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Oliver Sedlacek
04/02/12 06:13
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Uk


 
Msg Score: +1
 +1 Good Answer/Helpful
#186972 - FTDI chip ESD sensitivity
Responding to: Raj Nambiar's previous message
I've just designed an FT232RL into a product and it took a lot of effort to get acceptable ESD immunity. Your symptoms sound similar, so I would have a look in this area. USB links horrible from an ESD viewpoint because you can spark to the end point and the ESD spike can travel through the USB cable to the PC in preference to a local earth.

In the end my solution involved transient suppressors on the USB 5V, DM and DP lines and opto-isolators (actually ISO7221AD chips) on the UART TX and RX signals. The FT232RL was USB powered, so you don't need an extra isolated 5V supply. I did try common mode chokes between the FT232RL and my CPU (instead of opto-isolators) and they had some effect, but not enough to meet CE levels. The idea was to add impedance into the ground loop, therefore controlling where the ESD goes. I might have got an acceptable result with common mode chokes if I'd spent more time on it, but I didn't have the time.

Connecting the USB screen to the correct ground is vital, as you get quite different behaviour if it's the CPU 0V, USB 0V of the chassis metalwork.

List of 36 messages in thread
TopicAuthorDate
FTDI F232RL Noise issues      Raj Nambiar      03/31/12 08:42      
   GND,cables      Stefan KAnev      03/31/12 11:51      
      of this is it, then      Erik Malund      03/31/12 14:19      
   leakage effects..      Jim Granville      03/31/12 16:46      
      Thanks for the comments..      Raj Nambiar      04/01/12 02:02      
         changing the serial port data....      Stefan KAnev      04/01/12 05:11      
         cable, bought off the shelf      Andy Neil      04/01/12 09:00      
            Test standard solutions      Jim Granville      04/01/12 14:54      
               Options..      Raj Nambiar      04/01/12 23:44      
                  VCP /D2X      Stefan KAnev      04/02/12 03:37      
                     Problem exists with both drivers      Raj Nambiar      04/02/12 08:34      
                  Aten serial to USB cable uses a FTDI chip      Kalpak Dabir      04/02/12 04:16      
   FTDI chip ESD sensitivity        Oliver Sedlacek      04/02/12 06:13      
      Thanks Oliver...      Raj Nambiar      04/02/12 08:30      
         Zeners are slow      Erik Malund      04/02/12 08:59      
         show Your circuit      Stefan KAnev      04/02/12 11:04      
            F232 is USB powered but.. + circuit      Raj Nambiar      04/03/12 01:32      
         USB Isolator Chips      Neil Kurzman      04/02/12 21:50      
            Isolators      Raj Nambiar      04/03/12 02:00      
         Better than zeners      Oliver Sedlacek      04/03/12 07:30      
            just a thought      Erik Malund      04/03/12 07:45      
               Layout      Raj Nambiar      04/03/12 22:13      
                  VCP/Direct drivers      Raj Nambiar      04/03/12 23:49      
                  Layout attached      Raj Nambiar      04/04/12 00:51      
                     It's a high speed circuit !!!!      Oliver Sedlacek      04/04/12 05:09      
                        Totally 100% Agreed      Michael Karas      04/04/12 05:34      
                           the trouble with schematics ....      Erik Malund      04/04/12 07:36      
                              Bandwidth limitation      Per Westermark      04/04/12 09:08      
   22 ohms between serial port ground and FT232 ground helps...      Raj Nambiar      04/05/12 23:58      
      of course it does      Erik Malund      04/06/12 08:01      
         Erik,      Raj Nambiar      04/06/12 09:45      
            Links please      Bert Van Den Berg      04/13/12 13:44      
               Link...      Raj Nambiar      04/16/12 00:12      
                  Solved      Raj Nambiar      06/15/12 23:59      
                     Magnetics      Per Westermark      06/16/12 02:08      
                        Ethernet input is connected to serial port ground      Raj Nambiar      06/22/12 08:56      

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