AL5817, analog dimming

[Noir_47]

Hello.

Maybe someone has already used this chip and can give me some advice.
I wrote to DIOEDES support, but I think that due to the non-critical importance of my question I will not receive an answer soon...

Product page, where there is a datasheet and user manual for the evaluation board.
Datasheet
EVAL board user manual

Product brochure.


Excerpt from the brochure:

Can be dimmed by external analog and PWM signal on VFAULT

Some questions:
1) Is it possible to dim using an analog signal via the VSET pin?
2) I did not see a clear requirement for a current shunt in the datasheet. Can I use my 0.04 Ohm shunt if the strip consumes about 2.5 A and is powered by 12 V, which gives a 0.1 V voltage drop on the shunt at maximum load.
3) Why is there a 1nF limitation on the capacitance between VSET and GND?

The capacitance between VSET and GND, if needed, is recommended to be less than 1nF.

[PCB.Wiz]

Some questions:
1) Is it possible to dim using an analog signal via the VSET pin?

Looks fine to me.
Note they spec a 7mV max offset.

2) I did not see a clear requirement for a current shunt in the datasheet. Can I use my 0.04 Ohm shunt if the strip consumes about 2.5 A and is powered by 12 V, which gives a 0.1 V voltage drop on the shunt at maximum load.

It will be a ground-capable opamp, so 100mV drop will be ok, but keep an eye on that 7mV max offset which then becomes 7%
 

3) Why is there a 1nF limitation on the capacitance between VSS and GND?

The capacitance between VSET and GND, if needed, is recommended to be less than 1nF.

That does seem strange. You could test one ?

[Noir_47]

That does seem strange. You could test one ?

To be honest, I think I somehow damaged the chip as a result of my careless actions...
I ordered a pair of new ones, but they will arrive in a few weeks.

Another thing that confused me about the datasheet was:

The voltage across the external sense resistor (R1) is fed to the FB pin for sensing. When the voltage exceeds VSET voltage the OUT goes lower, decreasing the drive to the external transistor.

[PCB.Wiz]

Another thing that confused me about the datasheet was:

The voltage across the external sense resistor (R1) is fed to the FB pin for sensing. When the voltage exceeds VSET voltage the OUT goes lower, decreasing the drive to the external transistor.

That's just simple negative feedback.
Such chips are designed to linear regulate, so they will have that bit right, and you do not need to worry too much about the descriptive words.

[Noir_47]

@PCB.Wiz
Thank you for the tips. Will try to use them as soon as possible.