LM239ADR ψJT value

Hiroshi san,

A model has been requested.
Results usually come within 3 days.

Dear Ron

I have the same problem than Hiroshi, I have the RθJC(top) and RθJC(bottom) and I do not know how to apply them.

I have read the two following links one hundreds time every one:
www.ti.com.cn/.../spra953c.pdf
www.ti.com.cn/.../slva658.pdf

Nowadays I do not know what to do with RθJC(top) and RθJC(bottom).

In the datasheet it is specified the following parameters:
- RθJC(top)
- RθJC(bottom)
- RθJA
- RθJB
- ψJT
- ψJB

If I am not going to use a heatshink I would use the following formula:
Tj = Tb + Power x ψJB

If I want to use a heatshink above the IC I would use the following formula:
Tj= Ta + (RθJC + RθCS + RθSA)x Power

The problem is that RθJC is not provided, however RθJC(top) and RθJC(bottom) are provided. Plesae could you tell me how calculate Tj with a heatshink on the IC


Please I need your support.

Juan,

If no temperatures other than ambient is known then use this:
TJ = TA + RθJA * Power
least accurate

If the top of case temperature can be measured, then use this :
TJ = T[top] +ψJT * Power
much better accuracy

Tj = Tb + Power x ψJB is OK if you know the temperature under the part. I'm not sure how anyone would know that.

Dear Ron

The problema is that I am doing theorical calculations taking into account the use of heatshink so the following formula is not posible to use:

TJ = TA + RθJA * Power.

So I do not know which one of the two following formula I should have to use:

Tj= Ta + (RθJC(top) + RθCS + RθSA)x Power

or

Tj= Ta + (ψJT + RθCS + RθSA)x Power

In one of the link attached it is specified that ψJT should be used with not heatshink but the problem is that I can not do the calcuation with RθJC(top) because it

value is greater thatn RθJA.

 

Thank in advanced

Kind regards

Dear Ron

The problema is that I am doing theorical calculations taking into account the use of heatshink so the following formula is not posible to use:

TJ = TA + RθJA * Power.

So I do not know which one of the two following formula I should have to use:

Tj= Ta + (RθJC(top) + RθCS + RθSA)x Power

or

Tj= Ta + (ψJT + RθCS + RθSA)x Power

In one of the link attached it is specified that ψJT should be used with not heatshink but the proble is that I can not do the calcuation with RθJC(top) because it

value is greater thatn RθJA.

 

Thank in advanced

Kind regards

Juan,

Is a heat sink going to be used for the LM239?
Is it getting too hot?