STM32F4: Can DAC_OUT w/o Buffer direct drive a Speaker without getting damaged?

[Miro Mico]

Posted on June 29, 2017 at 14:30

I try to make some noise using a small 8 OHm @ 1 kHz Buzzer connected to the STM32F446 DAC_OUT1. Seams the PA4 pin got damaged due to high or reverse voltage induced by the buzzer. I used th push/pull GPIO config. Is it possible to directly drive this buzzer without an external PA IC maybe by enabling the internal DAC-Buffer? Or is it required to drive the buzzer via an PA? Or would the IO cell get damaged due to high or reverse voltage induced by the speakers large inductance?

[S.Ma]

Posted on June 29, 2017 at 14:52

The buffer won't give enough energy to directly drive a speaker, you'll need an external audio booster.

A digital GPIO with square waves might be able to drive some piezo with low volume. At 3V x 5mA = 15mW DC

[AvaTar]

Posted on June 29, 2017 at 15:12

Is it possible to directly drive this buzzer without an external PA IC maybe by enabling the internal DAC-Buffer?

Only if you find a buzzer with 15k Ohm impedance...

[Miro Mico]

Posted on June 29, 2017 at 16:52

But isn't it dangerous to connect such a large coil directly to the processors pin? I suspect the pin could be damaged through induced high or reverse voltage. Am I wrong?

[AvaTar]

Posted on June 29, 2017 at 17:43

Piezo buzzer usually have no coils, AFAIK.

But first find one with 15k impedance ...

What I meant to say - in practical terms, you cannot connect a speaker/buzzer to ST's DAC (and get useful output).

The power output would be less than 1 milliWatt ...