Datasheet

Laser Driver for Projectors
MAX3600
18
Power-On-Reset
The power-on reset monitors the supply voltages of
the circuit (Figure 15). It is recommended that V
CC
be applied to the IC before V
A1
to V
A4
are applied as
shown in Figure 16. On power-down, it is recommended
that V
A1
to V
A4
are powered down before V
CC
. Failure
to follow the sequencing recommendation can result
in device stress, but has not been observed to cause
immediate damage.
Design Procedure
Supply Filter
Element C
A
(see the Typical Operating Circuits) is pres-
ent to reduce supply noise and provide a ground return
path for switched current. Select C
A
R 10FF. C
A
can be
composed of two or three capacitors in parallel.
Use care to ensure V
A3
does not exceed +9V at any
time, including power-on, as this can damage the ESD
protection circuitry.
Compensation Network
Optional compensation elements R
C
and C
C
can be
used to compensate the inductive load of the laser
(Figure 17). The resulting filter reduces ringing and
increases the switching time of the laser driver. The best
values for R
C
and C
C
should be found by experimenta-
tion. Note that C
C
must be charged before light output
appears from the laser. If a compensation network is
used, minimize inductance in the ground return.
Typical starting values:
R
C
≈ R
L
to 2 x R
L
(R
L
= Laser Resistance)
C
C
≈ 1/(2G f
VIDEO
x R
L
)
Ringing of the green laser can be reduced with resistor
R
D
.
PCB Layout
Place the green laser as close to the laser driver as pos-
sible. The green laser typically has a small resistive com-
ponent and is more sensitive to inductance than other
laser connections. The green laser connection should
appear as a low-impedance transmission line. Use wide
traces located close to the ground plane for maximum
capacitance.
The connection from OUT2 to the laser should be as short
as possible, ideally < 1cm. The connection distance from
the laser cathode, across the ground plane, through the
filter capacitor, to V
A2
, is ideally < 1cm.
Figure 15. Power-On Reset
Figure 16. Power-Supply Sequencing
Figure 17. Optional Compensation Components
V
POR1
V
CCA
POWER-ON RESET
V
A1
V
POR2
AND POR1
V
A2
V
POR2
AND POR2
V
A3
V
POR3
AND POR3
V
A4
V
POR2
AND POR4
VOLTS
DATA AND CLOCK INPUTS
TIME
V
A_
V
CC
t
VCC_ON
(0.1µs)
OUT_
V
A_
R
D
LASER
R
C
C
C
C
A
+V
A_
LASER
DRIVER