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TS3A4751: Power Sequencing Protection

Randy May
Prodigy 60 points
Part Number: TS3A4751
Other Parts Discussed in Thread: SN74CB3Q3125

Greetings,

I am using a TS3A4751PWR analog switch in the following generalized application which optionally turns on/off a 3.3k pull-up on a net.

The problem is that I have no control over when 3.3V_Remote turns on relative to the 3.3V (VCC) and there is a requirement in the datasheet that VCOM < VCC+0.3V.  I'm looking for a solution that minimizes the changes to the design as much as possible.  We were considering a) moving the 3.3k resistor to the COM input to reduce current or b) powering VCC through a 10k resistor, again to reduce current back onto the 3.3V rail.  Without knowing the internal architecture of the device, it's difficult to determine whether either of our proposed solutions will work.

Thoughts?

Thank

  • 0 in reply to Randy May
    TI__Mastermind 45350 points

    Randy,

    This power sequencing is a common issue when using signal switches and other logic devices.  I would recommend looking for a device that has powered off protection feature that eliminates the need for power sequencing the switch.  When Vcc = 0V the signal path will be Hi-Z for switches with this feature.  

    More information can be found I this tech note.  

    When I filtered the Ti.com parametric search tool for 4-channel, 1:1, with powered off protection I found these devices.  What do you think about the SN74CB3Q3125 device? 

    Thank you,

    Adam