TMP390: how to program HOT and COLD threshold

Toshiro Imi

Part Number: TMP390
Other Parts Discussed in Thread: LM57, LM56

Hello,

Our customer has a question how to program HOT and COLD temperature by using TMP390. The datasheet has specified threshold setting table but he could not find out how he can set his own threshold like 3.5C (COLD) and 40.5C (HOT).

Would you mind letting us know the calculation method.

Best regards,

over 4 years ago

0 Jalen Tate89 over 4 years ago

TI__Genius 9675 points

Hi Toshiro,

The TMP390 does not have capability to choose thresholds between two settings. What thresholds do you need? We have an offering of quite a few resistor programmable or pin programmable temperature switches to help find the right part.

Jalen

0 Toshiro Imi over 4 years ago in reply to Jalen Tate89

TI__Expert 6250 points

Hi Jalen,

our customer need two temperature 2.5C for Channel B, 42.5C for Channel A. Does TP390 support this?

best regards,

0 Josh Wyatt over 4 years ago in reply to Toshiro Imi

TI__Guru* 90906 points

Dear Imi-san,

the closest the TMP390 can come to using those exact temperatures as trip points is 0C or 5C (for cold) and 42C (for hot)

A part like the LM57 would get you closer on the cold side, but still no 0.5C steps available.

A part like the LM56 may get you closer to what you are asking for, will any of these devices work for the customer here?

0 Toshiro Imi over 4 years ago in reply to Josh Wyatt

TI__Expert 6250 points

Hello, Josh-san,

Thank you for your answer. I understood TMP390 cannot program arbitrary temperature other than the temperature specified in Table 1 and Table 2.

I will recommend LM56 should be the best device to program arbitrary temperature by external resistor array.

Please correct me if my understanding is incorrect.

best regards,

0 Josh Wyatt over 4 years ago in reply to Toshiro Imi

TI__Guru* 90906 points

Dear Imi-san,

Yes, I think that is correct -

in this case, with the LM56; using 2.5C for T1 and calculating 410.5mV for VT1 ; 42.5C for T2 and calculating 891mV for VT2

I was then able to calculate the following starting resistor values for R1, R2, and R3

R1 = 8.87k, R2 = 10.37k, R3 = 7.75k, which satisfy the conditions where the three resistors have to add up to 27k, etc.

from page 8 of the datasheet

https://www.ti.com/lit/ds/symlink/lm56.pdf

0 Toshiro Imi over 4 years ago in reply to Josh Wyatt

TI__Expert 6250 points

Dear Josh-san,

Thank you very much for your help. I understood.

Best regards,

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TMP390: how to program HOT and COLD threshold