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USB Superspeed Peripherals

DaLi_3097136
New Contributor II

We have one question about protection of VBUS in FX3. From the datasheet, it has the required range between 4V and 6V. Is that also the same requirement during ESD event? If so, do you have any recommended solution? It seems hard to make sure such voltage doesn’t exceed 6V during ESD event, while allowing VBUS working voltage of 5.25V.

One more question: in our case, all FX3 rails are supplied externally, so can we put a voltage divider before VBUS pin to reduce the voltage a little bit, if VBUS pin is only for voltage detection?

Thanks,

Dawei

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1 Solution
Hemanth
Moderator
Moderator

Hi Dawei,

Regarding the following comment - "we have external regulators to generate 1.2V/1.8V/3.3V from VBUS pin of USB connector, which supplies FX3. VBATT is supplied with 3.3V, and FX3 VBUS (E11) is directly connected to VBUS of USB connector. So in this case, does FX3 draw any current from VBUS pin (E11)?"

>>I see that since VBUS pin of FX3 is connected from VBUS pin of connector and the IO power domains of FX3 are derived from VBUS pin of the connector (via regulators) - FX3 draws current from VBUS line.

For your information I mention the following:

Below two are the default cases:

a. USB Block of FX3 is powered by VBUS.

b. VBUS detection(which is necessary for a USB compliant device) is also done using VBUS pin voltage.

So, if VBUS from the USB connector is connected to VBUS pin then the USB block draws current from VBUS line. And at the same time if all the IO powers is also derived from this VBUS, then all the IOs and the USB block draws current from VBUS.

But, when you use the API CyU3PUsbVBattEnable(CyTrue), then the USB Block will be powered by VBATT pin voltage instead of VBUS.

Using CyU3PUsbControlVBusDetect(CyBool_t enable, CyBool_t useVbatt):

a. VBUS detection can be made to happen using VBATT pin (In this case useVbatt is set to true)

b. By making both the above parameters false, VBUS can be connected to a GPIO and necessary handling can be done in the firmware. (This case is irrelevant in your case since you are not doing it)

Regarding the ESD strike case:

VBUS pin is not expected to get voltage above 6V even during ESD scenario. Main cause for the ESD strike at VBUS pin would be a. User touching the USB connector b. Device Hot plug to the Host. In both of these cases OVP IC would be protecting the VBUS pin. That is the reason I had suggested it before.

Please let me know your comments.

Regards,

Hemanth

Hemanth

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Hemanth
Moderator
Moderator

Hi Dawei,

I understand from your comments that your device is self-powered.

So, are you connecting VBUS line from the connector to VBATT and supplying the VBUS pin externally?

Regards,

Hemanth

Hemanth
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Hemanth
Moderator
Moderator

Please refer to the schematic of FX3 Super Speed Explorer kit from the below link:

https://www.cypress.com/documentation/development-kitsboards/cyusb3kit-003-ez-usb-fx3-superspeed-exp...

Referring to the same we have used NCP360SNT1G as over voltage protection IC. This component has got ESD protection. You can get more details about NCP360SNT1G in it's datasheet.

Regards,

Hemanth

Hemanth
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DaLi_3097136
New Contributor II

Hi Hermanth,

Thank you for your response.

I don't quite understand your question. But for your reference, we have external regulators to generate 1.2V/1.8V/3.3V from VBUS pin of USB connector, which supplies FX3. VBATT is supplied with 3.3V, and FX3 VBUS (E11) is directly connected to VBUS of USB connector. So in this case, does FX3 draw any current from VBUS pin (E11)?

You have recommended the OVP IC, which seems to be a great protection. However, my original question was still not answered. Is the range of [4V, 6V] on VBUS pin of FX3 mandatory, even during ESD event, or it is spec only for working voltage? My guess is it is the latter, as it is almost impossible to maintain such range upon ESD strike.

Thanks,

Dawei

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Hemanth
Moderator
Moderator

Hi Dawei,

Regarding the following comment - "we have external regulators to generate 1.2V/1.8V/3.3V from VBUS pin of USB connector, which supplies FX3. VBATT is supplied with 3.3V, and FX3 VBUS (E11) is directly connected to VBUS of USB connector. So in this case, does FX3 draw any current from VBUS pin (E11)?"

>>I see that since VBUS pin of FX3 is connected from VBUS pin of connector and the IO power domains of FX3 are derived from VBUS pin of the connector (via regulators) - FX3 draws current from VBUS line.

For your information I mention the following:

Below two are the default cases:

a. USB Block of FX3 is powered by VBUS.

b. VBUS detection(which is necessary for a USB compliant device) is also done using VBUS pin voltage.

So, if VBUS from the USB connector is connected to VBUS pin then the USB block draws current from VBUS line. And at the same time if all the IO powers is also derived from this VBUS, then all the IOs and the USB block draws current from VBUS.

But, when you use the API CyU3PUsbVBattEnable(CyTrue), then the USB Block will be powered by VBATT pin voltage instead of VBUS.

Using CyU3PUsbControlVBusDetect(CyBool_t enable, CyBool_t useVbatt):

a. VBUS detection can be made to happen using VBATT pin (In this case useVbatt is set to true)

b. By making both the above parameters false, VBUS can be connected to a GPIO and necessary handling can be done in the firmware. (This case is irrelevant in your case since you are not doing it)

Regarding the ESD strike case:

VBUS pin is not expected to get voltage above 6V even during ESD scenario. Main cause for the ESD strike at VBUS pin would be a. User touching the USB connector b. Device Hot plug to the Host. In both of these cases OVP IC would be protecting the VBUS pin. That is the reason I had suggested it before.

Please let me know your comments.

Regards,

Hemanth

Hemanth

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DaLi_3097136
New Contributor II

Hi Hemanth,

Thank you! Now I understand that VBUS pin (E11) couldn't draw current if USB block is configured to be powered by VBATT in FW.

In terms of ESD scenario, I think I understand what you said, but I don't believe OVP IC, or possibly any ESD protection would perform fast enough to latch VBUS below 6V. Taking the example of OVP IC, NCP360SNT1G, its output turnoff time (toff, in page 5 of DS) is 0.8us (typ) and 1.5us (max). However, according to ESD model from IEC 61000-4-2, rise time of such ESD pulse is 0.8ns, and should finish around 100ns, which is much shorter than the 0.8us of turnoff time. That means by the time OVP IC reacts to ESD strike, VBUS has already been exposed such transient.

In addition, even with a dedicated ESD protection didoe, e.g. TPD1E10B06, it wouldn't clamp the pin, in this case, within 6V. As from the screenshot below, the voltage still rises up to 80V with +8kv contact ESD, within about 1ns. Given that such diode has to allow VBUS working voltage of 5.25V (upper limit), but clamping it down fast to 6V during ESD scenario seems like mission impossible.

pastedImage_1.png

Therefore, I think the 6V max voltage might only apply to VBUS working voltage. Also please advise if FX3 device has general ESD protection for VBUS pin, like for USB data lines mentioned in System Level ESD session of the datasheet.

Thanks,

Dawei

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Hemanth
Moderator
Moderator

Hi Dawei,

No, VBUS has not got internal ESD protection like the USB data pins.

Regards,

Hemanth

Hemanth
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DaLi_3097136
New Contributor II

Hi Hemanth,

Thank you for your confirmation!

Best,

Dawei

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