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Subject: Re: Is USB bus power stable enough?
Date: Thu, 24 Oct 2002 19:09:22 +0200
Organization: XS4ALL Internet BV
NNTP-Posting-Date: 24 Oct 2002 17:09:25 GMT
X-Newsreader: Forte Agent 1.92/32.570
On Thu, 24 Oct 2002 02:19:32 GMT, "Matthew Kendall"
>"Erik" wrote ...
>> At the moment I am working on an USB smartcard programmer.
>> The smartcard reader is bus-powered and has a step-up regulator
>> to generate a Vpp programming voltage (Vout is approximately
>> 13v). I have some doubts about powering the smartcard from the
>> Bus-power. Is this voltage stable enough? What about glitches
>> (I use a 4.7uF buffer cap)? Is the voltage high enough if there
>> are any hubs between the programmer and the root-hub?
>> Can someone give me some advice?
>Why don't you read the USB specification, available from
Exactly - the 0.5 mA max stby current before enumeration is usually a
problem. There are some dedicated chips handling that, thought TI did
some. For the card interface check LTC series (e.g. LTC1756)
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