DAC7558: Application Report page 3

Daniel Vasher

Intellectual 1135 points

Part Number: DAC7558

The application report page 3 for the DAC7558 shows IOV DD connected to 3.3v and the RST & PD connected to 5v.

Is this correct, or should the RST and PD be the same or lower than the 3.3v

over 7 years ago

0 Uttam Sahu over 7 years ago

TI__Genius 14220 points

Hi Daniel,

Thanks for your query. the requirements for the digital input pins is that the VIH shall be a minimum of 0.7*IOVDD and maximum of VDD+0.3V according to page 2 and page 3 of the datasheet. Hence, the circuit in the application note is correct. So, you can ideally connect these pins to either IOVDD or VDD.

Regards,
Uttam
Applications Engineer, Precision DACs

0 Daniel Vasher over 7 years ago in reply to Uttam Sahu

TI__Intellectual 1135 points

Thanks Uttam

0 pm over 7 years ago in reply to Uttam Sahu

TI__Expert 6030 points

Hi Uttam,

When measuring the voltages on the RST and PD pins, the customer is getting 4 V when these pins are connected to 5 V though a 10k resistor. I know we are within abs max spec, but does the IC have clamping circuitry on these pins below VDD?

Thanks,

Phil

0 Uttam Sahu over 7 years ago in reply to pm

TI__Genius 14220 points

Hi Phil,

The digital pins have level-shifting stages and hence, may have clamping circuitry with respect to IOVDD. Please give me some time to check this with the design team and get back.

Regards,
Uttam

0 Uttam Sahu over 7 years ago in reply to Uttam Sahu

TI__Genius 14220 points

Hi Phil,

I couldn't get any answer from the design team on this as this is a pretty old part. I need to test it on the EVM for confirming this. I will need approx a week's time for this as I am on travel this week.

Regards,
Uttam

0 Uttam Sahu over 7 years ago in reply to Uttam Sahu

TI__Genius 14220 points

Hi Phil,

I did a test on the EVM and looks like there is a clamp to IOVDD. Hence, it is a good idea to have the digital pull-ups tied to IOVDD instead of VDD.

Regards,
Uttam

0 pm over 7 years ago in reply to Uttam Sahu

TI__Expert 6030 points

Hi Uttam,

Thanks for following up on this test. Do you think we need to update the datasheet? Can you find out how much current these ESD clamps can handle to ensure device reliability?

Thanks,

Phil

0 Uttam Sahu over 7 years ago in reply to pm

TI__Genius 14220 points

Hi Phil,

I am checking with the team. Based on my previous discussion, I don't think there is any information on this as this is a very old part. I will let you know the response anyway.

Regards,
Uttam

0 Uttam Sahu over 7 years ago in reply to Uttam Sahu

TI__Genius 14220 points

Hi Phil,

We don't have data on this part. Usually the current limit on the ESD diodes is 10 mA. Hence, it is better to stay much below this limit if you need reliability. The customer can change the pull-up to IOVDD if possible or else it may be a better idea to increase the pull-up resistance.

Regards,
Uttam

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DAC7558: Application Report page 3