TPS61169: Driving HB LED string at 100mA

Hi Udi,

The LED configuration you have is 37.2V (12 * 3.1) + 0.22V (max Vref) = 37.42V which would cause the TPS61169 OVP detection to shutdown the boost output so it cannot support this application.

Best regards,
Randy

Hi Randy,

Thanks for pointing that out to me.

I have another LED string in my design with 4 NIR LEDs, each has maximum forward voltage of 3.5V.

I build a driver using TPS61169 with L=10uH, Cout=10uF and Rset=2 ohms but couldn't get the driver to output enough current/voltage to drive the LED string with 100mA.

Is there a limit to the maximum power I can get out of this device?

Thanks,

Udi

Hi Udi,

There should not be an issue driving the string that you describe.
Yes the power output is limited by VIN, SW ILIM and Efficiency (provided the application is within package thermal specification).
The output power for this configuration is:
((3.5V*4)+0.204V)*0.1mA = 1.42W
using 80% efficiency the input power would be 1.78W (1.42W/0.8)
The minimum VIN = 2.7 V, 1.78W/2.7V = ~0.66A SW current which is well below minimum of 1.2A.
Can you provide more detail on what is not working? Boost voltage? LED current?

Best regards,
Randy

Hi Randy,

Both current and voltage measured below what I would expect.

Is there a way I can send you drawings of the board layout?

Best regards,

Udi

Hi Udi,

Yes, do you have gerber files?
Was CRTL pin high? what was the output voltage and current?

Best regards,
Randy

Hi Randy,

The board is a double sided board. Print side is a full ground plane.
CRTL pin is high. I measured 10.6V on the output with current of 4mA.

Best regards,

Udi