RGB LED chip - WS2811 - crazy idle consumption??

[Saimoun]

Hi all

I've got some WS2811 chips which are RGB LED drivers. I got the "last" version which seems to be called WS2811F or "v2.1.1" - see datasheet.

The chip is working perfectly fine, but I'm getting crazy 10mA current idle consumption on the VDD pin - way above the max 0.5mA specified by the datasheet? (maybe "quiescent current" got lost in translation...)

I'm powering the chip with 4.5V and a 180ohm resistor, which means the actual voltage at the VDD pin is 2.7V, actually below the "maximum rating" for VDD... But the chip works fine. I tried removing the 180 res (so that the VDD pin is at 4.5V) - works exactly the same, same brightness as well.

Note that I'm using 5 chips and all have the same behavior, all 10mA idle current (with LED off).

Anyone has any idea of why this is so messed up? 

Saimoun

PS: and if you make the math with the values straight from the datasheet, with a 5V rail and the recommended 150ohm res between 5V and VDD, that would put the VDD pin at 3.5V, right on the edge og the Absolute maximum ratings...

[Saimoun]

Oh and let me add that the Absolute Max ratings also mention the inputs to be max VDD+0.7 (which makes sense with a protection diode), which with VDD=2.7V and a 3.3V MCU puts it right on the limit as well...

[Phil1977]

Can you just connect GND and VDD to a power supply? If you see 10mA idle power consumption without any other circuitry then the devices may be broken.

Else I´d somehow suspect the DOut-Line. It´s more or less the only intended sink the chip has without lighting up a LED.

[Saimoun]

Thanks for the reply - but no I doubt there is anything wrong with the chips. They all work fine, I have 2 boards with 5 chips per board, every chip has the same behavior.

Interesting theory about the DOut - the 5 chips are linked together (Dout -> Din of the next chip), but the Din line requires very little current (makes sense, probably a CMOS input), also the last chip of the series (which has its Dout unconnected/floating) has the same behavior.

I changed the voltage from 4.5V to 5.2V, and funnily the voltage at the VDD pin is still 2.7V (which would mean the current going through that 180ohm res is now 13mA), it's almost like the chip uses that resistor as a voltage regulator? I remember reading on an old datasheet that there is an internal regulator which works with that input resistor... But I could not find it again 
The best I could find is the adafruit datasheet - attached.

[Phil1977]

Are the 10mA for all 5 chips on the board or is it 50mA in total?

Is the data line sending anything while the LEDs are off? I assume the quiescent current is measured with the LEDs off and a quiet data line. 2mA per device with active communication sounds reasonable.

[Saimoun]

Are the 10mA for all 5 chips on the board or is it 50mA in total?

Is the data line sending anything while the LEDs are off? I assume the quiescent current is measured with the LEDs off and a quiet data line. 2mA per device with active communication sounds reasonable.

I followed the diagram in the datasheet, so for each chip, you have:
5V rail -> 180 ohm res -> VCC pin

And what I am measuring is the voltage at each side of the resistor, which is 5.2V -> 2.7V for each IC, which gives 13.9mA going through the resistor. As I said it seems that 2.7V is constant, as with a 4.5V rail the current reduces to (4.5V-2.7V) / 180R = 10mA.

The dataline is set to output low from the MCU (for the first IC, the other ICs are connected in series Dout -> Din as I mentioned).

[Phil1977]

That´s not as intended...

Did you check with a scope if anything is oscillating?

[Saimoun]

Oooohh I found the issue - finally!!
Those 180 ohm resistors are 0402 so they have no markings on them, it turns out they were 18k and not 180!!

What tipped me off was that the voltage across the resistor was big - which would indicate a high current - but then measuring the actual current taken from the rail did not match...
That board was ordered from JLCPCB with who I never have experienced an issue - turns out it was my mistake the part says 1802 and not 1800 

Oh well - thanks for the help in any case!!