DS1861B+ Maxim Integrated Products, DS1861B+ Datasheet - Page 24

• Manufacturer Part Number: DS1861B+
• Description: IC LASR CTRLR 1CHAN 5.5V 16CSBGA
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Controller (Fiber Optic)r

Specifications of DS1861B+

• Number Of Channels: 1
• Voltage - Supply: 2.85 V ~ 5.5 V
• Current - Supply: 5mA
• Operating Temperature: -40°C ~ 95°C
• Package / Case: 16-CSBGA
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Before calibrating, the APC register should be set to a
low value to ensure the laser’s maximum power level is
not exceeded before the power level is calibrated.
Additionally, the ER register should be set to its mini-
mum value (28 decimal) to ensure that a data test pat-
tern does not cause the laser to shut off. Once the APC
and ER registers are at minimal values, enable a data
pattern and calibrate the average power level first.
While sending data through the laser diode, increase
the value in the APC register until the light output
matches the desired average power level. The average
power level is the arithmetic average of the 1 and 0
power levels.
While sending data through the laser diode, begin
increasing the ER register from its minimum value of 28
decimal (1Ch), until the proper extinction ratio is
reached or the maximum setting (104 decimal or 68h)
of the low range is reached. If the maximum low range
value is reached, write the ER register to 156 decimal
(9Ch), which switches the extinction ratio value to the
minimum value of the high range. Continue increasing
the ER setting until the proper extinction ratio is
reached. If the maximum value of the high range set-
ting is reached (232 decimal or E8h) without reaching
the proper extinction ratio, then either the desired
extinction ratio cannot be reached or a problem is pre-
venting the system from operating properly.
Full Laser Control with Fault Management
24
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Calibrating APC and Extinction Ratio
Applications Information
Calibrating the Average Power Level
Calibrating the Extinction Ratio
Up to eight DS1861s can be addressed on a single I
bus by using the device’s address inputs (A
change its slave address. For information about device
addressing, see the I
To achieve best results, it is recommended that the power
supply is decoupled with a 0.01µF or a 0.1µF capacitor.
Use high-quality, ceramic, surface-mount capacitors, and
mount the capacitors as close as possible to the V
GND pins to minimize lead inductance.
The BMD shunt capacitor works with the internal resis-
tance of the BMD input to provide a lowpass filter that
reduces the effects of noise on the APC loop. Its
capacitance value must be chosen carefully to ensure
that it is both large enough to provide good filtering of
high-frequency noise and small enough that it does not
cause the control loop to become unstable. A 1nF, 10%
tolerant, X7R ceramic capacitor is recommended.
SDA is an open-collector bidirectional data pin on the
DS1861 that requires a pullup resistor to realize high
logic levels. Either an open-collector output with a
pullup resistor or a push-pull output driver can be used
for the SCL input. Pullup resistor values should be cho-
sen to ensure that the rise and fall times listed in the AC
Electrical Characteristics table are within specification.
SDA and SCL Pullup Resistors
Addressing Multiple DS1861s
2
C Communications section.
Power-Supply Decoupling
on a Common I
BMD Shunt Capacitor
2
, A
2
1
C Bus
, A
CC
0
and
) to
2
C