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General Category => Discussion - Hardware => Topic started by: N.H on February 05, 2022, 04:33:11 AM

Title: Handling the RESET# when using the FT234XD with USB self-power.
Post by: N.H on February 05, 2022, 04:33:11 AM

Hi

I am using FT234XD.
The power supply method is using the USB self-powered method.
There is an explanation to use "VBUS_SENSE" for reset in the item "6.2 Self Powered Configuration" of the specification sheet "DS_FT234XD.pdf", but it does not exist in the IC of this model.
I would like to use the Vbus from USB divided by two resistors and connect it to "RESET#" instead.

Let's consider the conditions under which USB becomes active without system power supply.
1) When the voltage is applied only to "RESET#", does it cause latch-up or other defects?


2) Is there a problem with leaving "RESET#" unconnected (OPEN) in order to avoid latch-up concerns?
Is there a possibility that the USB circuit will become inoperative because reset does not occur every time the USB Connector is inserted or removed?
The spec sheet also states that the RESET# pin can be Open when not in use.

Since the PCB is complete, I would like to know if there are any problems with methods 1) and 2) first.

I used a translation site.

Title: Re: Handling the RESET# when using the FT234XD with USB self-power.
Post by: FTDI Community on February 07, 2022, 05:01:56 PM

Hi,
There is an integrated Reset Generator Cell which provides a reliable power-on reset to the devices internal circuitry at power up. The RESET# input pin allows an external device to reset the FT234XD.    RESET# can be tied to VCCIO.

Regards
FTDI Community

Title: Re: Handling the RESET# when using the FT234XD with USB self-power.
Post by: N.H on February 13, 2022, 10:05:13 AM

Hello.
thank you for answering.
I understand how POR works.

I am concerned about the following two conditions.

1.
　・Self Power OFF (SYSTEM Power OFF)　
　　and
　・ (Connection USB Cable or Power ON USB Host Sysytem)

Q：The voltage rises only at the #RESET pin of FT234, but does it shift to a failure mode such as latch-up?



2.　Is there a problem with leaving "RESET#" unconnected (OPEN) in order to avoid latch-up concerns?
　
　CASE：I considered the case of operating in the order of 2-1)->2-2)->2-3)->2-4)
2-1) SYSTEM　Power ON　and　（Non Connection USB Cable or Power OFF USB Host Sysytem ）
     Occurs　POR.
　　
2-2) USB Plug Connection or USB Host Sysytem Power on
　　
2-3) USB Plug DisConnection or USB Host Sysytem Power Off
　　
2-4) USB Plug Connection or USB Host Sysytem Power on

Q：No reset occurs between 2-3) and 2-4), is there any problem for ft234?

（I'm using Google Translate.）