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M66515

LASER-DIODE DRIVER/CONTROLLER

Mitsumi 

MITSUBISHI 〈DIGITAL ASSP〉

M66515FP

LASER-DIODE DRIVER/CONTROLLER

FUNCTIONS

The M66515 is a semiconductor laser-diode driver/controller.

Its functions are the driving and laser power control of a spe-

cific type (Mitsubishi’s N type laser) of semiconductor laser

diode, in which the anode of a semiconductor laser diode

(LD) is connected in stem structure to the cathode of a moni-

toring photodiode (PD).

The functions to drive LD and to control laser power are car-

ried out by connecting an external capacitor to the CH pin and

applying a reference voltage to the Vr pin.

The PD current generated by LD illumination flows through

the resistor connected between 1RM and 2RM, thereby gen-

erating a potential difference (VM). VM is compared with the

voltage applied to the Vr pin. If VM < Vr, a constant current is

sourced through the CH pin so that the external capacitor is

charged. If VM > Vr, a constant current sinks through the CH

pin to discharge the external capacitor.

The above operation occurs when the S/H input is “L”

(sample). When the S/H input is “H,” the CH pin is maintained

at high impedance state (hold), irrespective of the state of VM,

Vr, and DATA input.

The LD drive current is made up of the switching current, ISW,

which is controlled by the DATA input, and IB, which is the

bias current to LD independent of the state of the DATA input.

PIN DESCRIPTIONS

Pin

Name

LD

Laser current output

PD

Monitoring diode input

Switching current

RS

Set load output

Bias current

RB

Set load output

VB

Bias current setting

voltage input

Description

Connect to cathode on semiconductor laser diode.

Connect to anode on monitoring photodiode.

Connect a load resistor between this pin and GND for the setting of current (ISW) to be

switched.

Connect a load resistor between this pin and GND for the setting of bias current (IB). Leave

this pin open if IB is not used.

Bias current (IB) is set by applying a voltage at this pin. Leave this pin open if IB is not

used.

DATA

1RM, 2RM

ENB

RO

S/H

CH

Vref

Switching data input

For monitoring

Load input

Laser current enable input

If this pin is “L,” a current of ISW + IB flows through laser diode; if “H,” current IB flows.

A load resistor is connected between pins 1RM and 2RM for conversion of current

generated by monitoring photodiode into changes in voltage.

If this pin is “H” all current source circuits are turned off.

Laser current load output Connect a laser current load resistor between this pin and Vcc.

Sample hold control input If this pin is “L,” sampling (APC) occurs, if “H,” holding (switching).

Holding capacitor load

input/output

Connect a holding capacitor between this pin and GND. Inside the M66515 this pin

connects to the output of the sample-hold circuit and the current source input for ISW.

Reference voltage output Internal reference voltage (1.2 V typ.) output pin of M66515

A reference voltage is applied to this pin to operate the comparator in the sample-hold

Vr

Reference voltage input circuit. Connect this pin to the Vref pin if the internal reference voltage of the M66515 is to

be used.

TEST

VCC1

VCC2

GND1

GND2

Test pin

Power supply pin 1

Power supply pin 2

GND pin 1

GND pin 2

This pin is used to test the M66515 when shipped. Leave open.

Power supply to internal analog circuits. Connect to a positive power source (+5 V).

Power supply to internal digital circuits. connect to a positive power source (+5 V).

GND for internal analog circuits.

GND for internal digital circuits.

2

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