SUMMIT
MICROELECTRONICS, Inc.
Laser Diode Adaptive Power Controller
SML2108
PRELIMINARY
FEATURES
!
Integrated Bias Current Monitor
"
Monitors & Measures Laser Temperature
Directly
"
Eliminates Need for External Thermistor &
Thermal Coupling Issues
"
Alarm Output on Over-temperature Condition
!
Adaptive Modulation Control (AMC)
"
Adjusts Modulation Current as a Function of
the Laser Temperature
"
8
×
8 Programmable Compensation Table
"
256 Independent Compensation Values
"
Integrated 8-Bit Modulation Control DAC
!
Flexible Biasing Architecture
"
Bias Control and Modulation Control:
0 to 10mA / 0 to 100 mA Source,
0 to 100mA Sink
!
Automatic Power Control (APC) with Integrated
10-Bit Programmable Offset
"
Automatic Initial Bias Optimization
!
Electronic Calibration Through 2-wire Interface
!
3V or 5V Operation
DESCRIPTION
The SML2108 is an adaptive power controller for laser
diodes. It is the industry's first integrated device that can
directly monitor and measure a laser diode's temperature,
and provide a variable modulation current. The
SML2108's integrated active feedback loop is used to
calibrate and control the mean and modulation power of
high speed, high power laser diodes.
Inherent manufacturing tolerances introduce variations of
performance in laser diodes. These variations, combined
with parametric changes over the laser’s extreme tem-
perature range and laser ageing, call for an efficient
temperature compensation scheme. Using an internal
digital control loop and a programmable nonvolatile com-
pensation lookup table, the SML2108 provides the most
optimum adaptive power control with a minimum number
of external components.
The SML2108 removes the need for any manual calibra-
tion of the laser control circuit, which is currently the
industry standard practice. All calibration values are
programmed through the 2-wire communication interface,
which can be controlled by most production ATE equip-
ment.
Programming of configuration, control and calibration
values by the user can be simplified with the interface
adapter and Windows GUI software obtainable from Sum-
mit Microelectronics.
The SML2108 is available in 48 lead TQFP.
SIMPLIFIED APPLICATION DIAGRAM
VDD
LASER
DIODE
IN+
IN–
LASER
MODULATION
DRIVER
MODSET
VDD
VDD
AUTOMON
SDA
Interface
SCL
MODN
IMOD
MONITOR
DIODE
BIASN
DETECT
SML2108
VSS
2053 SAD 1.0
©SUMMIT MICROELECTRONICS, Inc., 2000 • 300 Orchard City Dr., Suite 131 • Campbell, CA 95008 • Phone 408-378-6461 • FAX 408-378-6586 • www.summitmicro.com
Characteristics subject to change without notice
2053 2.2 11/07/00
1
SML2108
PRELIMINARY
FUNCTIONAL BLOCK DIAGRAM
DETECT
12
VCC
CAP1
11
CAP2
10
VDD
A0
1
A1 2
A2
3
SDA 4
SCL 5
(All Rs 100kΩ)
AUTOMON 6
CE# 48
Config
8-Bit
ADC
NV Scaling
& Offset
NV
POR
POR
Reg
2
2053 2.2 11/07/00
+
5
ADC Read &
Alarm Reg
8
NV Look-up
Table
8-Bit
DAC
10-Bit
NV Reg
10-Bit
DAC Reg
10-Bit
DAC
–
BIAS P
EXT TEMP
BIAS N
13 VSS A
14 VSS D
7 RDY
ALERT#
MOD P
MOD N
VSS
2053 BD 2.1
SUMMIT MICROELECTRONICS, Inc.
SML2108
PRELIMINARY
PIN CONFIGURATION
48-Pin TQFP
CE#
V
DD
V
DD
BIASP
BIASP
MODP
MODP
V
DD
V
DD
V
SS
V
SS
48
47
46
45
44
43
42
41
40
39
38
37
A0
A1
A2
SDA
SCL
AUTOMON
RDY#
ALERT#
EXT TEMP
CAP2
CAP1
DETECT
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
36
35
34
33
32
31
30
29
28
27
26
25
MODN
MODN
BIASN
BIASN
V
SS
V
SS
V
SS
V
SS
BIASN
BIASN
MODN
MODN
V
SS
A
V
SS
D
V
DD
V
DD
BIASP
BIASP
MODP
MODP
V
DD
V
DD
V
SS
V
SS
2053 PCon 2.0
PIN DESCRIPTIONS
DETECT (12)
This is the analog input from the laser monitor photodiode
for the integrator circuit. There is an on-board resistance
of 2MΩ between the DETECT input and CAP1 pin.
CAP1 and CAP2 (11 & 10)
Capacitor inputs for an external capacitor in the feedback
loop of the Mean Power Control Integrator. There is an on-
board capacitance of 500pF.
AUTOMON (6)
Active high input used to enable the internal auto-monitor
function, which provides automatic adjustments to the
modulation output currents (MODP and MODN) based on
the internal A/D output and the values stored in the
nonvolatile lookup table. This pin has an internal 100kΩ
pullup.
ALERT# (8)
Active low, open-drain output. This pin is driven low
whenever the bias current increases beyond a predefined
nonvolatile threshold. This can be used to predict laser
failure.
SUMMIT MICROELECTRONICS, Inc.
SDA, SCL (4 & 5)
Data and Clock lines, respectively, whose function and
use are based on the industry standard I
2
C interface.
Lookup table values, configuration data, and D/A and A/D
registers may all be accessed via these two pins of the
SML2108. These pins have internal 100kΩ pullups.
A0, A1, A2 (1, 2, & 3)
Address Pins for the interface provided to allow multiple
devices on a single bus. These pins have internal 100kΩ
pullups.
RDY# (7)
Active low, open-drain output. This pin is driven low
whenever the internal A/D is performing a conversion, or
while the on-board EEPROM is being programmed.
EXT TEMP (9)
Temperature input (or no connection). This pin can be
programmed as an input to the ADC and can interface a
temperature sensor. The EXT TEMP pin is multiplexed
with the bias current to provide a means of configuring the
input to the ADC. When EXT TEMP is programmed as the
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2053 2.2 11/07/00
SML2108
PRELIMINARY
input to the ADC using bit 5 of Register 1, the converted
value of the current entering this pin is used as the address
of the EEPROM lookup table. In this configuration the
modulation current can be controlled by temperature
rather than the bias current. Refer to the application
example on using the EXT TEMP pin. If this option is not
used the pin should be left floating.
V
SS
A, V
SS
D (13 & 14)
Analog and digital low-side supplies for on-board circuitry.
Must be at same potential as all other VSS pins.
V
DD
(15, 16, 21, 22, 39, 40, 45, 46, & 47)
High-side supply for the Bias and Modulation currents and
power supply input for the chip.
CE# (48)
The chip enable input is active low and provides an
additional method of enabling the serial interface. The
state of this pin has no effect on the auto-monitor function.
This pin has an internal 100kΩ pullup.
BIASP (17, 18, 43, & 44)
High-side mean bias control current. Current source
output range is programmable, with the optional ranges of
0 to 100mA or 0 to 10mA.
BIASN (27, 28, 33, & 34)
Low-side mean bias control current. Current sink input
range is 0 to 100mA.
MODP (19, 20, 41, &42)
High-side modulation control current. Current source
output range is programmable, with optional ranges of 0 to
100mA or 0 to 10mA.
MODN (25, 26, 35, &36)
Low-side modulation control current. Current sink input
range is 0 to 100mA.
4
2053 2.2 11/07/00
SUMMIT MICROELECTRONICS, Inc.
SML2108
PRELIMINARY
ABSOLUTE MAXIMUM RATINGS*
Temperature Under Bias ...................... –55°C to 125°C
Storage Temperature ........................... –65°C to 150°C
Lead Solder Temperature (10 secs) ................... 300 °C
*COMMENT
Stresses listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions
outside those listed in the operational sections of this specification is not
implied. Exposure to any absolute maximum rating for extended
periods may affect device performance and reliability.
ELECTRICAL TABLES
(Over
Recommended Operating Conditions; Voltages are relative to GND)
Symbol
S/N
THD
Parameter
Signal to Noise ratio
Total harmonic distortion
Peak harmonic intermodulation
distortion
2nd Order
3rd Order
Conditions
T
A
= 25ºC
Min.
70
–80
–80
–80
Typ.
Max.
Units
dB
dB
dB
dB
Typical ADC Performance
DC Accuracy
Resolution
Reolution for which no missing
codes are guaranteed
Relative accuracy
DNL
Positive full scale error
V
SS
= 5V
Unipolar offset error
V
SS
= 2.7V to
3.6V
8
±½
±1
±2
±2
±2
8
Bits
Bits
LSB
LSB
LSB
LSB
LSB
2053 Elect Table A
SUMMIT MICROELECTRONICS, Inc.
2053 2.2 11/07/00
5