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SN74HCS594-Q1: Operating current question

Zirui Su
Expert 5340 points
Part Number: SN74HCS594-Q1

Hi team

Here I have a question about its operating current.

After the chip is powered on, what is the device working current? I see a 20mA in the datasheet or what value is the chip working current?

At present, customer uses it as a control signal and do not use its driving function, but the power supply of the LED Driver still reaches more than 20mA. Could this drive current be reduced? Thank you.

Here is their schematic design, please help to improve it and reduce the driver current, thank you!

LED Driver.pdf

  • 0
    Guru 317450 points

    When you drive the base of an NPN transistor directly, then the current is limited only be the SN74HCS594-Q1's output impedance. This is likely to exceed the absolute maximum rating of 35 mA. (The maximum recommended current can be seen in the test condition for VOH; at 3.3 V, interpolation gives you 4 mA).

    You need a current-limiting resistor at each base. If you do not want to modify the board, use NPN transistors with integrated resistors (e.g., DTD113EKFRA), or MOSFETs (e.g., NX3008NBK or  DMG2302UK).