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2
LDA1-CP1
Analog Technologies, Inc.
Pin 8
LPS, laser power set-point voltage, analog input. 0V to 2.5V sets the laser output power from 0 to
the maximum value linearly. The input impedance of this pin is 100K
Ω. This pin can be set by an
external analog signal source, such as the output of a closed-looped op-amp, POT, or DAC.
Pin 9
GND, signal ground pin. Connect ADC and DAC grounds to here.
Pin 10 LPO, laser power output voltage, analog output. Low impedance output. The (positive-going)
output of a TIA (Trans-Impedance Amplifier) for the photodiode in the laser. The trans-
impedance is set by an external resister between LPO pin and PDCT (pin 11).
Pin 11 PDCT, photodiode cathode, analog input. The TIA’s input. Drawing current out from this pin
will bring the LPO pin voltage going up-ward.
Pin 12 LDA, laser diode anode, analog output. This pin is used to drive a laser of which the cathode is
connected to the case and the case is connected to the ground. See Figure 1.
Pin 13 LDC, laser diode cathode, analog output. This pin is internally connected to ground. Connect it
directly to the laser’s cathode which is also the case of the laser. See Figure 1.
Pin 14 GND, ground. Connect power supply return rail to here.
Pin 15 VPS, power supply, analog power input. The driver works from 3.2V to 5.5V.
Pin 16 SYNCO, sync output, digital output. This pin can be used to synchronize another switch mode
driver such as for TEC or power supply so that the other drivers will not interfere with this laser
driver. The switching frequency is set at 700 KHz. There is a 10K resistor before this pin to the
switcher output. This pin can also be used to see the switcher’s output voltage.
Mode Setting
A. Set the driver to constant current mode without over power protection
In this mode, the laser is always operating at constant current mode.
1. Set LIS = 2.5V
× I
laser 42.0A, where Ilaser is the set-point laser current.
2. Make sure LPS is greater than LPO, for example by connecting LPS to 2.5V reference and making
photodiode transimpedance amp resistor = 0 ohms.
B. Set the driver to constant current mode with over power protection
In this mode, the laser is operating at the constant current mode unless the laser output power reaches the
preset maximum power. When the laser output power reaches the protection power, the laser will be
operating in constant power mode.
1. Set LIS = 2.5V
× I
set 42.0A, where Ilaser is a laser set-point current.
2. Set LPS to the voltage generated at the LPO pin by the internal TIA (Trans-Impedance Amplifier)
when the laser is outputting the protection power level. The TIA converts the current of the power-
sensing PD (Photo Diode) into a voltage, with the gain set by an external resistor connected
between the PDCT and LPO pins. Make sure that the set-point laser current is at least 5% less than
the current needed to generate the protection laser power level.
C. Set the driver to constant power mode without over current protection
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