Difference between revisions of "OPTOUSB"
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[[File:OPTO-USB LTSpice Simulation.png]] | [[File:OPTO-USB LTSpice Simulation.png]] | ||
− | == Opto-Isolator Drive | + | == Opto-Isolator Drive Circuits == |
* Two isolated power domains | * Two isolated power domains | ||
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* Voltage can be either 3.3V or 5V | * Voltage can be either 3.3V or 5V | ||
− | |||
== Card Test == | == Card Test == |
Revision as of 09:55, 29 April 2020
Contents
Features
- USB to TTL level Serial (FTDI) Interface
- Genuine FTDI FT230XS part
- Standard FTDI drivers
- Buffered lines on the TTL level side
- Schmidt Trigger
- Voltage level hysteresis
- Improved slew rate
- Schmidt Trigger
- OptoIsolated Connections
- Transmit, Receive, RTS, CTS
- Configured for High Speed Serial
- The Host USB connection is independent of the state of the FTDI side of the interface
- Host side can communicate with the USB host whether or not the target is even powered up
- Target power on/off doesn't cause a USB disconnect - handy for debug
- Fast operation
- 3.3V or 5V FTDI voltage (order option)
- Transmit/Receive LED Connectors
- On-board LED resistors
- 49x49mm card
- (4) #4 Mounting Holes
Block Diagram
Separate Power Domains
- The OPTOUSB card has two distinct power domains.
- One of the domains is the USB side where the power comes from the USB connector/cable.
- The other power domain is on the TTL side where the power comes from the FTDI connector.
- This is unlike "normal" FTDI interfaces where the USB connection can power the FTDI side.
- This is the purpose of the optical isolation - to isolate the ground of the USB side from the target (FTDI) side.
Connectors
J1 - Mini USB Connector
- Standard USB Mini connector
J2 - Transmit/Receive LED connections
- PUP0 - LED Pullup to USB Power
- TXLED - Transmit LED
- PUP1 - LED Pullup to USB Power
- RXLED - Receive LED
J3 - FTDI Connector
- Signals are references to external system
- GND
- RTS (In to card)
- VCC (3.3V or 5V) - Power must be supplied to this pin
- Receive (Out from card)
- Transmit (In to card)
- CTS (Out from card)
Drivers
- [ FTDI Drivers]
Layout
Transfer Rate Characterization
- LTSpice Simulation results
- 8.6uS per bit = 115,200 baud
Opto-Isolator Drive Circuits
- Two isolated power domains
- USB side is powered from the USB 5V
- FTDI side is powered from external power
- Either 3.3V or 5V
USB side Drive Power
- 4N25 Optoisolator has Vf = 1.3V typical
- Optoisolator has 20% CTR (min)
- USB side has 2N3904 transistor for driving the optoisolator
- Vce(Sat) at 10 mA is 0.2V
- Vce(Sat) at 50 mA is 0.3V
TTL side Drive Power
- Voltage can be either 3.3V or 5V
Card Test
- UUT
- 5V Power Supply
- Loopback/FTDI Cable
- Pin 1 = Ground (5V Supply)
- Pin 3 = Vcc (5V Supply)
- Pin 2 - Pin 6 RTS/CTS Loopback
- Pin 4 - Pin 5 Tx/Rx Loopback
- Run puTTY
- Run Device Manager to determine COM port
- Set baud rate to TBD (115,200?)
- Loopback test