Method 1: block diode connected with V_BB. 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 7-20 Reverse Protection With Block 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 itself. Note 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 it is important that the FET comes 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, ensure the following proper connections for the normal operation:

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

Figure 7-21 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 HSD or the diode. So, TI recommends a resistor in parallel with the diode when driving an inductive load. The recommended selection are a 1-kΩ resistor in parallel with an I_F > 100-mA diode. If multiple high-side switches are used, the resistor and diode can be shared among devices.

  If multiple high-side power switches are used, the resistor can be shared among devices.

• Ground Resistor: The higher resistor value contributes to a better current limit effect when the reverse battery or negative ISO pulses.
  Equation 11.

  where

  • –V_CC is the maximum reverse battery voltage (typically –16 V).
  • –I_GND is the maximum reverse current the ground pin can withstand, which is available in the Absolute Maximum Ratings.
• Ground Diode: A diode is needed to block the reverse voltage, which also brings a ground shift (≈ 600 mV). Additionally, the diode must be ≈ 200-V reverse voltage for the ISO 7637 pulse 1 testing so that it does not get biased.