LM75A: Heat Flow

Henry Wang3

Expert 2645 points

Part Number: LM75A
Other Parts Discussed in Thread: LM70, LM75B, LM73

Hi Sir,

May I know the heat flow used on LM75A which pin-out?

Temperature sensors: PCB guide lines for surface mount devices: https://www.ti.com/lit/an/snoa967a/snoa967a.pdf

over 3 years ago

0 Cody Smith over 3 years ago

TI__Expert 3360 points

Hi Henry,

May you clarify the heat flow you are interested in?

The application note linked in the original post here: https://www.ti.com/lit/an/snoa967a/snoa967a.pdf, explains the main paths for heat transfer on ICs (section 1.2) and provides visual examples of this heat transfer for separate packages with later figures. The LM75A is available in SOIC and VSSOP packages, so the primary path for heat transfer will be through the leads.

The same app note will provide suggestions on PCB design for ambient air temperature sensing which is best when thermally isolated from heat-producing devices on the same PCB.

Thank you,

Chris

0 Henry Wang3 over 3 years ago in reply to Cody Smith

Expert 2645 points

Hi Sir,

My customer also asks questions as below.

1. Does the LM75A all pin-out can support detecting temperature?

2. The T_OS and T_HYST min temp value is 80C and 75C? can be set to negative temp value?

3. Need or not to do the calibrate? how to get the relative temperature? need to set the relative temp value on a different type of environment?

4. The LM75A folder has shown to get the UL recognized. may I know it pass those UL certifications?

0 Henry Wang3 over 3 years ago in reply to Henry Wang3

Expert 2645 points

Hi Sir,

Could you please help to reply those questions?

0 Josh Wyatt over 3 years ago in reply to Henry Wang3

TI__Guru* 91146 points

Dear Henry -

Sorry for the delay.

1. Yes, as Chris said, the leads of this device are primary path.

2. TOS default value is 80C, THYST default value is 75C, that is correct. These are two's complement based registers with 9 bits, so yes, it would seem they can be set to a negative value.

3. The devices will meet datasheet specs as shipped. Further calibration depends on your board and your requirements as to whether additional efforts are needed.

4. Digital sensors that are UL recognized in this family are the LM75B and LM75C. Additional devices are the LM73 and LM70 parts

0 Henry Wang3 over 3 years ago in reply to Josh Wyatt

Expert 2645 points

Hi Josh,

May I know the LM75A got what types of the UL certification?

+1 Josh Wyatt over 3 years ago in reply to Henry Wang3

TI__Guru* 91146 points

Dear Henry -

The UL category for these UL recognized sensors is XAPX2. (for Temperature Indicating and Regulating Equipment)

According to the UL Product IQ website, they applied UL873 to these parts when testing.

File # is E232195

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LM75A: Heat Flow