LM3489-Q1: current limit at 100%duty cycle

Martin Steube-Henkel

Intellectual 1740 points

Part Number: LM3489-Q1
Other Parts Discussed in Thread: LM3489, LM3489EVAL

Tool/software:

Hello

our customer Forvia is using LM3489 to charge a supercap (4x25F in series)

Vin=12V

Vout=10V

Iout=8A

Below is the test result waveform of the Buck converter (LM3489QMM). When the output voltage reaches approximately 10V, resulting in a 100% duty cycle. However, the expected current limiting behavior is not being observed in this scenario.

The Mosfet used https://www.diodes.com/assets/Datasheets/DMP3028LPSQ.pdf is 28mOhm typ.

Why is the current limiting function is not working when the MOSFET is fully on with a 100% duty cycle?

BR Martin

7 months ago

0 Joshua Austria 7 months ago

TI__Mastermind 24115 points

Hi Martin,

Thank you for sending your schematic and issue description.

Are you able to obtain the LM3489EVAL board? If so, I would suggest as a first step to debugging this, please conduct an ABA test by taking the IC from your system and placing it on the EVAL board. Then please do the same test that you did to your system on the EVAL board. This way we can determine if the issue is one on the IC or on the system. Following this, we can debug the issue.

Thank you,

Joshua Austria

0 Martin Steube-Henkel 7 months ago in reply to Joshua Austria

TI__Intellectual 1740 points

Hello Josh

They don’t have LM3489EVAL board available (I just ordered one). However they tested on two different boards. Response is same for both boards.

Below are some additional observation:

Target Output Voltage	Input voltage	100% P CH MOS ON issue
10V	10.5V	Observed when output voltage closer to 10V
	11V	Observed when output voltage closer to 10V. But duration is less as compared to 10.5V input
	12V	Not Observed

For above configuration they set current limit approximately @5A. But when P Ch Mosfet goes in 100% ON mode, current limit function is not working and current goes upto 10A.

Please help us to understand above issue.

BR Martin

0 Joshua Austria 7 months ago in reply to Martin Steube-Henkel

TI__Mastermind 24115 points

Hi Martin,

What boards did they test on? Can they share the schematic for these boards?

Thank you,

Joshua Austria

0 Martin Steube-Henkel 7 months ago in reply to Joshua Austria

TI__Intellectual 1740 points

Hi Josh

I would like to continue via email. I shared the circuit via email

Martin

0 Joshua Austria 7 months ago in reply to Martin Steube-Henkel

TI__Mastermind 24115 points

Hi Martin,

Sounds good. I will close this thread here then.

Thank you,

Joshua Austria

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LM3489-Q1: current limit at 100%duty cycle