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Original question:

DAC7760: DAC7760 voltage and current output problem

DAC7760: IC not responding

Swapniil Kanwar
Prodigy 160 points
Part Number: DAC7760
Other Parts Discussed in Thread: DAC7750,

i am using DAC7750 for some testing and setting registers as follows (using SPI MODE 0): 
 

 send_tDCS(DAC_Reset,  0x0001);                // Reset registers to default
  send_tDCS(DAC_NOP,    0x0000);                  // NOP operation
  delay(10); //milliseconds
  send_tDCS(DAC_Ctrl,   0b0001000000000110);   // o/p enable, o/p->0-20mA, current setting res enable
  send_tDCS(DAC_Config, 0b0000000000100000);   // disable HART, watchdog, error-check, calliberation
  send_tDCS(DAC_GAIN,   0x8000);                 // Gain of 1, default is 0.5

After setting these registers I am able to program the IC to whatever current I need by DAC data register. 

I recently bought DAC7760 (which has voltage output in addition). I have crosschecked the address of the registers are same as DAC7750. After crosschecking in datasheet i kept the register values same as above in DAC7750. CLR-SEL and CLR pin are kept LOW, same SPI MODE 0, REFIN and REFOUT shorted. 

But with these settings I am not able to get any current output. 

Can someone please help me what register settings should I use to set any desired current I want using DAC data register? 

  • +1
    TI__Guru* 93715 points

    Swapniil,


    Normally, think that the two devices are so similar, that the code for one would work for the other without any modification. I'll need to go through your communication a bit more carefully to verify the commands and register data. However, there are a few other things that you might be able to check.

    First, I would definitely check to see if there were any mistakes in the drawing of the schematic or if there might be any problems in the manufacturing/soldering of the device. The pinout is similar, but there are a few minor differences. Do you have schematics of each that you can share? Are you using the HTSSOP or RHA package for your design?

    Another thing to check would be the readback of the device. Just to verify the communications, after writing to a register, immediately read it back to see that the register contents is different than the default and that it is correct from the data that was previously written. In particular, how do you have the configuration register set up? Regardless of the readback, I think it would be important to be able to see the SPI lines toggling during communication. I would definitely be using a logic analyzer or oscilloscope to capture the digital signals.

    Once you start looking, you can post back with answers and scope plots that show the communication.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 160 points

    The problem got solved in a strange way. I de-soldered the CLR-SEL pin and left it floating. I made all the connections as before. I was able to read the registers now. Again I soldered CLR-SEL pin to ground and since then the IC is working. Still don't know why is this happening. But atleast the IC started working. Spent hours debugging  on this weird isse.