2
MITSUBISHI
DIGITAL ASSP
M66512P/FP
LASER-DIODE DRIVER
As the IC is equipped with a pin to provide a forced OFF of
current circuit, it is possible to prevent a large current flowing
through laser diodes at the moment of power ON.
Regarding the detection of laser power, a monitor current
generated by a monitoring photodiode, which is incorporated
in laser unit, is drawn and converted into changes in voltage
by means of an external resistor, in order to output as an ana-
log signal. Simultaneously, the converted voltage is com-
pared with the internal reference voltage, thence the result is
output in TTL level as logic information.
FUNCTION
The M66512 is a semiconductor laser-diode driver for driving
a specific type (Mitsubishi’s N type) of laser, in which the an-
ode of a semiconductor laser diode is connected in stem
structure to the cathode of a monitoring photodiode.
The amplitude of laser drive current is set by applying a con-
stant voltage from an external source. For that purpose, the
M66512 has two voltage applying pins, which they are inde-
pendent each other, This mechanism makes it possible to set
a drive current with great accuracy.
PIN DESCRIPTIONS
Pin
LD
PD
V
L1
1RC
V
L2
2RC
3RC
Name
Laser connection pin
Monitoring diode connection pin
Voltage input pin for I
L1
setting
Load resistor connection pin for I
L1
setting
Voltage input pin for I
L2
setting
Load resistor connection pin for I
L2
setting
Load resistor connection pin for I
L3
setting
Switching data input pin
Load resistor connection pins for monitoring
function
Analog output pin for monitoring function
Comparator output pin for monitoring function
Laser current forced OFF input pin
Load resistor connection pin for laser current
Power supply pin 1
Power supply pin 2
GND pin 1
GND pin 2
Functions
Connect to cathode on semiconductor laser diode.
Connect to cathode on monitoring photodiode.
Voltage input to set output current (I
L1
) of current source 1.
Connect load resistor between this pin and GND for I
L1
setting.
Voltage input to set output current (I
L2
) of current source 2.
Connect load resistor between this pin and GND for I
L2
setting.
Connect load resistor between this pin and GND for I
L3
setting.
Leave this pin open if I
L3
is not used.
Laser turns on and off by “L” and “H”, respectively.
Connect resistor between pins 1RM and 2RM for conversion of
current generated by monitoring photodiode into changes in voltage.
Analog output for monitoring laser power
Comparator output for monitoring laser power
If this is “L”, all current supply circuits are turned off.
Connect load resistor between RO and V
CC
for laser current.
Power supply for internal analog circuits. Connect to positive power
source (+5V)
Power supply for internal digital circuits. Connect to positive power
source (+5V)
GND for internal analog circuits
GND for internal digital circuits
DATA
1RM,
2RM
MO
CO
V
OFF
RO
V
CC1
V
CC2
GND1
GND2