M66510 データシートの表示（PDF） - MITSUBISHI ELECTRIC

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M66510

LASER-DIODE DRIVER

MITSUBISHI ELECTRIC  

MITSUBISHI 〈DIGITAL ASSP〉

M66510P/FP

LASER-DIODE DRIVER

DESCRIPTION OF OPERATION

1. Setting laser driving current

The M66510 is provided internally with three constant current

sources IL1, IL2 and IL3, allowing setting of each independent

output current.

The methods of setting IL1 to IL3 are given below in (1) to (3).

(1) Method of setting IL1

IL1 is approximated by the VL1 pin input voltage and the re-

sistor (RC1) connected between 1RC pin and GND as fol-

lows:

IL1[mA] = 12 ×

VL1[V]

RC1[kΩ]

However, 0 ≤ VL1 ≤ VCC – 1.8V, IL1(max.) = 60mA

(2) Method of setting IL2

IL2 is approximated by the VL2 pin input voltage and the re-

sistor (RC2) connected between 2RC pin and GND as fol-

lows:

IL2[mA]

=

6

×

VL2[V]

RC2[kΩ]

However, 0 ≤ VL2 ≤ Vcc – 1.8V, IL2(max.) = 30mA

(3) Method of setting IL3

IL3 is approximated by the internal reference voltage (Vref)

and the resistor (RC3) connected between 3RC pin and GND

as follows:

IL3[mA] = 10 ×

Vref[V]

RC3[kΩ]

However, Vref = 1.2V (standard), IL3(max.) = 30mA

Note: The expressions for setting IL1 to IL3 are typical. Actually, the set values

fluctuate several % depending on IC lot dispersion or operating ambient

temperature (See the ELECTRICAL CHARACTERISTICS).

2. Switching operation

The laser is turned on when DATA = “L”. At this time, the la-

ser driving current is IL1 + IL2 + IL3.

The laser is turned off when DATA = “H”. At this time, the la-

ser driving current becomes almost 0 regardless of IL1 to IL3.

3. Usage of VOFF input

The current which flows into the laser becomes 0 when

DATA = “H”. And the laser is turned off but the internal cur-

rent sources are active.

Contrarily, the internal current sources are turned off when

VOFF = “L”. It is therefore possible to prevent overcurrent from

flowing into the laser by setting VOFF input to “L” until VCC

reaches 3.5V (standard) at the power-ON time, for example

(See 6. Internal reset).

4. Laser power monitor operation

The M66510 outputs the information on monitor photodiode

(PD) built in the laser from the MO and CO pins in the flow

given below.

(1) The current equal to the PD current produced through

emission of the laser flows into the resistor (RM) connected

between 1RM and 2RM. The potential difference (VM) pro-

duced on RM is converted into a level from GND by the inter-

nal differential amplifier.

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

through the buffer amplifier and compared to the internal ref-

erence voltage Vref (1.2V standard) by the comparator. Then

the result of comparison is output from the CO pin on the TTL

level.

VM

LD

+

RM

–

Differential

amplifier

PD

Vref

–

+

Buffer

amplifier

MO output

+

CO output

–

Comparator

Condition

VM < Vref

VM > Vref

CO output

“L”

“H”

Monitor circuit schematic drawing

3

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