LM5085-Q1: As constant current driver

Arvind Munde

Part Number: LM5085-Q1
Other Parts Discussed in Thread: LM5085

Hi,
We are trying to use LM5085 DC-DC buck driver as buck constant current driver for LEDs. We are using Op-Amp and sense resistor to sense output current, Op-Amp output voltage is connected to Feedback pin. Also please note that the output current through LED is around 850mA. We have used voltage divider to limit maximum output voltage in case of LED Open circuit. In case of LED load connected the output voltage is up to 11.5V and In case of open load(led not connected) output voltage is 16V to 17V(Set by using Voltage divider and Diode D2). For more details please go through attached circuit diagram.

Is there any problem if we use LM5085 as constant current driver?

over 3 years ago

0 Timothy Hegarty over 3 years ago

TI__Guru 60727 points

Hi Arvind,

This may be okay assuming the normal ripple injection into FB isn't affected. See this app note for more detail on CC operation with the LM5085 by manipulating ISEN:

https://www.ti.com/lit/an/snva486a/snva486a.pdf

Regards,

Tim

0 Arvind Munde over 3 years ago in reply to Timothy Hegarty

Prodigy 90 points

Hi Timothy,

I have gone through this app note and due to BOM and current sensing sample to sample accuracy we are trying to use feedback pin instead of Isense pin. so is there any problem if we consider feedback back pin instead of app note. Also if possible can you please send design guide for app note, and it's sample to sample variation.

0 Timothy Hegarty over 3 years ago in reply to Arvind Munde

TI__Guru 60727 points

Arvind,

I have not tested such an implementation, but it should be okay -- just ensure that the COT injected ripple is unaffected.

Regards,

Tim

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LM5085-Q1: As constant current driver