Precision DAC sample rate

Hi, 

DACs under the "precision" category normally don't have a sample rate directly provided in the datasheet. It can be computed using the settling time spec, but since the specification is focused on precision, you might get a not-so-high, out-of-the-box sampling rate. 

My suggestion is to look into our new Fast Precision DACs, AD3551R Datasheet and Product Info | Analog Devices works for 0to10V and could support upt o33MSPS update rate.

See this table for other available fast precision DACs.
Selection Table for Fast Precision D/A Converters | Parametric Search | Analog Devices

~ian

Hello,

I got your point. Is there any DAC available with lower Sample rate like 1 MSPS with 0-10 V?, as the above DAC sample rate is 33 MSPS , which is higher. 

Also, I require 8 simultaneous DAC channel with 0 -10 V . so I was looking for the precision DAC selection , as my sample rate requirement is not so high, it is 1 MSPS only.

Kindly suggest and guide as soon as possible

DId a quick search, you could check out the LTC2664 Datasheet and Product Info | Analog Devices. Has 50MHz Serial interface clock. and settling time of 4.5us with a 5V step at +/-1LSB accuracy. a smaller voltage transition should be enough for 1MSPS. 
The settling time would also greatly vary depending on the capacitance of your intended output load. So actual tests would guarantee best results. 

Hello,

Thank you for your quick response. 

So, I have gone through the LTC2664 datasheet and from your reply, below is my understanding.

That as per datasheet, SPI freq=50 MHz , input code word=24 bits , so , if we measure the update rate for SPI interfacing ,

update rate = 23* tsclk(0.02 uS) + Tcss(60 ns)+ Tcss(60 ns) + Tcsh(7 nS) + tcshigh(10 ns) = 0.594 uS , that means update rate = 1.68 MSPS 

and as settling time given =4.5 us is for higher voltage step( 0 to 5 V) , it will be different with smaller voltage transition. 

So, we can consider update rate?

Is there any application note from analog devices that you can suggest that can provide details and guidance on calculation of DAC sampling rate, selection of capacitance, settling time relation with load capacitance? 

So that , I can accurately measure and select the same based on 1 MSPS sampling rate requirement.

Further I dig other DAC as well and found suitable quad DAC AD5724R, which has SPI clock 30 MHz and settle time of 10uS for 0 to 10 V step. and when I measure update rate , I found it 1.1 MSPS. 

Please verify and guide. 

Thank you in advance.

Hi, 

At the moment, I couldn't find a specific app note for this. You want to have an output update rate of 1MSPS. This means you need 1us for the output to settle to 12bit accuracy. And you need to choose a DAC that can have an interface update rate that is much lower than 1us. so that you could take the time while the output is settling, to send another command for the next output value. The image below should support this

Dac output settling time is measured from the time when the digital command has finished sending to the time the output settles to the set value given a certain %band. 

Output capacitance would greatly affect this settling time. The datasheet settling time spec for LTC2664 is given for 100pF load. 

The settling time is also greatly dependent on the output amplifier used. On some devices, the output amplifier is integrated. But if you want a faster settling time at your given voltage step or load capacitance you could look at DACs with no output amplifier integrated. 

 I'd suggest is the AD5760 (Rev. F) (analog.com) in this case, has an output settling time of 2.5us at 10V step. Using the ADA4898-1 Datasheet and Product Info | Analog Devices amplifier. Again, with a lower step or 12-bit accuracy should be fine. 

Or the AD5791 (Rev. F) (analog.com), which has a 1us settling at 10V step using the  AD845 Precision, 16 MHz CBFET Op Amp Data Sheet (REV. E) (analog.com)

Best regards,

Ian

Hi, 

At the moment, I couldn't find a specific app note for this. You want to have an output update rate of 1MSPS. This means you need 1us for the output to settle to 12bit accuracy. And you need to choose a DAC that can have an interface update rate that is much lower than 1us. so that you could take the time while the output is settling, to send another command for the next output value. The image below should support this

Dac output settling time is measured from the time when the digital command has finished sending to the time the output settles to the set value given a certain %band. 

Output capacitance would greatly affect this settling time. The datasheet settling time spec for LTC2664 is given for 100pF load. 

The settling time is also greatly dependent on the output amplifier used. On some devices, the output amplifier is integrated. But if you want a faster settling time at your given voltage step or load capacitance you could look at DACs with no output amplifier integrated. 

 I'd suggest is the AD5760 (Rev. F) (analog.com) in this case, has an output settling time of 2.5us at 10V step. Using the ADA4898-1 Datasheet and Product Info | Analog Devices amplifier. Again, with a lower step or 12-bit accuracy should be fine. 

Or the AD5791 (Rev. F) (analog.com), which has a 1us settling at 10V step using the  AD845 Precision, 16 MHz CBFET Op Amp Data Sheet (REV. E) (analog.com)

Best regards,

Ian

Hello ,

Thank you for your detailed explanation. 

As we require simultaneous 4 to 8 channels and the suggested combinations ( AD5760+ADA4898 and AD5791+ad845) both are single DAC as well the DAC resolution is very high(20 bit, 16 bit) .

Though it has a very fast settling time. So, for simultaneous DAC channels, what about the quad DAC AD5724R? as it has update rate of 1.1 MSPS and we could do some modification in terms of load capacitance to reduce the settling time as you suggested earlier?

As AD5724 has 12 bit resolution, Quad channels.

So, Is this be a good idea , please suggest.

Hi, 

It would be better if we refer to the update rate of the DAC output in MUPS, updates per second. MSPS is samples per second and is used in ADCs for sampling rate. 

It would be a different case if you want 1MUPS for multiple channels. you'd need N times faster update rate than the single-channel update rate, with N being the number of channels you want. ie. to be able to output 1MUPS on all 4 channels, you'd need a DAC with at least 4x MUPS update rate. 

At best, you could achieve a 1MUPS output on a single channel on the AD5724R. ~0.25MUPS if you want 4 channels. 

The LTC2664 on the other hand could give 2MUPS on a single channel, and 0.5MUPS for 4. 

You could also look at a parallel interface DAC, like the AD5725 (Rev. C) (analog.com), has a 10us settling time for a 10V step, and around 50MUPS interface rate. 

Or again, go back to considering the Fast Precision DACs AD3542R Datasheet and Product Info | Analog Devices, dual-channel DAC, 16MUPS single channel rate.

Best regards,

Ian

Hello ,

Thank you for your support and detailed guidance.

Hello support Team,

I have gone through the details of AD5696  , which has 25 MUPS update rate. Is this suitable for above case? What are your views.

For 0-10 V output, use of external Vref=5 V with gain=2. also, for multi channel, 25/4 = 6.25 MUPS is possible , right? 

Hello,

Kindly request you to provide feedback on the above case

Hello Maitry 

Apologies for the late response, The AD5696 is a lot slower as it uses I2C protocol, able to operate only at 400kHz max. The single channel update rate is around ~14 KUPS. 

For your application, our Fast Precision D/A Converters are the ones that could fit. 

Best regards,

~ian