MITSUBISHI
〈DIGITAL
ASSP〉
MITSUBISHI
〈DIGITAL
ASSP〉
M66512P/FP
M66512P/FP
LASER-DIODE DRIVER
LASER-DIODE DRIVER
DESCRIPTION
The M66512 is a semiconductor laser-diode driver for driving
a specific type* of semiconductor laser, in which the anode 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 volt-
age from an external source. the M66512 is capable of driv-
ing laser diodes on a maximum current of 120 mA.
It operates on a 5-V single power supply and switches laser
drive current at a rate of 40 Mbit/s.
*: The N type of Mitsubishi’s semiconductor lasers.
FEATURES
• Two kinds of outputs for monitoring laser power built in.
(comparator output and analog output)
• Pin provided for forced OFF of current circuit.
• High speed switching (40 Mbit/s)
• Large drive current (120mA max.)
• 5V single power supply
APPLICATION
Laser beam printers
PIN CONFIGURATION (TOP VIEW)
V
CC1
CURRENT SETTING INPUT 1
V
L1
CURRENT SETTING LOAD OUTPUT 1
1RC
CURRENT SETTING INPUT 2
V
L2
CURRENT SETTING LOAD OUTPUT 2
2RC
LASER CURRENT
FORCED OFF INPUT
V
OFF
CURRENT SETTING LOAD OUTPUT
3RC
GND1
MONITORING LOAD INPUT 1
1RM
MONITORING LOAD INPUT 2
2RM
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
RO
LOAD OUTPUT
NC
LD
LASER DIODE OUTPUT
GND2
PD
MONITORING DIODE INPUT
DATA
DATA INPUT
V
CC2
MONITORING
CO
COMPARATOR OUTPUT
MO
MONITORING ANALOG
OUTPUT
NC
LASER CURRENT
Outline 20P4
20P2N-A
NC: No Connection
M66512P/FP
BLOCK DIAGRAM
MONITORING
OUTPUT
MO
12
Linear amp
COMPARATOR
OUTPUT
CO
13
Comparator
(Vref=1.4V)
PD
16
LD
18
RO
20
1RM 9
2RM 10
V
L1
2
1RC 3
V
L2
4
2RC 5
Differential
amp
Current switching circuit
15 DATA
DATA INPUT
I
L
=I
L1
+I
L2
+I
L3
Constant current
source(I
L1
)
Max.60mA
Constant current
source(I
L2
)
Max.30mA
Constant current
source(I
L3
)
Max.30mA
6 V
OFF
LASER CURRENT
FORCED OFF
1 V
CC1
14 V
CC2
8 GND
1
17 GND
2
3RC 7
V
L1
, 1RC : Laser current (I
L1
) setting pin
V
L2
, 2RC : Laser current (I
L2
) setting pin
3RC : Laser current (I
L3
) setting pin
V
CC1
, GND1 : Power supply pin for analog circuits in IC
V
CC2
, GND2 : Power supply pin for digital circuits in IC
1
MITSUBISHI
〈DIGITAL
ASSP〉
M66512P/FP
LASER-DIODE DRIVER
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.
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.
PIN DESCRIPTIONS
Pin
LD
PD
V
L1
1RC
V
L2
2RC
3RC
DATA
1RM,
2RM
MO
CO
V
OFF
RO
V
CC1
V
CC2
GND1
GND2
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
Name
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
2
MITSUBISHI
〈DIGITAL
ASSP〉
M66512P/FP
LASER-DIODE DRIVER
OPERATION
1. Setting for Laser Drive Current
The M66512 has 3 built-in constant current sources, I
L1
, I
L2
,
and I
L3
. Each output current can be controlled independently.
The following (1) to (3) describe the method for how to set
I
L1
,I
L2
, and I
L3
.
(1) I
L1
setting method
The value of I
L1
is determined by the voltage on the V
L1
pin and the resistor (RC1) connected between the 1RC
pin and GND. The following equation is used for approxi-
mation.
V
L1
[V]
I
L1
[mA] = 12
×
RC1 [kΩ]
provided that 0≤V
L1
≤V
CC
–1.8V and I
L1(max.)
=60mA
(2) I
L2
setting method
The value of I
L2
is determined by the voltage on the V
L2
pin and the resistor (RC2) connected between the 2RC
pin and GND. The following equation is used for approxi-
mation.
V
L2
[V]
I
L2
[mA] = 6
×
RC2 [kΩ]
provided that 0≤V
L2
≤V
CC
–1.8V and I
L2(max.)
=30mA
(3) I
L3
setting method
The value of I
L3
is determined by the internal reference
voltage (V
ref
) and the resistor (RC3) connected between
the 3RC pin and GND. The following equation is used for
approximation.
I
L3
[mA] = 10
×
V
ref
[V]
RC3 [kΩ]
provided that V
ref
=1.4V (typ.) and I
L3(max.)
=30mA
Note: Each of the above equations is a typical on for ob-
taining I
L1
–I
L3
. In practice values vary by a few per-
cent due to some reasons such as differences of
ICs from lot to lot and variations in operation tem-
peratures.
2. Switching Operation
The laser turns on if DATA =“L”. The laser drive current at that
moment is I
L1
+I
L2
+ I
L3
.
If DATA = “H” the laser is turned off, and the laser drive cur-
rent is almost zero irrespective of the values of I
L1
to I
L3
.
3. Use of the V
OFF
Input
When DATA = “H” the current flowing through the laser is zero
so the laser is turned off, but the internal current sources are
in operation.
When V
OFF
= “L” in contrast, the internal current sources are
turned off. Accordingly, it is possible to prevent an excessive
current from flowing through the laser by, for example, fixing
the V
OFF
input to “L” until V
CC
, after turned on, reaches
3.5V(typ.). (See the section dealing with internal reset.)
4. Laser Power Monitoring Operation
At the MO and CO pins, the M66512 outputs data obtained
by the monitoring photodiode (PD) contained in the laser, in
the sequence explained below.
(1) A current equal to the PD current generated by laser light
flows through the resistor (RM) connected between 1RM
and 2RM. Then, a potential difference (V
M
) proportional to
the output of laser light occurs at RM.
(2) The V
M
is output at the MO pin as an analog signal
through a buffer amp. At the same time, V
M
is compared
with the internal reference voltage V
ref
(1.4V typ.) by the
comparator, thence the result of the comparison is output
at the CO pin in TTL level.
LD
PD
_
+
+
MO output
Buffer amp
VM
RM
Vref
_
CO output
Comparator
Condition
V
M
<V
ref
V
M
>V
ref
CO output
“L”
“H”
A Schematic Diagram of Monitor Circuits
3
MITSUBISHI
〈DIGITAL
ASSP〉
M66512P/FP
LASER-DIODE DRIVER
P=I
CC
×
V
CC
+I
(RO)
×
V
(RO)
+ I
(LD)
×
V
(LD)
+ I
OL(CO)
×
V
OL(CO)
Where V
(RO)
: voltage at RO pin
(LD)
: voltage at LD pin
V
: load current at RO pin
I
(RO)
I
(LD)
: load current at LD pin
V
OL(CO)
: “L” output voltage at CO pin
I
OL(CO)
: “L” output voltage at CO pin
If, for example, V
CC
= 5.25V, V
(RO)
= V
(LD)
= 2.75V, I
(RO)
=
I
(LD)
= 120mA, I
OL(CO)
= 8mA, and V
OL(CO)
= 0.5V, power dis-
sipation at times of turning on and off of laser will be as fol-
lows.
(1) Laser ON (DATA =“L” and I
CC
= 75mA)
P
ON
= 75
×
5.25 + 0 + 120
×
2.75 + 8
×
0.5 = 727.8(mW)
(2) Laser OFF (DATA =“H” and I
CC
= 74mA)
P
OFF
= 74
×
5.25 + 120
×
2.75 + 0 = 718.5(mW)
5. RO Pin
The RO pin is used to connect a load resistor (RO) for the
current sources (I
L1
, I
L2
, and I
L3
). The load resistor is con-
nected between the RO pin and V
CC
in order to reduce the
power dissipated in the IC.
The resistance of the load resistor should be such that does
not generate a voltage equal to or lower than 2.5V at the RO
pin. Accordingly, a value that satisfies the following equation
should be chosen.
V
CC
–2.5[V]
RO (Ω)
≤
maximum load current flowing through RO [A]
Example: If V
CC
=5V and the maximum load current is 120
mA, RO is 20Ω or under.
6. Internal Reset Function
The M66512 has a reset circuit for the protection of laser from
an excessive current flowing at the moment of power on. The
reset circuit functions in the range V
CC
< 3.5V(typ.), letting all
current sources turn off.
7. V
CC
and GND Pins
Pins related to the power supply function are V
CC1
, V
CC2
,
GND1, and GND2. The role of these pins in terms of the in-
ternal circuits are as follows.
V
CC1
, GND1 : connected to analog circuits
V
CC2
, GND2 : connected to digital circuits
In practical wiring, the following should be noted.
(1) Secure as much a width as possible for conductors and
avoid lengthy wiring.
(2) Allocate electrolytic capacitors for stable voltage near
V
CC1
and GND1.
(3) Allocate by-pass capacitors near V
CC2
and GND2.
Notes on the Wiring for peripheral Components
Lay out peripheral components necessary for the M66512 to
operate in closest possible proximity to the M66512.
Calculation Method for Power Dissipation
The M66512’s approximated power dissipation, P, is deter-
mined by the following equation.
4
MITSUBISHI
〈DIGITAL
ASSP〉
M66512P/FP
LASER-DIODE DRIVER
OPERATING WAVEFORMS
P
0
Laser output
Laser output
Laser current I
L
I
L3
I
L1
I
L2
I
L1 : 0~60mA
I
L2 : 0~30mA
I
L3 : 0~30mA
Drive current pulse
ABSOLUTE MAXIMUM RATINGS
Symbol
V
CC
V
I
V
O
I
L1
I
L2
I
L3
P
d
T
stg
Parameter
Supply voltage
Input voltage
Output voltage
Output current 1
Output current 2
Output current 3
Power dissipation
Storage temperature
DIP
SOP
For single integrated circuit; Ta=25˚C (Note 1)
IC Measured being mounted; Ta=25˚C (Note 2)
V
L1
, V
L2
DATA, V
OFF
CO
RO
Output: “H”
Conditions
Ratings
–0.5 ~ +7.0
–0.3 ~ V
CC
–0.3 ~ + 7
–0.3 ~ + 5.5
–0.3 ~ + 7
90
45
45
1300
1200
–65 ~ 150
Unit
V
V
V
mA
mA
mA
mW
°C
Note 1: For operation above 25°C free-air temperature, derating of 10.4mW/°C is necessary.
2: For operation above 25°C free-air temperature, derating of 9.6mW/°C is necessary.
RECOMMENDED OPERATIONAL CONDITIONS
Symbol
V
CC
I
L1
I
L2
I
L3
T
opr
Supply voltage
Output current 1
Output current 2
Output current 3
Operational ambient temperature
–20
Parameter
Conditions
Min.
4.75
Limits
Typ.
5
Max.
5.25
60
30
30
75
Unit
V
mA
mA
mA
˚C
5
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