9.3.6 DC Detect

The TPA3137D2 device has circuitry which will protect the speakers from DC current which might occur due to defective capacitors on the input or shorts on the printed circuit board at the inputs. A DC detect fault will be reported on the FAULT pin as a low state. The DC Detect fault will also cause the amplifier to shutdown by changing the state of the outputs to Hi-Z.

A DC Detect Fault is issued when the output differential duty-cycle of either channel exceeds 14% (for example, +57%, –43%) for more than 950 msec at the same polarity. This feature protects the speaker from large DC currents or AC currents less than 2 Hz. To avoid nuisance faults due to the DC detect circuit, hold the SD pin low at power-up until the signals at the inputs are stable. Also, take care to match the impedance seen at the positive and negative inputs to avoid nuisance DC detect faults.

The minimum differential input voltage required to trigger the DC detect is 130 mV. The inputs must remain at or above the voltage listed in the table for more than 950 msec to trigger the DC detect.