Datasheet

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B0093-01
DISABLE
SDOWN
Inverter
Inverter
MUX
MUX
IBEN
IMODEN
MONP
MONB
I1
I0
I0
I1
VCC
I
PD
I
BIAS/68
1.25V
2.8V
Comparator
Comparator
Flipflop
CMOS
Buffer
Comparator
APCSET
MODSET
MODTC
IBMAX
APCSET
MODSET
MODTC
RES
T Counter
RES
-
-
S
-
Q
Q
Q
Q
Q
Q
+
+
R
+
SHORT
START
IBMAX
FLTMODE
ShortCircuit
toVCCor
GNDDetect
+
-
+
-
ONET4211LD
SLLS688A – NOVEMBER 2005 – REVISED SEPTEMBER 2007
Figure 2. Functional Representation of the Fault Detection Circuitry
A fault mode is produced if the laser cathode is grounded and the photocurrent causes MONP to exceed its
programmed threshold. Another fault mode can be produced if the laser diode end-of-life condition causes
excessive bias current and photocurrent that results in monitor voltages (MONP, MONB) being greater than their
programmed threshold. Other fault modes can occur if there are any I/O pin single-point failures (short to VCC or
GND) and the monitor voltages exceed their programmed threshold (see Table 1 ).
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