LMX2582: want to know the typical power dissipation

Joanne Gu

Part Number: LMX2582

LMX2582 can be used as LO in the communication system, so its typical power dissipation is important to the system. But the datasheet did not give this spec. What is the value of power dissipation?

over 2 years ago

0 Noel Fung over 2 years ago

TI__Guru* 88930 points

Hi Joanne,

Power dissipation = power consumption = supply voltage x current consumption.

Supply voltage is 3.3V. Current consumption will depend on the configuration such as frequency and output power. Electrical characteristic in the datasheet has a typical current consumption at a certain configuration.

0 Joanne Gu over 2 years ago in reply to Noel Fung

TI__Prodigy 160 points

Hi Noel,

I set outA_PWR register by TICS_PRO. The value of outA_PWR is 12. Then I tested 3.6GHz and 3GHz output. I found that their powers were different. Output power of 3GHz is 1.56dBm, and 3.6GHz is 2.74dBm. Why did the power have such a difference?

0 Noel Fung over 2 years ago in reply to Joanne Gu

TI__Guru* 88930 points

Hi Joanne,

if the output is 50Ω pull-up, I don't expect this amount of variation in output power. are you using inductor pull-up?

0 Joanne Gu over 2 years ago in reply to Noel Fung

TI__Prodigy 160 points

Hi Noel,

These test results are from LMX2582EVM. According to the user guide, the inductor pull-up is used.

0 Noel Fung over 2 years ago in reply to Joanne Gu

TI__Guru* 88930 points

Hi Joanne,

Sorry I overlooked the key factor here. The power difference is likely due to the 3GHz signal is a divided down output while 3.6GHz is a direct VCO output.

0 Joanne Gu over 2 years ago in reply to Noel Fung

TI__Prodigy 160 points

Hi Noel,

Thanks for your reply!

You are right. 3Ghz signal and 3.6GHz signal are from different output. Can I understand that even if setting the same power value, the output method will still influence the output power?

0 Noel Fung over 2 years ago in reply to Joanne Gu

TI__Guru* 88930 points

Hi Joanne,

Correct. The power value is used to setup the buffer biasing (or gain), the actual output signal strength will depend on the input signal to the buffer.

0 Joanne Gu over 2 years ago in reply to Noel Fung

TI__Prodigy 160 points

Hi Noel,

If there is a demand to output a fixed power level, is there a recommended register setting value?

0 Noel Fung over 2 years ago in reply to Joanne Gu

TI__Guru* 88930 points

Hi Joanne,

This option is not available in the chip, user will have to develop a loop to make fixed output possible.

0 Joanne Gu over 2 years ago in reply to Noel Fung

TI__Prodigy 160 points

Hi Noel,

In the schematic above, R24,R25,R26,R27,R28,R29 is connected to the back of inductor pull up. Could you give further explanation about why use these resistors?

0 Noel Fung over 2 years ago in reply to Joanne Gu

TI__Guru* 88930 points

Hi Joanne,

They are typical 50Ω T-pad resistive attenuator.

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LMX2582: want to know the typical power dissipation