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SN74HC4851-Q1: Switch through current

Tomoaki Yoshida91
Genius 5255 points
Part Number: SN74HC4851-Q1
Other Parts Discussed in Thread: SN74CBT3251

Hi team,

We are looking for the decoder which has 3 control signals and 8 outputs.

We could not find a product that satisfys the required output current which is about 20mA.

So, I'm looking for a multiplexer that can supply current of about 20 mA.

I found several 8:1 multiplexers like SN74HC4851-Q1, but I can not judge to use when the switch current is around 20 mA.

I know that it can only be used less than 25mA, because it is written that the maximum rating of these devices is 25mA in the datasheet.

I want a material to judge how much current it can be used.

For example, it is Ron at 5mA, 10mA, 15mA and 20mA etc.


Please tell me if there are restrictions on switch current.

For our usage, Vdd and Vcom are supposed to be 5V.

Best regards,

Tomoaki Yoshida

  • 0
    TI__Mastermind 45340 points

    Tomoaki-san,

    If you are looking for a 8:1 device that can source or sink 20mA of current I don't think we have an option.  If you want to be able to pass 20mA of current through a multiplexers that shouldn't be an issue if you meet the current limit in the abs max rating.

    What do you think about the SN74CBT3251? 

    What are you trying to do in your system?  The SN74CBTXXXX family are NFET switches and will pass a signal ~Vcc - 1 due to the Vgs voltage of the FET getting low and operating in the cut off region.   You can see more information in this application note.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Genius 5255 points
    Hi Adam-san,

    Thank you for your support.
    I think that SN74CBT3251 is satisfied our requirement.
    But we need automotive grade.

    Do you have plans to release for Automotive grade?

    Best regards,
    Tomoaki Yoshida
  • 0 in reply to Tomoaki Yoshida91
    TI__Mastermind 45340 points

    Tomoaki-san,

    We currently do not have plans to release the SN74CBT3251 for automotive grade but that could always change based on market needs and business case. 

    The SN74HC4851-Q1 you already selected could support 20mA current

    I also found some other 8:1 switches that are automotive qualified using the TI.com switch search tool.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Genius 5255 points
    Hi Adam-san,

    Thank you for your support.
    I understood about the automotive grade.
    I am looking forward to being automotive.

    I understand that SN74HC4851-Q1 supports 20mA, but I'd like to know basic characteristics such as Ron when flowing 20mA to judge whether it can be used for our usage.

    If you have any information, please tell me.

    Best regards,
    Tomoaki Yoshida
  • 0 in reply to Tomoaki Yoshida91
    TI__Mastermind 45340 points

    Tomoaki-san,

    The on state resistance will not change with the current through the switch.  The on-state resistance will vary with supply voltage, I/O voltage, and temperature

    Below are my teste conditions

    Vcc = 6V

    A,B,C = 0 V

    COM = current sink

    Y0 = 3.3 V

    Ron was calculated by (Vcom - Vyo)/ current sink on COM pin

    Thank you,

    Adam