DAC8760: About Zero-scale error

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Guru 21045 points

Part Number: DAC8760
Other Parts Discussed in Thread: LM7705, LM27761

Hi Team,

We are evaluating DAC8760 at Unipolar range(AVDD＝11V、AVSS＝GND) and Voltage range is 0V to 5V.

If Data resister is 0x0000, VOUT is around 12mV, so higher than expected value.

Therefore, we would like to know this cause.

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[Q1]

We guess that Maximum Zero-scale error is ±0.6mV(max) at 25℃.

However, our result is 12mV.

Could you please let us know if you have any concern?

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[Q2]

Could you please let us know the meaning of footroom?

Does footroom affect Zero-scale error?

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Regards,

Hide

over 2 years ago

0 Akhilesh K over 2 years ago

TI__Mastermind 18546 points

Hi,

In this case, zero-scale error assume some level of footroom - which is what creates both polarities in these errors (+/-0.6mV). If there were not -0.5V of footroom in the unipolar case, the zero-scale error would only be positive as the output buffer would not have the ability to swing negative.

Without -500mV footroom, we can expect more zero scale error for this device.

Regards,

0 Hide over 2 years ago in reply to Akhilesh K

Guru 21045 points

Hi AK-san,

Thank you for your prompt reply.

I understand that I have to set it to “AVSS=-500mV” to get “footroom=500mV”.

Is my understanding correct?

If no, could you please let us know how to realize “footroom=500mV”?

Regards,

Hide

+1 Akhilesh K over 2 years ago in reply to Hide

TI__Mastermind 18546 points

Hi,

yes, we need -500mV on AVSS

Regards,

0 Hide over 2 years ago in reply to Akhilesh K

Guru 21045 points

Hi AK-san,

Thank you for your prompt reply.

Regards,

Hide

0 Joseph Wu over 2 years ago in reply to Hide

TI__Guru* 92715 points

Hide-san,

I have seen cases where a small negative supply is generated from for the AVSS for this part. The LM7705 can be used for this purpose. While, this negative supply is about -0.23V, it may be enough for operation down to GND.

I did find a post about it here:

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/358718/dac8760-running-with-single-supply-0v-12v

And there was another post about using an LM27761 for a -1.5V supply here:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/683883/lm7705--0-5-v-source-for-avss-dac7760

Joseph Wu

0 Hide over 2 years ago in reply to Joseph Wu

Guru 21045 points

Hi AK-san, Joseph-san,

Thank you for the information.

I have two questions.

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[Q1]

I would like to maintain footroom=around 0.23 ~ 0.5V using HTSSOP package.

Could you please let us know how to handle the terminals of Supply input?

-1pin(AVSS)=-0.23V to -0.5V

- Thermal pad=AVSS=-0.23V to -0.5V

-10 & 11pin(GND)=0V

-24pin(AVDD)=11V

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[Q2]

If I supply negative voltage(-0.23V to -0.5V) to AVSS pin.

I guess that AISS(consumption current) will increase.

How much will it increase?

Could you please let us know if you have any information?

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Regards,

Hide

0 Akhilesh K over 2 years ago in reply to Hide

TI__Mastermind 18546 points

Hi,

Pin 10 is SDO in HTSSOP package, Do not ground this pin. Rest everything is OK.

Coming back to power consumption due to AVSS supply, there will be additional current drawn from AVSS supply based on the output conditions. Please see the table below for AVSS current

Regards,

0 Hide over 2 years ago in reply to Akhilesh K

Guru 21045 points

Hi AK-san,

Thank you for your prompt reply and advice.

And, there was a mistake in the comment I sent just a before.

Incorrect: 10 & 11pin(GND)=0V

Correct: 11 & 12pin(GND)=0V

Regards,

Hide

+1 Akhilesh K over 2 years ago in reply to Hide

TI__Mastermind 18546 points

Hi,

Pin 11 and 12 is GND.

Regards,

0 Hide over 2 years ago in reply to Akhilesh K

Guru 21045 points

Hi AK-san,

I have one more question.

I would like to use -5V (not -0.5V) for AVSS.

I understand that there is no concern.

Is my understanding correct?

Regards,

Hide

+1 Akhilesh K over 2 years ago in reply to Hide

TI__Mastermind 18546 points

Hi,

There will be increase in power consumption.

Otherwise no issues.

Regards,

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DAC8760: About Zero-scale error