Low Noise Constant Current Laser Driver
ATLS1A101
Analog Technologies
Figure 1 is the actual size top view of the ATLS1A101, which
shows the pin names and locations.
FEATURES
Ultra Low Noise: <6µA*
High Output Current: 1A
High Absolute Accuracy: <0.1%
High Stability: 100ppm/°C
Dual Modulation Ports: High/Low Speed
Complete Shielding
APPLICATIONS
Figure 2 shows a stand-alone application circuit, where W1
sets the current limit and the output current at the same time. It
is recommended that the current limit is set to 1.1 times of the
output current. S1 is the shut down switch. The internal
equivalent input circuit of SDN pin is a pull-up resistor of
100K being connected to VPS. If choose not to use a switch
(S1) to control the laser, leave the SDN pin unconnected. D1 is
the laser diode, which is float from the ground and the VPS,
with its anode connected to the LDA, pin 9, and cathode
connected to the LDC, pin 10. D2 is an LED, indicating when
the control loop works properly, that is: the output current
equals to the input set value. If choose not to use an LED for
Compact Size
SMT Package Available
*Total RMS between 0.1Hz to 2MHz.
APPLICATIONS
Drive laser diodes with low noise, including DPSSL, EDFA,
fiber laser, direct diode lasers, etc.
indicating the working status, leave the LPGD pin
unconnected. Adjusting W1, set input voltages of LILM, pin 3,
and LISL, pin 4, and the current limit and the output current
will respectively be:
DESCRIPTION
The ATLS1A101 is an electronic module designed for
driving diode lasers with low noise current of up to 1A.
I_limit = 1.1*LILM(V)/2.5V (A),
I_output = LISL(V)/2.5V (A).
The ATLS1A101 can be modulated by an external signal.
There are two modulation ports for the input signal, one for
high speed modulation and the other for low speed.
LILM and LISL should never be left float. Otherwise, the
output current will go too high a value and the laser might be
damaged.
The controller can drive a 1A laser diode of 2V to 3V
without using a heat sink. When driving a 1A laser diode of
<2V, additional heat sinking is needed.
In addition to using the LPGD pin for monitoring the working
status of the controller, the output current can be monitored
directly by measuring the voltage of LDC pin. The equation is:
The output current can be set linearly by an input voltage
and monitored linearly by an output voltage at the same
time.
I_out = LDC(V)/0.5V (A).
For example, when seeing LDC = 0.25V, the output current is
0.25V/0.5V = 0.5A.
A high stability low noise 2.5V reference voltage is
provided internally for setting the output current. This
reference can also be as the voltage reference for external
ADCs (Analog to Digital Converters) and DACs (Digital to
Analog Converters).
Figure 3 shows an application where ATLS1A101 is interfaced
with a micro-controller. In this circuit, the input current can be
set by a DAC (Digital to Analog Converter), the current limit
can either be set by a POT (Potentiometer), a pair of resistors,
or the same DAC. The output current can now be monitored by
an ADC (Analog to Digital Converter). By sensing the logic
level of LPGD, pin 8, the working status of the controller can
be monitored by a micro-controller (MC), when it is 1, the loop
is good; 0, the loop is at fault, which includes open circuit at
the laser diode connections, or short circuit at the LDC pin to
ground. Shut down pin can also be controlled by the micro-
controller, setting it to 1 turns on the controller, 0 off. Please
notice that this pin comes with an internal pull up resistor of
100K, it can be ORed by multiple digital ports of several
micro-controllers, with each of the port having an open-drain
output. The internal voltage reference output, 2P5V, pin 2, can
be used as the reference voltage for the ADCs and the DACs.
The ATLS1A101 is packaged in a 6 sided metal enclosure,
which blocks EMIs (Electro-Magnetic Interferences) to
prevent the controller and other electronics from interfering
each other.
The controller has 2 types of packages: through hole mount
and surface mount. The latter saves PCB space the
controller takes.
1
AGND
2P5V
LILM
LISL
P5V
VPS
12
11
10
9
8
7
PGND
LDC
LDA
LPGD
SDN
2
3
4
5
6
19.4
LISH
Figure 4 shows the equivalent input circuits of different pins.
14.5
Understanding the internal equivalent circuits well helps
designing external circuitries.
Figure 1 Pin Names and Locations
550 E. Weddell Drive, Suite 4, Sunnyvale, CA 94089, U. S. A. Tel.: (408) 747-9760, Fax: (408) 747-9770, Web: w w w .analogtechnologies.com
© Copyrights 2000 – 2005, Analog Technologies, Inc. All Rights Reserved.
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