SN74CB3Q3257: Specification Question

Jason Ciou

Expert 3600 points

Part Number: SN74CB3Q3257
Other Parts Discussed in Thread: TMUX1574, TS3A44159, TMUX1134, TMUX1575

Hi Team.

My customer has some issue of SN74CB3Q3257.

This is my customer specification,

I/O voltage is 1.8V

Vcc is 3.3V

Here is my customer question:

1.) According to this table. if Vcc is 3.3V, the VIH MIN voltage is 2V, does this mean if I/O voltage is 1.8V the output always low? If I want to avoid the problem, I need to reduce the VCC voltage?

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 316880 points

The SN74CB3Q3257 does not have any active outputs. These specifications are only for the control pins (S and /OE), not for the analog I/Os.

A closed switch behaves like a resistor of about 4 Ω, i.e., the pins on both sides are connected together, and any analog voltage between 0 and 5.5 V shows up on the other side.

+1 Jason Ciou over 3 years ago in reply to Clemens Ladisch

TI__Expert 3600 points

Hi Ladisch,

If I give a 1.8V signal on 1A pin, which mean the output voltage is around 1.8V?

If I want let select pin be high, the voltage should be above 2V when Vcc = 2.7 V to 3.6 V.

If I want let select pin be high, the voltage should be above 1.7V when Vcc = 2.3 V to 2.7 V.

Is this correct?

Jason

0 Clemens Ladisch over 3 years ago in reply to Jason Ciou

Guru 316880 points

Yes.

0 Jason Ciou over 3 years ago in reply to Clemens Ladisch

TI__Expert 3600 points

Hi Ladisch,

Thanks.

Could you recommend a multiplexers to me which can support my customer case.

the Vcc is 3.3V, and my customer only has 1.8V to control the select pin. It seems like SN74CB3Q3257 cannot support it.

Jason

+1 Clemens Ladisch over 3 years ago in reply to Jason Ciou

Guru 316880 points

The TMUX1574, TMUX1575, TS3A44159, and TMUX1134 work with 1.8 V control signals.

0 Rami Mooti1 over 3 years ago in reply to Jason Ciou

TI__Mastermind 35508 points

Hey Jason,

You can narrow down the devices you need by using the TI.com search tool.
You can select the configuration and channel count similar to the 3257 part (4ch 2:1) and the voltage range your customer is working with (Vcc = 3.3V), then on the left side in 'Features' check the 1.8 and 1.2V compatible logic.
This is the list I've narrowed it down to for devices that will fit this criteria

www.ti.com/.../products.html

Thanks,
Rami

0 Jason Ciou over 3 years ago in reply to Clemens Ladisch

TI__Expert 3600 points

Hi Ladisch,

Thanks for your help.

Jason

0 Jason Ciou over 3 years ago in reply to Rami Mooti1

TI__Expert 3600 points

Hi Rami,

I got it, it is more clear to me to find the device. thanks.

Jason

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SN74CB3Q3257: Specification Question