LM3466: led question

Hello,

1) It is in the datasheet though you have a choice in how to calculated it. Below is an example where Vsen is chosen at 0.35V. If setting the LED current to 350 mA per string Rsen would be 1 ohm. So if there was a current source of 1400 mA and four equal channels of LM3466 string would have 350 mA, Vsen would be 350 mV.

Chosing Vsen is a trade off between accuracy and power dissipation. You can use 200 mV, 300 mV or as the below example 350 mA or some other value you desire. Too low it will lose accuracy, too high and the resistor will dissipate more power.

From the datasheet:
EXTERNAL COMPONENTS
RSEN: To set the LED current of all 5 LED strings equal, the sensing resistors corresponding to all 5 LM3466 are
equal. It is recommended that the nominal voltage of the SEN pin VSEN should be around 0.3 V.
Therefore, RSEN is selected to be 1 Ω. As a result, VSEN should be 0.35 V if the LED current is 0.35 A.
CLED: If the cable connecting the LED string is long, the parasitic inductance of the cable may generate noise. If
this happens, a high quality ceramic capacitor should be connected between the ILED pin and ground. In
this example, a 100 V, 1 μF ceramic capacitor is used.
CIN: A high quality ceramic capacitor for decoupling should be connected from the VIN pin to ground. In this
example, a 100 V, 0.01 μF ceramic capacitor is used.
REQ and CEQ: The VEQ pins of all LM3466 are shorted together and then connected to ground through REQ and
CEQ. Only one REQ and one CEQ are required for each LM3466 lighting system. It is recommended that
REQ be 51.1 Ω and CEQ be 1 μF.

2) Yes, the intent of the LM3466 is to share current even when the LED string voltages do not match.

3) Rsns is what you calculated for your design per #1 above, it is Rsen. Example, if you have a 1 amp current source and two channels of LEDs sharing equally they will each have 500 mA. If you pick Vsen of 300 mV Rsen becomes 300 mV/500 mA = 0.6 ohms. If you chose Vsen of 200 mV Rsen becomes 200 mV/500 mA = 0.4 ohms.

The current limit protection circuit above will be very inaccurate with regards to temperature due to relying on Vbe. If you chose a low Vsen voltage it will become more inaccurate. In your design do you need this added protection? Or are you just looking for current sharing between multiple strings.

Regards,