Open Drain pin influenced by Pull-Down configuration

Erich Ebenhoch

Hello,

on our TMX570LS3137AUPGEQQ1 we use some NHET Pins as testing output for an voltage comparator.

The configuration of those are:
*) GIO
*) Open Drain
*) Direction = Output
*) GIOPSL= 0 for pull-down

By measuring on these Pins, we see that the setting of the PULDIS register does influence the voltage.

Behaviour PULL Disabled: Measured voltage as expected
Behaviour PULL Enabled:  Measured voltage decreases slightly (about 0,07 V)

This minimal voltage drop leads in our case to unwanted behaviour on the voltage comparators.

In the TRM SPNU499 is stated, that the PULL control is disabled if the pin is set to the configuration above. 
But it seems that this is not the case and we have to do it explicitly by setting the PULDIS to 1.

Is this behaviour wanted or only visible in this development chips?


BG,
Erich Ebenhoch

over 13 years ago

0 Abhishek Shankar over 13 years ago

TI__Intellectual 2310 points

Erich,

Thanks for using the forum.

I have checked against design and can confirm that this is the intended behavior. But to be absolutely sure, pls tell me the precise pin you are using to make sure that this is indeed happening.

0 Erich Ebenhoch over 13 years ago in reply to Abhishek Shankar

Intellectual 255 points

Hello,

following PINs are used:

PIN	Function
23	N2HET1[01]
25	N2HET1[0]
30	N2HET1[02]

In this case I do have to set the PULL register explicit to disabled for the PINs I use with open drain function?

0 Abhishek Shankar over 13 years ago in reply to Erich Ebenhoch

TI__Intellectual 2310 points

Erich

I am assuming that you have used the NHET pins in GIO mode and not used the GIO module's functionality on these pins. I am guessing this is the case because the pins you have indicated are not muxed with the GIO module.

I confirmed that on the NHET module, the PULDIS register has to be explicitly set to disable pull functionality IF in open drain mode. If not in Open drain mode he pull is automatically disabled.

When I confirmed to you earlier that the PULDIS register need not be set I was referring to the GIO module's behavior (from your initial post I gathered you were using the muxed GIO functionality).