LM3409: Can find related webench calculator

Hello Yaroslav,

Due to the American holiday, E2E responses will likely be delayed. We will get back to you about this on Monday, September 29. Thank you for your patience!

Best Regards,

Caroline

Hello,

Webench was replaced with PSpice for modeling, Webench is no longer supported.  LM3409 is an older part an may not have tools the newer parts have.  If you have a particular design that needs to be calculated I can do that rather quickly.

Best Regards,

Hello,

Webench was replaced with PSpice for modeling, Webench is no longer supported.  LM3409 is an older part an may not have tools the newer parts have.  If you have a particular design that needs to be calculated I can do that rather quickly.

Best Regards,

Hello Irwin,

actually I need to accomplish this two configurations:

- 1.00A to 1.50A regulable current on LEDs at 24V;
- 1.00A to 1.50A regulable current on LEDs at 48V;

Since application is for camera vision, circuit should have a very fast turn-on, fully ON in about 100us. About ON time, it's very short of about 500us every 50ms.

If it's possible a unique configuration for both power supply 24-48V would be the best even if efficiency is low, since it's not a critical parameter for this application.

I've already added a second FET in parallel to LEDs witch will be used as Enable. While LM3409 enable is actually always on.

Hello,

Is the 24V and 48V the input voltage?  What is/are the LED voltage or voltages?

I'd like to know:

Vin, Vled, Iled which is above, desired switching frequency range and if output capacitance is used.  If you are adding a shunt FET (in parallel with the LEDs) you will need to add the Roff2 resistor to allow it to run when shunted.

100 us is actually quite long, you may be able to use UVLO for PWM depending on output capacitance, Vin, Vled, etc.

Best Regards,

Sorry for delay in my answer.

I need the possibility to power up the board (and LEDs) trought 24V or, if necessary, by 48V. This depends by attached LED board LEDs configuration, if is  required higher voltage or if 24V is enough.

So Vin can be 24V or 48V. Vled (Vf) is 11.64V when used with 24V LED board or 29.10V when used with 48V LED board.
Current is 2A on LED board. No desired switching frequency, only start speed requirements. No output capacitance.

Hello,

We are looking into this, and will get back to you by the end of the day.

Best Regards,

Caroline

Hello,

I ran two calculations for your two designs and added also what the 48V input would be using the 24 Vin Roff value.  This can be changed however you want it to.  I calculated the rise time to 2A using a 33 uH inductor as seen below.  If you don't want to use shunt FET dimming this is how long it would take to ramp to 2A.  If the off-time is long use UVLO for PWM dimming (not shunt FET).  If you decide to use Shunt FET dimming you will have to add the second Roff resistor as noted in the datasheet.

Best Regards,

Thank you for your calculations. In the case I want change output current to a lower value as 1.1A to 1.3A using Iadj , is it possible with this component configurations? Or side question is, what is the lowest output current archivable with this configuration without problems?

Hello,

Yes that is possible, note that it will be a linear transition since the LM3409 regulates peak current.  The offset is half of the current ripple.  For example 0.6A peak to peak current so the current sense resistor is calculated from 2A + 0.6A/2 = 2.3A.  For 1.1A you would scale Viadj down from maximum to 1.4A/2.3A*Viadjmax.  Current regulation accuracy will go down with lower Viadj voltage however it can be dimmed to very low levels.

The above is an example, it can be configured any way you want. such as 1.0A to 1.5A above or 1.1A to 1.3A.  If you want less current ripple the inductor value can go up.  Also ramp up time will go down proportional to the current setpoint.  1.3A would have a ramp up time of 1.3A/2A*5.34 sec for your 24V version or 3.47 seconds.

Being you load is almost half of your input voltage the ramp up and ramp down times will be similar.

Best Regards,