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CD4051B-Q1: Operation possible with VEE=-2.5V, VSS = GND, VDD = +3.3V?

Joachim Wuerker
Mastermind 21765 points
Part Number: CD4051B-Q1
Other Parts Discussed in Thread: CD4051B, TS5A22364-Q1, ADS1261-Q1

Hi colleagues,

I have some issues understanding the CD4051B-Q1 datasheet.
In my system I have following supplies available: -2.5V, +2.5V and 3.3V.
I need to pass analog signals ranging from (GND -1.25V) to (GND + 1.25V) through the Mux.
I would like to control the Mux with GPIOs coming from an MCU that has 3.3V IO levels.

Can I supply CD4051B-Q1 with VEE=-2.5V, VSS = GND, and VDD = +3.3V and then control the Mux with 3.3V GPIOs?

If there is another analog Mux which could do that I am open to alternatives as well.

Regards,

  • 0
    TI__Mastermind 46347 points

    Hi Joachim,

    Unfortunately the CD4051B -Q1 vdoes not support passing negative signals through them. We do have a few switches that meet that capability. 

    The only Q1 part that we have that supports negative voltages is the  TS5A22364-Q1. It is a singe sided supply only. This part has an absolute minimum IO voltage of VCC - 6 and a recommended operating condition that the minimum IO voltage be VCC - 5.5V. This will provide the closest possible part to meet your needs, as with a VCC of 3.3 gives a -2.2Vio for recommended and then -2.7Vio for the absolute maximum range. The other drawback is that it is a 2:1 configuration, so to mimic a 8:1 a multi-chip solution is needed. 

    If there is anything else I can assist you with don't hesitate to ask!

    Best Regards,

    Parker Dodson

  • 0 in reply to Parker Dodson
    TI__Mastermind 21765 points

    Hi Parker,

    are you absolutely certain the analog input signal cannot swing between the VDD and VEE range? In my case between -2.5V and 3.3V when using VEE = -2.5V and VDD = 3.3V?
    The datasheet mentions:

    • 'if VDD = +4.5 V, VSS = 0 V, and VEE = –13.5 V, analog signals from –13.5 V to +4.5 V can be controlled'
    • 'signal input range for VDD – VEE = 18 V'
    • 'Logic-level conversion for digital addressing signals of 3 V to 20 V (VDD – VSS = 3 V to 20 V) to switch analog signals to 20 VP-P (VDD – VEE = 20 V).'

    This would indicate to me that what I try to accomplish is possible. But it doesn't explicitly say that in any of the specifications.

    The TS5A22364-Q1 doesn't look like a viable solution.

    Regards,

  • 0 in reply to Joachim Wuerker
    TI__Mastermind 46347 points

    Hi Joachim,

    I seemed to have misread the abs-max section of the data sheet, it showed Vio max to -0.5V, but that was with respect to the voltage range, I apologize.

    Yes this part uses a transmission gate topology which allows it to pass "rail to rail" signal levels. There is one caveat, and I have attached a graph from the datasheet to help show:

    The higher the current you are pulling through the switch, i.e. the lower the impedance of the load is, the resistance of the switch will have a greater affect due to insertion loss.Also the abs max current for the part is 10mA.

    My remaining question would be what does your load look like?  

  • 0 in reply to Parker Dodson
    TI__Mastermind 21765 points

    Thanks Parker.

    Can you also confirm that control with 3.3V is possible?
    The specifications do not mention any minimum supply anywhere or what the VIH, VIL levels would be at VDD = 3.3V

    We are not pulling any current. The Mux is placed in front of a precision ADC (e.g. ADS1261-Q1) which has high input impedance.

    Regards,

  • 0 in reply to Joachim Wuerker
    TI__Genius 9132 points

    Hi Joachim,

    Based on the datasheet Vil/Vih spec you can see that the control logic is the standard CMOS input buffer control logic and follows the rule of thumb VIH = VDD x 0.7 & VIL = VDD x 0.3.  With this rule of thumb, the VDD= 3.3 V :

    VIH = 0.7 x VDD = 2.3V

    VIL = 0.3 x VDD = 1V

    Regards

    Saminah

  • 0 in reply to Saminah C
    TI__Mastermind 21765 points

    Thanks Saminah.

    My biggest worry was if 3.3V digital works at all because there is no minimum VDD specified anywhere.
    Based on all above feedback my proposal should work fine then.

    Regards,