ZHCS229C September 2011 – January 2020 BQ24725A
PRODUCTION DATA.
Q6, R12 and R13 in Figure 18 gives system and IC protection from reversed adapter voltage. In normal operation, Q6 is turned off by negative Vgs. When adapter voltage is reversed, Q6 Vgs is positive. As a result, Q6 turns on to short gate and source of Q2 so that Q2 is off. Q2 body diode blocks negative voltage to system. However, CMSRC and ACDRV pins need R10 and R11 to limit the current due to the ESD diode of these pins when turned on. Q6 must has low Vgs threshold voltage and low Qgs gate charge so it turns on before Q2 turns on. R10 and R11 must have enough power rating for the power dissipation when the ESD diode is on. In Figure 26, the Schottky diode D3 gives the reverse adapter voltage protection, no extra small MOSFET and resistors are needed.
In Figure 26, the Schottky diode Din is used for the reverse adapter voltage protection.