LM75A: the different among LM75A, LM75B and LM75C

Chieh Hao Chung

Part Number: LM75A
Other Parts Discussed in Thread: LM75B, , TMP1075

HI Team,

I have some questions about LM75, could you help to reply these questions below.

Customer use LM75BD(NXP) solutions, we try to propose our solutions to them.

The project timescale is really short and they do not want to spend a lot effort on it. so I try to promote the same pin out and software compatible solutions first.

I found that we have three different PN of Tem sensor LM75A, LM75B and LM75C.

What’s different among LM75A, LM75B and LM75C?
Which part is better to propose to customer (competitor LM75BD)
Does customer need to modify the software if they change to our LM75 solution?
I know we have the new solution tmp1075, and also P2P, do they need to modify software or register setting if we promote it to them next time.

Thanks

over 4 years ago

0 Ren Schackmann over 4 years ago

TI__Mastermind 35895 points

1. The differences are very minor. LM75A is a different process, LM75C has a different output stage than LM75B.

2. It is better to propose TMP1075.

3. No.

4. No.

Thanks,

Ren

0 Chieh Hao Chung over 4 years ago in reply to Ren Schackmann

TI__Prodigy 125 points

HI Ren,

but I saw the datasheet NXP have 11bits resolution and tmp1075 have 12bits.

don't they need to modify the code for the temp sensor?

thanks.

Best Regards,

jay

0 Ren Schackmann over 4 years ago in reply to Chieh Hao Chung

TI__Mastermind 35895 points

Hi Jay,

No, they don't have to modify the code. They can ignore the additional bit and the result will come out correctly with less resolution.

Thanks,

Ren

0 Chieh Hao Chung over 4 years ago in reply to Ren Schackmann

TI__Prodigy 125 points

Hi Ren,

what do you mean ignore additional bit? they still have to write something in code to ignore the bits, right?

I want to know that could they change the device from NXP to TI directly.

thanks

Best Regards,

Jay

0 Josh Wyatt over 4 years ago in reply to Chieh Hao Chung

TI__Guru* 91086 points

Dear Jay -

I think the 11 bit resolution (on the device from the other vendor) means there are is 2048 steps, each equal to (from this device) 0.125 degrees C, the TMP1075 has 12 bit resolution, which means there are 4096 steps, each equal to 0.0625 degrees C. The output on the I2C for the temp value, on the TMP1075 is the first twelve bits of the 16 bit register. On the NXP device its the first 11 bits of the same register. So their current firmware would still read or at least process just the first 11 bits of this in two's complement format - so the 0x7FF0 would appear when temp was actually 127.9375 degrees would be read in as 11 bit as 0x3F8 and indicate +127.000, as 15 value" steps" are lost to the lower resolution. Looks like same thing is done with the LM75 devices when operating in 9 bit mode (from 11).

See page 8 here https://www.nxp.com/docs/en/data-sheet/LM75A.pdf

and compare to top of page 10 here http://www.ti.com/lit/ds/symlink/tmp1075.pdf

I hope that helps!

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LM75A: the different among LM75A, LM75B and LM75C