Mitsubishi M61880FP Datasheet

DESCRIPTION

controller. Its functions are the driving and laser power control of a specific type(Mitsubishi's N-type laser)of semiconductor laser diode,in which the anode of a semiconductor laser diode is connected in stem structure to the cathode of a monitoring photodiode. The IC has a laser drive current output pin of sink type and is capable of driving a laser diode on a maximum bias current of 40mA and a maximum switching current of 100 mA,which is switching at a rate of 200Mbps. Since the M61880FP has a built in sample-hold circuit,it is possible to realize an internal APC* system that requires no external device for laser power control. *:Automatic Power Control

The M61880FP is a semiconductor laser-diode driver/

MITSUBISHI < DIGITAL ASSP >

M61880FP

Laser-diode driver / controller

PIN CONFIGURATION (TOP VIEW)

FEATURES

Built-in sample-hold circuit for internal APC function Hold error voltage is less than 1% for 1µs(C=0.047µF)

High speed switching 200Mbps

Large driving current 100mA (max)

Capable of setting bias current (40mA max)

5V single power supply

APPLICATION

Semiconductor laser-diode applied equipment Laser beam printer(LBP) Plain Paper Copier(PPC)

BLOCK DIAGRAM

OUTPUT TO SWITCHING CURRENT SETTING LOAD

OUTPUT TO BIAS CURRENT SETTING LOAD

BIAS CURRENT SETTING VOLTAGE INPUT

REFERENCE VOLTAGE OUTPUT

REFERENCE VOLTAGE INPUT

HOLDING CAPACITOR LOAD INPUT/OUTPUT

SAMPLE-HOLD CONTROL INPUT

RB VB

Vcc1

5 6 7

8 9

GND1

Vref

S / H

Outline 20P2N-A

Vcc2

N C

GND2

PD DATA

ENB 2RM

1RM

LASER CURRENT LOAD OUTPUT

LASER CURRENT OUTPUT

MONITORING DIODE INPUT

SWITCHING DATA INPUT

LASER CURRENT ENABLE INPUT

MONITORING LOAD INPUT 2

MONITORING LOAD INPUT 1

NC : No connection

Vcc2 RO N C GND2 PD 2RM 1RM

181920

1 2 3

GND1

RS RB VB Vref Vr Vcc1 NC

ISW

50K

1.5V

5 6

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TTL/ECL

2.5V

Reference voltage

DATA

ENB

1314

8 9

COMP

S/H

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is not used.

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

M61880FP

Laser-diode driver / controller

FUNCTIONS

The M61880 is a semiconductor laser-diode driver/controller. Its functions are the driving and laser power control of a specific 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 monitoring photodiode (PD). The functions to drive LD and to control laser power are carried 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-

PIN DESCRIPTIONS

Pin Name LD PD

Laser current output Connect to cathode on semiconductor laser diode. Monitoring diode input Switching current

Set load output Bias current

Set load output

Connect to anode on monitoring photodiode. Connect a load resistor between this pin and GND for the setting of current (lsw)

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.

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" and DATA = "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, lsw, which is controlled by the DATA input, and IB , which is the

Description

DATA

1RM,2RM

ENB

RO S/H

Vref

Vcc1 Power supply pin 1

Bias current setting voltage input

Switching data input

For monitoring Load input

Laser current enable input Laser current load output

Sample hold control input

Holding capacitor load input/output

Reference voltage output

Reference voltage input

Bias current (IB) is set by applying a voltage at this pin. Leave this pin open if I

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. ( 2RM pin connects to GND in the IC.)

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

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

If this pin is "L" ,sampling (APC) occurs, if "H" ,holding (switching).

Connect a holding capacitor between this pin and GND. Inside the M61880

this pin connects to the output of the sample-hold circuit and the current source

input for Isw.

Internal reference voltage (1.5Vtyp.) output pin of M61880.

A reference voltage is applied to this pin to operate the comparator in the sample-hold circuit. Connect this pin to the Vref pin if the internal reference voltage of the M61880 is to be used.

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

Vcc2 GND1

GND2

Power supply pin 2 GND pin 1 GND pin 2 GND for internal digital circuits.

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

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OPERATION

1.Laser Drive Currents Setting Method

Laser Drive Current=Isw(switching current)+IB(bias current) at switching mode (1)Isw(Switching Current) First it is necessary to decide the center value(Isw0) of maximum switching current Isw(max).Isw0 is depend on Rs ( load for switching current setting) by the following equation. (a)

Isw0 [mA] = 30 X

(b) When switching current is center value( Isw0) , it is necessary to set up Rm ( load resistor for monitor of photodiode current ) as follows: VM(voltage across resistor Rm) = Vr (reference voltage ) at this condition CH pin voltage =2.5V. When CH pin voltage < 2.5V , Isw <Isw0 When CH pin voltage > 2.5V , Isw >Isw0 (CH pin voltage changes from 2V to 3V at APC mode) (c) The usable range of ISW at APC mode That is 20 ~180% of Isw0 accurately.

(2) IB(Bias Current) Bias current (IB) is set by RB (resistor for the setting of bias current) and VB (voltage for the setting of bias current).

IB [A] = 1 X

1.2V ≤ VB ≤ Vcc-2.7V IB(max.)=40mA

2.Switching Operation

If DATA = "L" , the LD drive current is Isw+IB if DATA = "H" , IB.

3.ENB input

When the laser drive current is controlled by the DATA input, the M61880's internal current source is maintained turned on. In contrast, the control by ENB is turning on and off at the current source. If ENB = "L" the current source turns on ; if ENB = "H" off. When ENB = "H" the CH pin is compulsorily fixed to "L" in order to discharge the capacitor connected to the CH pin.

Vref(1.5V) [V] Rs [kΩ]

VB [V] RB [Ω]

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M61880FP

Laser-diode driver / controller

4.Internal Reset Function

The M61880 has a reset circuit built in for the protection of laser from an excessive current flowing at the moment of

power on. The internal current source goes off in the range Vcc < 3.5V(typ.), and the CH pin is compulsorily fixed to "L" at the same time.

5.RO Pin A load resistor for laser drive current is connected to the RO pin, through which a current almost equal to Isw flows in. The load resistor is connected between the RO pin and Vcc to reduce power dissipated in the IC. Due to reasons related to the operation of circuits, the voltage at this pin should be 2.5V or higher. Consequently, the maximum resistance, RO(max.), of load resistor RO is :

RO(max.) [Ω] =

where Isw(max.) is the maximum of Isw. If, for example,

Vcc(min.)= 4.75V and Isw(max.)= 100mA, RO(max.)=22Ω.

Accordingly, if the resistance of RS is selected so as to gain

maximum Isw of 100mA, RO should be 22Ω at the maxi-

mum.

6.Sample-Hold Circuit

(1) Circuit Operation Overview

The following is an overview of the operation of the sample-

hold circuit contained in the M61880.

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. This operation occurs

when the S/H input is "L" and DATA= "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.

Vcc(min.) -2.5 [V] Isw(max.) [mA]

2Isw0

Isw0

1.0

3.0

4.0

2.5

2.0

CH pin voltage VCH (V)

200%

100%

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Constant

Comparator

current source for charging

SW1

Control

S / H

ENB

circuit

SW2

Constant current source for discharging

Conceptual Diagram: sample-hold circuit

Output

External capacitor

Tr1

FUNCTION TABLE

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M61880FP

Laser-diode driver / controller

Input

ENB S/H Vm,Vr

X : Don't care

(2) APC Timing Chart The following diagram is an APC timing chart, operation of which is based on sample hold control signals.

DATA

X X H

X X

X Vm < Vr Vm > Vr

Switch condition

SW1 SW2 OFF

OFF OFF OFF

OFF

OFF OFF

Vcc

ENB input

sample

S / H input

hold

Tr1

ON OFF OFF OFF OFF

sample

Output

Fixed to "L" High impedance state (hold)

High impedance state (hold) Constant current sourcing (sample)

Constant current sinking (sample)

Note that in the example it is assumed that the leak current occurring at the CH pin under hold condition flows into the M61880 (in the positive direction).

sample

hold

DATA input

∆I LD

Laser drive current

An example of APC Timing Chart

7.Vcc and GND Pins

Pins related to the power supply function are Vcc1, Vcc2, GND1, and GND2. The role of these pins in terms of the internal circuits are as follows. Vcc1, GND1: connected to analog circuits Vcc2, 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 Vcc1 and GND1. (3) Allocate by-pass capacitors near Vcc2 and GND2.

Notes on the Wiring for Peripheral Components

Lay out peripheral components necessary for the M61880 to operate in closest possible proximity to the M61880.

Calculation Method for Power Dissipation

The approximate power dissipation, P, of the M61880FP is determined by the following equation. P = Icc x Vcc + I(RO) x V(RO) + I(LD) x V(LD) where V(RO):voltage at RO pin V(LD): voltage at LD pin I(RO): load current at RO pin I(LD) : load current at LD pin If, for example, Vcc = 5.25V, V(RO) = V(LD) = 2.5V, and I(RO) = I(LD) = 100mA, power dissipation at times of turning laser on and off will be as follows. (1) Laser ON (DATA = "L" and Icc = 55mA) PON = 55 x 5.25 + 0 + 100 x 2.5 = 538.8(mW) (2) Laser OFF (DATA = "H" and Icc = 55mA) POFF = 55 x 5.25 +0+100 x 2.5 = 538.8(mW)

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