LT3922 Buck Mode Schematic

HI Kazu 

Can you send/post your LTspice file and let us have a look at it?

Regards

6064.asc

Hi,

Please check my schematic and let me know if something wrong.

Regards,

Kazu

HI,

Would you help take care of this case?

Thanks,

Kazu

Hello Kazu,

May I know what are your design specifics? e.g., input voltage range, on current, output voltage limit (for buck), etc.

Also, your above schematic will not work since the voltage at EN/UVLO is below its operating voltage.

Thanks,

Regards

Hi,

My design specific is below.

Vin=3.3V to 5V, LED=1 piece (Vf=0.8V to 1.5V, If=1.5Amax), 10% to 90% PWM (f=10kHz) and DC voltage dimming needed. Does not accept uModule due to its package.

If you have any suitable part (buck LED Driver), please let me know and give your recommeded schematic.

Regards,

Kazu

Hi,

Would you let me know if you have any suitable solutions covering my spec?

Regards,

Kazu

Hello Kazu,

Above is my recommended circuit for your buck LED driver. It is CC controlled up to 1.4A but note that CV is controlled via the FB pin.

Also, Rpot values from 0 to 190k controls the PWM Duty cycle from 10% to 90%, respectively.

By the way, are okay using a Buck-boost topology?

Thanks

Hello,

Thank you. 

Buck-boost converters are acceptable but your recommendation needs many external components.

Do you have other solution that has fewer ex components?

Regards,

Kazu

Hello,

LT3518 seems to meet my specific.

According to its datasheet, the FB pin is connected to GND for buck converter mode.

In buck mode case for LED drive, I don't have to set the output voltage?

Best Regards,

Kazu

Hi Kazu,

LT3518 is also suitable to your application.

FB pin is connected to GND since the buck converter is in constant current operation, and the current is controlled using the Rsense resistor. At Vctrl > 1V (since the CTRL pin is connected to Vref), the converter maintains the output current to be Iout = 100mV/Rsense. 

The only thing left is proper selection of components. I will try to design a buck converter with this IC base on your specification.

Regards,

Dave

Hi Kazu,

LT3518 is also suitable to your application.

FB pin is connected to GND since the buck converter is in constant current operation, and the current is controlled using the Rsense resistor. At Vctrl > 1V (since the CTRL pin is connected to Vref), the converter maintains the output current to be Iout = 100mV/Rsense. 

The only thing left is proper selection of components. I will try to design a buck converter with this IC base on your specification.

Regards,

Dave

Hello Dave,

Thank you for your prompt reply.

I look forward to your buck converter design.

Regards,

Kazu

LT3518_Buck-Conveter_CC.asc

Hello Kazu,

Please see the schematic, and tell us your feedback.

Vin: 3.3V to 5V

Note that the LED used has a Vf of ~3V. The schematic will regulate the LED current at 1.5A regardless of the forward voltage of the LED, given that Vinput > Vf.

Thanks

Hello,

Sorry for the late reply. 

Your schematic works well. Thank you.

Regards,

Kazu