<P>The programmable parameters for the USB 2.0 interface are contained =
within=20
U9, a small serial eeprom. For details of these parameters, refer to the =
<A=20
href=3D"http://www.cypress.com/cfuploads/img/products/CY7C68300A.pdf"=20
target=3D_top>CY7C68300A datasheet.</A> For the programming file and =
details on=20
how to perform the programming, refer to my <A=20
href=3D"http://www.frankvh.com/mp3player/usb2.htm" target=3D_self>USB =
2.0 page.</A>=20
(Note that kits contain the serial eeprom already programmed.)</P>
<P>Cypress=92s website is: <A href=3D"http://www.cypress.com/"=20
target=3D_top>http://www.cypress.com/</A> </P>
<P>The use of the Cypress part means that no USB programming is =
required; it's=20
all internal to that chip. The part performs a full USB-to-IDE =
implementation;=20
all that's required from the AVR is to monitor the USB port and enable =
or=20
disable the Cypress part. Not having to write a mass-storage class =
interface, or=20
a PC driver, saves a tremendous amount of work.</P>
<P>For those reading the CY7C68300A datasheet, here's a clarification I =
received=20
from Cypress technical support. In the datasheet "absolute maximum =
ratings"=20
section it states that the maximum DC voltage that may be applied to =
output pins=20
in the high-Z state is VCC+0.5V. Given that VCC is 3.3V, this would be =
3.8V.=20
However the IDE specification allows 5V signalling, so it appears from =
the=20
datasheet that this part does not meet IDE spec.</P>
<P>This is not actually the case; Cypress tech support informed me this =
is an=20
oversight in the datasheet. That parameter only applies to non-IDE pins. =
The IDE=20
pins are all rated for 5V tolerance, even when they are tri-stated. They =
also=20
pointed out that the reason for this parameter in the datasheet was to =
prevent=20
designers from powering-down the chip when it's not in use. This would =
not work;=20
the chip could be damaged if VCC=3D0V with 5V on its IDE pins. In the =
design of=20
this player the CY7C68300A is always powered up so there is no concern =
about=20
damage to the part.</P>
<P>&nbsp;</P>
<H3>Power Supply</H3>
<P>For details on power-supply selection to power the player, read <A=20
href=3D"http://www.frankvh.com/mp3player/powersupply.htm">this =
page</A>.</P>
<P>This player accepts a DC supply in the 12.5 - 16 volt range. This =
voltage=20
range was chosen to allow operation from a car battery. A low-dropout =
linear=20
regulator U1 generates the 12V required for the disk drive as well as =
the LCB=20
backlighting. (I have not tested the player in a car; if you've tried it =
please=20
let me know how it went.)</P>
<P>A buck topology step-down switchmode power supply U2 and related =
parts=20
generates 5V for the AVR as well as for U7 the stereo DAC. +5V is also =
required=20
for the LCD display and pushbuttons, and the disk drive. The transil (or =

tranzorb), D1, provides overvoltage and reverse-polarity protection. =
Essentially=20
just an overgrown zener diode, it'll conduct if the voltage is too high =
(above=20
17 volts or so) or if the polarity is reversed. If the power fault is =
severe=20
enough that'll cause the fuse F1 to blow. Either way the player gets a=20
reasonable amount of protection. This is important in a car where the =
12V power=20
can get pretty nasty during engine starts and stops. It's also nice =
during=20
development because, as we all know, accidents can happen, and you don't =
want an=20
accidental reversed polarity to destroy your player.</P>
<P>The small linear regulator U3 generates 3.3V from the 5V to provide =
power to=20
the Cypress USB chip and the STA013 MP3 decoder chip.</P>
<P>Ground planes are poured on the PCB as much as possible. This is most =

noticeable around J3 and J4, the RCA audio connectors, where an isolated =

audio-ground plane exists on both sides of the PCB to maximise audio =
quality.=20
Filters L2 and L5 are used to provide that power and ground isolation to =
make=20
this possible.</P>
<P>Digital ground pours are common on the rest of the PCB. These act to =
reduce=20
the ground impedance and improve signal integrity. Ground pours are also =
used=20
around the power-supply components to act as a PCB heatsink.</P><!-- =
InstanceEndEditable -->
<HR color=3D#0000cc noShade>

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      Home</A></FONT></TD>
    <TD width=3D"70%">
      <DIV align=3Dright><FONT face=3D"Arial, Helvetica, sans-serif" =
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