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Internal circuit of SN74HC4852

Vio Liu
Expert 3045 points
Other Parts Discussed in Thread: SN74HC4852

Hi Logic team,

SN74HC4852 is a analog switch, pin to pin compatible with CD4052. But it has injection-current effect control function. I can't find any document or data about the max transient injection current. Could you please help me provide more details about the internal circuit of SN74HC4854, especially the injeection-current effect control circuit?

THank you very much!

  • 0
    TI__Guru 58320 points
    Hi Vio ,

    I am sorry that I cant provide any further info on the injection current control circuits . I do not have access for the circuit schematics and I cant find any good document to provide you the info regarding this . The datasheet talks about the shift of output voltage data with injected current into the disabled channel. Fig 1 and Fig 2 shows the basic application diagram of the device .
  • 0 in reply to ShreyasRao
    TI__Expert 3045 points

    Hi Shreyas,

    Thank you for your answer. I can see from figure 2 that there's clamp diodes inside 4852 and of course it can tolerant higher voltage. But we don't have any data about the input voltage range if the input signal exceeds power supply voltage. Could you please help me check for that?
    If we can't provide these data, customer don't dare to use 4852 in their products.

    Thank you!

    Vio Liu

  • 0 in reply to Vio Liu
    TI__Guru 58320 points

    Hi Vio ,

    Input voltages(including I/O ports) can not exceed (Vcc +0.5)V . This will turn on the ESD diode connected to Vcc and could damage and /or affect the reliability of the part .The info can be found on the abs max table on the datasheet .

  • 0 in reply to ShreyasRao
    TI__Expert 3045 points

    Hi ShreyasRao,

    Thank you a lot for your reply. Compared to CD4052, SN74HC4852 has integrated clamp diode and input resistor so that it can tolerant higher voltage, which is even higher than power supply. 

    Best regards,

    Vio Liu

  • 0 in reply to Vio Liu
    TI__Guru* 96842 points

    It should be noted that the input voltage can be driven far above that listed on the absolute max table so long as the max diode current is not exceeded.  A series resistor is a common method to reduce this current to safe levels.  In this case, 20 mA is the max diode current.

  • 0 in reply to Emrys Maier
    TI__Expert 3045 points
    Thank you, Emrys!

    I've make it clear that the major improvement of 4852 than 4052 is the input resistor and the input clamp diode. Thank you!