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I'm using the LED driver PCA9633 (8-pin.) After reboot, with default settings, the output of the LED pins are high, turning the LEDs on at reboot.

  1. Is there a good reason why I should want this?
  2. Is there a similar chip with default output state low?

Relevant default values:

  • SLEEP = 1 (low power mode, oscillator off)
  • INVRT = 0 (output logic state not inverted, value to use when no external driver used)
  • OUTDRV = 1 (LED outputs are configured with a totem pole structure)
  • LEDOUT = 00000000 (LED driver is off)

The 8-pin version doesn't have an OE pin.

The datasheet states:

If LEDOUT = 00, INVRT = 0, and OUTDRV = 1, LED state = VDD.

I'm using 12V LEDs, connected as shown at LED3 of the typical application:

typical application pca9633

I don't want to turn off the LEDs immediately after startup, the peak current at startup might cause problems. I'd like to avoid using additional hardware inverting the output signal.

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  • \$\begingroup\$ Could you flip the LED's around and low side switch them instead? Then, the default state would be off. \$\endgroup\$
    – Klas-Kenny
    Commented Sep 12, 2023 at 11:25

2 Answers 2

Reset to default
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You would normally connect the LEDs with a current-limiting resistor from the output to Vdd, so output = Vdd is 'off'. From the datasheet:

enter image description here

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  • \$\begingroup\$ This will not work for me, as I'm using 12V LEDs connected as shown at LED3. I will add this information to my question, thank you. \$\endgroup\$
    – Jay
    Commented Sep 12, 2023 at 12:01
  • \$\begingroup\$ In that case, you're scuppered since the reset condition of INVRT is 0 and no OE pin. You would need an extra inverter or a high-side driver per pin or some other additional circuitry. If you use a ULN2803 you can get 4 drivers and 4 inverters in one package (one additional quad resistor network required for pullups). \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Sep 12, 2023 at 12:08
  • \$\begingroup\$ Thank you, I will consider replacing the chip. \$\endgroup\$
    – Jay
    Commented Sep 14, 2023 at 7:59
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Replacing the chip with a PCA9632 solved this problem. It's almost the same chip as the PCA9633, but the default value of OUTDRV = 0. The LED output is by default High-Z.

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