MAX3967AE/D Maxim Integrated, MAX3967AE/D Datasheet - Page 8

• Manufacturer Part Number: MAX3967AE/D
• Description: LED Lighting Drivers 270Mbps SFP LED Driver
• Manufacturer: Maxim Integrated

Specifications of MAX3967AE/D

• Input Voltage: 2.97 V to 5.5 V
• Maximum Supply Current: 39 mA
• Power Dissipation: 1354 mW

internal compensation. The compensation network can
be optimized by adding additional components
between V
The MAX3967A includes a complementary output dri-
ver, which is switched 180° out of phase with the main
output. This configuration helps to maintain constant
current flow from the voltage supply, reducing noise
and EMI. A large diode and a 5Ω resistor are connect-
ed in series with the negative output (OUT-) to emulate
the LED load at OUT+.
The prebias resistor provides peaking current to improve
the LED switching speed. The peaking magnitude is
given by the following equation:
The peaking amplitude is equal for rising and falling
data transitions.
For best performance, select a high-efficiency, low-
inductance LED. LED inductance causes large voltage
swings and ringing.
Select a modulation-current tempco that provides near-
ly constant LED output power as temperature varies.
For the minimum tempco, connect TCMIN to the TC pin.
For a tempco of approximately 3600ppm/°C, connect
TC to TCNOM and leave TCMIN unconnected. For the
maximum tempco, leave TCMIN, TCNOM, and TC
unconnected.
270Mbps SFP LED Driver
Table 1. LED Prebias Voltage
8
Program the Modulation-Current Tempco
_______________________________________________________________________________________
Open
Open
Open
Open
PB1
V
V
V
V
EE
EE
EE
EE
CCOUT
I
PEAK
and OUT+.
Open
Open
Open
Open
PB2
V
V
V
V
EE
EE
EE
EE
=
V
LED
Design Procedure
- V
78
PREBIAS
Ω
Open
Open
Open
Open
PB3
V
V
V
V
EE
EE
EE
EE
Peaking Current
Select an LED
PREBIAS (V)
0.400
0.475
0.550
0.625
0.700
0.775
0.850
0.925
See the Modulation Current Tempco vs. R
the Typical Operating Characteristics to program a cus-
tom tempco. From the graph, determine the appropriate
resistor and connect it between TCMIN and TC.
For example, if an LED requires a 5000ppm/°C tempco,
choose R
Determine the required modulation current at T
Then select the appropriate value of R
Modulation Current vs. R
Operating Characteristics.
For example, to program 75mA modulation current, the
graph indicates an R
mum tempco (12,000ppm/°C) and 1kΩ for nominal
tempco (3600ppm/°C). By interpolation, choose an
R
Determine the LED prebias voltage that produces an
acceptable trade-off between peaking current and extinc-
tion ratio. See
For optimum performance, total load inductance should
not exceed 10nH. Load inductance includes LED
inductance, LED package lead inductance, and circuit-
board traces. Keep the connections between the
MAX3967A OUT pins and the LED as short as possible
to minimize inductance.
Chip-and-wire (hybrid) technology reduces package
inductance significantly, and provides the best possible
performance.
Use good high-frequency layout techniques and a
multilayer board with an uninterrupted ground plane.
Power supplies should be capacitively bypassed to the
ground plane with surface-mount capacitors located
near the power-supply pins.
MODSET
TC
of 792Ω for a tempco of 5000ppm/°C.
of 8.3kΩ.
Table 1 for PB1, PB2, and PB3 settings.
Program the Modulation Current
MODSET
Program Prebias Voltage
MODSET
Layout Considerations
value of 750Ω for maxi-
graph in the Typical
MODSET
TC
A
= +25°C.
graph in
from the