ESD protection

[Rajinder1268]

Hi,
I have selected a FTDI231xs USB to UART device. Operating at USB 2.0 full speed 12Mbps. Power to the FT231x will be from 5V (filtered VBUS), then using the internal 3V3 LDO to power up the microcontroller etc.

I need to add ESD protection for 2 x data lines (D+/D-) and 5V. I realise the max capacitance allowable (line to line) is 5pF for USB 2.0. This should not be exceed, otherwise rise fall times can be affected. The ESD must be adequate for EN6100-4-2.

My question is
1. Voltage requirement for the ESD TVS array as it needs to protect the 5V and 2 x datalines
2. Clamping voltage required
3. Working voltage
4. Uni or bi-direction TVS array?

Is there anything else to consider. I have seen the RClamp0503F but not sure as it is for OTG applications.

 

[dick_freebird]

An alternative is to do something like on-chip ESD protection.
A plurality of forward-clamp diodes from Gnd to line, from line
to a VESD rail (which might or might not be 3.3V - LVDS has
only about 2V max).

Now put a fat zener from that ESD rail to local GND, and a fat
cap for filtering, and that VESD will be about 2.6V pumped by
3.3V, and all the forward diodes (except that one) will be
reverse biased all the time, but ready to dump overrange
currents into either Gnd or VESD.

Now you only care about the central zener, for conduction
qualities, and you care very little about the diodes - though
you do want adequate pulsed current capacity, and at the
threat current level, no more than maybe 2V forward, and all
that at your <=5pF. This is a well bounded component selection
problem, to solve by tedious inspection of parts tables.

 

[FenTrac]

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Look at a CG0603MLC-05E varistor. This is used on USB D+ and D- on Arduino Uno R3 in series with a BLM21 inductor to USB ground.