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DAC8760: About OVR setting

Hide
Guru 21045 points

Part Number: DAC8760

Hi Team,

 

We would like to use DAC8760 for “1V to 5V” and “4mA to 20mA” at OVR=1b.

 

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[Q1]

We would like to set “full scale voltage=around 5V” at OVR=1b, VREF=5V, GAIN=1, N=16.

Then, I have to set CODE of case3.

Is my understanding correct?

 

My understanding is as follows.

Case1: if OVR=0b, full scale voltage is 4.999924V at CODE(DAC Data register)=FFFFh.

Case2: if OVR=1b, full scale voltage is 5.49916V at CODE(DAC Data register)=FFFFh.

Case3: if OVR=1b, full scale voltage is 4.949966V at CODE(DAC Data register)=E666h.



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[Q2]

We would like to set output current=”4mA to 20mA” at OVR=1b, N=16.

My understanding is as follows.

Case1: if OVR=0b, output current is 19.99976mA at CODE(DAC Data register)=FFFFh.

Case2: if OVR=1b, output current is 19.99976mA at CODE(DAC Data register)=FFFFh.

 

So, OVR setting(0b or 1b) does not affect output current value.

Is my understanding correct?



--------

 

Regards,

Hide

  • 0
    TI__Guru** 100855 points

    Hide-san,


    For question 1, you are correct. When you set the OVR bit to 1, the gain range is increased by 10%. The resulting range with OVR set to 1 is shown in Table 10:

    If the reference voltage is 5V, then to get 5V out on the DAC, you would need a code of about E8BAh = 59578d. This comes from:

    VOUT = 5V * 1.1 * 59578/2^16 = 5V

    Note that even with this code, you would need a larger supply voltage to get values higher than 5V. The voltage output amplifier will be limited by the supply voltage.

    For question 2, you are also correct, the IOUT output range is not affected by the OVR bit. The IOUT current will be the same if OVR is set to 0 or 1.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Guru 21045 points

    Joseph-san,

     

    Thank you for your prompt reply.

    I apply AVDD=more than 10V.

    So, I understand that can provide 5.5V output voltage.

    Is my understanding correct?

     

    >you would need a larger supply voltage to get values higher than 5V. The voltage output amplifier will be limited by the supply voltage.


     

    Regards,

    Hide

  • 0 in reply to Hide
    TI__Guru** 100855 points

    Hide-san, 

    You are correct. With the overrange bit set, the DAC should be able to reach +5.5V. In the paragraph before Table 10. The last line says that "if the OVR bit is set, the output voltage range follows Table 10, as long as there is headroom with the supply". 

    Joseph Wu

  • 0 in reply to Joseph Wu
    Guru 21045 points

    Hi Joseph-san,

    Thank you for your prompt reply.

     

    Regards,

    Hide