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SN74HC373: SN74HC373 ULN2003A

minoru mayumi
Prodigy 80 points

Part Number: SN74HC373
Other Parts Discussed in Thread: ULN2003A, , TPL7407LA, TLC6C598-Q1

I apologize for just confirming this.
I'm using the SN74HC373 and ULN2003A to control LEDs, and each channel is about 20mA.
1. According to the graph in Figure 5-7. Maximum and Typical Saturated VCE vs Output Current for the ULN2003A, VCE is about 0.7V at 20mA. Is this the correct way to read it?
2. Taking into account the hi-z output of the SN74HC373, it's correct to add a 10kohm pull-down resistor.
Are there any other points to note? Please let me know.
Are there any problems with combining the SN74HC373 and ULN2003A?

  • 0
    TI__Mastermind 43995 points

    Hi,

    I would recommend asking these questions in the forum for the ULN2003A. This is the Logic forum that only supports the SN74HC373. 

    At least for #2, adding a pull-down would depend on when the device will be in Hi-Z output. Can the input to ULN2003A be left floating? 

  • 0
    Guru 321620 points

    1. Yes. The ULN uses Darlington transistors, i.e., the second transistor's VCE cannot become lower than the first transistor's VBE. (If you want lower output voltages, use low-side switches with MOSFETs, i.e., TPL7407LA.)

    2. The ULN2003A and TPL7407LA already have internal pull-down resistors.

    If you can control the LEDs with a shift register instead of latches, consider integrated power logic like the TLC6C598-Q1.