DAC902: Understanding DAC ....

Mandar Kothavade

Part Number: DAC902
Other Parts Discussed in Thread: THS3091, THS5661A

Hello,

I want to generate a 500KHz sine wave using a DAC attached to microcontrollers GPIO pins (8-12 bits). I need these waves with smooth curve so i was planning to define around 100pts per waves. That leads to sampling speed of my DAC 500k*100=50 MSPS. So, I need faster DAC. Maybe DAC902 will work.

But when I was checking its datasheet I do not find analog voltage output pin in it. Again there is CLK pin (is it necessary to give Clock pulses? why can't it work continuously like R2R resistor ladder? Or maybe how to use it for continuous conversion?). Actually I am not understanding meaning of most of the pins other than 12 bit inputs.(As i am trying to do this very first time and dont have much knowledge about it.) .

Actually i tried making DAC with R2R resistor ladder but it is not so precise due to little variation in resistor values and circuit parasitic capacitance.

on output side my current requirement is around 200mA. I want to drive a piezo with 5nf capacitance. But I can use an opamp buffer after DAC.

So please help me out understanding this.

over 7 years ago

0 Jim Brinkhurst1 over 7 years ago

TI__Mastermind 43930 points

Hi Mandar

At 50 MSPS it is necessary to latch the input data into the DAC to prevent glitches in the output. The input data is latched using the CLk signal, and the output is only updated once per input CLK cycle. Please refer to the TIMING DIAGRAM on page 5 of the DAC902 datasheet for the relationship between CLK, D11:D0 and Iout.

The DAC902 has complementary current mode outputs. The outputs can be converted to voltage using a few different configurations depending on the frequency of the output signal, the need for DC-coupling, etc. Please refer to figures 3 and 4 of the DAC902 datasheet for recommended output configurations for AC and DC coupled single ended output applications. The circuit of Figure 4 can be modified by substituting in an amplifier with the needed bandwidth and output current capability.

Best regards,

Jim B

0 Mandar Kothavade over 7 years ago in reply to Jim Brinkhurst1

Intellectual 355 points

Thank You Jim B,
As i need more time to understand this. Can you please just tell me that DAC902 will fullfill my requirement or not? So that I will place order and meanwhile study it (During the period it reaches to me).

I am using Launchpad F28377s GPIO for giving input to DAC. Maybe i can give CLK to it using the same launchpad. On output side I have opamp ths3091. I need modified sine pulses with 500kHz frequency. I am defining 100pts per wave so my sampling frequency will become 50 MSPS. resolution of 12bits is sufficient.

Kindly, tell me this DAC will be able to handle such fast conversion or not? if not then suggest me another DAC.

Thank You.

0 Jim Brinkhurst1 over 7 years ago in reply to Mandar Kothavade

TI__Mastermind 43930 points

Hi Mandar

I'm not sure if the DAC902 is compatible with the Launchpad you are using. You will need to check on the timing capabilities of the 12 bit data and 1 clock that would be sent to the DAC. The timing alignment of these signals must be relatively well controlled.

I also want to point out that the DAC902 does not have an EVM (evaluation module) available.

A very similar alternative device you could consider is the THS5661A. That device does have an EVM currently available.

http://www.ti.com/tool/ths5661evm

Best regards,

Jim B

0 Mandar Kothavade over 7 years ago in reply to Jim Brinkhurst1

Intellectual 355 points

Thanks Jim B,

Can you please suggest me a DAC which is compatible with my launchpad. So, that i can easily use it in my application without attaching extra hardware to control just an ADC. May be it is possible to generate clock source at 50MHz from my launchpad which will be given to DAC clock input.
Kindly check If i am wrong at anything?

Thank You.

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DAC902: Understanding DAC ....