DAC70501: Reference capacitive load

Hi Scott,

I will get the max capacitive load capability of the reference ouput from my design team.

Meanwhile, I was interested in the way you are planning to use the reference ouput with AD7052. Since AD7052 uses AVDD as reference for the device also, I believe other than load regulation, you need to look into the bandwidth of the reference drive. With 1MSPS, 14bit ADC, I dont think this can cope up with the dynamic requirements of the ADC as such.

So my suggestion will be to use some kind of op amp based buffer before driving ADC. I will try to get the bandwidth information of the reference ouput also if possible.

Regards,

AK

Hello AK,

Thanks for looking into this. An example reference in the ADS7052 data sheet (Figure 43) is the REF1933. Figure 32 in the REF1933 data sheet is the output impedance plot showing 1uF and 10uF loads. My interpretation of the plot is that the high frequency output impedance is determined solely by the cap. The REF1933 transient response is shown in Figures 21 and 23, where I estimate the closed loop bandwidth to be about 1 kHz. The 1 kHz bandwidth is also apparent in the output impedance plot where the impedance flattens out at about 20 ohms around 1kHz. The relatively slow response of the REF1933, coupled with the 3.3uF cap gives great performance as shown in the ADS7052 FFT plot (Figure 44). Therefore, my conclusion, based on the ADS7052 example circuit, is that the 3.3uF cap is what is key to the performance, and not the bandwidth of the reference.This is why I thought the DAC70501 reference would be acceptable.

Regards,

Scott

Hello Akhilesh,

Thanks for confirming that the max cap value is 10uF. Is there a minimum suggested cap on the reference? I could not find it in the data sheet.

Regards,

Scott