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SN74LVC1G3157: SN74LVC1G3157 ioff function

Part Number: SN74LVC1G3157

customer conplain when I/O B is high leven, Vcc will have 1.6V even power down. is it related to ioff protection? SN74LVC1G3157 have no Ioff protectio, the 1.6V is caused by backflow current from I/O? any danger to the device? if I/O A is high, Vcc will also have voltage even power down ?

  • Zhang, 

    The SN74LVC1G3157 doesn't have powered off protection to prevent backflow through the ESD diodes when the Vcc = 0V.

    You will need to select a device like TS5A63157 with powered off protection to prevent this issue.  This device includes a leakage spec when Vcc= 0V.    

    Thank you, 

    Adam

  • In reply to Adam Torma:

    hi adam,
    sorry, VNO/VNC/VCOM's maximum is V+ + 0.5V in TS5A63157 SPEC page.3. one example is V+ is only 0V, VNO/VNC/VCOM can only to be 0.5V? i dont't think so, but could you hlep to explain? thanks!
    another question: I/O range usually is -0.5 ~VCC+0.5V in many SPEC, is it due to I/O's body diode with CMOS technology?
  • In reply to zhang myth:

    Zhang,

    1) The powered off protection specification applies when Vcc = 0 V.  You can see this in the powered off leakage current that when Vcc =0V up to 5.5 V can be placed on COM/NO/NC and <1uA will leak through the switch.

    2) There is typically an ESD protection circuit on the inputs of the signal path that is like a diode to Vcc or GND.  This is why the abs max specifies not to exceed  ~about a diode drop beyond the rails because there will be much exponential leakage current as the voltage increases beyond the supply rails. 

    Thank you, 

    Adam