MAX3867ECM Maxim Integrated Products, MAX3867ECM Datasheet - Page 8

• Manufacturer Part Number: MAX3867ECM
• Description: Laser Driver Integrated Circuits (ICs)
• Manufacturer: Maxim Integrated Products

Specifications of MAX3867ECM

• Case: TQFP
• Dc: 02+

laser package is used to convert the optical power into
a photocurrent. The APC loop adjusts the laser bias
current so that the monitor current is matched to a ref-
erence current set by R
the APC loop is determined by an external capacitor
(C
ciated with the APC loop-time constant, and to guaran-
tee loop stability, the recommended value for C
0.1µF.
When the APC loop is functioning, the maximum allow-
able bias current is set by an external resistor, R
An APC failure flag (FAIL) is set low when the bias current
can no longer be adjusted to achieve the desired aver-
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
Figure 4. Functional Diagram
8
APC
_______________________________________________________________________________________
). To eliminate the pattern-dependent jitter asso-
ENABLE
DATA
CLK
MAX3867
MODSET
R
D
MODSET
APCSET
Q
R
. The time constant of
LATCH
BIASMAX
172X
0
1
BIASMAX
MUX
FAIL
BIASMAX
5X
APC
DETECTOR
FAILURE
40X
is
.
C
APC
CAPC
age optical power. To filter out the APC loop noise, use
an external capacitor at APCFILT with a recommended
value of 0.1µF.
APC closed-loop operation requires the user to set three
currents with external resistors connected between
ground and BIASMAX, MODSET, and APCSET. Detailed
guidelines for these resistor settings are described in
the Design Procedure section.
If necessary, the MAX3867 is fully operational without
APC. In this case, the laser current is directly set by two
external resistors connected from ground to BIASMAX
I
MOD
I
MD
R
APCSET
APCSET
I
OUT+
BIAS
OUT-
L
L
BIAS
MD
P
P
V
CC
V
CC
25
C
D
Open-Loop Operation
R
R
D
C
F
F
1000pF