Digital To Analogue Converter Characteristics

Archibald
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Joined: Mon Mar 05, 2018 12:44 am

Digital To Analogue Converter Characteristics

Postby Archibald » Thu Mar 22, 2018 1:54 am

There seems to be very little information on the drive capability of a digital to analogue converter (DAC). I have found that they are good at sourcing current into a resistance connected to ground but are very poor at sinking current from a resistor connected to Vcc.

I measured a DAC with open circuit (except digital multimeter) and with a 220Ω resistor to ground. There was good linearity. The minimum output voltage was 0.05V and the maximum 3.16V (Vcc measured as being 3.28V), so not quite full swing from ground to Vcc.

The small drop in output voltage with the resistor connected indicated an output resistance of about 20Ω. However at higher output voltages there appeared to be a current limit of 12.7mA. This is shown in the graph below. Measurements were made at intervals of 16 (decimal), the red line being with the resistive load . . . .
220ohms.png
220ohms.png (42.98 KiB) Viewed 6385 times
I used a much higher value of resistor to assess the ability of the DAC output to sink current: 22kΩ. Even with this relatively very high resistance, performance was very poor. The red line is with the resistor connected . . . . .
22kohms.png
22kohms.png (31.11 KiB) Viewed 6385 times

mlibby
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Re: Digital To Analogue Converter Characteristics

Postby mlibby » Wed Apr 18, 2018 2:31 pm

Hello, does any one know what is the DAC maximum output value? And for ADC what is the maximum input value?
I do not see those in the datasheets.
This is for ESP-WROOM-32 and ESP-WROOM-32U

Thank you
Best regards

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ESP_krzychb
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Re: Digital To Analogue Converter Characteristics

Postby ESP_krzychb » Wed Apr 18, 2018 3:18 pm

Hello mlibby,
mlibby wrote:Hello, does any one know what is the DAC maximum output value?
http://esp-idf.readthedocs.io/en/latest ... _t7uint8_t
mlibby wrote:And for ADC what is the maximum input value?
http://esp-idf.readthedocs.io/en/latest ... dc_atten_t

Archibald
Posts: 110
Joined: Mon Mar 05, 2018 12:44 am

Re: Digital To Analogue Converter Characteristics

Postby Archibald » Wed Apr 18, 2018 4:16 pm

mlibby wrote:Hello, does any one know what is the DAC maximum output value?
The maximum DAC output value on the graph in my original post was 3.16V with VDD=3.28V. So the maximum output value is not VDD as stated in the Espressif guide. The minimum value was 0.05V.

mlibby
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Joined: Wed Apr 04, 2018 6:39 pm

Re: Digital To Analogue Converter Characteristics

Postby mlibby » Thu Apr 19, 2018 2:06 pm

Thank you so much.
Best regards

Marc Boon
Posts: 2
Joined: Sat Aug 07, 2021 7:07 pm

Re: Digital To Analogue Converter Characteristics

Postby Marc Boon » Sat Aug 07, 2021 7:21 pm

I came across the same problem with a ESP32-S2-WROVER, mounted on the ESP32-S2-Saola-1 development module. I guess the DAC is the same as in the original ESP32. Using a 10K load to GND gives a linear response, no curvature at the high end with the 220 ohm load as pictured above. So, if you need to sink current, or source more than a few mA, an output buffer would be necessary.

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