The first stage is to utilize the built-in loopback mode to determine the reference value for the phase measurement. This reference will nullify any phase offset in the device and measure only the phase of the load. This is measured for channels 1 and 3 only. Channel 2 will use the results of channel 1 for the calculations. Channel 4 will use the results of channel 3 for the calculations. Measure channel 1 and channel 3 sequentially, they cannot be measured at the same time.
For loopback delay detection, use the following test procedure:
BTL Mode
- Set the AC_DIAGS_LOOPBACK bit (bit 7 in register 0x16) to 1 to enable loopback mode
- Set the appropriate test frequency in register 0x2A, the default is set for 18.75kHz
- For channel 1 set bit 3 in register 0x15 to 1. For channel 3 set bit 1 in register 0x15 to 1
- Read back the hexadecimal, AC_LDG_PHASE1 value. Register 0x1B holds the MSB and register 0x1C holds the LSB
- For channel 1 set bit 3 in register 0x15 to 0. For channel 3 set bit 1 in register 0x15 to 0
PBTL Mode
- Set the AC_DIAGS_LOOPBACK bit (bit 7 in register 0x16) to 1 to enable AC loopback mode
- Set the PBTL CH12 and PBTL CH34 bits (bits 5 and 4 in register 0x00) to 0. This must be performed while the device is in the STANDBY state to enter BTL mode only for load diagnostics
- Set the appropriate test frequency in register 0x2A, the default is set for 18.75kHz
- For channel 1 set bit 3 in register 0x15 to 1. For channel 3 set bit 1 in register 0x15 to 1
- Read back the hexadecimal, AC_LDG_PHASE1 value. Register 0x1B hold the MSB and register 0x1C holds the LSB
- Set the PBTL CH12 and PBTL CH34 bits (bits 5 and 4 in register 0x00) to 1 to go back to PBTL mode for load diagnostics
- For channel 1 set bit 3 in register 0x15 to 0. For channel 3 set bit 1 in register 0x15 to 0
When the test is complete, the channel reporting register (0x0F) indicates the status change from the AC diagnostic mode to the Hi-Z state. The detected reference phase is stored in the appropriate I2C register when the device transitions to the Hi-Z state.