ADS8588S: REFSEL detection circuit works abnormal without 3.3VDD

Stone Zeng

Part Number: ADS8588S

Hi Team,

my customer is using ADS8588 and found REFSEL detection circuit works abnormal without 3.3VDD.

Here is the test condition:

1. with 5VDD power up and REFSEL pull down, 3.3VDD is zero, the internal reference should be disabled while test result shows 2.5V on REFOUT.(See picture1)

2. with 3.3VDD power up, the test shows REFOUT discharge slowly(see picture2), which means internal reference is disabled and REFSEL works as expected.

Could you help to check:

1. Does REFSEL detection circuit need 3.3VDD to work?

2. customer is using external reference(REFSEL pull high), 5VDD and 2.5V external refence power up first, before 3.3VDD power up, the REFIN/REFOUT pin may have both internal reference and external reference, is there any issue?

Regrards,

Stone

11 months ago

Stone Zeng 11 months ago

TI__Prodigy 550 points

PIC1

PIC2

Dale Li 11 months ago in reply to Stone Zeng

TI__Mastermind 39075 points

Hi Stone,

There is no detection circuit, however REFSEL is a digital input pin, so it has a digital implementation circuity (like a buffer) between the REFSEL and reference multiplexer.

This is a risk. Powering up DVDD is recommended to avoid the conflict in this case.

Regards,

Dale

Stone Zeng 11 months ago in reply to Dale Li

TI__Prodigy 550 points

Hi Dale， thanks for your prompt reply.for this case, we need power up 5vdd and 3.3vdd before 2.5v external reference, is that correct?

stone

Dale Li 11 months ago in reply to Stone Zeng

TI__Mastermind 39075 points

Hi Stone,

Usually the AVDD of external reference is the same power supply as the +5V AVDD of the ADC. If this is not the case here, powering up the reference later than other supplies is recommended.

Regards,

Dale

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ADS8588S: REFSEL detection circuit works abnormal without 3.3VDD