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10

Analog Technologies

ATLS25A219GUI

32V 25A Constant Current Laser Driver

working properly. When LPGD pin is low, <0.3V, the laser

diode control loop is not working properly, there might be a

short or open circuit at the laser diode, or the laser driver is

put into Standby or Shutdown mode. The LPGD pin can also

be connected to a digital input pin of a micro-driver, when

software/firmware is utilized in the system. See Figure 11.

The equivalent circuit of this pin is a 3k

Ω resistor pulling it

up to 4.5V rail and an open drain FET, 500

Ω, pulling it down

to the ground. The pull-up current can be increased by

connecting an external pull-up resistor between LPGD and VPS.

Tie this added additional pull up resistor to a 3.3V or 5V power

supply if they are available. Make sure that the pull up current is

not too high, otherwise, the internal open drain FET cannot pull-

down the LPGD pin low enough to turn off the LED.

The laser diodes are connected between LDA and LDC pins. It

is worth mentioning that the power supply return terminal

should be connected to the pin 3 LDC.

Figure 12. Digitally Controlled Analog Modulation Principle

Turning on/off the Controller

The driver can be turned on and off by setting the SDBN pin

high and low respectively. It is recommended to turn the

driver on by this sequence:

To turn on: turn on the power by providing the power supply

voltage to the driver on VPS pin, turn on the driver by

releasing the SDBN pin.

To turn off: turn off the driver by lowering the voltage of

SBDN pin, turn off the power by stopping the voltage supply

on the VPS pin.

When not controlling by the SBDN pin: leave it

unconnected and turn on and off the driver by the power

supply.

Adjusting the Output Current

The output current is set by adjusting W1, which sets input

voltages of LISL and LISH. See Figure 10. The output

current will be:

LIS can also be set by using a DAC to replace the W1 in

Figure 10. Make sure that the DAC has low output noise.

Monitoring the Output Current

The output current of the driver can be monitored by

measuring the voltage on the LIO pin. This feature is very

useful for micro-driver based system where the ADC is

available and monitoring the current in real time is required.

This pin provides a very low noise voltage signal and is

proportional to the output current:

For example, when the output signal is 4.096V, the output

current is 25A.

LIO can be used to drive an ADC directly, and also be

measured by a multi-meter.