9.2.1.2.4 Oscillator

The built in oscillator frequency can be trimmed by an external resistor from the FREQ_ADJ pin to GND. Changes in the oscillator frequency should be made with resistor values specified in Recommended Operating Conditions while RESET is low.

To reduce interference problems while using a radio receiver tuned within the AM band, the switching frequency can be changed from nominal to lower or higher values. These values should be chosen such that the nominal and the alternate switching frequencies together result in the fewest cases of interference throughout the AM band. The oscillator frequency can be selected by the value of the FREQ_ADJ resistor connected to GND in master mode.

For slave mode operation, turn off the oscillator by pulling the FREQ_ADJ pin to DVDD. This configures the OSC_I/O pins as inputs to be slaved from an external differential clock. In a master/slave system inter-channel delay is automatically set up between the switching of the audio channels, which can be illustrated by no idle channels switching at the same time. This will not influence the audio output, but only the switch timing to minimize noise coupling between audio channels through the power supply. Inter-channel delay is needed to optimize audio performance and to get better operating conditions for the power supply. The inter-channel delay will be set up for a slave device depending on the polarity of the OSC_I/O connection as follows:

• Slave 1 mode has normal polarity (master + to slave + and master - to slave -)
• Slave 2 mode has reverse polarity (master + to slave - and master - to slave +)

The interchannel delay for interleaved channel idle switching is given in the table below for the master/slave and output configuration modes in degrees relative to the PWM frame.