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3

Analog Technologies

ATLS250MA103

Low Noise Constant Current Laser Controller

APPLICATIONS

Figure 4.1 and 4.2 shows a typical application circuit. W1

and W2 set the output current limit and output current

respectively. Resistor R1 and capacitor C1 form a low pass

filter, to lower the noise from the voltage reference.

Laser diode D1 is connected between LDA and PGND. It is

worth mentioning that the power supply return terminal should

be connected to the pin 11 PGND and the cathode of the laser

diode should be connected to the pin 10 PGND. These 2 nodes

should not be connected together externally and they are

connected together internally already by the controller.

Figure 4.1. Typical Stand-alone Application Schematic for ATLS250MA103

Figure 4.2. Typical Stand-alone Application Schematic for ATLS250MA103-PD

Turning the Controller On and Off

The controller can be turned on and off by setting the SDN

pin high and lower respectively. It is recommended to turn

the controller on by this sequence:

To turn on: For ATLS250MA103, turn on the power by

providing the power supply voltage to the controller, turn on

the

controller

by

releasing

the

SDN

pin.

For

ATLS250MA103-PD, turn on the power by providing the

power supply voltage to the controller, turn on the controller

by connecting the SDN pin to VPS.

To turn off: turn off the controller by lowering the voltage

of SDN pin, turn off the power by stopping the voltage

supply on the VPS pin.

When not controlling by the SDN pin: leave it unconnected

and turn on and off the controller by the power supply.

In Figure 4.1 and 4.2, S1 is the shut down switch. For

ATLS250MA103, the internal equivalent input circuit of SDN

pin is a pull-up resistor of 100k being connected to VPS in

parallel with a 10pF capacitor to the ground. For

ATLS250MA103-PD, the internal equivalent input circuit of

SDN pin is a pull-down resistor of 100k being connected to the

ground in parallel with a 10pF capacitor to the ground. The

switch S1 can also be an electronic switch, such as an I/O pin

of a micro-controller, with an either open drain or push/pull

output. If not using a switch (S1) to control the laser, leave the

SDN pin unconnected. D2 is an LED, indicating when the

control loop works properly, that is: the output current equals

to the input set value. This pin has an internal pull up resistor

of 5k to the power supply pin, VPS, pin 10. The pull down

resistance is 200

Ω. This 5k resistor can drive a high efficiency

LED directly. When higher pull up current is needed for

driving such as a higher current LED, an external resistor can

be placed between the VPS and the LPGD pins. Make sure

that the resistor is not too small that the pull down resistor will

not be able to pull the pin low enough when the controller loop

Power Supply 0V

(Clock-wise)

Power Supply 5V

S1

SPST

D1

Laser Diode

Shut Down

Loop Good Indication

Current Limit Set

LIO

6

VPS

12

LDC 10

LPGD

7

LDA 9

GND

2

LIS

5

PGND 11

TMPO 8

2.5VR

3

LILM

4

SDN

1

Laser Controller

1

2

C1

1uF to 10uF

Current Set

To ADC

To ADC

(Clock-wise)

2

W1

20k

2

W2

20k

1

2

R1 1M

2

1

D2

LED

Power Supply 0V

(Clock-wise)

Power Supply 5V

S1

SPST

D1

Laser Diode

Shut Down

Loop Good Indication

Current Limit Set

LIO

6

VPS

12

LDC 10

LPGD

7

LDA 9

GND

2

LIS

5

PGND 11

TMPO

8

2.5VR

3

LILM

4

SDN

1

Laser Controller

1

2

C1

1uF to 10uF

Current Set

To ADC

To ADC

(Clock-wise)

2

W1

20k

2

W2

20k

1

2

R1 1M

2

1

D2

LED

5V