TLE4309, Dimmer using 10K pot, 3W white led

[Vindhyachal.takniki]

1. I have to connect a 3W white led light as here:   http://tinyurl.com/jpj3gnu & control its intensity using a 10K potentiometer.

2. If = 0.7A
Vf min = 3.2V
Vf max = 4.0V

Input voltage range: 5.4V to 8.4V
I think TLE4309 should work in this application.

3. Max adjustable current in IC: 500mA
So to be on same side I keep max 450mA.

Vref = 178mV.(From table)
so Rref = 178mV/450mA = 0.3955ohm

This is very close to 0.39ohm minium of Rref. Should I select higher resistance value then this r this is also ok? But if I go higher then Iref will reduce further & led will glow less.

4. Pin connection
Pin1: Connected to input voltage 5.4V to 8.4V, decoupled by 0.1uF
Pin3: Open
Pin4: Ground
Pin5: 0.39ohm shunt
Pin6: Open
Pin7: Led connected


Query:
1. Now I want to control the intensity of the led through 10K potentiometer. How do I do it?
Should I connect one terminal of potentiometer to pin1 i.e input, third terminal to pin4 i.e ground
and middle pin of pot to Pin2 of TLE4309.
Will this work?

[danadak]

This part controls current via PWM input, not a V input as your
10K pot would effect.

You could contact the Infineon FAE and ask for a V controlled part, or
ask what relationship exists between PWM voltage and bias supply.....


Regards, Dana.

[Vindhyachal.takniki]

Attached find a file named board. This is the circuit which works with potentiometer directly. A 10K pot is connected, varying it vary the led intensity linearly.
Package of IC is TO263-7, I think
Attached find schematic file. It is the reversed schematic of the board.

I had looked for many IC from different vendors for Led driver application in TO263-7 package. But they all are PWM control.

What is that IC.?
This board works ok.

[orolo]

If it is your chip, it could be that the potentiometer is being used to tune the current sense voltage at the REF pin. I think your schematic has a mistake: the 22K resistor is in series with the wiper of the potentiometer, so the REF pin is between the 22K and the 470 ohm resistor.

Compute the Thevenin equivalent of the middle point of the wiper plus 22K. That, in parallel with 470 ohms to the current sense voltage, is what the REF pin sees. For about 5 volts of input voltage, that would tune the current sense voltage from almost is raw value to about +0.1 volts, which is a dimming effect, since the chip senses more current than there is.

[Vindhyachal.takniki]

4 Can I do the equivalent in TL4309 with below connections:
Pin1: Connected to input voltage 5.4V to 8.4V, decoupled by 0.1uF
Pin2: Dont know what do connect?
Pin3: open
Pin4: Ground
Pin5: same ckt as in attached schemtaic. Five 1.8ohms, one 470ohm, 22K & 10k pot.
Pin6: Open
Pin7: Led connector