AFE031: Inductor on PA output pin, and Pin 13 questions

Hello Brian,

Errol, our AFE applications specialist, is currently on travel. I will do my best to address your questions.

The schematic shows a 1uH inductor (L1) connected to PA output pins.  What is that for? 

The 1 uH inductor is part of the PA electrical over-stress protection circuitry, along with D1, D2, D3 and possibly C16. This circuitry is in place to protect the AFE031 power amplifier stage from high-voltage impulses that could be coupled into it from the line coupling circuit. The line coupling circuit connects directly to the powerline where HV transients, and lightning induced spikes can occur and travel into the AFE031 circuits if not prevented. 

This inductor carries the PA output current and must be selected to handle up to 1.5 amperes, without saturating. Should saturation occur it may not provide the  performance necessary to protect the PA from an electrical over-stress event.

If we use the SPI interface and your internal DAC, what should I do with Pin 13.  Ok to leave it not connected to anything?

Figure 49 shows a Typical Powerline Communications Modem Application. In that application circuit pin 13, the Tx_PGA_IN Transmit PGA input, is left  unconnected. This pin is intended as an alternate input where an external source such as a DAC can be applied. However, because the internal switch is set to connect the internal DAC output to the TX_PGA_IN input pin 13 can be left disconnected.  

Regards, Thomas

Precision Amplifiers Applications Engineering