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# AD5760B Vrefp and Internal Amp

Hello,

I'm a DFAE in Japan. Our customer is designing the schematic using AD5760 and gives us questions as follows.

1. The min value of Vrefp is 5V. The voltage reference's min value of Vout is 4.99875V. In this case, how much will the DAC affect INL and DNL? Or does it affect other performance?

2. He wants to know the specifications of the internal amp on Figure53. He places particular emphasis on stability, accuracy and noise performance.

3. Regarding Fig.52, VREFP = +10 V and VREFN = −10 V, he thinks that is the condition when deciding the specifications as Table2. On the other hand, Fig.53 is single ended reference input. Is there a difference in performance between those configurations? If so, what kind of item is it?

Regards,

Hiroyuki

• Hi,

1. The min value of Vrefp is 5V. The voltage reference's min value of Vout is 4.99875V. In this case, how much will the DAC affect INL and DNL? Or does it affect other performance?

Reference voltage directly impacts the transfer function, so any change in this proportionally changes the transfer function, which is the gain spec. However, the gain spec provided in the DS is measured assuming the conditions given thus it would be hard to determine insert the effect of a reference voltage error. what we can do is consider the reference error as a separate parameter, converting this  1.25mV error to LSB or ppm FSR then when you calculate the system error budget, just include this error on the RSS of the other errors. ie SQRT ( DNL^2 + INL^2, +Offset^2 + Gain^2 + Ref.err^2 ....)

2. He wants to know the specifications of the internal amp on Figure53. He places particular emphasis on stability, accuracy and noise performance.

Let me get back to you on this.

3. Regarding Fig.52, VREFP = +10 V and VREFN = −10 V, he thinks that is the condition when deciding the specifications as Table2. On the other hand, Fig.53 is single ended reference input. Is there a difference in performance between those configurations? If so, what kind of item is it?

The specs given in table 2 are measured using only the conditions stated there. There is no external output amplifier used. These 2 configurations in fig. 52 & 53 will both give a different performance which is not covered in the Typical Performance Characteristics provided in Table 2. If you're looking to do some simple system error budget calculations, our DAC error budget tool might help.

Best regards,

Ian