THS4551: ths4551 shutdown

Marco Bevilacqua

Part Number: THS4551
Other Parts Discussed in Thread: TINA-TI, OPA837

Hi,

could you confirm that in shutdown the ths4551 outputs became high impedance? In the datasheet it is not specified this impedance.

I have seen this following answer on another thread but I am still confused about that particular state; in my application I would connect two THS4551 outputs together and enable only one THS4551 at time.

Hello Dave,
The outputs of the THS4551 will not become high impedance in shutdown. One of the issues in a fully-differential amplifier is that even if the amplifiers outputs became high-Z in shutdown, there still exists a relatively low impedance path through the feedback and gain resistors to the outputs of the previous driving stage.

-Samir

Thanks

Best Regards

over 6 years ago

0 kai klaas69 over 6 years ago

Guru 140200 points

Hi Marco,

what's confusing about that? Even if the outputs of THS4551 become high impedance, the feedback components are still there. The shutdown signal does not magic them away... :-)

Kai

0 Marco Bevilacqua over 6 years ago in reply to kai klaas69

Prodigy 110 points

Ok that's clear but my doubt it's about connecting two ths4551 and enable one at time; if one see at their outputs the feedback path of the other as load that should not be a problem no?

Thanks very much

0 kai klaas69 over 6 years ago in reply to Marco Bevilacqua

Guru 140200 points

Hi Marco,

you can run a TINA-TI simulation with the THS4551 TINA-TI reference design:

www.ti.com/.../toolssoftware

Kai

0 Sean Cashin over 6 years ago in reply to kai klaas69

TI__Mastermind 23226 points

Hi Marco,

Unless explicitly specified in the datasheet, as for the OPA837 for example, the disable pin does not make the output high impedance. It only powers the amplifier off. The output is still connected to a class AB output structure and any voltage applied to it will likely back power parts of the device through parasitic diodes and affect the signal to which it is connected. You will need to use a multiplexer or another ADC for the function above.

Best regards,

Sean

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THS4551: ths4551 shutdown