MAX3905 MAXIM [Maxim Integrated Products], MAX3905 Datasheet - Page 7

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

Figure 1. Functional Diagram
The MAX3905 is comprised of a differential LVDS- or
PECL-compatible input buffer, a TTL-compatible input
buffer, signal detection, DT
rent generator, bias-current generator, and output dri-
ver (Figure 1). The device implements temperature
compensation in the bias and modulation that can be
customized to accommodate the variation of VCSEL
properties with process and temperature. See Figure 2
and Table 1 for driver current and temperature coeffi-
cient definitions.
The MAX3905 has two input buffers, one for TTL-com-
patible DC-coupled input data, and the other for AC-
coupled, differential LVDS or PECL input data. The
differential input is relatively high impedance. This
allows external resistors to be configured in several
ways to meet the AC- and DC-termination requirements
of LVDS or PECL.
The active data input buffer is set by the DIFF input. To
select the single-ended TTL input, leave DIFF open. To
select the differential input, connect DIFF to ground.
When using the differential input buffer, input noise can
be sufficient to prevent normal operation of the squelch
IN_TTL
SQEN
DIFF
IN+
IN-
BUFFERS
INPUT
_______________________________________________________________________________________
GND
OPEN
Detailed Description
0
V
CC
V
set block, modulation-cur-
EE
DETECT
SIGNAL
150Mbps Automotive VCSEL Driver
MAX3905
TEMPSENS
Input Buffers
K
3DB
SQUELCH
MODULATION
GENERATOR
CURRENT
I
MOD
function. A small offset on the input ensures proper
functioning of the squelch feature. A 1MΩ resistor from
IN- to ground or V
When no data transitions are present at the input, the
signal detection issues a squelch signal to the bias and
modulation current, disabling the VCSEL output. This
ensures that the receiver IC can easily detect the differ-
ence between transmitter on and transmitter off. The
squelch function is enabled when SQEN is left uncon-
nected. The squelch function can be disabled by con-
necting SQEN to ground.
With squelch enabled, the delay of the squelch function is
suitable for use with biphase-encoded data (maximum of
three consecutive identical digits (CIDs)) or 8B-/10B-
encoded data (maximum five CIDs). To use the MAX3905
with scrambled data, disable the squelch function.
Inputs DT01 and DT02 are the 2-bit control of the cen-
ter of the temperature-stable region, DT
ture set by DT0[1, 2] should correspond to the T
VCSEL. Connect DT01 or DT02 to V
high, or leave open to set the bit low.
The typical DT
MOD[1, 2]
V
CC
TEMP
I
MOD
Signal Detection and Data Squelch
OUTPUT
DRIVER
DT0[1, 2]
0
DT
SET
can be calculated by:
0
CC
creates a 7mV offset.
GENERATOR
CURRENT
I
BIAS
BIAS
TC[1, 2, 3]
I
BIAS
LOW[1, 2]
DT
CC
0
TEMP
. The tempera-
0
to set the bit
Set Block
OUT
OUT
0
of the
7