LM5165: PFM or COT operation?

steve wenner

Part Number: LM5165
Other Parts Discussed in Thread: LMR36503

Good morning.....

I have been reading through the above subject datasheet and have a few questions/concerns:

My application is a high voltage from Li-Ion batteries (15-21V) to 3.3V. I will be required to supply a maximum pulsed current for a radio / etc. of 130mA. This will be very infrequent with most of the time the system being in a LPM3 state....My application would be such that I would have instances of bursting RF information (8 bytes) every 80ms for 10 seconds or so with long periods (hours) of sleep

1. Can I use the LM5165 in PFM? (Datasheet 7.3.6 suggests for BCM that at best I will see 100mA when tying Ilim to ground....) Ilim to ground should be peak current of 240mA which implies 120mA out in BCM NOT 100mA???

2. Would COT be a better solution? (datasheet seems to imply this would be the way to go but when using WebBench I was not able to get the simulator to do COT for my application).....per datasheet

"Meanwhile, the corresponding output current capability in COT mode is higher as the ripple current is determined by the input and output voltage and the chosen inductance"

3. If neither of these modes of operation on this particular part are up to the task do you have another option (highly efficient, high input voltage converter)? (Searching on your site this seemed to be the part coming up)...

Sincerely...

Steve

over 3 years ago

0 Andy Chen over 3 years ago

TI__Mastermind 27045 points

Hi Steve,

At light loads, the PFM converter has a relatively longer sleep time interval and thus operates with lower input quiescent current and higher efficiency.

Please also check if LMR36503 meets your application requirements.

B R

Andy

0 steve wenner over 3 years ago in reply to Andy Chen

Expert 2355 points

Andy....

Thank you for the response. Before I go down the road to the 36503 can you please answer ALL my questions regarding the 5165...The 36503 is an advanced part N/A at digikey currently.

I looked into the EVM for the 5165 and it definitely shows it being used at 5V, 150mA which is a good sign. Can you please answer the question below:

(reposted from another post)

Datasheet (page 15) suggest when in PFM mode the inductor is tied to the switching frequency.....On page 16 the suggestion is when in COT mode Rt is tied to switching frequency.....My question is how do I come up with an inductor value when in COT mode?

Thanks

Steve

0 Andy Chen over 3 years ago in reply to steve wenner

TI__Mastermind 27045 points

Hi Steve,

The maximum output current at PFM mode is 120mA. so PFM mode maybe not applicable if you require 130mA load capability.

The inductor calculation on COT mode:

1. decide switching freq, for example 300KHz

2. Calculate RT for Fsw=300KHz

3. Select inductor current ripple is 30%~60%, for example 40%

4. Vin nominal voltage, for example 18V

5. load current 130mA.

6. calculated inductor =172uH, 150uH also can be used.

You also can download LM5165 Quick Start Calculator for your application design:

https://www.ti.com/tool/LM5165DESIGN-CALC

B R

Andy

0 steve wenner over 3 years ago in reply to Andy Chen

Expert 2355 points

Thanks Andy.....

Power management

Power management forum

LM5165: PFM or COT operation?