TPS65381-Q1 Power down by CANWU event

Hi Shimizu-san,

A1)  The WR_CAN_STBY will start to execute in the device when the nCS is released on the SPI frame where the WR_CAN_STBY command is sent.  It will normally take several internal device clock cycles to latch and then the device will pull the NRES for MCU RESET and start powering down the device to standby state.  The device needs at least 5ms to power down as outlined in figure 5-1, on page 32 (revision E) of the datasheet.   Below is the VDD6 ramp down section from the larger diagram.  There will be additional ramp down time depending on the specific application output capacitance and load during ramp down.

So the application should wait until the device has fully powered down before having CANWU go high again. 

A2) If CANWU goes high again while or just after WR_CAN_STBY command is written there is a risk the TPS65381 will not go through its power on reset state.  Since the device will not be fully powered down and will receive the new CANWU HIGH it will latch the CANWU HIGH into the CANWU_L and restart the device without finishing the power down and thus possibly may not go through the device RESET state. This means the TPS65381 registers may not be initialized like going through POR from STANDBY state so the registers normally initialized by POR will not be re-initialized. The external NRES will be pulled low so the MCU will have been reset. The MCU should re-initialize all registers at start up each time (Write, followed by read to confirm proper settings). 

Scott

Hi Shimizu-san,

Q1:  the TPS65381 registers may not be initialized like going through POR from STANDBY state so the registers normally initialized by POR will not be re-initialized.
->  Does "the registers" mean register which can is set user or not?

A1: Sorry should have been will not power down to STANDBY state and then pass though RESET state.  The registers means, registers that should get reset by going through the RESET state, one example is the WD_FAIL_CNT should get reset to 5 when going through RESET, but it may not as that step might be bypassed. 

Q2:  If CANWU goes high again while or just after WR_CAN_STBY command is written there is a risk the TPS65381 will not go through its power on reset state.
->  I think this mean is TPS65381 can not be out standby state as long as TPS65381 doesn't reset in this situation.
Is it correct?    If it is correct, I think this must be wrote datasheet.

A2:  Sorry should have been POR it may not go through Standby to RESET.  It may skip those and thus the RESET state may be bypassed not POR. 

Scott