[OMAPL138] Resistance Specification for Internal Pull-Up and Pull-down Resistors

Michael Questo

Other Parts Discussed in Thread: OMAPL138

OMAPL138 Champs,

I've looked through both the datasheet and the TRM but have been unable to find the internal reistance values of the Pull up and Pull down resistors that are determined by the PUPD_ENA and PUPD_SEL registers. These registers have default states which are listed in 11.5.22 Pullup/Pulldown Enable Register and 11.5.23 Pullup/Pulldown Select Register in the TRM

There is also information on how oppose and compliment the resistors.

Opposing - A 1-kohm resistor can be used to oppose the IPU/IPD while meeting the above criteria.

Complimenting - A 20-kohm resistor can be used to compliment the IPU/IPD on the boot and configuration pins while meeting the above criteria.

However, I can't find the actual value of the resistance?

Thanks,

over 12 years ago

0 Mukul Bhatnagar over 12 years ago

TI__Guru* 83705 points

Hi Michael

You will find the following posts useful

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/t/113557.aspx

https://e2e.ti.com/support/dsp/omap_applications_processors/int_omapl1x_dsps/f/116/p/13220/149022.aspx (internal post)

Regards

Mukul

0 fdm over 12 years ago

Expert 1070 points

Hi Michael,

This post might be useful also:

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/p/124259/445855.aspx

Regards,

Denis

0 Michael Questo over 12 years ago in reply to fdm

TI__Expert 6000 points

Thanks to everyone who responded, your links were useful. Upon reviewing them i've come to the conclusion that the equivalent resistance of the IPU/IPD is aproximately 12.2kohms max. Please correct me if i'm wrong.

Thanks!

0 fdm over 12 years ago in reply to Michael Questo

Expert 1070 points

My rough estimations for the equivalent resistance are (10...50)kOhm for 3.3V and (5...28)kOhm for 1.8V

Denis

0 Michael Questo over 11 years ago in reply to fdm

TI__Expert 6000 points

Bringing all the discussion together, here are the calculations.

OMAPL138 DS - http://www.ti.com/lit/ds/symlink/omap-l138.pdf

Section "5.3 Recommended Operating Conditions" in Datasheet

Recommended I/O Operating Range (DVDD)

3.3V I/O - 3.15V to 3.45V

1.8V I/O - 1.71V to 1.89V

Section "5.5 Electrical Characteristics Over Recommended Ranges of Supply Voltage and Operating JunctionTemperature"

LVCMOS Pull-Up Current

Min 70 uA

Max 310 uA

LVCMOS Pull-Down Current

Min -75 uA

Max -270 uA

Resistance Calulations: Pull Down

Resistance Pull Down 3.3V I/O:

Max : 3.15V / 75 uA = 42k

Min : 3.45V / 270 uA = 12.8k

Typ : 3.30V / 172.5 uA = 19.1k

Resistance Pull Down 1.8V I/O:

Max : 1.71V / 75 uA = 22.8k

Min : 1.89V / 270 uA = 7k

Typ : 1.80V / 172.5 uA = 10.4k

Resistance Calulations: Pull Up

Resistance Pull Up 3.3V I/O:

Max : 3.15V / 70 uA = 45k

Min : 3.45V / 310 uA = 11.1k

Typ : 3.30V / 190 uA = 17.4k

Resistance Pull Up 1.8V I/O:

Max : 1.71V / 70 uA = 24.4k

Min : 1.89V / 310 uA = 6.1k

Typ : 1.80V / 190 uA = 9.5k

Similar Calculations for the OMAPL137:

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/p/29868/1153775.aspx#1153775

0 fdm over 11 years ago in reply to Michael Questo

Expert 1070 points

Hi Mike,

Taking into account that these IPU/IPD structures are implemented as current source/sink rather than constant resistance (see that post) I suppose that U_MAX/I_MIN and U_MIN/I_MAX pairs should formally be used instead.

From the practical point of view, it is more useful to calculate maximum values of external R_PU/R_PD to oppose IPD/IPU (as it suggested e.g. in OMAP-L138 Errata Advisory 2.3.23) rather than internal resistances.

In addition we should account for tolerance of DVDD and resistors and also add some noise margin.

-Denis

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[OMAPL138] Resistance Specification for Internal Pull-Up and Pull-down Resistors