tza3041ahl NXP Semiconductors, tza3041ahl Datasheet - Page 13

• Manufacturer Part Number: tza3041ahl
• Description: Gigabit Ethernet/fibre Channel Laser Drivers
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Bias alarm for TZA3041AHL
The bias current alarm circuit detects whenever the bias
current is outside a predefined range, and generates a
flag. This feature can detect excessive bias current due to
laser ageing or laser malfunctioning. The current applied
to pin ALARMHI should be the maximum permitted bias
current value attenuated by a ratio of 1:1500. The current
applied to pin ALARMLO should be the minimum
permitted bias current value attenuated by a ratio of 1:300.
Like the reference currents for the laser current control
loop, the alarm reference currents can be set by
connecting external resistors between V
pins ALARMHI and ALARMLO (see Fig.8). The resistor
values can be calculated using the following formulae:
Example: The following reference currents are required to
limit the bias current range from 6 to 90 mA:
The corresponding resistor values are:
If the alarm condition is true, the voltage on pin ALARM
(see Fig.14) goes to a HIGH level (CMOS). This signal
could be used, for example, to drive pin ALS to disable the
laser driver; the signal to pin ALS has to be latched to
prevent oscillation.
A hysteresis of approximately 10% is applied to both alarm
functions. The attenuation ratios of 1:300 and 1:1500 are
valid if the bias current rises above the reference current
levels. If the bias current decreases, the ratios are 10%
lower.
2002 Aug 13
R
R
I
I
R
R
ALARMLO
ALARMHI
ALARMHI
ALARMLO
ALARMHI
ALARMLO
Gigabit Ethernet/Fibre Channel laser
drivers
=
=
=
=
=
=
90 10
------------------------
6 10
-------------------- -
---------------------------------
I
------------------------------- -
I
1.5 1500
--------------------------- -
90 10
1.5 300
----------------------- -
O BIAS max
O BIAS min
1.5 1500
1500
6 10
1.5 300
300
–
–
3
3
–
–
3
=
3
=
=
20 A
=
60 A
75 k
25 k
and
and
CC(R)
and
(10)
(9)
13
Accuracy of voltage on inputs: ONE, ZERO,
ALARMLO, ALARMHI
It is important to consider the accuracy of the 1.5 V level
with respect to V
are used to set the reference currents. Although this value
is independent of V
caused by:
handbook, halfpage
Input current: At T
V
to 1.45 V at 65 A and 1.41 V at 100 A. The range
between 65 A and 100 A is only specified for
ALARMLO. In the application, the input current is
virtually fixed, so this variation has little effect.
Variation in batch and individual device characteristics,
not exceeding 2% from the nominal product: This
variation can be compensated for where devices in the
application are individually trimmed.
Temperature: The variation in T
At 30 A (middle of the specified range) the total
variation in T
<3%.
CC
varies from 1.58 V at an input current of 6 A, down
TZA3041AHL; TZA3041BHL;
j
is <1%, at 65 A it is <2% and at 6 A it is
CC(R)
Fig.14 ALARM output.
CC(R)
j
= 25 C, the voltage between pin and
on pins ONE and ZERO if resistors
, deviations from 1.5 V can be
GND
20
43
V CC(R)
MGS909
j
is shown in Fig.15.
ALARM
Product specification
TZA3041U