ZHCSF68D May 2015 – July 2019 DRV8305-Q1
PRODUCTION DATA.
When the motor shaft of BLDC or PMSM motor is turned by an external force, the motor windings will generate a voltage on the motor inputs. This condition is known as generator mode or motor back-drive. In the generator mode, a positive voltage can be observed on SHx pins of the device. If there is a switch between VDRAIN and PVDD (SWVDRAIN in Figure 24 ), and the following conditions exist in the system, the absolute maximum voltage of VCPH with respect to PVDD must be reviewed:
If SHx voltage (VSHx) exceeds the VCPH voltage, the VCPH voltage starts following VSHx because of the device internal diodes D1 and D2 (or D3). If the VCPH-PVDD voltage exceeds the absolute maximum voltage of DRV8305-Q1, the ESD diode D4 starts conducting, and results in a big current from SHx to PVDD through the diodes D2, D1, and D4. To avoid this condition, TI recommends to add an external diode DVDRAIN_PVDD between VDRAIN and PVDD.