MAX3905 MAXIM [Maxim Integrated Products], MAX3905 Datasheet - Page 8

• Manufacturer Part Number: MAX3905
• Description: 150Mbps Automotive VCSEL Driver
• Manufacturer: MAXIM [Maxim Integrated Products]

150Mbps Automotive VCSEL Driver
Figure 2. Driver Current and Temperature Coefficient Definitions
Table 1. Driver Current and Temperature
Coefficient Definitions
8
PARAMETER
_______________________________________________________________________________________
TC
TC
I
I
I
HIGH
DT
I
I
LOW
MOD
OFF
DT0
T
MOD
LOW
W
0
Total VCSEL current when the data input is
logic-low.
Total VCSEL current when the data input is
logic-high.
I
The center of the temperature-stable low-
current region (T
corresponds to T
I
The size (in °C) of the region where no
temperature coefficient is applied to I
The temperature coefficient applied to I
The temperature coefficient applied to I
This coefficient is negative below DT
and positive above DT
Total VCSEL current while squelched.
HIGH
LOW
at T
- I
LOW.
I
MOD
JUNCTION TEMPERATURE
J
= DT
= I
HIGH
DESCRIPTION
I
0
HIGH
DT
- I
T
W
.
0
W
LOW
O
). DT
of the VCSEL.
TC
MOD
0
0
I
LOW
+ T
roughly
W
TC
/2.
LOW
+ TC
TC
LOW
MOD
0
LOW
- T
MOD
LOW
W
.
/2
.
.
I
I
HIGH
LOW
where DT0[1, 2] = 1 when bonded to V
when left open.
The modulation-current generator provides wirebond-
selectable current amplitude with temperature compen-
sation. The temperature coefficient (TC
sates for the slope-efficiency change of the VCSEL over
temperature. The modulation current is set with inputs
MOD1 and MOD2. Connect MOD1 or MOD2 to V
set the bit high, and leave open to set the bit low.
The typical modulation current at +25°C can be calcu-
lated by:
where MOD[1, 2] = 1 when bonded to V
[1, 2] = 0 when left open.
The power-reduction feature is useful for in-system test
and diagnostics. When the 3DB input is low, the modu-
lation current is reduced by 50%. When 3DB is high or
V
For compatibility with 5V POF transmitters, the power
mode can be set by connecting a resistor from 3DB to
V
mode, while R
The bias-current generator provides a current that
closely tracks the VCSEL properties with temperature.
This current is summed with the modulation current at
the OUT pad. The bias current at T
CC
CC
I
MOD
, the modulation output is normal.
. A resistor R
≈ [3.01 + (0.64 x MOD1) + (1.27 x MOD2)]mA
DT
0
≈ [36 + 13(DT01) + 25(DT02)]°C
GAIN
Modulation-Current Generator
GAIN
> R
< R
GAINL
TIME
Bias-Current Generator
GAINN
sets the low-power mode.
sets the normal power
Power Reduction
CC
MOD
; DT0[1, 2] = 0
J
) compen-
= DT
CC
; MOD
CC
0
to
is