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CD4503B: Designing a Buffer using CD4503B

Shibin Varghese
Expert 1130 points
Part Number: CD4503B
Other Parts Discussed in Thread: CD40109B

Hi Friends.
I have a small doubt.
If the VDD pin is connected to +12V, is it possible to switch the output Q1 by providing 0 and +3.3V at the input D1

In the circuit given I am using the buffer CD4503B,  the GPIO is switching at 3.3V logic is it possible to control +12V at its output level using 3.3V at the input provided the DISABLE pins are connected to ground directly.

  • 0
    TI__Guru* 96681 points

    Hello Shibin,

    The input must match the supply for this device -- if you are supplying the device with 12V, then the input must be 0V or 12V.  3.3V will not be a large enough voltage to switch the input.

    The CD40109B Quad Low-to-High Voltage Level Shifter will allow you to convert a 3.3V input logic signal to a 12V output logic signal.

  • 0 in reply to Emrys Maier
    Expert 1130 points

    Hi Emrys Maier,
    Thank you for your reply.
    The CD40109B is a level shifter but I am looking for a unidirectional buffer or line driver. is this chip is suitable for my application?.

    I don't know whether CD40109B is unidirectional or not. But as per the functional diagram, the chip is unidirectional.

    Here is the datasheet  of CD4503B, as per the datasheet, the input voltage at any input pin is in the range of -0.5V to VDD +0.5V


  • 0 in reply to Shibin Varghese
    TI__Guru* 96681 points

    Hi Shibin,

    The CD40109B is just a fancy buffer - it has two supplies to allow for voltage level shifting, but otherwise is just a buffer. In other words, it is unidirectional.

    It looks to me like you were looking at the CD4503B datasheet. The CD40109B datasheet does not have the same limitation on input voltage range.

  • 0 in reply to Emrys Maier
    Expert 1130 points

    Hi Emrys Maier,
    Thank You for your reply.

    In the datasheet of CD4503B, it is clearly written the input voltage at any input pin is -0.5V to VDD +0.5V.  

    Still, I have a doubt whether 3.3V is sufficient enough to switch the 12V output.

  • 0 in reply to Shibin Varghese
    Guru 263000 points

    The absolute maximum ratings tell you at which voltages TI guarantees that the device will not to be damaged permanently. This is not a guarantee that the device will actually work.

    The voltage at which the device is guaranteed to read an input as a high value is specified as VIH. Interpolating between the 10 V and 15 V specifications gives 8.6 V, which is much more than 3.3 V.