OPA454: Alternate P/N required High Temp

Hi Hari,

You may want to consider OPA455 to substitute OPA454. OPA462 will work as well. 

LMC662 part is in stock. If you are able to tell me the application/design requirements, I can assist you to find an equivalent. For instance, if you are looking for ultra low input bias current, then LMP7721 may be a good replacement, but it does not operate up to 15V.  

I noticed that Thomas has replied your inquiries sometime ago. Is there anything we can do? Please let me know. 

Best,

Raymond

Hi Raymond,

Thank you for your time

Thomas replied to me those parts are working fine

May I know the OPA455 will work from -40 to 125 temperature range? As per the datasheet its operating temperature is –40°C to +85°C

My board will be going in thermal chamber and operating temperature range is -40 to 100Deg

Regards

HARI

Hi Hari,

Based pm thermal information, OPA455 will be running cooler than OPA454. if the power amplifier is consumed the same amount power (assumed that ground lug is soldered onto PCB board as suggested). The junction to board thermal resistance in OPA455 is approx. half of OPA454 per the datasheet. 

My board will be going in thermal chamber and operating temperature range is -40 to 100Deg

You should not have thermal issues if the OPA455s or OPA454s are operating at low temperature (e.g. -40C). When a thermal chamber reached at Tamb =100C, the wattage in OPA455 or OPA454 will determine if the part is operating at 100C. 

Yes, these parts are recommended to operate up to 85C. There may be performance degradation when operating beyond 85C. Based on the thermal information, it may withstand and survive 100C heat soaking tests (assumed you have air flow in a thermal chamber).  

If you are able to provide me with the Voltage, current, types of load and dynamic input/output signals you are driving at output (OPA454/OPA455 + LMC662), I may be able to estimate the junction temperature of these parts and give me ideas if the circuit is able to withstand near or at 100C thermal tests. 

Best,

Raymond

Hi Hari,

I want to clarify OPA455 recommended operating temperature from -40C to 85C. The performance in datasheet is specified and guaranteed from -40C to 85C. It does not mean that the part is unable to withstand the performance at Tamb = 100C.

OPA455 power amplifier is rated at higher current and Tamb will be naturally lowered if full power dissipation is designed at a product. Although the part's Tamb is only rated up to 85C, the IC's internal or junction temperature is operated a lot higher,. The junction temperature in both parts in OPA455 and OPA454 are comparable or near identical, therefore, it is expected that OPA455 should withstand 100C thermal test, if the power dissipation in both parts are the same.

If this thermal test is related to the final product and performance tests, then it will make sense to test OPA454 or equivalent op amps (because OPA454's specification is rated and recommended up to 125C in Tamb). 

Please let me know if you have additional questions. 

Best,

Raymond

HI Raymond,

Thank you very much.

Below is my circuit.

I/P voltage range is 34V to 36V and output voltage range is also the same.

Regards

HARI

Hi Hari,

I am not clear what your load is in LMC662A part. Since LMC662A op amp is configured in bootstrapped suppliy voltage, the voltage delta between Vupper and Vlow has to be <15Vdc at any given time. 

Based on the circuit shown below, LMC662A is estimated to dissipate at approx. 15V*1.1mA + (26.875-21.448)*0.143mA= 15.9mW.  Let us assume the thermal resistance at a rate of 165C/W, the junction temperature at Tamb of 100C inside of the LMC662A is approx. 100C + 165C/W*15.9mW < 103C (In fact 165C/W is estimated significantly higher than the actual figure, but let us assume that is the case). 

The conclusion is that LMC662A will be ok in withstanding 100C thermal temperature or soak tests. 

LMC662 Float 09242024.TSC

(Tj range in the table below may be typos). 

In terms of OPA454  power amplifiers, let us assume that OPA454 is running quiescent current of 4mA + 2mA at the LMC662 load, the total power dissipation at OPA454 will be 50V*(4mA + 2mA) = 100mW per op amp. 

Based on the thermal resistance figure below, OPA454's junction temperature will be approx. 100C + 20.7C/W*100mW = 102.7C < 103C approximately. In other words, OPA454's junction temperature is fairly low as well, if you do not place a heavy load at the output of OPA454 as drawn in the circuit. 

Enclosed is the simulation of the above circuit. There is some issue with floating supply voltage in LMC662 (floating supply voltage > 15Vdc). Since I do not know what is the input requirements, I will leave the simulation as is. 

LMC662 w OPA454 09242021.TSC

If you have additional questions, please let us know. 

Best,

Raymond