CD54HCT4051: Using Analog/Digital Mux for voltage selection and digital signals

Srinivas H K

Prodigy 150 points

Part Number: CD54HCT4051
Other Parts Discussed in Thread: TPS2552, TPS2044, TPS2054

I need some technical advice. We are doing a test card for our internal testing. We have few requirements

We need to fan out same voltage with output of x8 ,one output at a time. Our input voltages are 1.8V and 3.3V.
We need to fan out some digital signals with output of x8, one output at a time. Digital signals clock (<25MHZ) , SDI (shift register dat )….

For both these options I selected couple of your parts

CD54HCT4051
TMUX1208PWR

Both these parts seem to be ok for my requirement. But 1208 seem to work better having less RON value and has better switching characteristics to support digital signals mentioned above . I have attached the block level diagram and spec snapshot

My question is the Vih,Vil spec (shown below from spec) is more for Select signals ( S0-S2) . For the channel input[A0:A7] and COM is there any such requirement ? I doubt though. While they mention fmax until 145 MHZ can I consider anything driving <145MHZ or 100MHZ clock as an example we don’t see any issue .

Krish

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 303820 points

These are analog switches; the I/O pins can have any voltage (between the power rails).

When a switch is on, it behaves pretty much like a resistor. What limits the signal frequency is the low-pass filter formed by this resistance and any parasitic capacitances.

0 Bryan Marshall over 3 years ago

TI__Genius 10974 points

Hi Krish,

You are correct in assuming the VIH/VIL levels in the datasheet only apply to the select/address pins for switching the active channel(s). The only requirement for the input channel voltage is that it has to be less than or equal to the VDD rail and greater than or equal to GND/lower rail.

In regards to the bandwidth, the value in the datasheet is set based on a fixed set of loading conditions, this can be increased or decreased based on the load of your application (lower RC at the load would lead to higher bandwidth and vice versa).

Thanks!

Bryan

+1 Srinivas H K over 3 years ago in reply to Clemens Ladisch

Prodigy 150 points

Thanks a lot Clemens. It helped.

+1 Srinivas H K over 3 years ago in reply to Bryan Marshall

Prodigy 150 points

Thanks a lot Bryan. It helped.

0 Srinivas H K over 3 years ago in reply to Srinivas H K

Prodigy 150 points

Bryan/Clemens ,

I have one more requirement. Basically i would be using this analog mux out to power on other circuitry. As an example these 8 channels out are connected to 8 different boards .These boards consume very less current. I would like to protect this switch from short circuit on the board. One option is to provide individual current limit switch similar to TPS2552 but this adds more components. Does TI has multiple channel current limit switch that i can use ? I couldn't find one or should i go for discrete approach. The voltages that i am powering through the analog switches are 1.8V and 3.0V

Krish

0 Clemens Ladisch over 3 years ago in reply to Srinivas H K

Guru 303820 points

Couldn't you put the current limiter in front of the mux?

0 Srinivas H K over 3 years ago in reply to Clemens Ladisch

Prodigy 150 points

Yes that's what i am planning to but instead of putting current limiter in each channel is there 4-channel current limiter that i can use so that overall circuit can be optimized.

0 Ziv Zhang over 3 years ago in reply to Srinivas H K

TI__Mastermind 18031 points

Please check TPS2044, TPS2048, TPS2054 and TPS2058.

For TI's policy, I will first click resolved button.

If you have any other concern, contact me any time.

If you think resolved, please help click 'Issue is solved button'.

Thanks.

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CD54HCT4051: Using Analog/Digital Mux for voltage selection and digital signals