DAC8811: Questions about DAC8811 power on reset circuit.

Kazuya Nakai59

Part Number: DAC8811

Hello guys.

One of my customers is evaluating DAC8811 for their new products.
At this moment, they have the following question. Could you please give me your reply for them?

Q. What is the minimum VDD volts which the power-on reset circuit of DAC8811 can operate correctly?
Because a leak current (>10nA) is sourced from IOUT pin of DAC8811 when VDD is less than about 1.5V.
I think the leak current should be less than 10nA when the power on reset circuit operates correctly.

Your reply would be much appreciated.

Best regards,
Kazuya.

over 3 years ago

0 Katlynne Jones over 3 years ago

TI__Mastermind 37738 points

Hi Nakai-san,

Is your customer seeing this behavior when the device is coming up from 0V, or when the supply is coming down from the VDD?

Is there an external op amp on the IOUT of the DAC? Is so, is what is the supply of the op amp at this time?

Best,

Katlynne Jones

0 Katlynne Jones over 3 years ago in reply to Katlynne Jones

TI__Mastermind 37738 points

Please also provide us with the schematic.

Best,

Katlynne Jones

0 Kazuya Nakai59 over 3 years ago in reply to Katlynne Jones

Guru 21215 points

Hi Katlynne,

Thank you very much for your reply.

The customer use the schematic same as Figure 22 on page 13 of DAC8811 datasheet.
they are seeing this behavior when the device is coming up from 0V.

I found the following E2E thread.
https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1052854/dac8811-dac8811-behavior-without-code

According to the thread, OTP output for default value setting is not stable
until VDD is powered up around 2V.
I think this OTP output is the reason of the customer phenomenon.
Is my understanding correct?

Thank you again and best regards,
Kazuya.

0 Katlynne Jones over 3 years ago in reply to Kazuya Nakai59

TI__Mastermind 37738 points

Hi Nakai-san,

So there is an external op amp connected? What is the supply of the op amp when the leakage is measured?

I spoke with the designer of this device yesterday. The device has a reset signal that is sent to the internal OTP when the device hits a certain threshold. The threshold is not always the same from device to device, but 1.5V falls in the range. The POR should be complete by ~2V like the e2e you found mentioned. The output is not valid as specified in the datasheet until the minimum supply of 2.7V is reached, but the designer didn't think the leakage the customer is seeing should be there at a supply of 1.5V.

He said: The trigger level for the POR is more for it switching off (the reset signal) than actually resetting the device. So for a supply voltage of 0V to the threshold, the part should be reset, and also stay in that reset condition as the supply goes all the way up to nominal.

Can the customer remove the external op amp and measure the DAC output?

Best,

Katlynne Jones

0 Kazuya Nakai59 over 3 years ago in reply to Katlynne Jones

Guru 21215 points

Hi Katlynne,

Thank you very much for your reply.
I ask them to measure the output current of DAC8811 when VDD is powered up.
I will inform you as soon as I get the current data from the customer.
Could I have a few days?

Thank you again and best regards,

Kazuya.

0 Joseph Wu over 3 years ago in reply to Kazuya Nakai59

TI__Guru* 95745 points

Kazuya-san,

Katlynne is out of the office for the week. However, I think that she'll be keeping track of email and E2E posts. Once you get your responses from your customers, I think she'll be able to help.

Joseph Wu

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DAC8811: Questions about DAC8811 power on reset circuit.