For load-impedance detection, use the
following test procedure:
- Set the channels to be tested into the Hi-Z state.
- Set the AC_DIAGS_LOOPBACK bit (bit 7 in register 0x16) to '0'.
- Apply a full-scale input signal from the DSP for the tested
channels with the desired frequency (recommended 10 kHz to 20 kHz).
Note:
The device ramps the signal up and down
automatically to prevent pops and clicks.
- Set the device into the AC diagnostic mode (set bit 3
through bit 0 as needed in register 0x15 to '1' for CH1 to CH4. For PBTL mode, test
channel 1 for PBTL12 and channel 3 for PBTL34)
- Read back the AC impedance (register 0x17 through register register 0x1A).
When the test
is complete the channel reporting register indicates the status change
from the AC diagnostic mode to the Hi-Z state. The detected impedance is
stored in the appropriate I2C register.
The hexadecimal register value must be converted to decimal and used to
calculate the impedance magnitude using
Equation 1.
Equation 1.