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CD74HC4052: ENABLE MAX TOGGLE SPEED

[FAE] Andrew Wang
Genius 10685 points
Part Number: CD74HC4052

Hi Team,

Customer has quick question.

  1. below graph was testing EN (pin6) at 5ms condition 

S0 & S1 were fixed at LOW

Output AN depends on EN LOW (on) ，HIGH (off)

2. Below graph was testing EN at 50us condition 

S0 & S1 were fixed at LOW

As we see, Output AN show abnormal waveform, seems EN toggling being too fast.

Customer's design 74HC4052 supply is +3.3 V ( with bypass 0.1uF)  

 Based on datasheet timing table, EN should be able to toggle in 100nS level, customer wants to understand what is legal MAX toggle speed of this device? Thanks!

 Andrew

  • 0
    TI__Mastermind 45575 points

    Andrew,

    The maximum frequency you can toggle the signals witch is not specified in the datasheet. 

    Based on my experience with the signal switches toggling at 20kHz shouldn't be an issue.  I usually only start seeing issues in the MHz range with some devices. What is your loading condition on the An pin?  It is possible the that when the An pin goes high impedance that capacitance on that bus won't allow that node to be pulled to ground fast enough. 

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    TI__Genius 10685 points

    Hi Adam,

    Customer tried to disconnect input(A0) and output (AN), and even control GPIO (EN/S0/S1) and only keep Supply and A1~A3 contact with the PCB, to make sure no loading effects, they are still seeing signal cannot go LOW at 50uS. Customer will not change circuit or layout because of tight schedule.

    Customer is asking if we can provide EN TOGGLE MAX FREQ ?

    Many thanks!

    Andrew

  • 0 in reply to [FAE] Andrew Wang
    TI__Mastermind 45575 points
    Andrew,

    We didn't characterize EN max toggling frequency but I will order some units and boards and take some measurements in the lab next week to see where the limit of the switch frequency is.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    TI__Mastermind 35528 points

    Andrew,

    After running tests in the lab with the similar setup on the toggling speed we found that the switch was able to perform properly toggling the enable at 50us with the circuit layout shown below. I tested an order of magnitude quicker as well (5us) and it looked fine. All the waveforms are also shown below.

    1.
    The graph below shows tests under the same test conditions as your initial case:

    EN pin at 5ms
    S0 & S1 low
    Power Supply 3.3V

    1.8k Ohm pull down, 5ms Period

    Here we found similar results, with the offset present. By changing the pull down resistor at the output (AN) to 200Ohm the offset was minimized. It’s not recommended to pull down with a lower resistor as the current draw begins to increase with lower resistance. The results are shown on the next graph:

    200OHm pull down resistor @ AN , 5ms Period

     

    2. When decreasing the switching time with the same circuit shown above with the 1.8k resistor on AN and a switching time of 50us the below graph was the result:
    EN pin toggling at 50us
    S0 & S1 low


    1.8k ohm pull down @ AN, 50us

     

    3. This toggling period can be decreased a bit more with the same 1.8kohm pull down at output and see decent results. I ran the speed down to 5us with the same circuit above and saw the following:

    At higher frequencies you will need to adjust the circuit to see better results.





    Rami

  • 0 in reply to Rami Mooti1
    TI__Mastermind 35528 points
    Andrew,

    Let me know if that made sense. If you have any further questions or want more clarification on anything, please let me know!

    Rami
  • 0 in reply to Rami Mooti1
    TI__Mastermind 45575 points

    Andrew ,

    We haven't heard from you in several days so I'm going to close this thread and assume you have your issue resolved.  If you have additional questions you may post them here to reopen the thread or you may create a new thread. 

    Adam

  • 0 in reply to Adam Torma
    TI__Genius 10685 points

    Hi Adam,

    Rally appreciate your strong support!! 

    I couldn't reach this RnD for few times. I will try later.

    I think currently you can close this issue. no problem.

    Thanks again, have a good weekend!

    Andrew