ZHCSHB1B January 2018 – August 2018 TPA3220
PRODUCTION DATA.
The TPA3220 input stage is a fully differential input stage and the input impedance changes with the gain setting from 7.7 kΩ at 34 dB gain to 47 kΩ at 18 dB gain. Table 1 lists the values from min to max gain. The tolerance of the input resistor value is ±20 % so the minimum value will be higher than 6.2 kΩ. The inputs need to be AC-coupled to minimize the output DC-offset and ensure correct ramping of the output voltages during power-ON and power-OFF. The input ac-coupling capacitor together with the input impedance forms a high-pass filter with the following cut-off frequency:
If a flat bass response is required down to 20 Hz the recommended cut-off frequency is a tenth of that, 2 Hz. Table 3 lists the recommended ac-couplings capacitors for each gain step. If a -3 dB is accepted at 20 Hz 10 times lower capacitors can used – for example, a 1 μF can be used.
| Gain | Input Impedance | Input AC-Coupling Capacitance | Input High Pass Filter |
|---|---|---|---|
| 18 dB | 48 kΩ | 4.7 µF | 0.7 Hz |
| 24 dB | 24 kΩ | 10 µF | 0.7 Hz |
| 30 dB | 12 kΩ | 10 µF | 1.3 Hz |
| 34 dB | 7.7 kΩ | 10 µF | 2.1 Hz |
The input capacitors used should be a type with low leakage, like quality electrolytic, tantalum, film or ceramic. If a polarized type is used the positive connection should face such that the capacitor has a positive DC bias.