ISO6740-Q1: Functionality of enable Pin

Srivatsa Kolhapur

Part Number: ISO6740-Q1
Other Parts Discussed in Thread: ISO6740, ISO7741, ISO7710

Hi,

I am searching for an digital isolator where i can tristate outputs whenever required from the input side. ISO6740-Q1 has enable EN2. Is EN2 referenced to VCC2? VCC1 is 3.3V and VCC2 is 5V for my design. If EN2 is referenced to VCC2, I cant drive it from my FPGA which is working on CMOS3V3 logic. In this case, are there any digital isolators where i can tristate outputs from input side?

Thanks,

Srivatsa

over 2 years ago

0 Koteshwar Rao over 2 years ago

TI__Guru 52190 points

Hi Srivatsa,

Thanks for reaching out and for your interest in ISO6740.

Since this is an isolator, the circuits on a given side are only referenced to their local ground. Therefore EN2 is referenced to GND2.
You are right, EN2 can't be driven from VCC1 side. This is provided to be controlled by the MCU on the VCC2 side, for the applications where it is needed.

Please see below example connection diagram which describes how the EN pin can be controlled and used. Thanks.

https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/991655/faq-how-to-connect-spi-mcu-to-multiple-isolated-spi-nodes

Regards,
Koteshwar Rao

0 Srivatsa Kolhapur over 2 years ago in reply to Koteshwar Rao

Prodigy 108 points

Hi Koteshwar,

Thanks for the reply, Can you please suggest any isolator that meets my output disable requirement ? I searched but was unable to find isolator where i can disable outputs from the input side.

Thanks,

V K Srivatsa

+1 Koteshwar Rao over 2 years ago in reply to Srivatsa Kolhapur

TI__Guru 52190 points

Hi Srivatsa,

It isn't a typical use case for most applications where I see a requirement to enable/disable an output from its input side. Hence, we currently do not have digital isolators that support this.

Could you please elaborate the reason why you need to disable the outputs from the inputs side?

If it is critical for your application to achieve this functionality, then you could use a separate single channel digital isolator (ISO7710) whose output can be connected to EN2 of ISO7741 so that you can control their outputs from the additional channel created by ISO7710. Thanks.

Regards,
Koteshwar Rao

0 Srivatsa Kolhapur over 2 years ago in reply to Koteshwar Rao

Prodigy 108 points

Hi Koteshwar,

In avionics application, customer has put a requirement stating that all the control signals need to be tristated by Main processor in case of failure.These control signals are output from main processor. Hence the requirement. I have considered the same solution as you suggested i.e using extra isolator for enable.

Thanks,

V K Srivatsa

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ISO6740-Q1: Functionality of enable Pin