MAX3946ETG+T Maxim Integrated Products, MAX3946ETG+T Datasheet - Page 21

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

Specifications of MAX3946ETG+T

• 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

1) IBIASMAX[7:0] = Maximum_Bias_Current_Value
2) SET_IBIAS
Note: The total bias current is calculated using the
SET_IBIAS[8:0] DAC value. SET_IBIAS[8:1] are the bits
that can be manually written. SET_IBIAS[0] can only be
updated using the BIASINC register.
When implementing an APC loop it is recommended to
use the BIASINC register, which guarantees the fastest
bias current update.
3) BIASINC
4) If (SET_IBIAS
5) Else (SET_IBIAS
The total bias current can be calculated as follows:
6) I
1) IMODMAX[7:0] = Maximum_Modulation_Current_Value
2) SET_IMOD
Note: The total modulation laser current is calculated
using the SET_IMOD[8:0] DAC value and the SET_TXDE
register value. SET_IMOD[8:1] are the bits that can be
manually written. SET_IMOD[0] can only be updated
using the MODINC register.
When implementing modulation compensation, it is rec-
ommended to use the MODINC register, which guaran-
tees the fastest modulation current update.
3) MODINC
4) If (SET_IMOD
5) Else (SET_IMOD
The following equations give the modulation current
(peak-to-peak) seen at the laser when driven differen-
tially. R
laser plus any added series resistance.
6a) TXDE_MD[1:0] = 00, then
I
MOD
IBIAS
IMOD
BIAS
EXTD
=
i
= [SET_IBIAS
i
[8:0] = SET_IBIAS
1.0625Gbps to 11.3Gbps, SFP+ Laser Driver
[8:0] = SET_IMOD




with Laser Impedance Mismatch Tolerance
0.3mA SET_IMOD 8 : 0
−
i
i
0.15mA SET_IMOD 8 : 3
[4:0] = New_Increment_Value
[4:0] = New_Increment_Value
i
[8:1] = Initial_Modulation_Current_Value x 1.06
Programming Modulation Current
is the differential load impedance of the
i
[8:1] = Initial_Bias_Current_Value
(
______________________________________________________________________________________
i
i
[8:1] P IBIASMAX[7:0]), then (SET_
[8:1] P IMODMAX[7:0]), then (SET_
i
i
(
[8:0] = SET_IBIAS
[8:0] = SET_IMOD
Programming Bias Current
i
[8:0] + 16] x 200FA
i-1
Design Procedure
i
-
[
1
[8:0] + BIASINC
[8:0] + MODINCi[4:0])
[
]
+
16
]
+
)
i
2
-
i
-
1
)
1




[8:0])
[8:0])
×
50
Ω +
i
[4:0])
50
Ω
R
LD
6b) TXDE_MD[1:0] = 01, then
6c) TXDE_MD[1:0] = 10, then set SET_TXDE[5:0] can be
When SET_TXDE[5:0] is increased, the deemphasis
current increases and the overall peak-to-peak modu-
lation current decreases. This effect saturates when
SET_TXDE[5:0] = 0.2 x (SET_IMOD[8:0] + 16) - 1, and
further increases to SET_TXDE[5:0] do not increase the
deemphasis current.
6d) TXDE_MD[1:0] = 11, then
Note: When TXDE_MD[1:0] = 10 and the SET_TXDE
register is set by the user, the minimum allowed deem-
phasis is 3% and the maximum is 10%. These limits are
internally set by the MAX3946.
1) TXDE_MD[1:0] = Transmit_Deemphasis_Mode
2) SET_TXDE[5:0] = Transmit_Deemphasis_Value. If
For Transmit_Deemphasis_Mode:
00 = deemphasis is fixed at 6% of the modulation ampli-
tude (the device controls the SET_TXDE value), default
setting
01 = deemphasis is fixed at 3% of the modulation ampli-
tude (the device controls the SET_TXDE value)
10 = deemphasis is programmed by the SET_TXDE
register setting
11 = deemphasis is at its maximum of approximately 9%
(the device controls the SET_TXDE value)
I
MOD
Programming Transmit Output Deemphasis
I
I
MOD
MOD
TXDE_MD[1:0] = 00, 01, or 11, the value of SET_TXDE
is automatically set by the device and there is no
need to enter data to SET_TXDE.
set to any value ≥ SET_IMOD[8:4] and
=
0.9
=
=








0.3mA SET_IMOD 8 : 0
−
0.3mA SET_IMOD 8 : 0
−
×
0.15mA SET_IMOD 8 : 4
0.15mA SET_TXDE 5:0


0.3mA SET_IMOD 8 : 0
(
(
(
(
(
[
[
[
[ ]
[
]
]
+
+
16
]
]
16
+
+
+
1
)
1
)
16
)
)








×
)
×


50
×
50
50
Ω +
Ω +
50
50
Ω +
50
Ω
Ω
R
R
LD
Ω
LD
R
LD
21