Post Go back to editing

Choice of multiplying DAC for 30kHz sine

Category: Hardware
Product Number: AD5543 / AD5545 / LTC2756

I am looking for a multiplying DAC which I can use to take one sine wave and derive another with precisely controlled relative amplitude for a bridge application. The higher resolution the better, so I'm looking at the 18-bit LTC2756 and the 16 bit AD5543/5. The former has this diagram in the datasheet:

I'm not sure how to read this. Clearly, at 30kHz, there is some capacitive pass-through. But is it:

1) Codes below about 0x0008 have the same output, but above about 0x000F everything is fine, DNL stays good. Or

2) The least significant three bits are the wrong size across the full range, DNL is poor both around 0x0008 and higher.

3) something else?

Relatedly, if this chip won't give me what I want then my next choice is probably AD5543. I can't see an equivalent plot or specification - how do I work out from the datasheet what the DNL is like at 30kHz?

Top Replies

    •  Analog Employees 
    •  Super User 
    Jul 6, 2023 +2 verified

    Hi  , 

    The plot from LTC2756 provides the frequency response vs the gain setting of the DAC. Your first statement is generally correct. This means that at 30kHz you should have a precise gain factor…

  • Hi  , 

    The plot from LTC2756 provides the frequency response vs the gain setting of the DAC. Your first statement is generally correct. This means that at 30kHz you should have a precise gain factor from -60dB (D6)and above. We could relate it to the multiplying bandwidth of the device. LTC2756 has 1MHz at full scale, while the AD5545 has 6.9MHz at the same condition. If -60dB is not enough for you application, you could consider the AD5545 instead. 

    Best regards,

    Ian