When the MC121-Q1 does not detect a Hall transition for longer than the locked rotor detection time (t_LRD), a locked rotor fault is recognized, all FETs are disabled (Hi-Z) and the FG/RD pin indicates the locked rotor fault according to Table 6-4. t_LRD is set by t_{LRD_START} during start-up sequence, while t_LRD is set by t_{LRD_RUN} during motor run (steady state). The locked rotor retry sequence (when LRD_RETRY_DIS = 0x0) during start-up is as shown in Figure 6-22. During the first start-up after power-up/wake-up, the number of quick retry attempts is set by LRD_NRETRY_STARTUP; the quick retry time is same as the locked rotor detection time (t_{LRD_START}). If the locked rotor condition persists after LRD_NRETRY_START attempts are completed, MC121-Q1 enters a long retry time (t_{lock_long_retry}) which is (LRD_LONG_RETRY_SEL x t_{LRD_START}). Once the long retry time lapses, MC121-Q1 attempts to spin the motor again; on the second start-up attempt after power-up/wake-up, the number of quick retry attempts is set by LRD_NRETRY_RUN while the locked rotor detection time (t_{LRD_START}) and quick retry time remain the same. If the locked rotor condition persists after LRD_NRETRY_RUN attempts are completed, MC121-Q1 enters a long retry time (t_{lock_long_retry}) again. Subsequent motor start-up sequences uses the same retry pattern as the second start-up cycle as shown in Figure 6-22. Every motor start-up attempt after retry time lapse (quick or long retry) is initiated from the pre-start phase as shown in Figure 6-6.

Figure 6-22 Locked rotor retry sequence and timing during start-up when LRD_RETRY_DIS = 0x0

When a locked rotor condition is detected during motor run (no Hall transition for t_{LRD_RUN}), all FETs are in disabled (Hi-Z) and the FG/RD pin indicates the locked rotor fault according to Table 6-4. MC121-Q1 waits for one interval of long retry time before starting the locked rotor retry sequence as shown in Figure 6-23.

Figure 6-23 Locked rotor retry sequence and timing during run when LRD_RETRY_DIS = 0x0

MC121-Q1 provides the option of latching a locked rotor fault after 5 consecutive start attempts result in a locked rotor by setting LRD_RETRY_DIS = 0x1 as shown in Figure 6-24. Motor operation can resumed either by a power reset or wake-up (sleep exit).

Figure 6-24 Locked rotor retry sequence and timing when LRD_RETRY_DIS = 0x1