Looking for a 20 Bit DAC for Industrial Control

[Chris Smolinski]

I'm revising a circuit for a client, and am looking for a 20 bit D/A.
The present circuit uses the TI PCM1702, which is recently gone to "not
recommended for new design" status. The DAC is used to produce a control
voltage for a PWM circuit. It seems that most, if not all, of the 20+
bit DACs out there now are delta-sigma type. I've never used one of
these in such a circuit, they all seem to be for digital audio. I'm not
concerned about any DC errors, as the DAC is in a feedback loop and they
will be taken care of. I am concerned about noise in the DAC output
causing jitter in the PWM signal, though appropriate filtering should
take care of that. The DAC output only needs to update at about a 1kHz
rate.

That brings up the other problem - do these audio DACs need to be
updated at a 44.1 kHz rate? Or can they just be updated at an arbitrary
rate? Also, how critical is the clock used to drive the modulator? I'm
not likely to have the necessary clock on the board already, although I
could add it if necessary (I like to keep the number of clocks to an
absolute minimum).

Thanks for any insights.

 

[MK]

I'm revising a circuit for a client, and am looking for a 20 bit D/A.
The present circuit uses the TI PCM1702, which is recently gone to "not
recommended for new design" status. The DAC is used to produce a control
voltage for a PWM circuit. It seems that most, if not all, of the 20+
bit DACs out there now are delta-sigma type. I've never used one of
these in such a circuit, they all seem to be for digital audio. I'm not
concerned about any DC errors, as the DAC is in a feedback loop and they
will be taken care of. I am concerned about noise in the DAC output
causing jitter in the PWM signal, though appropriate filtering should
take care of that. The DAC output only needs to update at about a 1kHz
rate.

That brings up the other problem - do these audio DACs need to be
updated at a 44.1 kHz rate? Or can they just be updated at an arbitrary
rate? Also, how critical is the clock used to drive the modulator? I'm
not likely to have the necessary clock on the board already, although I
could add it if necessary (I like to keep the number of clocks to an
absolute minimum).

Thanks for any insights.

--

Hello Chris,

I have used DAC1220 (Burr Brown from TI) (a pair simulating a load cell in a
functional tester). No huge issues. They are sigma delta but not audio -
they quote settling time as 2mS so your 1kHz may be a little high.

Michael Kellett

www.mkesc.co.uk

 

[Chris Smolinski]

I have used DAC1220 (Burr Brown from TI) (a pair simulating a load cell in a
functional tester). No huge issues. They are sigma delta but not audio -
they quote settling time as 2mS so your 1kHz may be a little high.

Hi Michael,

Thanks for the info.

I see they quote a settling time of 10 msec for 20 bit mode, and 2 msec
for 16 bit mode. Have you found it to really be 2 msec for 20 bit mode?
I see the settling time is for large signal changes, most likely I will
be making small changes in normal operation.