DS1862B+ Maxim Integrated Products, DS1862B+ Datasheet - Page 15

• Manufacturer Part Number: DS1862B+
• Description: IC LASR CTRLR 7CHAN 5.5V 25CSBGA
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Controller (Fiber Optic)r

Specifications of DS1862B+

• Data Rate: 10Gbps
• Number Of Channels: 7
• Voltage - Supply: 2.9 V ~ 5.5 V
• Current - Supply: 3mA
• Operating Temperature: -40°C ~ 100°C
• Package / Case: 25-CSBGA
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The DS1862’s block diagram is described in detail
within the following sections and memory map/memory
description.
The DS1862’s APC is accomplished by closed-loop
adjustment of the bias current (BIASSET) until the feed-
back current (BMD) from a photodiode matches the
value determined by the APC registers. The relation-
ship between the APC register and I
where APC
84h that controls the coarse BMD current, and
APC
current.
The BMD pin appears as a voltage source in series with
two resistors. The overall equivalent resistance of the
BMD input pin can be closely approximated by the plot
in Figure 8. The voltage that appears on the BMD pin,
assuming no external current load, is 1.2V if BMD is in
sink-current mode (SRC_SINK_B = 0) or 2.0V if BMD is
set to source current (SRC_SINK_B = 1). This allows the
photodiode to be referenced to either V
When the control loop is at steady state, the BMD current
setting matches the current that is measured by the I
voltage across the internal resistance. During a transient
period, the DS1862 adjusts the current drive on the
BIASSET pin to bring the loop into steady state. The
DS1862 is designed to support loop gains of 1/20 to 10.
Figure 8. Approximate Model of the BMD Input
F
<1:0> is the 2-bit value that controls the fine BMD
XFP Laser Control and Digital Diagnostic IC
C
I
BMD
<7:0> is the 8-bit value in Table 04h, Byte
BMD RESISTANCE vs. BMD SUPPLY CURRENT
600
584
565
546
527
508
489
470
0
Automatic Power Control (APC)
(1.464μA x APC
0
= 5.859μA x APC
0.25 0.50 0.75 1.00
Detailed Description
I
BMD
F
(mA)
<1:0>)
C
<7:0> +
BMD
1.25
____________________________________________________________________
is given by:
1.50
CC3
or GND.
BMD
On power-up, the BMD current ramps up to the previ-
ously saved current setting in EEPROM APC registers.
While operating, the DS1862 monitors the BMD current.
If it begins to deviate from the desired (set) I
the current on the BIASSET pin is again adjusted to
compensate.
The DS1862 uses a temperature indexed lookup table
(LUT) to control the extinction ratio. The MODSET pin is
capable of sinking current based on the 8-bit binary
value that is controlling it. The DS1862 also features a
user-configurable current range to increase extinction
ratio resolution. Five current ranges, as described in
Table 1, are available to control the current entering
MODSET.
Table 1. Selectable Current Ranges for
MODSET
TABLE 04h, BYTE 86h<2:0>
LUT CURRENT RANGE
000
001
010
011
100
V
BMD
CONTROLLED BY THE
R
SRC_SINK_B BIT IN
BMD
NOTE: V
Extinction Ratio Control
TABLE 04h.
VOLTAGE
I
BMD
BMD
Lookup Table (LUT)
IS
CURRENT RANGE
0 to 1200
0 to 150
0 to 300
0 to 600
0 to 75
(μA)
BMD
BMD
value,
15