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TCA6418E: Max current sink and usage as LED sink

Cameron Wutzke
Expert 3542 points
Part Number: TCA6418E
Other Parts Discussed in Thread: TCA9548A, TLC59283, TCA6507, TPIC6C596, , SN74LV595A, SN74HCS595

Hey!

I'm looking at a use case like this:

Two questions that come to mind: 

1) what would be the maximum current sink? Other newer devices have a "max ground pin current" spec or something and I can't find that for this device. Curious if the 25mA is per GPIO or total for the device.

2) If the highside 4V is higher than the device's supply, will the device continue to sink current? I believe yes per:

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1070800/tca6418e-gpio/3963241?tisearch=e2e-sitesearch&keymatch=TCA6418E%20current#3963241 "The device by default starts up with all GPIO ports configured as inputs with a 50 kΩ pull-down"

Happy to give more background on the use case if you have a small chip you'd recommend. Pretty sure this guy ain't it. Customer previously used a few NPIC6C596ABQ as a lowsides for 112 LEDs. The enable pin is used for PWMing. That part is now NRND.

I've been scanning our LED portfolio and logic portfolio for solutions, so far the top contenders seem to be 7x TLC59283 (LED) or maybe 16x TCA6507 with a bunch of I2C switches like TCA9548A

  • +1
    Guru 316690 points

    This sounds like a job for the TPIC6C596/5.

  • 0
    TI__Mastermind 26806 points

    Cameron,

    I agree that the TPIC6C596 is probably the most straightforward implementation if they already used the NPIC6C596. I'm going to pass this thread to our LED team to get their thoughts.

    Regarding the TCA6418E, the 50 mA absolute maximum and 25 mA recommended operating currents are per pin, but the main overall consideration for the component when it comes to total consumption is thermal.

    Best,

    Danny

  • +1 in reply to Danny Bacic
    TI__Guru* 97046 points

    It looks like this thread made it to logic, so I guess the LED guys didn't have anything to add.

    My recommendation would be to use a '595 logic function -- each device can drive up to 8 outputs and they are dead easy to control and daisy-chain. All you need is a SPI clock + data line, and one GPIO to 'copy' the outputs from the internal shift registers (this prevents random blinking while loading the data). The '595 also has an OE pin, so a PWM signal could be applied there for dimming purposes. There will need to be a limiting resistor on each output (probably can share with 2 LEDs).

    I have an app note that goes into great detail on the use of these devices and all the 'gotchas' that you might run into.  https://www.ti.com/lit/scea117 

    The shift registers can be supplied from 4V and eliminate the need for Vout > Vcc. Considering that there are only 3 or 4 control signals, a translator could be used to convert from whatever the controller has to the 4V supply.

    I'd probably look at the SN74LV595A and the SN74HCS595.

  • 0 in reply to Emrys Maier
    TI__Expert 3542 points

    I appreciate the help everyone! Been searching high and low for some solutions and this gave me some threads to pursure Slight smile