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OPA2674: Max out current OPA2674 is 350mA but its OP1dB=19dBm Why??

Gordon Liu
Intellectual 835 points
Part Number: OPA2674

Dear Sir,

This is Gordon Liu of WNC in Taiwan.

I want to use OPA2674 be a RF PA at 13MHz.

I use the below test circuit ti test it and I got OP1dB is only 19dBm but datasheet show the max output current is 350mA.

Could you teach me where wrong is??

PS: Load=50 ohm that is spectrum analyzer

BRs,

Gordon Liu

 

12V DC_In (mA) Pin (dBm) Pout (dBm) Gain (dB)
30 0 12 12
32 1 13 12
32 2 14 12
34 3 15 12
36 4 16 12
40 5 17 12
42 6 18 12
44 7 18.6 11.6
46 8 18.9 10.9
48 9 19.1 10.1
50 10 19.2 9.2

OPA2674 verify_20180910.TSC

  • 0
    TI__Genius 15975 points
    Hi Gordon,

    The OP1dB is limited to 19.2 dBm because you are not operating at the maximum output current drive of OPA2674 while driving an Rload of 100-ohms. From the OPA2674 datasheet (page 3), the maximum output voltage with an Rload of 100-ohms is limited to ±5.0V, which results in only ±50 mA (Vout/Rload) of output current drive. The resulting OP1-dB can be calculated as 20.96 dBm at DC using the below Pout equation, which probably gets reduced to 19.2dBm at 13MHz.

    Pout = 10log10[Vout^2/(2*0.001*Rload)]

    In-order to increase the OP1-dB, you would need to reduce the Rload while keeping the same output voltage swing (which will subsequently increase the output current drive). While doing so, it is important to not exceed the maximum internal power dissipation that will raise the junction temperature beyond 150'C. Output voltage and current limitation graph in the OPA2674 datasheet (page 9) gives this internal power dissipation boundary which is helpful in determining the lowest Rload you can achieve for maximizing the OP1-dB.

    I hope this clarifies the output P1-dB calculation for the OPA2674.

    Best Regards,
    Rohit
  • 0
    TI__Expert 8530 points

    Hi Gordon, 

    I've also noticed that you asked the same questions in the thread listed below. I am going to close that thread, please ask any further questions in response to this thread.

    e2e.ti.com/.../727640

    Regards,
    Jacob

  • 0 in reply to Rohit Bhat
    Intellectual 835 points
    Dear Sir,
    Thanks for your reply quickly.
    My test circuit is different ith your calculation.
    I use single 12V and 50ohm load so that I get Pout=31.58dBm base on your quation(Pout = 10log10[Vout^2/(2*0.001*Rload)]).

    Please check my confuses again.
  • 0 in reply to Gordon Liu
    TI__Genius 15975 points
    Hi Gordon,

    I think you are choosing the Vout value as 12V which is the supply voltage for the part instead of the actual output voltage of ±5V. You need to plug in 5V in the Vout value, which yields a Pout value of ~24dBm with an Rload of 50 ohms.

    Best Regards,
    Rohit