TPS65381 Hot to Assert NRES Low (189)

Toshio-san,

This post has been assigned to an applications engineer. Due to the holidays you may see a delay in response. Thank you for your patience.

We are looking at and will answer by next week

There are 4 basic methods to force the NRES to be pulled and reset the TPS65381 via MCU actions.

Method 1:  WD Timer forced failure (reset device by WD reset when WD_RST_EN is set to ‘1’)

• In active or diagnostic mode with watchdog reset enabled (WD_RST_EN set) and just turn off the watchdog servicing routine of the MCU so the watchdog fail counter in TPS65381 will increment.  This will cause the watchdog fail counter to hit 7 and then the next bad event including a missing watchdog will reset the MCU by pulling NRES low (ie fail counter = 7 +1).

• To speed up the reset time, you could program the open and closed windows to a low time so the failures will accumulate faster or “speed-up” sending of WD triggers to increment the WD Failure Counter faster and force the reset event faster.

Method 2:  Device in ACTIVE state and MCU ERROR pin is monitored, force MCU ERROR pin failure

• Response time is fast and places device into SAFE state

• SAFE state to RESET state transition is controlled by SAFE_TO settings in SAFETY_ERR_CFG register

   

Method 3:  MCU with bi-directional RESET

• USE MCU application to create a ‘warm’ reset event that will drive NRES low

• TPS65381 will detect it as ‘NRES’ driver error and transitions to reset state

   

  Method 4:  If device was started by CAN_WU event

• Send MCU WR_CAN_STBY command

- Scott

Hello Scott-san,

Thank you for your answer.

I’m sorry my explanation might not be enough.

I set following registers as follows in DIAGNOSTIC mode.

   WD_RST_EN = 0

   IGN_PWRL = 0

   NO_SAFE_TO = 1 and SAFE_LOCK_THR = 0

And IGN and CANWU terminal are High in ACTIVE mode.

With above condition, I want to assert NRES low by some action from MCU.

Method 1: ( Use WD RST)

WD_RST_EN is set “0” in Diagnostic mode and can’t be change to “1” in Active mode so TPS65381 can’t generate Global Reset.

Method 2: (Use MCU ERROR)

MCU ERROR can cause state transition from ACTIVE to SAFE, but can’t transit from SAFE to RESET because NO_SAFE_TO = 1 and SAFE_LOCK_THR = 0 are set in Diagnostic state to stay in SAFE mode when transition to SAFE mode happened. (NO_SAFE_TO and SAFE_LOCK_THR can’t be written in Safe state.)

Method 3: (MCU with bi-directional RESET)

Driving NRES low from MCU can cause state transition from ACTIVE to SAFE, but can’t transit from SAFE to RESET by same reason with Method 2.

Method 4: (Send WR_CAN_STBY)

There is a case TPS65381 wake-up by IGN event so can’t use Method 4.

Could you please answer method to assert RESET again?

Best Regards.

Hi Ushikubo-san,

So you only have the option of issuing the reset with the constraints: 

I set following registers as follows in DIAGNOSTIC mode.

   WD_RST_EN = 0

   IGN_PWRL = 0

   NO_SAFE_TO = 1 and SAFE_LOCK_THR = 0

 And IGN and CANWU terminal are High in ACTIVE mode.

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The 4 methods I listed are the ones I know.  I will check with a few others to see if there are some other alternatives under the constraints given. 

- Scott

Hello Scott-san,

Thank you for your response.

Please find alternative method and let me known.

Best Regards.

Hi Ushikubo-san,

The only way we can figure to reset in this set of condition is to cycle the IGN.

Do you think this user case is a valid condition for a vehicle and driving cycle? 

- Scott

Hello Scott-san,

Thank you for your answer.

I understand that there are no method to issue reset with customer’s condition.

I will consult with customer.

Best Regards.