So I'm looking into the stm32f469 series of chips (datasheet here), and see if I can play good audio with one with the build in DAC. To my knowledge, the built-in ones on chips usually aren't that great, but with 12 bits of resolution, I'd like to give it a shot. The problem comes in with if it can drive headphones or not:

Down on page 163/219, it says that with the built-in buffer (reportedly included to be able to drive loads) the minimum impedance is 5 kOhm, which seems extraordinarily high. I'd be using it with earbuds, and I've never seen cheap earbuds listed with any more than 50 ohms impedance. With the buffer disabled, it reports a maximum of 15 kOhm, but I'm worried that if it's meant to be in the kOhm range it might not handle earbuds too well.

Am I reading this completely wrong and it can drive a set of earbuds or will I be looking into an external audio chip?

  • \$\begingroup\$ Why not just add an external buffer? Much easier than an external audio chip/DAC as you say. \$\endgroup\$ – DSWG Oct 16 '18 at 3:07
  • \$\begingroup\$ Yes, you'll need a small power amplifier stage. \$\endgroup\$ – pjc50 Oct 16 '18 at 4:52
  • \$\begingroup\$ DAC is not intended to drive power outputs. It is very low power peripheral and you need an amplifier \$\endgroup\$ – P__J__ Oct 17 '18 at 19:14

The datasheet refers to the minimum impedance you can use at the output of the DAC. (Minimum Resistive Load with buffer On, page 163).

Which means, if the chip is powered at 3.3V and 5kOhm it can drive 0.66mA max.

This won't be enough for your earbuds, so you will need an external buffer.


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