Supply connector
- V+: Power supply input (24 V).
- V-: Power supply return.
A power supply providing at least 800 mA is recommended.
Load connections
The load must be connected between the OUT+ and the OUT- = GND terminals. Maximum tightening torque is 0.5 N.m.
Communication connector
- ALM: Alarm output (3V3 logic, see Alarm).
- INT: Interlock pin (see Interlock).
- TX: UART TX pin.
- RX: UART RX pin.
Analog connector
- AIN+ / AIN-: Analog input with a differential voltage range between 0 and 2.5 V. Common-mode voltage (V(AIN+) + V(AIN-)) / 2 must be between 0 V and 3.3 V. The voltage at the pin AIN can be retrieved with the ain command.
- TH+ / TH-: Thermistor pins for optional remote temperature measurements (10 kΩ). The thermistance can be retrieved with the rtact command.
The VREF voltage (2.5 V) is suitable for ratiometric measurements with AIN (maximum current 5 mA).
Configuration switch
- 1: CFG If CFG is ON at start-up, the board will start with the user-defined configuration. Otherwise, the default configuration is loaded.
- 2: BM This pin is used for firmware update. Set to OFF for normal operation.
Basic operation
The current source supply voltage VSDRV (adjustable between 2.5 V and 14.8 V) must be set manually via the vsdrv command. As a starting point you should set:
where VLOAD is the expected load voltage and IOUT is the required load current. This gives sufficient voltage headroom for the current source to regulate properly. You can then use the iout command to set the desired output voltage and enable the output using curron 1.
For long term operation, we recommend to adjust vsdrv to obtain between 0.5 V and 1 V voltage drop in the FET pass element. The drop voltage is available using the vdrop command.
Serial interface
The serial interface can be accessed either via the micro USB connector or via the TX and RX UART pins of the terminal block. Only one communication interface can be used at a time. UART TX/RX digital voltage level is 3.3 V (5 V tolerant).
The serial interface is the only way of configuring the DRV700 operating parameters. Once the configuration is done, it can be saved to the internal memory with the save command. If the configuration switch 1 is ON at start-up, the DRV700 will load the user-defined configuration and the serial interface is no longer needed.
The DRV700 can be controlled directly from a serial port terminal (e.g. Teraterm on Windows) with the following configuration:
- Baud rate: 115200
- Parity: None
- Bits: 8
- Stopbits: 1
- Flow control: None
Control commands
| Command | Description | Type | Unit | Default | Min | Max |
|---|---|---|---|---|---|---|
| Settings | ||||||
| curron | Disable | enable driver current | R/W | 0 | 0 | 1 | |
| vsdrv | Set the current driver supply voltage | R/W | V | 2.5 | 2.5 | 14.8 |
| iout | Set the output current | R/W | mA | 0.0 | imin | imax |
| iraw | Set the output current using DAC code | R/W | 0 | 0 | 1048575 | |
| imin | Minimum output current | R/W | mA | 0 | 0 | 675 |
| imax | Maximum output current | R/W | mA | 600 | 0 | 675 |
| imodgain | Set AIN modulation gain | R/W | mA/V | 0 | -100000 | 100000 |
| dithon | Disable | enable dithering | R/W | 0 | 0 | 1 | |
| lckon | Disable | enable interlock functionality | R/W | 0 | 0 | 1 | |
| Monitoring | ||||||
| tboard | Board temperature | R | °C | |||
| tjunc | FET junction temperature | R | °C | |||
| vbus | Input supply voltage | R | V | |||
| ibus | Input supply current | R | A | |||
| imon | Monitored output current | R | mA | |||
| vmon | Monitored output voltage | R | V | |||
| vdrop | Voltage drop in FET pass element | R | V | |||
| rtact | Thermistor resistance | R | Ω | |||
| Analog Input | ||||||
| ain | Measured voltage | R | V | |||
| ainfs | Sampling frequency | R/W | Hz | 10 | 10 | 630 |
| pgaauto | Automatic input ranging | R/W | 0 | 0 | 1 | |
| Misc | ||||||
| version | Firmware version | R | v0.1 | |||
| save | Save configuration in internal memory (no argument) | W | ||||
| model | Return the board model | R | ||||
| serial | Return the serial number | R | ||||
| userdata write | Write the user data (e.g. userdata write ABC) | W | 31 chars | |||
| userdata | Read the user data | R | ||||
| brate | UART baud rate | R/W | baud | 115200 | 9600 | 460800 |
| err | Return the error code in hexadecimal format (no argument) | R | ||||
| errclr | Clear the error code (no argument) | W |
Interlock
An optional interlock functionality can be activated with the lckon 1 command. Output current is then disabled when the LCK pin is pulled low. Once current has been disabled, the serial command curron 1 must be sent to re-enable the current. The behavior of the interlock pin can be inverted with the command lckon 3.
Alarm
This output is raised when an error occured. The error can be retrieved with the err command.
Error codes
The command err returns a 32-bit number in hexadecimal representation which concatenates the detected errors (B0 is the Least Significant Bit):
- B0: UART_BUFFER_OVERFLOW (err = 1)
- B1: UART_CMD_BEFORE_PROMPT (err = 2)
- B2: RESERVED (err = 4)
- B3: RESERVED (err = 8)
- B4: BUS_UNDERVOLTAGE (err = 10)
- B5: BUS_OVERVOLTAGE (err = 20)
- B6: BUS_OVERCURRENT (err = 40)
- B7: BUS_OVERPOWER (err = 80)
- B8: BOARD_OVERTEMPERATURE (err = 100)
- B9: CMD_UNKNOWN (err = 200)
- B10: CMD_INVALID_ARG (err = 400)
- B11: FET_OVERTEMPERATURE (err = 800)
- B12: BOARD_MODEL_UNKNOWN (err = 1000)
- B13: INTERLOCK_TRIGGERED (err = 2000)
- B14: DRIVER_ON_WHILE_INTERLOCK (err = 4000)
The ALM pin on the terminal block goes high whenever err > 0.
Dithering
When the dithering mode is activated (dithon 1) a sub-ppm setpoint resolution is achieved. This is particularly useful for closed control loop applications.
As an example we compare the output current resulting from a ramp setpoint with or without dithering. Here the output current is set to 500 mA and the load is a 10 Ω resistor.
Thermal management
For reliable operation, the baseplate must be properly heatsunk.
If tboard exceeds 85 °C, the controller keeps operating and a BOARD_OVERTEMPERATURE warning is raised.
This flag indicates an excessive ambient temperature or improper heatsinking.
If tjunc exceeds 120 °C, the temperature control shuts down and a FET_OVERTEMPERATURE error is raised.
For reliable operation, tjunc should not exceed 105 °C for extended periods.
Note that operating the board above 70 °C might impact the accuracy of the device in a non-reversible way.
