SCSI2SD Schematic Notes: Difference between revisions
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== Power Supply == | == Power Supply == | ||
5V supply from hard drive molex connector | 5V supply from hard drive molex connector should provide more than sufficient current. | ||
3.3V current | A [http://www.national.com/mpf/LM/LMS1585A.html LMS1585A] linear LDO regulator will be used to convert the 5v supply to the required 3.3v. | ||
* 5A max current is more than enough | |||
* Easy TO-220 mounting | |||
* 1.3V dropout @ 3A allows for 5V supply to drop to 4.6V | |||
* Significantly cheaper than a switching regulator | |||
* Simpler than a switching regulator. | |||
* At an expected peak current of 800mA, the regulator will dissipate: (5-3.3)*0.8 = 1.36W | |||
* Thermal Resistance Junction-to-Case: 2.3C/W | |||
* Assuming 40C ambient temperature, a 10C/W (or lower) heatsink will keep temperatures under 57C. [http://www.daycounter.com/Calculators/Heat-Sink-Temperature-Calculator.phtml]. Choosing a better heatsink will reduce temperatures further. eg. [http://au.element14.com/multicomp/mc33265/heatsink-to220-218-3-9-c-w-notched/dp/1710608 Multicomp MC33265] w/ 3.9C/W will keep temps under 49C for $1.71 | |||
Maximum power requirements: | |||
{| border="1" | |||
! | |||
!3.3V | |||
!5V | |||
|- | |||
|LPC1751 | |||
|600mA | |||
Rated at 100mA per supply pin.<br /> | |||
Analog supply pin unused. | |||
|0 | |||
|- | |||
|SD Card | |||
|200mA | |||
[http://www.embeddedrelated.com/groups/msp430/show/14851.php] | |||
|0 | |||
|- | |||
|UCC5617 | |||
Optionally powered by SCSI TERMPWR | |||
|0 | |||
|440mA | |||
|- | |||
|74HCT05 | |||
|0 | |||
| ? | |||
Likely to be insignificant | |||
|- | |||
|'''Total''' | |||
|'''800mA''' | |||
|> '''440mA''' | |||
|} | |||
== In-circuit programming == | == In-circuit programming == | ||
Revision as of 11:50, 12 October 2011
Details for the circuit design of SCSI2SD.
SMT Type
- 0805 sized components will be used where applicable. These represent a good tradeoff between hand-solderability and PCB board space.
Crystal Oscillator
- LCP1751 requires a 25MHz crystal, which results in a 100MHz clock with x4 PLL
- The crystal requires 2 caps for stability. The required value is:
2 * (CL - CS)
Where CL is the crystal's load capacitance, as specified by the crystal manufacturer, and CS is the PCB's stray capacitance (around 5pF for a reasonable PCB).
TXC - 9C-25.000MEEJ-T Load capacitance 18pF. Therefore, use 2x 22pF standard ceramic capacitors.
Power Supply
5V supply from hard drive molex connector should provide more than sufficient current.
A LMS1585A linear LDO regulator will be used to convert the 5v supply to the required 3.3v.
- 5A max current is more than enough
- Easy TO-220 mounting
- 1.3V dropout @ 3A allows for 5V supply to drop to 4.6V
- Significantly cheaper than a switching regulator
- Simpler than a switching regulator.
- At an expected peak current of 800mA, the regulator will dissipate: (5-3.3)*0.8 = 1.36W
- Thermal Resistance Junction-to-Case: 2.3C/W
- Assuming 40C ambient temperature, a 10C/W (or lower) heatsink will keep temperatures under 57C. [1]. Choosing a better heatsink will reduce temperatures further. eg. Multicomp MC33265 w/ 3.9C/W will keep temps under 49C for $1.71
Maximum power requirements:
| 3.3V | 5V | |
|---|---|---|
| LPC1751 | 600mA
Rated at 100mA per supply pin. |
0 |
| SD Card | 200mA | 0 |
| UCC5617
Optionally powered by SCSI TERMPWR |
0 | 440mA |
| 74HCT05 | 0 | ?
Likely to be insignificant |
| Total | 800mA | > 440mA |
In-circuit programming
UART0 pins, + active low program enable power supply while programming ? Custom header ? Custom bootloader as well ? Reuse for serial debug output ?
Switches
TERMPWR, terminator, parity, SCSI ID
