M66512 データシートの表示（PDF） - Mitsumi

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M66512

LASER-DIODE DRIVER

Mitsumi 

MITSUBISHI 〈DIGITAL ASSP〉

M66512P/FP

LASER-DIODE DRIVER

OPERATION

1. Setting for Laser Drive Current

The M66512 has 3 built-in constant current sources, IL1, IL2,

and IL3. Each output current can be controlled independently.

The following (1) to (3) describe the method for how to set

IL1,IL2, and IL3.

(1) IL1 setting method

The value of IL1 is determined by the voltage on the VL1

pin and the resistor (RC1) connected between the 1RC

pin and GND. The following equation is used for approxi-

mation.

IL1 [mA] =

12

×

VL1[V]

RC1 [kΩ]

provided that 0≤VL1≤VCC–1.8V and IL1(max.) =60mA

(2) IL2 setting method

The value of IL2 is determined by the voltage on the VL2

pin and the resistor (RC2) connected between the 2RC

pin and GND. The following equation is used for approxi-

mation.

IL2[mA]

=

6

×

VL2[V]

RC2 [kΩ]

provided that 0≤VL2≤VCC–1.8V and IL2(max.) =30mA

(3) IL3 setting method

The value of IL3 is determined by the internal reference

voltage (Vref) and the resistor (RC3) connected between

the 3RC pin and GND. The following equation is used for

approximation.

IL3[mA] = 10 × Vref[V]

RC3 [kΩ]

provided that Vref =1.4V (typ.) and IL3(max.) =30mA

Note: Each of the above equations is a typical on for ob-

taining IL1–IL3. 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 IL1 +IL2 + IL3.

If DATA = “H” the laser is turned off, and the laser drive cur-

rent is almost zero irrespective of the values of IL1 to IL3.

3. Use of the VOFF 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 VOFF = “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 VOFF input to “L” until VCC, 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 (VM) proportional to

the output of laser light occurs at RM.

(2) The VM is output at the MO pin as an analog signal

through a buffer amp. At the same time, VM is compared

with the internal reference voltage Vref(1.4V typ.) by the

comparator, thence the result of the comparison is output

at the CO pin in TTL level.

LD

PD

VM RM

Vref

_

MO output

+ Buffer amp

+

_

CO output

Comparator

Condition

VM<Vref

VM>Vref

CO output

“L”

“H”

A Schematic Diagram of Monitor Circuits

3

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