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MITSUBISHI
< DIGITAL
ASSP >
M61880FP
Laser-diode driver / controller
DESCRIPTION
The M61880FP 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 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
PIN CONFIGURATION (TOP VIEW)
OUTPUT TO SWITCHING CURRENT SETTING LOAD
RS
1
20 19 18 17 16 15 14 13 12 11
Vcc2 RO NC LD GND2 PD
MONITORING DIODE INPUT SWITCHING DATA INPUT LASER CURRENT OUTPUT LASER CURRENT LOAD OUTPUT
GND1 2
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
3 4 5 6 7 8
Vref Vr CH S/H
FEATURES
Built-in sample-hold circuit for internal APC function Hold error voltage is less than 1% for 1s(C=0.047F) High speed switching 200Mbps Large driving current 100mA (max) Capable of setting bias current (40mA max) 5V single power supply
DATA ENB 2RM 1RM
LASER CURRENT ENABLE INPUT MONITORING LOAD INPUT 2 MONITORING LOAD INPUT 1
Vcc1 9 NC
10
APPLICATION
Semiconductor laser-diode applied equipment Laser beam printer(LBP) Plain Paper Copier(PPC)
NC : No connection
Outline 20P2N-A
BLOCK DIAGRAM
Vcc2
20
RO
19
NC
18
LD
17
GND2
16
PD
15
DATA
14
ENB
13
2RM
12
1RM
11
+ TTL/ECL
ISW
COMP
2.5V
IB 50K Reference voltage
1.5V
1 2 3 4
5
6
7
8
9
10
RS
GND1
RB
VB
Vref
Vr
S/H
Vcc1
NC
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MITSUBISHI
< DIGITAL
ASSP >
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 generating 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 bias current to LD independent of the state of the DATA input.
PIN DESCRIPTIONS
Pin LD PD Rs Name Laser current output Monitoring diode input Switching current Set load output Bias current Set load output Bias current setting voltage input Switching data input For monitoring Load 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 (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. Bias current (IB) is set by applying a voltage at this pin. Leave this pin open if IB is not used. 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).
RB
VB
DATA 1RM,2RM
ENB RO S/H
Laser current enable input Laser current load output Sample hold control input Holding capacitor load input/output
CH
Connect a holding capacitor between this this andand GND. Inside the M61880 Connect a holding capacitor between pin pin GND. Inside the M61880 this this connects to the the output of the sample-hold circuit and the current source pin pin connects to output of the sample-hold circuit and the current source input for Isw. 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). Power supply to internal digital circuits. Connect to a positive power source(+5V). GND for internal analog circuits. GND for internal digital circuits.
Vref Vr
Reference voltage output
Reference voltage input
Vcc1 Vcc2 GND1 GND2
Power supply pin 1 Power supply pin 2 GND pin 1 GND pin 2
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MITSUBISHI
< DIGITAL
ASSP >
M61880FP
Laser-diode driver / controller
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. Vref(1.5V) [V] (a) Isw0 [mA] = 30 X Rs [k] (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 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). VB [V] IB [A] = 1 X RB [] 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. 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 : Vcc(min.) -2.5 [V] RO(max.) [] = Isw(max.) [mA] where Isw(max.) is the maximum of Isw. If, for example, Vcc(min.)= 4.75V and Isw(max.)= 100mA, RO(max.)=22. Accordingly, if the resistance of RS is selected so as to gain maximum Isw of 100mA, RO should be 22 at the maximum. 6.Sample-Hold Circuit (1) Circuit Operation Overview The following is an overview of the operation of the samplehold circuit contained in the M61880. The PD current generated by LD illumination flows through the resistor connected between 1RM and 2RM, thereby generating 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.
2Isw0
200%
Comparator Vr Vm
Isw0
100%
Constant current source for charging
SW1 Output CH SW2
S/H
Control circuit
External capacitor
Constant current source for discharging
ENB 0
1.0 2.0
2.5 0%
Tr1
3.0
4.0
CH pin voltage VCH (V)
Conceptual Diagram: sample-hold circuit
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MITSUBISHI
< DIGITAL
ASSP >
M61880FP
Laser-diode driver / controller
FUNCTION TABLE
Input ENB H L S/H X H DATA X X H L L L 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. 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). Vm,Vr X X X Vm < Vr Switch condition SW1 OFF OFF OFF ON OFF SW2 OFF OFF OFF OFF ON ON OFF OFF OFF OFF Fixed to "L" High impedance state (hold) High impedance state (hold) Constant current sourcing (sample) Constant current sinking (sample) Tr1 Output
Vcc
ENB input
sample sample hold hold sample hold
S / H input
DATA input I LD
Laser drive current
An example of APC Timing Chart 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)
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.
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MITSUBISHI
< DIGITAL
ASSP >
M61880FP
Laser-diode driver / controller
ABSOLUTE MAXIMUM RATINGS (Ta = -20 ~ 70C unless otherwise noted)
Symbol Vcc VI VO Isw IB Pd Parameter Supply voltage CH, Vr Input voltage DATA, ENB, S/H Output voltage RO Switching current Bias current Power dissipation Conditions Ratings -0.3 ~ +5.5 -0.3 ~ +Vcc -0.3 ~ +Vcc -0.3 ~ +Vcc 120 50 Measured being mounted Ta = 25C(Note) 980 -60 ~ +150 Unit V V V mA mA mW C
Tstg Storage temperature Note: For operation above 25C, derating of 9.8mW/C is necessary. Limits Typ. Max. 5.0 5.25 100 40 70
RECOMMENDED OPERATIONAL CONDITIONS (Ta = -20 ~ 70C unless otherwise noted)
Symbol Parameter Min. 4.75 Unit V mA mA C
Supply voltage Vcc Switching current Isw IB Bias current Topr Operating ambient temperature Note: Isw + IB 100mA
-20
ELECTRICAL CHARACTERISTICS (Ta = -20 ~ 70C, Vcc = 5V5% unless otherwise noted)
Symbol VIH VIL Vr Vref VLD VI VOH VOL II Isw IB Icg Idg Ioz LOFF Parameter "H" Input voltage "L" Input voltage Reference voltage input DATA,ENB,S/H Test conditions Limits Min. Typ. 2.0 0.35 1.4 Max. 0.8 1.5 0.1 -0.1 2.5 2.7 Vcc-1.6 3.0 0.6 20 -0.2 75 20 -1.0 0.66 -0.5 1.0 +0.5 50 50 43 43 63 mA 63 Vcc 2.0 1.6 Unit V V V V mV/C V V V V A mA mA mA mA mA A A A
DATA,ENB,S/H Vr Vref Io = 10A Reference Ta = -20 ~ 25C Temperature voltage coefficient output Ta = 25 ~ 70C Operating voltage range LD Maximum effective voltage CH "H" output voltage CH ENB= "L" ,IoL= (-0.6mA) "L" output voltage CH ENB= "L" ,IoH= (0.6mA) Input current Switching current Bias current (Note) Load charging current Load discharge current Output current under off condition Output current under off condition DATA,ENB LD LD CH CH CH LD VI = 2.7V VI = 0.4V CH=3.5V,Rs=1.2k,VLD=3V VB=1.5V,RB=70,VLD=3V ENB= "L" ,Vo=( 0.6 ~ Vcc-1.6V) ENB= "L" ,Vo=( 0.6 ~ Vcc-1.6V) Vo=2.0 ~ 3.0V, Hold condition ENB= "L" ,DATA= "H" ,Isw=50mA ENB= "H" ,DATA= "L" ,Isw=50mA Vcc=5.25V,ENB=0V, DATA=0V CH=3.5V,VB=1.4V Isw=75mA,IB=25mA DATA=4.5V RO=LD=5.0v
-0.66
Icc
Supply current
*Typical values are gained under conditions of Ta=25C and Vcc=5V. Note: This parameter indicates the conversion characteristics of the input voltage and output current.In actual use, Isw and IB shall be within the range specified as limits in the recommended operating conditions.
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MITSUBISHI
< DIGITAL
ASSP >
M61880FP
Laser-diode driver / controller
SWITCHING CHARACTERISTICS (Ta=25C,Vcc=5V)
Test pin Symbol fop Parameter Operating frequency ILD=50mA, Rs=840, CH=0.047F LD current APC adjustment; RM=adjustment(CH=2.5V) Vr=1.5V 0.5% (Note1) ILD=50mA, Rs=840, CH=0.047F APC adjustment; LD current RM=adjustment(CH=2.5V) Vr=1.5V 2.5% (Note1) Test condition Input Output Min. Limits Unit Typ. Max. 100 Mbps
tRP1
Circuit response time1
Vr voltage
1
S
tRP2
Circuit response time2
Vr voltage
3
S
tON tOFF
Circuit ON time Circuit OFF time
ENB voltage LD current ILD(H)=50mA (Note2) ENB voltage LD current ILD(H)=50mA (Note2) NOTE2:TEST CIRCUIT
350 5
S S
NOTE1:TEST CIRCUIT 20 oscilloscope (Input) P. G. PD
0.047F
20 LD Vcc oscilloscope ( Output ) ILD CH
0.047F
PD
LD oscilloscope ( Output ) ILD
CH Vr RS 1RM
Vcc RO PD LD Current probe RM 840 1.5V Vr RS
RO PD LD
50 840
Current probe 1RM 2RM GNDENB 50 S/H DATA oscilloscope ( Input ) P.G. t r=t f= 6ns
RM
S/H DATA 2RM ENB GND Other pins are open
Other pins are open
TIMING CHARTS
1.5V change value 1.5V Vr voltage 0%
TIMING CHARTS
3V ENB voltage 1.5V TON ILD(H) ILD(L) LD current 90 % 10 % 1.5 V 0V TOFF ILD (H)
TRP1(TRP2) TRP1(TRP2)
LD current
90% 10%
ILD (L)
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MITSUBISHI
< DIGITAL
ASSP >
M61880FP
Laser-diode driver / controller
APPLICATION EXAMPLE
LD driver M61880FP
5V Vcc 5V Vcc2 digital
20
300pF 36 RO 10 N C
19 18
Control signal Data stream LD
17 16
2RM
12
1RM
11
GND2 digital PD
15
DATA
14 13
ENB
+
TTL/ECL
ISW
COMP
2.5V
IB 50K Reference voltage
1.5V
1 2 3 4
RS GND1 RB VB 1.5K analog 150
Vref
5
Vr 0.047F
6
7
8
9
10
S/H S/H signal
Vcc1 NC analog 5V
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MITSUBISHI
< DIGITAL
ASSP >
M61880FP
Laser-diode driver / controller
Explanation for setting Laser switching current
Vcc
The circuit of setting center value (Isw0)of maximum switching current(2X Isw0) 2XISWO 1.5V +
AMP1
1:1
D1 2XISWO I1 I2 Q1 Vd 2.5V CH 2K
Id
ISW1 ISW2
D2
VB
- ISW
ISW2
V1
Q2
V2
Vcc
RS
LD
CURRENT SW
250A 2XISWO
250A
1:1 The circuit of setting switching current Fig.1 Equivalent circuits of setting switching current
1. The circuit of setting center value(Isw0) of maximum switching current
The setting center value(Isw0) of maximum switching current, 2 X Isw0,set up Rs ( load for switching current setting). Isw0 (the value that is initialized) is So Isw2 is
Isw2=2 * Isw0 x
Isw is as follows
I1 I1+I2
(6) (7)
Vref(1.5V)[V] RS[k] 2. The circuit of setting switching current Isw0[mA]=30 x
(1)
Isw=2 * Isw0-Isw2
Next the relation between Isw and V would be introduced . Isw is able to solve with (6), (7),(3) and (2)equation.
When V is a difference voltage of between CHpin and 2.5V,Id is
Id = V 2K
So I1 and I2 is as follows
Isw=2 * Isw0(
(2)
I2 ) I1+I2 Id Isw=Isw0(1+ ) 250A Isw=Isw0(1+ V/2K ) 250A
(8) (9) (10)
I1=250A-Id ( I2=250A+Id
(3)
D1,D2,Q1 and Q2 construct a Gilbert circuit. The relation of I1,I2,Isw1, Isw2 and Isw0 is
I1 = Isw2 I2 Isw1 Isw1+Isw2=2 * Isw0
(4) (5)
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MITSUBISHI < DIGITAL ASSP > Laser-diode driver / controller TYPICAL CHARACTERISTICS
THERMAL DERATING Reference Voltage -Ambient Temperature
M61880FP
Vcc=5V 1200 1000 800 600 400 200 0 -25 0 25 50 75 100 125 AMBIENT TEMPERATURE Ta (C) 100.0 90.0
Vcc=5V,Ta=25C
1.54 1.52 1.50 1.48 1.46 1.44 0 -25 0 25 50 75 100 125 AMBIENT TEMPERATURE Ta (C)
VB PIN INPUT VOLTAGE * BIAS OUTPUT CURRENT
VB PIN INPUT VOLTAGE-CURRENT
60 50 40 30 20 10 0 0.5
Vcc=5V,Ta=25C RB=51
80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0
1.0 1.5 2.0 2.5 3.0 3.5 INPUT VOLTAGE VB (V)
0
0
2.0 1.0 INPUT VOLTAGE VB (V)
BIAS CURRENT SET RESISTORBIAS OUTPUT CURRENT
SWITCHING CURRENT SET RESISTORSWITCHING OUTPUT CURRENT
Vcc=5V,Ta=25C 60
VB=1.5V
Vcc=5V,Ta=25C 120
VCH=2.5V
50 40 30 20 10 0 0 100 200 300 400
RESISTOR FOR BIAS CURRENT SET RB()
100 80 60 40 20 0 0 1 2 3 4
RESISTOR FOR SWITCHING CURRENT SET Rs(K)
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MITSUBISHI < DIGITAL ASSP > Laser-diode driver / controller
APC COMPARATOR INPUT VOLTAGE-OFFSET VOLTAGE
10.0 9.0 100 80 60 40 20 0 1
Rs=820
M61880FP
CHpin VOLTAGE - SWITCHING CURRENT
120
8.0 7.0 6.0 5.0 4.0 3. 0 2.0 1.0
Vcc=5V,Ta=25C
Vcc=5V,Ta=25C
1.5
2
2.5
3
3.5
0
0
CHpin VOLTAGE Vch(V)
2.0 1.0 2RMpin INPUT VOLTAGE Vm (V)
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MITSUBISHI
< DIGITAL
ASSP >
M61880FP
Laser-diode driver / controller
PACKAGE OUTLINE
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