Datasheet

22 _____________________________________________________________________________________
MAX3946
1Gbps to 11.3Gbps, SFP+ Laser Driver
with Laser Impedance Mismatch Tolerance
Programming Pulse-Width Control
The eye crossing at the Tx output can be adjusted using
the SET_PWCTRL register. Table 5 shows these set-
tings. The sign of the number specifies the direction of
pulse-width distortion. The code of 1111 corresponds to
a balanced state for differential output. The pulse-width
distortion is bidirectional around the balanced state (see
the Typical Operating Characteristics section).
Applications Information
Laser Safety and IEC 825
Using the MAX3946 laser driver alone does not ensure
that a transmitter design is compliant with IEC 825. The
entire transmitter circuit and component selections must
be considered. Each user must determine the level of
fault tolerance required by the application, recognizing
that Maxim products are neither designed nor authorized
for use as components in systems intended for surgical
implant into the body, for applications intended to sup-
port or sustain life, or for any other application in which
the failure of a Maxim product could create a situation
where personal injury or death could occur.
Table 5. Eye-Crossing Settings for
SET_PWCTRL
Table 6. Register Summary
SET_PWCTRL[3:0] PWD SET_PWCTRL[3:0] PWD
1000 -7 0111 8
1001 -6 0110 7
1010 -5 0101 6
1011 -4 0100 5
1100 -3 0011 4
1101 -2 0010 3
1110 -1 0001 2
1111 0 0000 1
REGISTER
FUNCTION/
ADDRESS
REGISTER
NAME
NORMAL
MODE
SETUP
MODE
BIT
NUMBER/
TYPE
BIT NAME
DEFAULT
VALUE
NOTES
Transmitter
Control Register
Address =
H0x05
TXCTRL
R RW 5 TXDE_MD[1] 0 MSB deemphasis mode
R RW 4 TXDE_MD[0] 0 LSB deemphasis mode
R RW 3 TXEQ_EN 0
Input equalization
0: disabled, 1: enabled
R RW 2 SOFTRES 0 Global digital reset
R RW 1 TX_POL 1
Tx polarity
0: inverse, 1: normal
R RW 0 TX_EN 1
Tx control
0: disabled, 1: enabled
Transmitter
Status Register 1
Address =
H0x06
TXSTAT1
R R 7 (sticky) FST[7] X
TX_PORàTX_VCC low-
limit violation
R R 6 (sticky) FST[6] X
BMON open/shorted to
V
CC
R R 4 (sticky) FST[4] X
BMAX current exceeded
or open/short to ground
R R 3 (sticky) FST[3] X
V
TOUT+/-
common-mode
low-limit
R R 2 (sticky) FST[2] X V
TOUT+/-
low-limit violation
R R 1 (sticky) FST[1] X
BIAS open or shorted to
ground
R R 0 (sticky) TX_FAULT X
Copy of FAULT signal
in case POR bits 6 to 1
reset to 0