Need help debugging a board utilizing the Lumissil IS31FL3733 LED driver

[pini.grigio]

Hi all!
I received a board fabricated by JLCPCB today incorporating a pretty boilerplate RP2040 setup with the IS31FL3733 12x16 LED matrix driver.
https://www.lumissil.com/assets/pdf/core/IS31FL3733_DS.pdf
https://www.lumissil.com/assets/pdf/core/IS31FL3733_EB.pdf

I have a 12 cathode by 16 anode led matrix display, and I can confirm the LEDs themselves are fine and turn on when I drive them manually.

The RP2040 and power circuitry also work fine, and I am able to see the IS31FL3733 chip on the i2c bus, and it behaves as expected - for instance I am able to write a value to the only R/W register and read it back.

However - it does not drive the LEDs no matter what I do.
I've read through the datasheet and compared my code with existing code examples to make sure I am configuring it right - but no luck.


A few points and observations I have made so far -
1. I am driving the IC (and thus the LEDs) with 3.3V, which according to the data sheet should be fine?
2. My leds are 2.0V forward voltage
3. There is no voltage on the Rset pin, which is connected to ground via a 33k resistor - which definitely seems to be part of or a result of the problem

I'm not sure how to debug this issue and would appreciate suggestions from anyone who has had experience with this chip or similar ones.

I'm adding my schematic and will gladly share any more information with anyone willing to assist.

[ Specified attachment is not available ]
Much appreciated!

[temperance]

I have no idea why you renamed Rext to Rset but:

Iout is: (840 x GCC) / (Rext x 256). See page 21 of the data sheet.

[pini.grigio]

That's how the pin was named in that footprint.
I have set Rext to 33.6k, the resistor is marked DNP since I'm manually soldering it