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TS12A12511: TS12A12511: Ron value exceeds upto 300/400 ohm.

Part Number: TS12A12511

Hello,

First I was using CDx4HCT4053, S0 S1 pins were directly connected to microcontroller which outputs 3.3V and 0V but the problem was the Ron was exceeding more than 200ohm, so I switched to TS12A12511 as it has lower Ron.
Now I'm using TS12A12511 with dual supply(5V) and the IN pin is directly controlled by microcontroller(3.3V). GPIO pins outputs either 3.3V or 0V to the IN pin for switching from NC to NO but there was no proper switching(In datasheet min voltage is 2.4V). When I read one of your application notes "Preventing Excess Current Consumptionon Analog Switches", I supplied 5V(single supply) and 0V externally to the IN pin to check and there was proper switching but Ron keeps changing upto 400 ohm.

How can or what are the possibilities that the Ron keeps changing, is it due to current?

And I need the Ron to be constant for my calculation as I'm using it with the voltage divider

  • SMK,

    The CDx4HCT4053 device on-state resistance should be <200ohms with +/-5V supply.  How are you measuring the on resistance?

    The TS12A12511 is lower on-state resistance switch <10 ohms.

    Are you able to provide scope captures of the switch not switching properly?  It would be helpful to see the COM, NC, NO and IN pin toggling?  Also I'm wondering if the GND pin and V- are internally connected and the Vih threshold is actually being referenced to -5V.  This would mean you would need -5 V for a logic low level and > -2.6 V for a logic high.  I will order some devices and a board to experiment with the Vih threshold.

    The on-state resistance will vary based on the input voltage as seen on the graph below and it will also vary based on temperature.

  • Thank you. Sorry but i'm not getting this point  ''the Vih threshold is actually being referenced to -5V. This would mean you would need -5 V for a logic low level and > -2.6 V for a logic high''.

    My setup: I'm using TS12A12511 with single supply(+5V), supplying +5v or Gnd to IN pin(can I supply 3.3V directly from the microcontroller?), V- is tied to ground as mentioned in the datasheet.

  • SMK,

    Ignore what I said about the Vih.   I confirmed no issue on my bench.

    I went to measure the on-state resistance for the device with V+ = 5V and IN pin 3.3 V or 0V.  I used a multimeter to measure the resistance from COM to NO and COM to NC and didn't see any issue. 

    How are you measuring the on-state resistance?

    Thank you,

    Adam

  • Please find the pdf attached below.

    Instead of 74HCT4053 now I'm using TS12A12511. VIN is AC input voltage(125V rms is max). Ignore R220 resistance.

    Setup: 2 TS12A12511 chip (dual supply 5V), IN pin is directly connected to the microcontroller(3.3V). I guess the problem is when I use this chip with AC signal.

    Using  multimeter to measure the on-state resistance.

    Thank you,

    smk

    switch.pdf

  • SMK,

    The IN pin of the TS12A12511 is the control logic pin or select pin for the device. To control the select pin you will need to place a voltage above the Vih for logic HI or Vil for logic LO. If you place 12V (I assume 125V is a typo because it will damage device) AC signal on the IN you should see connection change back and forth between signal path COM to NC or COM to NO.

    What is the frequency of the AC signal you placing on the IN pin of the TS12A12511 I don't think this device can switch faster than ~100kHz? It is possible the switch can turn on and off fast enough.

    Adam
  • No.

    Please refer the PDF which I had attested in my previous post.

    I'm controlling the IN pin using microcontroller, IN pin is directly connected to microcontroller(3.3V or 0V). VIN is the input voltage to my main circuit not to TS12A12511 IC. In the PDF VIN is the input voltage which is AC, and 74HCT4053(U203-A  and  U203-B) is replaced by  two  TS12A12511. VIN(can be upto 125V RMS)  goes through the attenuation network. One attenuation network is R205 to R209 - R210 ,R213, TS12A12511 and  another is  R205 to R209 - R211 , R214, TS12A12511. Because  of this attenuation network the VIN signal is attenuated to +/- 5V while passing through the switch IC, so no damage is done to switch IC. 

    Setup: Two TS12A12511 chip (dual supply +/- 5V), IN pin is directly connected to the microcontroller(3.3V). I guess the problem is when I use this chip with AC signal(range is from +/- 5V).

    Thank you.

  • SMK,

    Thank you for more clarity.  

    The Ron of the device does change with input voltage as you can see in the plots in the datasheet.  With an AC signal you can see that the Ron would vary as the voltage changes but it doesn't vary ~100s of ohms.  Also with your attenuation network the switch will only see a couple of millivolts which will keep the Ron vary constant. 

    In both cases you power the TS12A12511 with +/- 5 V and control the IN pin with 3.3 V logic.

    In case 1: are you applying AC 125V to VIN and placing mutlimeter probes on COM and NO/NC? 400ohms?

    In case2: are you applying DC 3.3 V to VIN and placing mutlimeter probes on COM and NO/NC?  Measuring 4 ohms ?

    Adam

  • Case 1:

    Yes, gives me Ron more than 300 ohms and multimeter probes on COM and NO/NC.

    I have not tested case 2.

    When I test only switch IC it works and gives Ron around 8 ohm but when placed in my circuit(the one in the PDF) it doesn't.

    Thank you.

  • SMK,

    That is good news that the device is not damaged and you measure 8 ohms when the device is out of your system.  

    In stead of using a multi meter to measure the resistance in your system would you check the voltage drop across the COM and NO/NC pin and the current.  We can check the switch resistance with ohm's law V=IR equation.

    Thank you,

    Adam

    Thank you,

    Adam  

  • SMK,

    Do you have any update to share on additional testing?

    Thank you,
    Adam
  • The switch is working fine. 

    Thank you so much for the help.