SN74CBTLV3251: SN74CBTLV3251 output voltage issue

Hi Ofer,

If you have tied /OE to VCC through a pull-up resistor, then The FET multiplexers/demultiplexers are disabled (high impedance)

To help understand the issue, can you provide the following details:

• When you say "unconnected" pins S0,S1,S2, are they floating? 
• At which pin do you measure 3.3V?
• Can you share schematic of your application?

Regards

Saminah

Hi Saminah,

Here is a part of my schematics:

I have 8 of them in my design.

By unconnected, I mean that the output that is not selected is not connected to input A.

1. S0, S1, S2 are connected to MSP430 IO and they are 3.3V or 0V.

2. OE - has a 10kohm pullup to 3.3V and it is also connected to MSP430 IO.

3. A = has a 10kohm pullup to 3.3V and  it is also connected to MSP430 IO.

I see in B1-B8 (except for the output selected by S0,S1,S2) about 0.6V ~ 0.7V (no load is connected to any of them).

Thanks,

Ofer.

The disabled outputs are indeed high-Z. This means that the switch does not force them to any specific voltage, and they are floating. When you measure them, you can see any voltage between 0 and 3.3 V.

If you want disabled outputs to have a high voltage, you have to add pull-up resistors to the outputs, not to the input.

Hi Clemens,

Thank you for your reply. 

If the disabled outputs are high Z, then why when I connect a resistor (like 1kohm) I see voltage across it?

All the best,
Ofer.

How do you connect the resistor?

From one of the outputs to ground