LM87: Unused pins

Hello Harry,

Thanks for your reply. I read the datasheet for more detail because I have to answer the question.

Regarding VIDx/IRQx pins, each pin has an internal pull-up and default setting is VID monitor. So I think just floating without any register change should be OK.

Regarding FAN2/AIN2 pin, the defaul setting is assingted to FAN2.
I think it is OK to connect to GND as a H/W setting.
The user has to set bit 7 of Interrupt Mask Register to disable the corresponding interrupt.

Regarding CI, this signal is active HIGH event input. So coneecting GND should be safe. 

Regarding DACOUT/NTEST_IN, it is DACOUT if not forced to HIGH during power up. So I think just floating should be safe.

What do you think?

And I can't understand how to terminate D1-/D1+ (and configure the register). Whad shoul the customer do for these pins?

Regards,
Oba

Hello Oba,

What is the goal of the customer's design if I may ask? Is it a local application?

Regards,

Harry

Hello Harry,

They will use only FAN1, +12Vin, +5Vin, Vccp1  functions. So they don't use many pins.
As of now, all unused pins are just floating. So if it is not acceptable, please let me know.

Regards,
Oba

Harry,

Thanks for your reply.

>I would suggest leaving the outputs you're not using floating and grounding all the unused inputs.

I want to confirm one thing. What does floating "and" grounding mean? floating "or" grounding?

Thanks for your suggestin, I have introduced LM96163 before. But because they has used LM87 in other products for a long time, they want to use it.

Regards,
Oba

Hello Harry,

Sorry, I'm confused.
I understand the defenition of "float" and "ground".

>I would suggest leaving the outputs you're not using floating and grounding all the unused inputs.

You said that unused pins should be left floating AND grounding (at the same time).
It is impossible to do both("and") for the same pin. So I just wanted to confirm if it is "float" OR "grounding" which means either is acceptable.

Regads,
Oba

Hello Harry,

I have an additional question.
Regarding grounding for input pins, is it OK to coonect to GND directly?

Regards,
Oba

Hello Harry,

I checked the datasheet again and found that several pins are not so simple, not just inputs and outputs and some have interal pull-ups/downs.
Let me ask again.

1.
DACOut/NTEST_IN is described as "Analog output/Digital input".Is just foationg OK?

2:
For CI, I can't understand this function. It is descibed as digital I/O, active high input and open drain output.
Which is better, floating or grounding?

3:
For VIDx/IRQx, they are input pins but have internal 100Kohm pull-ups. I think it can be floating. Grounding is not needed. Is grounding really needed?

4:
Regarding Vccp2\D2- and +2.5Vin/D2+, according to P8 of the datasheet, there are R1+R2 resistors(130K).
I think it can work as internal pull-down. So grounding is not needed. Is grounding really needed?

Regards,
Oba

Hello Harry,

Thanks. I have one more question.

Regarding D+/D-, I have answered "both should be gournding" to the customer.
Is D+ just an analog input? Doesn't it bias the temperature senser(diode) if connected?
I mean if this pin is also bias output, I feel connecting GND may not be good.
So, this is a confirmation just in case . Is grounding really OK for D+/D-?
And is floating for both D+/D- acceptable because their current circuit is just floating for both pins?

Regards,
Oba

Hello Meredith,

Thanks for your reply.

So D+ can be floating, correct?
And can D- be also floating? or should be connected to GND?
They don't use D+/D- at all. So floating is the easiest way.

Regards,
Oba

Hello Meredith,

Thanks.  Is just shorting D+ / D- without grounding OK?

Regards,
Oba