During closed loop operation, the driving speed (FG output frequency) and the actual motor speed are synchronized. During open-loop operation, however, FG may not reflect the actual motor speed. During motor-lock condition, the FG output is driven high.

The MCT8316A provides three options for controlling the FG output during open loop, as shown in Figure 8-46. The selection of these options is configured through FG_SEL.

If FG_SEL is set to,

• 00b: When in open loop, the FG output is based on the driving frequency.
• 01b: When in open loop, the FG output will be driven high.
• 10b: The FG output will reflect the driving frequency during open loop operation in the first motor start-up cycle after power-on, sleep/standby; FG will be held high during open loop operation in subsequent start-up cycles.

Figure 8-46 FG Behavior During Open Loop