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CD74HC4051: CD74HC4051

yenwu lo
Prodigy 160 points
Part Number: CD74HC4051
Other Parts Discussed in Thread: TMUX1208, CD74HCT4051, TMUX4051

Dear Technical Support, I have questions regarding P. 8 of CD74HC4051 device, Attached is the related datasheet & P. 8 of the related datasheet of this device for your easy reference.. 

It seems that the circled area in P. 8 of CD74HC4051 datasheet shows 2 sets of Ron ( on resistance ) data, not sure what different test conditions in the test which will cause these 2 different sets of resistance values to happen?

Also, Io=1mA is shown in the "PARAMETERS" section for this set of test data, not sure if Io is changed to 10mA in the test, will the related ON resistance values be changed or remain the same as Io=1mA test case or not? If the resistance values do change when Io=10mA in the test, Not sure why the resistance value will change and will the resistance values be increased or decreased when Io=10mA? 

Thanks and look forward to hearing from you when convenient. 

yenwu lo

Acrobat Document_CD74HC4051.pdfAcrobat Document_CD74HC4051.pdf

  • 0
    Prodigy 160 points

    sorry, it seems that 2 attached files are same, I will attach the P. 8 of CD74HC4051_datahsset file here for your reference. Thanks. yenwu lo

     

  • 0
    Guru 317280 points

    The on-resistance of a transmission gate is lowest at the rails and highest somewhere in the middle. Compare with figure 2 in the TMUX1208 datasheet:

  • 0 in reply to Clemens Ladisch
    Prodigy 160 points

    Thanks. Guru, I see.

    But can you help to answer my question asked as shown below directly? Look forward to hearing from you when convenient. Thanks. yenwu lo

    It seems that the circled area in P. 8 of CD74HC4051 datasheet shows 2 sets of Ron ( on resistance ) data, not sure what different test conditions in the test which will cause these 2 different sets of resistance values to happen?

    Also, Io=1mA is shown in the "PARAMETERS" section for this set of test data, not sure if Io is changed to 10mA in the test, will the related ON resistance values be changed or remain the same as Io=1mA test case or not? If the resistance values do change when Io=10mA in the test, Not sure why the resistance value will change and will the resistance values be increased or decreased when Io=10mA? 

  • 0 in reply to yenwu lo
    TI__Mastermind 35638 points

    Hey Yenwu,

    It's a very small difference and it's hard to catch and it definitely took me a few read throughs to see it but the top section is when the input voltage (VIS) is vcc OR vee and the bottom section is vcc TO vee.

    So the VCC or VEE will be at the ends of the rail. So like Clemens shows above, you'll see that those RON values are slightly lower.
    VCC to VEE will encompass the entire sweet of Voltage inputs. So that will include those middle peaks which will be a little higher and will skew the RON typ values higher and of course have a higher RON max.

    I hope that clears things up! Don't hesitate to ask another follow up if I haven't cleared everything up!

    Thanks,
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 160 points

    Thanks, Rami, and also thanks to Clements for previous reply, I see your points, I hope to ask the other question as shown below, not sure if you can help to answer this following question if that is convenient and possible? Thanks. yenwu lo

     Also, Io=1mA is shown in the "PARAMETERS" section for this set of test data, not sure if Io is changed to 10mA in the test, will the related ON resistance values be changed or remain the same as Io=1mA test case or not? If the resistance values do change when Io=10mA in the test, Not sure why the resistance value will change and will the resistance values be increased or decreased when Io=10mA in the test? 

  • 0 in reply to yenwu lo
    Guru 317280 points

    The resistance of a MOSFET stays pretty much constant (unless you overload it, but you must stay below 25 mA anyway).

  • 0 in reply to Clemens Ladisch
    Prodigy 160 points

    Thanks. Clements, I see.

    1. So if I load the device with Io= 10mA in the test , the resistance value should stay about the same as using Io=1mA? 

    2. another question is related to the logic level of this device, please see the attached P. 7 of the related datasheet, in the circled area of this P. 7 attachment file, it seems to show that the logic level; when at Vcc=4.5V, the ViH=3.15V within the temperature from-40 to 125 deg. C range. So look like this device CD74HC4051 is a direct CMOS input logic level compatible device,

    So can I say that this device should be able to be compatible with the CMOS input logic level directly? and if the input side drive is a CMOS logic level device, then there is no issue to use this CD74HC4051 directly?

    Can you help to confirm if my above statement is correct or not? 

    Thanks.

    yenwu 

  • 0 in reply to yenwu lo
    Guru 317280 points

    Yes; the control inputs can be driven with CMOS logic signals.

  • 0 in reply to Clemens Ladisch
    Prodigy 160 points

    Thanks. Clemens, I see, Another question:

    If the control input signal is generated from a TTL compatible logic device, can this CMOS input logic compatible device CD74HC4051 be driven with that TTL logic compatible drive device without causing logic mistake issues?

    Thanks

    yenwu lo 

  • +1 in reply to yenwu lo
    TI__Mastermind 35638 points

    Hey Yenwu,

    That depends on your supply level. But assuming a 4.5V supply, since that's the supply you previously highlighted, it wouldn't be compatible in some conditions. The min VOH is 2.4V in TTL logic while the VIH is 3.15 for the CD74HC4051 @4.5V. So if you could guarantee a output voltage greater than 3.15V then it could work. You shouldn't have an issue on the VIL side as the max VOL is 0.4V for TTL. 

    So bottom line it isn't entirely compatible but you could make it work.

    Thanks,
    Rami

  • 0 in reply to yenwu lo
    Guru 317280 points

    The CD74HCT4051 has TTL-compatible control inputs, and the TMUX4051 can use control signals down to 1.8 V.

  • 0 in reply to Rami Mooti1
    Prodigy 160 points

    thanks. Rami, I see. Not sure do you have the related information source for the definition of min VOH is 2.4V in TTL logic? If so? can y0ou share with me if convenient. Thanks 

    yenwu lo

  • 0 in reply to Clemens Ladisch
    Prodigy 160 points

    Thanks. Clemens, I see. appreciate. yenwu lo

  • 0 in reply to yenwu lo
    TI__Mastermind 35638 points

    Hey Yenwu,

    Please see this Logic Guide on page 4 the logic levels.

    https://www.ti.com/lit/sg/sdyu001ab/sdyu001ab.pdf?ts=1694709394078&ref_url=https%253A%252F%252Fwww.google.com%252F

    For the 5V case, you'll notice that the CMOS VIlL is 3.5 while the 5-V TTL VOH goes down to 2.4 but can also go up to 5V. 

    Thanks,
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 160 points

    Thanks. Rami, I see. Appreciate. yenwu lo