RasPi-GVS

Features

• Daughtercard to the Raspberry Pi (you supply the Raspberry Pi)
• 3.3V to 5V bidirectional voltage translators on GPIO (General Purpose Input/Output) lines
• (7) 5V GPIO lines on GVS connectors
• (2) 5V SPI interfaces (can be used as 5 GPIO lines)
• (1) 5V UART (serial port) interface
• (1) 5V I2C interface (can be used as 2 GPIO lines)
• GPIO_4 enables/disables the voltage translators
• Resettable Fuse protection on the 5V power lines
• 7-9V input voltage on the Power Supply connector (option) which has a regulator that can power the GVS connectors (within thermal limits of the regulator) removing any 5V load from the Raspberry Pi itself
• Jumper to select power for GVS (allows the GVS connectors to be powered from either the on-board regulator (option) or powered from the Raspberry Pi)
• 49x49mm card form factor

Voltage Translators

The Raspi-GVS board uses Texas Instrument TXS0108 voltage translators.

Voltage Translators Features

• No Direction-Control Signal Needed
• Max Data Rates
  • 60 Mbps (Push Pull)
  • 2 Mbps (Open Drain)
• 1.2 V to 3.6 V on A Port and 1.65 V to 5.5 V on
• B Port (VCCA ≤ VCCB)
• No Power-Supply Sequencing Required –
  • Either VCCA or VCCB Can Be Ramped First
• Latch-Up Performance Exceeds 100 mA Per JESD 78, Class II
• ESD Protection Exceeds JESD 22 (A Port)
  • 2000-V Human-Body Model (A114-B)
  • 150-V Machine Model (A115-A)
  • 1000-V Charged-Device Model (C101)
• IEC 61000-4-2 ESD (B Port)
  • ±6-kV Air-Gap Discharge
  • ±8-kV Contact Discharge

Voltage Translators Architecture

Datasheet

The TXS0108E can be used in level-translation applications for interfacing devices or systems operating at different interface voltages with one another. The TXS0108E is ideal for use in applications where an open-drain driver is connected to the data I/Os. The TXS0108E can also be used in applications where a push-pull driver is connected to the data I/Os, but the TXB0104 might be a better option for such push-pull applications. The TXS0108E device is a semi-buffered auto-direction-sensing voltage translator design is optimized for translation applications (e.g. MMC Card Interfaces) that require the system to start out in a low-speed open-drain mode and then switch to a higher speed push-pull mode.

To address these application requirements, a semi-buffered architecture design is used and is illustrated above (see Figure 1). Edge-rate accelerator circuitry (for both the high-to-low and low-to-high edges), a High-Ron n-channel pass-gate transistor (on the order of 300 Ω to 500 Ω) and pull-up resistors (to provide DC-bias and drive capabilities) are included to realize this solution. A direction-control signal (to control the direction of data flow from A to B or from B to A) is not needed. The resulting implementation supports both low-speed open-drain operation as well as high-speed push-pull operation.

When transmitting data from A to B ports, during a rising edge the One-Shot (OS3) turns on the PMOS transistor (P2) for a short-duration and this speeds up the low-to-high transition. Similarly, during a falling edge, when transmitting data from A to B, the One-Shot (OS4) turns on NMOS transistor (N2) for a short-duration and this speeds up the high-to-low transition. The B-port edge-rate accelerator consists of one-shots OS3 and OS4, Transistors P2 and N2 and serves to rapidly force the B port high or low when a corresponding transition is detected on the A port.

When transmitting data from B to A ports, during a rising edge the One-Shot (OS1) turns on the PMOS transistor (P1) for a short-duration and this speeds up the low-to-high transition. Similarly, during a falling edge, when transmitting data from B to A, the One-Shot (OS2) turns on NMOS transistor (N1) for a short-duration and this speeds up the high-to-low transition. The A-port edge-rate accelerator consists of one-shots OS1 and OS2, Transistors P1 and N1 components and form the edge-rate accelerator and serves to rapidly force the A port high or low when a corresponding transition is detected on the B port.

Power Supply

The RaspPi-GVS offers flexible power supply options. The 5V for the GVS Connnectors and translators can come either from the Raspberry Pi or from the 5V power supply on the RaspPi-GVS.

A three pin header and jumpers are used to select the voltage source(s). Installing a single jumper from pins 2 to 3 allow the Raspberry Pi to power the GVC connectors and voltage translators. Installing a jumper from 1 to 2 powers the GVS connections and voltage translators from the 5V power supply.

Connectors

P1 - Raspberry Pi GPIO Connector Raspberry Pi Connector

RasPi-GPIOs.png

J1 - I2C bus GND 5V SDA=GPIO2 SCL=GPIO3 J2 - UART I/F GND 5V Tx=GPIO14 Rx=GPIO15 J3 - IO_18 GVS GND 5V GPIO_18 J4 - IO_17 GVS GND 5V GPIO_17 J5 - IO_27 GVS GND 5V GPIO_27 J6 - IO_23 GVS GND 5V GPIO_23 J7 - IO_22 GVS GND 5V GPIO_22 J8 - IO_24 GVS GND 5V GPIO_24 J9 - IO_25 GVS GND 5V GPIO_25 J10 - SPI0 (Serial Peripheral Interface) GND 5V MOSI (GPIO_10) MISO (GPIO_9) SCK (GPIO_11) CE0 (GPIO_8) J11 - SPI1 (Serial Peripheral Interface) GND 5V MOSI (GPIO_10) MISO (GPIO_9) SCK (GPIO_11) CE1 (GPIO_7) DC Power 7-9 VDC Shell - Ground Center - Power (7-9 VDC) J13 - Power Select 1-2 = Power GVS and voltage translators from the voltage regulator on the RasPi-GVS 2-3 = Power GVS and voltage translators from the Raspberry Pi

Drivers

• GitHub Repo

Assembly Sheet

• RasPi-GVS Assembly Sheet