CTL300E v1+ User Guide

Last updated: 2023-05-10 PDF version
CTL300E Industrial laser diode controller connections
CTL300E connections

Laser connections

The CTL300E-1 / CTL300E-2 is compatible with Type 1 / Type 2 butterfly laser diodes. Note that it is only compatible with floating diodes.

Butterfly laser type 1 pin configuration
Butterfly laser type 1 pin configuration
Butterfly laser type 2 pin configuration
Butterfly laser type 2 pin configuration


The CTL300E mates with the TB300 breakout board.

CTL300E Industrial laser diode controller connector schematics
CTL300E connector schematics
  • VCC: (pins 17, 18 and 20) Input power supply from 6 V to 33 V.
  • RFIN: (pin 4) Modulation input with ±1 V range and 50 Ω impedance.
  • ALM: (pin 5) Alarm output (3V3 logic).
  • DIO: (pin 7) Digital Input/Output (3V3 logic).
  • CFG: (pin 8) Configuration input (3V3 logic, internally pulled-up to 3V3 with 100 kΩ). If CFG is HIGH at start-up, the board will start with the user-defined configuration. Otherwise, the default configuration is loaded.
  • BM: (pin 9) Digital Input (3V3 logic, internally pulled-up to 3V3 with 100 kΩ). This pin is used for firmware update. Leave this pin unconnected or drive this pin high for normal operation.
  • LCK (pin 10) Interlock pin (see Interlock section).
  • TX (pin 11) UART TX pin.
  • BSEL (pin 12) Bias selection pin (see Bias switching section). This pin is internally pulled-low with a 100 kΩ resistor.
  • RX (pin 14) UART RX pin.
  • AIN (pin16) Analog input with a voltage range between 0 and 2.5 V. The voltage at the pin AIN can be retrieved with the ain command.

Connector mates with Samtec references FSH-110-04-L-RA-SL and FSH-110-04-L-DH-SL.

Serial interface

The serial interface can be accessed via TX and RX pins on the 20-pin connector (3V3 logic level / 5V tolerant). The serial interface is the only way to configure the CTL300E operating parameters. Once the configuration is done, it can be saved to the internal memory with the save command. If the CFG input is HIGH at start-up, the CTL300E will load the user-defined configuration and the serial interface is no longer needed.

The CTL300E 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

Example use of the serial port terminal

>>rtset 12000

Note: Each command must be followed by \r\n.

Graphical User Interface

A Graphical User Interface is available for Windows. The installer can be downloaded at this link. The GUI provides an effective mean of tuning the PID gains of the temperature controller.

CTL300E Industrial laser diode controller graphical user interface main
CTL300E graphical user interface main
CTL300E Industrial laser diode controller graphical user interface advanced
CTL300E graphical user interface advanced

Control commands

Command Description Type Unit Default Min Max
lason Disable | enable laser current R/W 0 0 1
ilaser Laser current R/W mA 0.0 0.0 ilmax
vlaser Laser voltage R V
lckon Disable | enable interlock functionality R/W 0 0 1
ilmon Monitored laser current R mA
vslaser Laser driver supply voltage R/W V 4.5 1.14 5.1733
vslmon Monitored laser supply voltage R V
ldelay Time between when the controller lights up and when the laser lights up R/W ms 1000.0 10.0 100000.0
ilmax Software current limit R/W mA 1200.0 0.0 2000.0
vldrop Laser driver transistor drop R/W V 0.2 0.0 2.0
vldauto Disable | enable automatic adjustment of vslaser R/W 0 0 1
bsel Status of the laser bias selection pin R 0 1
tecon Disable | enable TEC current R/W 0 0 1
tprot Disable | enable temperature protection R/W 1 0 1
rtset Thermistor resistance setpoint R/W Ω 10000.0 rtmin rtmax
rtact Actual value of thermistor resistance R Ω
itec TEC current R A
vtec TEC voltage R V
pgain Proportional gain of the temperature controller R/W 10.0 0.0 100.0
igain Integral gain of the temperature controller R/W 0.4 0.0 4.0
dgain Differential gain of the temperature controller R/W 0.0 0.0 100.0
vstec TEC driver supply voltage R V
tilim TEC current limit R/W A 1.5 0.25 2.5
rtmin Minimum thermistor resistance. If temperature protection is enabled, the laser current is automatically disabled below this value. R/W Ω 5000.0 2000.0 50000.0
rtmax Maximum thermistor resistance. If temperature protection is enabled, the laser current is automatically disabled above this value. R/W Ω 15000.0 2000.0 50000.0
vtmin Minimum TEC voltage R/W V -2.0 -4.5 0.0
vtmax Maximum TEC voltage R/W V 3.0 0.0 4.5
tjunc TEC driver junction temperature R °C
iphd Photodiode current R mA 0.0 5.0
ain AIN pin voltage R V 0.0 2.5
tboard Board temperature R °C
vbus Input supply voltage R V
ibus Input supply current R A
version Firmware version R v0.2
status Return lason, vlaser, ilmon, itec, vtec, rtact, iphd, ain R
save Save configuration in internal memory (no argument) W
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

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)
  • B9: LASER_OVERVOLTAGE (err = 200)
  • B10: CMD_UNKNOWN (err = 400)
  • B11: CMD_INVALID_ARG (err = 800)
  • B12: TEC_AMP_OVERTEMPERATURE (err = 1000)
  • B13: LASER_ON_WHILE_INTERLOCK (err = 2000)
  • B14: INTERLOCK_TRIGGERED (err = 4000)
  • B15: LASER_ON_WHILE_TURNING_OFF (err = 8000)

Adjusting the laser driver supply voltage vslaser

The CTL300E allows to adjust the laser driver supply voltage vslaser in order to optimize the voltage drop vldrop in the transistor that regulates the laser current. vldrop must stay above 200 mV for proper current regulation and below 1 V to prevent excessive heating of the transistor. In most situations, a voltage drop of 400-600 mV is a good trade-off between current regulation performance and power consumption.

An automatic adjustment mode can be enabled with the command vldauto 1. In this mode, the laser driver supply voltage vslaser is adjusted continuously so that the transistor voltage drop stays close to the value defined with the command vldrop.

Bias switching

The CTL300E allows to switch between two independent current setpoints in about 400 ns. The two setpoints are defined with the ilaser command. For instance with:

>> ilaser 100.0 600.0
100.000 600.00

The laser current will be 100 mA when BSEL is low and 600 mA when BSEL is high.

The pin BSEL is internally pulled low with a 100 kΩ resistor. If the bias switching functionnality is not needed, you can leave the pin BSEL floating and define only the first setpoint:

>> ilaser 200.0
200.000 600.00

Modulation input

DC coupled modulation input for modulation between DC and 5 MHz. Modulation range is ±1 V (50 Ω input impedance).

Thermal management

The TEC voltage limits (vtmin and vtmax) and the thermistor resistance limits (rtmin and rtmax) provide an effective way of protecting the laser against thermal runaway. For reliable operation, the aluminium cooling base plate must be properly heatsunk.


An optional interlock functionality can be activated with the lckon 1 command. Laser current is then disabled when the LCK pin is pulled low. Once laser current has been disabled, the serial command lason 1 must be sent to re-enable the laser current. The behavior of the interlock pin can be inverted with the command lckon 3.

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