TMP1826: DC level violation with 3.3V Processor (OSD6254).

Danilo A.

Part Number: TMP1826
Other Parts Discussed in Thread: SN74LVC1G07

Hi Team,

Posting on behalf of our customer.

I am performing a DC analysis for a new design using the TMP1826NGRR as a 1-Wire temperature sensor, and I have identified a logic level violation regarding the threshold when operating at 3.3V.

System Parameters:

VCC/VPUR/Vs: 3.3V
Host Processor: OSD6254-1G-IPM
Sensor: TI TMP1826NGRR
Interface: 1-Wire (SDQ)

The Violation:

According to the TMP1826 datasheet, the Input Logic High Level (VIH) is defined as 0.8 x Vs. At a supply of 3.3V, this results in a VIH (min) of 2.64V.

However, my host processor (OSD6254) specifies a VOH(min) of only 2.4V. This creates a negative noise margin of -0.24V, where the processor's minimum "High" output does not meet the sensor's minimum input voltage requirement.

Can you please confirm whether this apparent VIH violation affects data read/write operation between the host SoC and TMP1826, and whether it can be resolved solely by an appropriate external pull-up resistor on the open-drain SDQ line or if a level shifter is required.

Please suggest the appropriate resolution.

Regards,

Danilo

1 month ago

0 HarryG 1 month ago

TI__Expert 6360 points

Hello Danilo,

Let me check with our design team and get back to you as soon as I have a response.

Regards,

Harry

0 HarryG 1 month ago in reply to HarryG

TI__Expert 6360 points

Hello Again Danilo,

I just wanted to give you a quick update before the holidays, but our backend team is actively looking into this and whether your customer will need to make any design changes. Once they have a response, I will follow-up via email.

Please keep in mind that due to the holidays there may be a slight delay in getting back to you on this.

Thanks,

Harry

0 Nirav Kateshiya 1 month ago in reply to HarryG

Prodigy 60 points

Hi Harry,

Hope you’re doing well. Just a quick follow-up to check if there are any updates from the design/backend team regarding the VIH level concern between the OSD6254 and TMP1826 at 3.3 V.

0 Alex Thompson 1 month ago in reply to Nirav Kateshiya

TI__Genius 14335 points

Hi Nirav,

Unfortunately we are staffed very thin this week, but Harry should definitely be able to get an answer from our backend team early next week. Please reply back on the thread on Monday morning so that our team does not forget this.

Thanks

-Alex Thompson

0 Nirav Kateshiya 1 month ago in reply to Alex Thompson

Prodigy 60 points

Hello Hary,

Happy New Year. Hope you’re doing well. Just a quick follow-up to check if there are any updates from the above mentioned query.

Regards,

Nirav K

0 Meredith McKean 1 month ago in reply to Nirav Kateshiya

TI__Genius 11070 points

Hello Nirav,

There are currently no updates. Harry is currently still out. Thank you for your patience.

Best Regards,

Meredith McKean

0 Ren Schackmann 1 month ago

TI__Mastermind 45035 points

Hi Danilo,

Can we do a schematic review? The TMP1826 requires a pull-up resistor for the bus.

thanks,

ren

0 Danilo A. 1 month ago in reply to Ren Schackmann

TI__Mastermind 31730 points

Hi Nirav,

Kindly share the schematic diagram here or if there are confidential information you can share it with Ren thru private message.

Thank you!

Regards,

Danilo

0 Nirav Kateshiya 1 month ago

Prodigy 60 points

Hi Denilo,

Currently, it is under internal review. Once we are done, we will share it with you for review.

Regards,

Nirav K.

0 Nirav Kateshiya 29 days ago

Prodigy 60 points

Hello Ren/Danilo,

Please find the temperature sensor section of the schematic attached for your review. Kindly review this section and let me know if any changes or modifications are required.

Thank you for your support.

Regards,

Nirav K.
Temp Sensor Section.pdf

0 Ren Schackmann 28 days ago in reply to Nirav Kateshiya

TI__Mastermind 45035 points

Hi Nirav,

This schematic is fine for the TMP1826. However, to address the original question about VIH, I would need to see the circuitry driving the SDQ pin.

thanks,

ren

0 Nirav Kateshiya 22 days ago in reply to Ren Schackmann

Prodigy 60 points

Hi Sahil Nayak

Can you please explain to Ren how we are driving the SDQ pin based on the schematic design?

Thanks,

Nirav K.

0 Sahil Nayak 22 days ago in reply to Ren Schackmann

Prodigy 220 points

Hi Ren,

The SDQ pin has a 10K PU of 3.3V and is connected to the AM6254 pin.

Please let me know if you require any additional specific details regarding the connection.

Thanks & Regards,
Sahil Nayak

0 Ren Schackmann 20 days ago in reply to Sahil Nayak

TI__Mastermind 45035 points

VOH only applies to the moments when the AM6254 is sourcing current to create a high output. To create the 1-Wire bus directly from a GPIO pin, the GPIO must never source current. You must program it to only output Z and 0 states. When the GPIO pin is in a Z state, the pull-up resistor creates the logic high. I recommend using an open-drain driver, such as SN74LVC1G07, to create the Z and 0 instead. However, such an implementation would need another GPIO dedicated to input-only.

thanks,

ren

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TMP1826: DC level violation with 3.3V Processor (OSD6254).