > 100mA diode. If multiple high-side switches are used, the resistor and diode can be shared among devices. In this case, combined I_GND of multiple high-side switches needs to be considered while determining the ground resistor and ground diode.
• Ground Resistor: The higher resistor value contributes to a better current limit effect when the reverse battery or negative ISO pulses.
  Equation 9. ${\mathrm{R}}_{\mathrm{G}\mathrm{N}\mathrm{D}}\ge \frac{\left(-{\mathrm{V}}_{\mathrm{C}\mathrm{C}}\right)}{\left(-{\mathrm{I}}_{\mathrm{G}\mathrm{N}\mathrm{D}}\right)}$

  where

  • –V_CC is the maximum reverse battery voltage (can come from ISO 7637 pulse 1 and 3a testing).
  • –I_GND is the maximum reverse current the ground pin can withstand, which is available in Section 6.1.
• Ground Diode: A diode is needed to block the reverse voltage, which also brings a ground shift (≅600mV). Additionally, the diode must be ≅300V reverse voltage for the ISO 7637 pulse 1 and 3a testing so that the diode does not get biased.