LMG1205: How to get more efficiency

Hi Chase,

1. Where are these inputs and outputs being measured?
2. Are they using the same FETs in both designs?
3. Are they able to run the systems under identical conditions?

Thanks,

Daniel W

Dear Daniel,

Thank you for your support.

Here is more information for you first.

1. input is power supply 8V -> DCDC boost -> 16.6V on F2. they measured voltage and current on power supply.

output is RF_OUT1, the very right of the schematic. they connected 50 ohm power attenuator on RF_OUT1, and measured a power using spectrum analyzer (conducted method)

2. Yes, they used same FETs. they just changed gate driver only.

3. I think they can't. Because the input(8V) is originally pulse signal, so they cannot test under identical conditions.

and here are my question. (my customer already did few tests.)

1. They changed the value of R355 and R351 to 1Ω and 0Ω. it did work. but does it have any side effect for the circuit?

2. second they changed the value of R89 and R99 to lower value. it did work too, but they worried about zero cross. what is the minimum value of R89 and R99 to avoid zero cross?

3. is it effective to shorten the routing between U65.7pin and U61.B4pin / U65.5pin and U61.A4pin?

current length of routing is about 2mm, and maybe we can shorten it to minimum 1mm.

Please check these issues. Thanks.

Best regards,

Chase

Hi Chase,

Thank you for the continued information and updates.

1. There could be more ringing seen at the FET gates. This can be checked by probe to see if it is a concerning amount.
2. For questions on the SN74LVC3G14, please start a new thread with this subject.
3. I would not expect a such a change to make a large difference in the digital signals

Thanks,

Daniel W

Hi Chase,

What is the old part they were using?

I am looking into methods to increase efficiency in this system.

Thanks,

Daniel W

Dear Daniel,

I attach a URL of old part.

https://www.psemi.com/products/power-management/gan-fet-drivers/pe29102

and it would be a great help to us to confirm about relationship between propagation delay and efficiency.

(I clicked wrong resolved button.. Sorry!)

Best regards,

Chase

Hi Chase,

Out device expert is currently out of office. He will reply early next week when he's back. Thank you for your patience.

Best regards,

Andy Robles

Dear Andy,

Thank you for your reply. Please let me know if there are any updates about the issue above.

Best regards,

Chase

Hi Chase,

The competitor part has a much higher source current strength. This is the most likely cause of the difference in efficiency. A lower drive strength causes the FET to stay in a partially on state longer which causes more power dissipation.

Thanks,

Daniel W

Dear Daniel,

Thank you for your support.

I saw the specs what you mentioned. the competitor part has 2A peak source current, and LMG1205 has 1.2A peak source current.

Then how about LMG1210? it has 1.5A peak source current. Do you think that the efficiency of LMG1210 is much lower than the competitor part?

Actually we thought that the important factor which affects to efficiency is propagation delay, because low propagation delay makes less dead time.

Please give me your opinion about it. Thanks.

Best regards,

Chase

Hi Chase,

If the device is given the same input signals, the dead time should not be affected. The switch of both will be delayed about equally, varying by the mismatch (1.5ns typical)

Thanks,

Daniel W