SLLSFE8B November 2024 – November 2025 TCAN2845-Q1 , TCAN2847-Q1
PRODUCTION DATA
Restart mode is a transitional mode. This mode can be entered from any of the other modes depending upon whether fail-safe mode is disabled. In this mode the enabled LDOs are ramping or are on. At initial power up, once VCC1 ≥ UVCC1R for tRSTN_act (approximately 2ms), the device transitions to standby mode. While in restart mode, nRST is latched low. When restart mode is entered, a restart timer is started. This timer can be selected between tRSTTO and tINACTIVE (SWE) timer time by programming register 8'h4F[0], RSTRT_TMR_SEL. The default is tRSTTO. If tINACTIVE (SWE) timer is selected, the SWE timer needs to be enabled be setting SWE_EN = 1b at SWE_TIMER register 8'h1C[7]. If the device has not exited restart mode prior to the timer timing out, the device transitions to fail-safe mode if enabled or sleep mode if fail-safe mode is disabled. Each time restart mode is entered from normal or standby modes, the restart mode counter, RSRT_CNTR, is incremented. The exception to this is if exceeding the restart counter caused the device to enter fail-safe or sleep mode. When re-entering restart mode due to this event, the counter is ignored and device enters standby mode. Once in standby mode, the counter must be cleared. This counter is programmable from register 8'h28[7:4], which sets the number of times restart can be entered before transitioning to sleep or fail-safe mode, up to 15 times. The default value is 4. Register 8'h16[3:0] is RSRT_CNTR. The counter can be disabled by programming the counter to 0000b. To prevent the transition to sleep or fail-safe mode, the counter must be cleared periodically.
The nRST output pin behavior depends upon the reason the device entered restart mode.
When entered due a watchdog failure, from fail-safe mode or an external nRST toggle, the nRST pin is pulled low for tNRST_TOG which defaults to 20ms. This pulse width can be configured to 2ms by changing register 8'h29[5] = 0. After this time, the device transitions to standby mode and release nRST pin to high. See Figure 8-25 on how restart mode is entered and exited after Watchdog failure.
When restart mode is entered from sleep mode or due to an under-voltage event, the device latches nRST low until VCC1 > UVCC1R for tRSTN_act, and then transitions to standby mode and release nRST high. See Figure 8-24 on how restart mode is entered and exited.
The nRST pin is also reset input pin of the TCAN284x-Q1 which transitions the device into restart mode when the pin is pulled low for tnRSTIN, see Figure 8-25