The gain of TPA3221 is set by the voltage divider connected to the GAIN/SLV control pin. Controller or Peripheral mode is also controlled by the same pin. An internal ADC is used to detect the 8 input states. The first four stages sets the GAIN in Controller mode in gains of 18, 24, 30, 34dB respectively, while the next four stages sets the GAIN in Peripheral mode in gains of 18, 24, 30, 34dB respectively. The gain setting is latched when RESET goes high and cannot be changed while RESET is high. Table 8-1 shows the recommended resistor values, the state and gain:

Figure 8-6 Gain and Controller / Peripheral Setup

For easy multi-channel system design TPA3221 has a Controller / Peripheral feature that allows automatic synchronization of multiple peripheral devices operated at the PWM switching frequency of a controller device. This benefits system noise performance by eliminating spurious crosstalk sum and difference tones due to unsynchronized channel-to-channel switching frequencies. Furthermore the Controller / Peripheral scheme is designed to interleave switching of the individual channels in a multi-channel system such that the power supply current ripple frequency is moved to a higher frequency which reduces the RMS ripple current in the power supply bulk capacitors.

The Controller / Peripheral scheme and the interleaving of the output stage switching is automatically configured by connecting the OSCx pins between a controller and multiple peripheral devices. Connect the OSCx pins in either positive or negative polarity to configure either a Peripheral1 or Peripheral2 device. Connect the OSCM of the Controller device to the OSCM of a peripheral device to configure for Peripheral1 or OSCP to configure for Peripheral2. Then connect the remaining OSCx pins between the controller and peripheral devices. The Controller, Peripheral1 and Peripheral2 PWM switching is be 30 degrees out of phase with each other. All switching channels are automatically synchronized by releasing RESET on all devices at the same time.

Figure 8-7 Gain and Controller PCB Implementation

Placement on the PCB and connection of multiple TPA3221 devices in a multi channel system is illustrated in Figure 8-7. Peripheral devices should be placed on either side of the controller device, with a Peripheral1 device on one side of the Controller device, and a Peripheral2 device on the other. In systems with more than 3 TPA3221 devices, the controller should be in the middle, and every second peripheral devices should be a Peripheral1 or Peripheral 2 as illustrated in Figure 8-7. A 47kΩ pull up resistor to AVDD should be connected to the controller device OSCM output and a 47kΩ pull down resistor to GND should be connected to the controller OSCP CLK outputs.