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