MAX3946ETG+ Maxim Integrated Products, MAX3946ETG+ Datasheet - Page 12

• Manufacturer Part Number: MAX3946ETG+
• Description: IC LASER DVR SFP 11.3GBPS 24TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driverr

Specifications of MAX3946ETG+

• Data Rate: 11.3Gbps
• Number Of Channels: 1
• Voltage - Supply: 2.85 V ~ 3.63 V
• Current - Supply: 68mA
• Current - Modulation: 80mA
• Current - Bias: 80mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 12-WFQFN, Exposed Pad
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX3946 SFP+ laser driver is designed to drive
5I to 50I lasers from 1Gbps to 11.3Gbps. The device
contains an input buffer with programmable equaliza-
tion, pulse-width adjustment, bias current and modula-
tion current DACs, output driver with programmable
deemphasis, power-on reset circuitry, bias monitor, laser
current limiter, and eye-safety circuitry. A 3-wire digital
interface is used to control the transmitter functions.
The registers that control the device’s functionality are
TXCTRL, SET_IMOD, SET_IBIAS, IMODMAX, IBIASMAX,
MODINC, BIASINC, SET_TXEQ, SET_PWCTRL, and
SET_TXDE.
The input is internally biased and terminated with 50I to
a common-mode voltage. The first amplifier stage fea-
tures a programmable equalizer for high-frequency loss-
es including SFP connector. Equalization is controlled
by the SET_TXEQ register and TXEQ_EN bit, TXCTRL[3]
(Table 1). The TX_POL bit in the TXCTRL register con-
trols the polarity of TOUT+ and TOUT- vs. TIN+ and TIN-.
The SET_PWCTRL register controls the output eye cross-
ing (Table 5). A status indicator bit (TXED) monitors the
presence of an AC input signal.
The device’s bias current is optimized to provide up
to 80mA of bias current into a 5I to 50I laser load
with 200FA resolution. The bias current is controlled
through the 3-wire digital interface using the SET_IBIAS,
IBIASMAX, and BIASINC registers.
For laser operation, the laser bias current can be set
using the 9-bit SET_IBIAS DAC. The upper 8 bits are set
by the SET_IBIAS[8:1] register, commonly used during
1.0625Gbps to 11.3Gbps, SFP+ Laser Driver
with Laser Impedance Mismatch Tolerance
Table 1. Input Equalization Control Register Settings
12
TXCTRL[3]
TXEQ_EN
_____________________________________________________________________________________
0
1
1
1
1
Input Buffer with Programmable
SET_TXEQ[2:1]
X
0
0
1
1
Detailed Description
X
0
1
0
1
150mV
Optimized for 1in to 4in FR4, 190mV
Optimized for 4in to 6in FR4, 190mV
Optimized for 1in to 4in FR4, 450mV
Optimized for 4in to 6in FR4, 450mV
Bias Current DAC
P-P
Equalization
to 1000mV
P-P
differential input amplitude (default setting)
the initialization procedure after POR. The LSB (bit 0)
of SET_IBIAS is initialized to zero after POR and can
be updated using the BIASINC register. The IBIASMAX
register should be programmed to a desired maximum
bias current value (up to 96mA) to protect the laser. The
IBIASMAX register limits the maximum SET_IBIAS[8:1]
DAC code.
After initialization the value of the SET_IBIAS DAC reg-
ister should be updated using the BIASINC register
to optimize cycle time and enhance laser safety. The
BIASINC register is an 8-bit register where the first 5
bits contain the increment information in two’s comple-
ment notation. Increment values range from -8 to +7
LSBs. If the updated value of SET_IBIAS[8:1] exceeds
IBIASMAX[7:0], the IBIASERR warning flag is set and
SET_IBIAS[8:0] remains unchanged.
The modulation current from the device is optimized to
provide up to 80mA of modulation current into a 5I to
25I differential laser load (60mA for 50I laser load)
with 300FA to 200FA resolution. The modulation current
is controlled through the 3-wire digital interface using
the SET_IMOD, IMODMAX, MODINC, and SET_TXDE
registers.
For laser operation, the laser modulation current can be
set using the 9-bit SET_IMOD DAC. The upper 8 bits
are set by the SET_IMOD[8:1] register, commonly used
during the initialization procedure after POR. The LSB (bit 0)
of SET_IMOD is initialized to zero after POR and can
be updated using the MODINC register. The IMODMAX
register should be programmed to a desired maximum
modulation current value (up to 96mA) to protect the
laser. The IMODMAX register limits the maximum
SET_IMOD[8:1] DAC code.
P-P
P-P
P-P
P-P
DESCRIPTION
to 450mV
to 450mV
to 700mV
to 700mV
P-P
P-P
P-P
P-P
differential launch amplitude from source
differential launch amplitude from source
differential launch amplitude from source
differential launch amplitude from source
Modulation Current DAC