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Class D Audio Amplifier IC Forum Discussions

Bravaudio
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Hi, I have just repaired a commercial product power amplifier.

It uses an IRS2092 to drive 2x IRFB4227 directly from HO and LO via 6.8ohm gate resistors with a drive voltage of 15v.

When Idling and driving a load of 8ohms the temperature of the IRS2092 is showing 60-65c on my thermal camera.

Is 60-65c a normal/safe running temp for IRS2092?

I'll attach thermal images of temperature from directly beside the IC, the coolest part of it and the hot centre.

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Nishanth
Moderator
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Hi @Bravaudio 

The IRS2092 can operate safely at a temperature of 65C.

I would advise reducing VCC to 12V if you want to improve it even further. The benefit is that RDS(ON) won't significantly increase while Qg of the FETs is reduced. This will further reduce the temperature.

Kindly let me know if you have any further queries.

Regards,

Nishanth

 

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Nishanth
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Moderator 25 replies posted 10 solutions authored 50 sign-ins
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Hi @Bravaudio,

Thank you for contributing to the Infineon community.

Can you please provide the following inputs:

1. What is the ambient operating temperature?

2. Is the captured data a steady-state value?

3. What is the calculated power dissipation in the IRS2092?

4. Are you using the SOIC16N or DIP16 package?

Regards,

Nishanth

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Bravaudio
Level 1
5 replies posted 5 sign-ins First reply posted
Level 1

IRS2092 IRFB4227.png

Sorry for delay, attached is an image of the IRS2092 & IRFB4227's in circuit for visualisation.

1) 23c

2) Yes

3) The net dissipation in the IC is the sum of the switching and conduction losses. Since there's no information on the output impedance of the driver, we're, unfortunately, not in a position to calculate the latter. The gate resistors are 6.8ohm, PWM frequency is 400kHz & drive voltage is 15v.

4) Soic16n

Thanks for your time.

 

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Nishanth
Moderator
Moderator 25 replies posted 10 solutions authored 50 sign-ins
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Hello @Bravaudio,

Thank you for the valuable information.

The power dissipation in the IRS2092 is the sum of  the following  terms:

PD = PMID + PLSM + PLOW + PLSH + PHIGH

Where,

PMID: Power dissipation of the input floating logic and protection circuitry
PLSM: Power dissipation of the Input Level Shifter
PLOW: Power dissipation on the low side

 PLSH: Power dissipation of the High-side level Shifter
PHIGH: Power dissipation on the high side

Kindly find the link attached for the calculation of power dissipation. Refer junction temperature estimation part.

Click here 

The formula shown below can be used to get the junction temperature Tj. For a given RthJA.

TJ = RthJA × Pd + TA < 150°C

RthJA: Thermal resistance from junction to ambient. for SOIC16N it is 115 degrees Celsius /W 
TA: Ambient temperature

The junction temperature should be well below the maximum allowable limit for the safe operation of IRS2092(Considering a safety factor is always advisable).

Regards,

Nishanth

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Bravaudio
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Hi, this is getting very complicated ... is there not a simple best practice average operating temperature range for the IRS2092 IC? .... I mean temperature of the IC itself as measured in the original post (not ambient).

 

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Nishanth
Moderator
Moderator 25 replies posted 10 solutions authored 50 sign-ins
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Hello @Bravaudio,

I understand that the theoretical process is complicated.

The junction temperature of the IC cannot be predicted with great accuracy using thermal camera data. We can get more accurate data by using thermocouples.

According to the rule of thumb, a temperature increase of 60 to 65 degrees rise is acceptable as long as it has attained its steady-state value and there is no cumulative increase in temperature due to self-heating over time.

It is always a good practice to do theoretical analysis and compare it with practical values.

Kindly let me know if you have any further queries.

Regards,

Nishanth

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Bravaudio
Level 1
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Level 1

The ambient temperature  here is 23c

The IC casing measures 65c steady state, that is the best measurment I can make here because there is a powerful fan blows directly over the top of the chip and any contact thermocouples that are used get cooled by the airflow so do not give an accurate measurment.

I am not designing a product here I have repaired it and it works well (all PWM waves look great) I just find the fact that the IRS2092 (65c) is at a higher temperature than the mosfets (35c) to be unusual & was seeking your opinion on if this was ok or not.

The IC case temperature has increased from 23c to 65c = 42c rise from ambient.

So are you saying that up to a 65c increase from ambient is ok? (a 65c rise would mean the IC casing measuring 88c).

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Bravaudio
Level 1
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Hi, I have been reading the answers again and I am not asking for a prediction of the junction temperature. It is the case temperature I have been measuring.

To make things a lot simpler can you please tell me the RthJC (thermal resistance from junction to case) parameter?

Then we will calculate the case temperature here.

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Bravaudio
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Full schematic attached.

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Nishanth
Moderator
Moderator 25 replies posted 10 solutions authored 50 sign-ins
Moderator

Hi @Bravaudio 

The IRS2092 can operate safely at a temperature of 65C.

I would advise reducing VCC to 12V if you want to improve it even further. The benefit is that RDS(ON) won't significantly increase while Qg of the FETs is reduced. This will further reduce the temperature.

Kindly let me know if you have any further queries.

Regards,

Nishanth

 

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