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ADS5444: internal connection of GND pins not match with datasheet

aseok tag
Intellectual 290 points
Part Number: ADS5444
Other Parts Discussed in Thread: ADS5463,

Hello

The pin numbers 2, 52 and 65 are specified as ground pins that are connected to other GND pins in the datasheet. but as i tested in short circuit mode, these three pins are connected to each other but not to other GND pins. other ground pins are ok.

Is it a problem? what may be the reason?

  • 0
    TI__Mastermind 29220 points

    Hi,

    Looking at a datasheet of another device that was released about the same time and from the same parent design (ADS5463) I see that those pins were labeled as digital ground on the ADS5463.  The rest of the ground pins were labeled as analog ground in the ADS5463.   So I suspect that that is the reason that these three pins on the ADS5444 are connected to each other and not to the rest of the ground pins - these pins are digital ground.  Also, you can see that these three ground pins encompass the LVDS digital output section of the pinout.   On our EVMs our general design practice is to not split the ground planes between digital and analog ground, so we would still have had them all connect to a common ground plane on the EVM even if the data sheet did identify them separately as digital and analog grounds.   So there is no problem with your devices - that is the way they are.

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    Intellectual 290 points
    Thanks, and as a general question: are internal ground (or supply pins as well), e.g all analog ground pins, connected to each other (short circuited) regardless of being supplied or not? In what condition, it will not be true? i.e it will needs powering the chip to make the supply pins internally shorted?
  • 0 in reply to aseok tag
    TI__Mastermind 29220 points

    Hi,

    usually if supply or ground pins in the datasheet share the same name then they would be connected internally on the chip, but not always.   In the case of the device you asked about, all the analog grounds connect together and all the digital grounds connect together, but for some reason the datasheet author chose to call them all ground.    There are more exceptions when it comes to supply pins, however.  Sometimes I will see a supply or ground pin controlling a manufacturing function such as scan chain or fuse trim be 'named' as a normal supply pin or ground.   That is, if there were a pin for enabling scan chain for example, then the datasheet might name the pin as reserved and require it to be grounded or tied to a supply as needed, or the datasheet might just name it as 'ground' even though it is not really connected to the rest of the grounds.  Sometimes there have been exceptions such as these.

    Regards,

    Richard P.