Can the FX3's IO power rail be set to 1.8V when using JTAG?

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MaXi_1246331
Level 4
Level 4
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In my PCB, FX3's IO power rail is set to 1.8V, which is also the power rail for FX3's JTAG interface. But problem occurs when openning segger GDB server, its GUI disappear. I think the voltage may be too low for the dongle to recognize the PCB. Is it true? Thank you.

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Thank you. I solve the problem by disconnect VREF and Vsupply pin at the Jtag interface of the PCB. Now JTAG related io voltage can be 1.8V. Vsupply is constant 3.3V sourced by the J-link.

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MaXi_1246331
Level 4
Level 4
50 replies posted 25 replies posted 10 replies posted

This because the Segger JTAG device output 3.3V and I connect the Vsupply pin with Vref pin at PCB. Vref pin is 1.8V. Short circuit occurs between 1.8V and 3.3V.

My circuit design follows that in cypress development board. I think cypress development board will have the same problem. Please confirm. Thank you.

Hemanth
Moderator
Moderator
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First like given First question asked 750 replies posted

Hi,

We don't see the problem when all the VIOs are set to 1.8V.

Please see the below figure:

pastedImage_0.png

Regards,

Hemanth

Hemanth

Thank you. I solve the problem by disconnect VREF and Vsupply pin at the Jtag interface of the PCB. Now JTAG related io voltage can be 1.8V. Vsupply is constant 3.3V sourced by the J-link.