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.