Disabling Outputs

[Cosford]

Hi Guys,

In all the fun of interfacing this TLC5917 LED Driver, I've discovered it draws around 15mA, even while not sinking any current from the LEDs. As this is a battery powered unit and the 5917 is only being used very sporadically, I need to 'switch it off' so-to-speak.

I believe the best way to do this would be to adapt the circuitry I've used to do the same for the WS2812B's, which in turn is based on the circuitry discussed in this thread (Here).

I do, however, need to prevent the TLC5917 drawing power from any inputs (from the Teensy). What would be the best way of doing this? Of course I could just keep those lines low with digitalWrite while the chip isn't powered up, but as I've discovered through testing on breadboard, allowing current to be drawn through these inputs for more than a second or so, blows the 5917 and I don't wish to end up having to change out 5917's on PCB due to programming errors. Is there a better method?

Thanks in advance,
Cosford.

EDIT: One idea; could I use an SN74AHCT126D Tri-state buffer (http://www.farnell.com/datasheets/1857313.pdf), tie all the OE pins together using those as one single enable pin (as-well as the enable pin for my load switching circuitry), to make the inputs to the 5917 high-impedance?

 

[PaulStoffregen]

Maybe use a FDV304P transistor?

Or if the current will be lot more than 15 mA when the TLC5917 is in use, you might need a transistor with lower a Rds spec. Typically those have much higher gate capacitance/charge, so a 330 ohm resistor might be needed between the Teensy pin and the transistor gate.... and a brief delay in your code to allow time for the gate to charge and the transistor to be turned fully on.

 

[Cosford]

Thanks for your reply; I'm still a little unfamiliar with transistors, so bare with me.

The current draw of the 5917 shouldn't go any higher than that 15mA. The driver works by sinking current, so there's no additional power draw when it's in use (at least, not that I can find on the datasheet).

I had intended to use high side switching with an MMBT3904 N-type transistor, to activate a TSM2311CX MOSFET. I'd selected this method, simply because I'd used it with the WS2812b's, so knew it would work.
Are you suggesting the FDV304P would be a better method? How would I implement it?