Cyclone III and SA58631 mode pin

Programmable Devices

CPLDs, FPGAs, SoC FPGAs, Configuration, and Transceivers

Cyclone III and SA58631 mode pin

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a short background info:

the SA58631 is an audio amplifier from NXP. it has a mode pin with 3 states.

0 to 1.5V = on

1.5V to Vcc - 1.5V = mute

Vcc - 1.5V to Vcc, or pin left floating = off.

in my system the SA58631's Vcc = 7V and the FPGA Vio is 3.3V.

it made sense to me that I could control the chip using an IO at 0 (on) 1 (mute) and tri state (off).

I also added a 1K series resistor between the IO and the amp for buffering.

in realty, when I use the tri state option, the device is in mute. the amp mode pin is at 4.5V. I expected an internal weak pull up inside the amp to set Vcc on the pin.

could it be that there is some clamping diode on the IO?

any assignments I can use to fix that?

thanks in advance

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