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3

Analog Technologies

Low Noise Constant Current Laser Controller

ATLS1A103

APPLICATIONS

Figure 4.1 and 4.2 show 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 LDC. 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 LDC. 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 CW Operation Schematic for ATLS1A103

Figure 4.2. Typical Stand-alone CW Operation Schematic for ATLS1A103-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:

providing the power supply voltage to the controller, turn on

the controller by releasing the SDN pin. For ATLS1A103-

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.

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

supply on the VPS pin.

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

ATLS1A103, 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 ATLS1A103-

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. Pin

LPGD 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 is not good. When choosing

not to use an LED for indicating the working status, leave the

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