iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 1/12 FEATURES APPLICATIONS ° ° ° ° ° ° ° ° ° ° LD driver for continuous or pulsed operation (CW to 300kHz) of up to 100mA Average control of laser power Simple LD power adjustment via external resistor Adjustable watchdog supervises digital input signals Soft starting after power-on Driver shutdown in the case of overtemperature and undervoltage Operation at 2.7V..6V suits battery-powered systems with two to four AA/AAA cells Reverse battery protection Battery-powered LD modules LD Pointers PACKAGES SO8 BLOCK DIAGRAM DRIVER STAGE VCC C1 47µF 5 R2 2 VB 2.7..6V REF REFERENCE D1 Z6V8 C3 2nF RSET 2.7..330k THERMAL SHUTDOWN ISET KLD 4 LD 8 MD R1 0..2 VCC INPUT POWER DOWN REF AMD 7 IN 3 1 6 WATCHDOG iC-WJB CWD CI GND 2 3 1 CWD (..pF) © 2000 iC-Haus GmbH Integrated Circuits Am Kuemmerling 18, D-55294 Bodenheim CI 470nF alternative LD model LD MD ( VCC > 4.5V ) Tel +49-6135-9292-0 Fax +49-6135-9292-192 http://www.ichaus.com iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 2/12 DESCRIPTION The iC-WJB device is a driver IC for laser diodes in continuous or pulsed operation of up to 300kHz. The broad power supply range of 2.7V to 6V and the integrated reverse battery protection allows for batteryoperation with two to four AA/AAA cells. The laser diode is activated via switching input IN. A control to the mean value of the optical laser power (APC) and integrated protective functions ensure nondestructive operation of the sensitive semiconductor laser. The IC contains protective diodes to prevent destruction due to ESD, a protective circuit to guard against overtemperature and undervoltage and a soft-start circuit to protect the laser diode when switching on the power supply. Short-term reversed battery connection destroy neither the IC nor the laser diode. An external resistor at ISET is employed to adapt the APC to the laser diode being used. The capacitor at CI determines the recovery time constants and the starting time. A watchdog circuit monitors the switching input IN. If IN remains low longer than preset by the capacitor at CWD, the capacitor of the APC is discharged at pin CI. This ensures that the current through the laser diode during the next high pulse at input IN is not impermissibly high. PACKAGES SO8 to JEDEC Standard PIN CONFIGURATION SO8 (top view) PIN FUNCTIONS No. Name Function GND 1 8 KLD CWD 2 7 AMD CI 3 6 IN ISET 4 5 VCC 1 2 3 4 5 6 7 8 GND CWD CI ISET VCC IN AMD KLD Ground Capacitor for Watchdog Capacitor for Power Control Attachment for RSET +2.7V to +6V Supply Voltage Input Monitor Diode Anode Laser Diode Cathode iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 3/12 ABSOLUTE MAXIMUM RATINGS Values beyond which damage may occur; device operation is not guaranteed. Item Symbol Parameter Conditions Fig. Unit Min. Max. -0.3 6 V -500 50 mA -4 4 mA G001 VCC Supply Voltage VCC G002 VCC Reverse Voltage at VCC T< 10sec -4 G003 I(VCC) Current in VCC T< 10sec G101 I(CI) Current in CI G102 V(KLD) Voltage at KLD IN= lo 0 9 V G103 I(KLD) Current in KLD IN= hi IN= lo -4 -4 400 4 mA mA G104 I(AMD) Current in AMD -6 6 mA G201 I(IN) Current in IN -10 2 mA G301 I(ISET) Current in ISET -2 2 mA G401 I(CWD) Current in CWD IN= lo -2 2 mA EG1 Vd() ESD Susceptibility at CWD, CI, ISET, IN, AMD, KLD MIL-STD-883, HBM 100pF discharged through 1.5kS 1 kV TG1 Tj Junction Temperature -40 150 °C TG2 Ts Storage Temperature -40 150 °C V THERMAL DATA Operating Conditions: VCC= 2.7..6V Item Symbol Parameter T1 Ta Operating Ambient Temperature Range (extended range on request) T2 Rthja Thermal Resistance Chip / Ambient Conditions Fig. Unit Min. -25 soldered on PCB, no additional cooling areas All voltages are referenced to ground unless otherwise noted. All currents into the device pins are positive; all currents out of the device pins are negative. Typ. Max. 90 °C 140 K/W iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 4/12 ELECTRICAL CHARACTERISTICS Operating Conditions: VCC= 2.7..6V, RSET= 2.7..27k S, I(AMD)= 0.15..1.5mA, Tj= -25..125°C, unless otherwise noted. Item Symbol Parameter Conditions Tj EC Fig. Unit Min. Typ. Max. Total Device 001 VCC Permissible Supply Voltage 2.7 002 Idc(VCC) Supply Current in VCC RSET= 5kS, IN= hi, Idc(KLD)= 40mA 003 I0(VCC) RSET= 5kS, IN= lo Standby Supply Current in VCC 004 Iav(VCC) Supply Current in VCC (average value) Ipk(KLD)= 80mA, f(IN)= 200kHz ±20%, twhi/twlo= 1 005 tp(INKLD Delay Time Pulse Edge V(IN) to I(KLD) IN(hi76lo), V(50%):I(50%) 006 Pcon Power Consumption VCC= 3V, V(KLD). 0.6V, RSET= 5kS, Idc(KLD)= 40mA E001 Vc()hi Clamp Voltage hi at I()= 2mA, other pins open VCC,IN,AMD,KLD,CI,CWD, ISET 4 27 7 6 V 13 mA 5 9 65 mA 15 mA 135 ns 50 6.2 27 7.5 27 0.11 mW 9 V V 0.3 V V Driver Stage 101 Vs(KLD) Saturation Voltage at KLD IN= hi, I(KLD)= 80mA 102 Vs(KLD) Saturation Voltage at KLD IN= hi, I(KLD)= 100mA 0.4 V 103 I0(KLD) Leakage Current in KLD IN= lo, V(KLD)= VCC 10 µA 104 V(AMD) Voltage at AMD I(AMD)= 1.5mA 1.0 V V 100 ns ns 100 ns ns 105 tr 106 tf Current Rise Time in KLD Current Fall Time in KLD 0.4 27 0.84 Imax(KLD)= 20..80mA, Ip(): 10% to 90% 27 30 Imax(KLD)= 20..80mA, Ip(): 90% to 10% 27 20 107 K/KL Control Tolerance K= I(AMD) × RSET KL constant for each lot, VCC steady 0.85 1 1.15 108 CR1() Current Ratio I(AMD) / I(ISET) I(CI)= 0, closed control RSET= 2.7..27kS RSET= 27..330kS 2.4 2.4 3 3.6 3.8 5.4 2.7 3 3.3 0.01 -0.1 -0.25 %/°C %/°C 109 CR2() Current Ratio I(AMD) / I(CI) V(CI)= 1..2V, ISET open 110 TC1() Temperature Coefficient of Current Ratio I(AMD) / I(ISET) I(CI)= 0, closed control RSET= 2.7..27kS RSET= 27..330kS Input IN 201 Vt()hi Threshold hi 45 70 %VCC 202 Vt()lo Threshold lo 40 65 %VCC 203 Vt()hys Hysteresis 20 27 204 Rin Pull-Down Resistor V(IN)= -0.3..VCC 4 27 205 V0() Open-loop Voltage I(IN)= 0 mV mV 65 16 kS kS 0.1 V 10 iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 5/12 ELECTRICAL CHARACTERISTICS Operating Conditions: VCC= 2.7..6V, RSET= 2.7..27k S, I(AMD)= 0.15..1.5mA, Tj= -25..125°C, unless otherwise noted. Item Symbol Parameter Conditions Tj EC Fig. Unit Min. Typ. Max. Reference und Thermal Shutdown 301 V(ISET) Voltage at ISET 1.19 27 V(CI)= 1..2V, I(AMD)= 0 1.27 1.22 0.9 1 V V 302 CR() Current Ratio I(CI) / I(ISET) 1.12 303 RSET Permissible Resistor at ISET (Control Setup Range) 2.7 330 kS 304 Toff Thermal Shutdown Threshold 125 150 °C 305 Thys Thermal Shutdown Hysteresis 10 40 °C 2.7 V V 2.6 V V 150 mV Power-Down and Watchdog 401 VCCon Turn-on Threshold VCC 2.4 27 402 VCCoff Undervoltage Threshold at VCC 2.6 2.3 27 403 VCChys Hysteresis VCChys= VCCon-VCCoff 2.5 70 100 404 Vs(CI)off Saturation Voltage at CI in case of Undervoltage I(CI)= 300µA, VCC < VCCoff 1.5 V 405 Vs(CI)wd Saturation Voltage at CI for IN= lo I(CI)= 300µA, t(IN= lo) > tp (*) 1.5 V 406 Isc(CWD) Pull-Up Current at CWD V(CWD)= 0, IN= lo 15 µA 407 tpmin Min. Activation Time for Watchdog IN= lo, CWD open 45 µs µs Constant for Calculating the Watchdog Activation Time IN= lo 0.57 µs/pF µs/pF 408 Kwd (*) 2 10 27 (*): tp = ( C(CWD) × Kwd ) + tpmin (see Applications Information) 25 0.19 27 0.25 iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 6/12 APPLICATIONS INFORMATION Laser Power Adjustment The iC-WJB device can be adapted to CW laser diodes of up to 40mW. When the supply voltage is higher than approx. 4.5V, LD models with a common cathode can also be used. The pin ISET is used for the adjustment to the sensitivity of the monitor diode and to set the desired optical laser power. The setpoint for the averaging control of the monitor diode current is preset at this pin. Fig. 1: Circuit diagram for LD models with a common cathode To calculate the current required at ISET, the average optical laser power is to determine: Pav ' Ppeak × twhi T twhi with peak value Ppeak and pulse/period duration t whi/T Example for CW operation at Pcw= 1mW (pin IN to VCC, pin CWD open) LD: maximum optical output 3mW, monitor diode with 0.75mA at 3mW; twlo T Fig. 2 At Pav= Pcw= 1mW, the monitor photocurrent is 0.25mA and RSET is calculated as: RSET ' CR1(V (ISET) 3(1.22V ' . 14.6k Iav (AMD) 0.25mA with the Electrical Characteristics No.301 for V(ISET) and with No.108 for the current ratio CR1 Example for pulse operation with a pulse duty factor twhi/T of 20% and at Ppeak= 3mW; LD: as above, maximum optical output 3mW, monitor diode with 0.75mA at 3mW; The average optical power is set to 0.6mW by the pulse duty factor; the mean monitor photocurrent Iav is then 0.15mA and for RSET, it follows that: RSET ' CR1(V (ISET) 3(1.22V ' . 24.4k Iav (AMD) 0.15mA with the Electrical Characteristics No.301 for V(ISET) and with No.108 for the current ratio CR1 iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 7/12 Averaging control (APC) The control of the average optical laser power requires a capacitor at pin CI. This capacitor is used for averaging and must be adjusted to the selected pulse repetition frequency and the charging current preset with RSET. The ratios are linear in both cases, i.e. the capacitor CI must be increased in size proportionally as the pulse repetition frequency slows or the current from ISET increases: CI $ 440 × I (ISET) 440 ' f × V (ISET) f × RSET Example: Pulse repetition frequency 100kHz, RSET= 10kS: CI= 440nF, chosen 470nF Otherwise the charging of the capacitor CI during the pulse pauses (with I(ISET)= 1.22 V/RSET) will create an excessive mean value potential and may destroy the laser diode during the next pulse. The capacitor CI is correctly dimensioned when the current through the laser diode and the optical output signal do not show any overshooting following the starting flank. In steady-state condition and for a pulse duty factor of 50% (pulse/pause 1:1), signals as shown in Fig. 3 are present at the IC pins. Fig. 4 shows the corresponding signals for a pulse duty factor of 20%. The influence of the pulse duty factor on the peak value of the monitor current proportional to the laser current is apparent. The average kept constant by the control (RSET unchanged) means a peak value increased by the factor 2.5. The pulse duty factor for which RSET was dimensioned should therefore be kept constant if at all possible. Turn-on and turn-off behavior Capacitor CI also determines the starting time from switsching on the supply voltage VCC to steady-state laser pulse operation or after a discharge of CI by the watchdog. The following applies for estimating the starting time (Fig. 5): Ton . 1.7V × CI 1.7V × CI × RSET ' 1.22V I (ISET) Example: Fig. 3: Steady-state APC, f(IN)= 100kHz (1:1), CI= 470nF, RSET= 10kS Fig. 4: Steady-state APC, f(IN)= 100kHz (1:4), CI= 470nF, RSET= 10kS Fig. 5: Turn-on behavior, f(IN)= 100kHz (1:1), CI= 470nF, RSET= 10kS CI= 470nF, RSET= 10kS: Ton . 6.5ms Figure 6 shows a detailed view of the start of laser operation; Figure 7 shows the shut-down behavior. The decline in the voltage at CI and the absence of the laser pulses are signs that the undervoltage detector is active. Fig. 6: Turn-on behavior, detailed view f(IN)= 100kHz (1:1), CI= 470nF, RSET= 10kS iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 8/12 Watchdog The watchdog ensures that the capacitor CI is discharged during protracted pulse pulses at IN. During the pulse pauses the potential at CI increases by )V (Fig. 3): V ' I (ISET) × twlo CI The discharge of capacitor CI by the watchdog protects the laser diode from being destroyed by an excessive turn-on current during the next pulse. The capacitor CWD should be dimensioned such that the response time tp of the watchdog is slightly longer than the pulse pause twlo of the input signal. As a result, the watchdog is just short of being activated. For response times tp longer than tpmin: CWD ' tp & tpmin Kwd Fig. 7: Turn-off behavior, f(IN)= 100kHz (1:1), CI= 470nF, RSET= 10kS with tpmin and Kwd from Electrical Characteristics No. 407, 408 Figure 8 shows the signal curves during normal operation, without the watchdog being activated. The potential at CWD rises during pulse pauses but does not reach the watchdog activation threshold. Fig. 8: Watchdog, CWD open, f(IN)= 100kHz (1:1), CI= 470nF, RSET= 10kS Figure 9 shows the watchdog behavior when the input frequency is reduced from 100kHz to 10kHz. The pulse pauses are longer than the watchdog’s response time. The watchdog begins to discharge the capacitor CI current limited. The remaining charge time during the pulse pauses before further watchdog intervention is not sufficient to maintain the initial potential at CI. The potential is thus gradually reduced until it reaches the saturation voltage Vs(CI)wd (Electrical Characteristics No. 405). The watchdog therefore protects the laser diode from destruction when the input signal change in such a manner that the capacitor CI is not longer adequate for averaging. Furthermore, the intervention of the watchdog permits long pulse pauses and activation of the laser diode with pulse packets. Fig. 9: Watchdog, CWD open, f(IN)= 100kHz 6 10kHz (1:1), CI= 470nF, RSET= 10kS iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 9/12 CW OPERATION In case of CW operation, the input IN can be connected to the power supply VCC. The pin CWD may be unloaded, because the capacitor for the watchdog is not necessary. The capacitor CI for the averaging control can be reduced to 100nF. 2.7..6V D1 ZD6V8 R2 2 S1 C1 47µF VCC 1 GND KLD 8 0..2 AMD 2 CI 100nF R1 7 CWD KLD C3 4.7nF LD MD LD supply cord AMD WDOG 3 RSET 15k 4 CI IN 6 VCC 5 REF ISET C2 100nF iC-WJB Fig. 10: CW operation via cable plus protective circuitry Operation of laser diode via cable, protective circuitry It is recommended to connect a capacitor from 1nF up to 10nF across the laser diode in order to protect the laser diode against destruction due to ESD or build-up transients. This capacitor should be placed close to the laser diode and not at the entry of the LD supply line. An approx. 12S series resistor at pin KLD reduces the IC power consumption and damps possible resonances of the load circuit caused by the inductive LD supply line. This resistor is useful for many applications, also for those which do not operate via cable. When the LD supply line is printed on the PCB, the forward path VCC should be arranged in parallel with, i.e. be close to the return path to KLD, even when the line is only a few centimeters in length. Additional protective components for the clipping of strong, positive and negative spikes can be useful, especially when contact bouncing occurs in an inductive accumulator power supply line. Elements which come into question here are D1 and R1 as in Fig. 10. Analog modulation during CW operation The modulation cut-off frequency is determined by the capacitor CI as well as by the operating point set with the resistor RSET. With CI= 100nF and RSET= R3= 15kS the cut-off frequency is approx. 30kHz, with CI= 22nF and the same resistor value of about 150kHz. Fig. 11: Analog modulation during CW operation iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 10/12 The laser power can also be modulated by adapting a current source, e.g. by using an operational amplifier with a current output (OTA). To limit the current at pin ISET while turning on the power supply for the OTA circuitry, however, the OTA output should be linked to the base point of RSET (instead of to GND). The maximum current possible at ISET must be taken into consideration when dimensioning the capacitor CI. PC BOARD LAYOUT The ground connections of the external components CI, CWD and RSET have to be directly connected at the IC with the GND terminal. iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 11/12 DEMO BOARD The iC-WJ/WJZ/WJB devices are equipped with a demo board for test purposes. The following figures show the wiring as well as the top and bottom layout of the test PCB. ALD J1 VCC LD C3 2nF C1 47µF MONITOR IN LASER IC1 1 GND GND KLD 8 R1 2 KLD AMD AMD 7 2 CWD WDOG 3 IMOD RMOD 15k IN CI I 6 II REF 4 CWD ....... CI 470nF ISET VCC 5 iC-WJ/WJZ/WJB RSET 15k AGND C2 100nF Fig. 12: Schematic diagram of the demo board Fig. 13: Demo board (components side) Fig. 14: Demo board (solder dip side) iC-WJB 2.7V LASER DIODE DRIVER Rev C1, Page 12/12 ORDERING INFORMATION Type Package Order designation iC-WJB WJB demo board SO8 iC-WJB SO8 WJB DEMO For information about prices, terms of delivery, options for other case types, etc., please contact: iC-Haus GmbH Am Kuemmerling 18 D-55294 Bodenheim GERMANY Tel +49-6135-9292-0 Fax +49-6135-9292-192 http://www.ichaus.com This specification is for a newly developed product. iC-Haus therefore reserves the right to modify data without further notice. Please contact us to ascertain the current data. The data specified is intended solely for the purpose of product description and is not to be deemed guaranteed in a legal sense. Any claims for damage against us - regardless of the legal basis - are excluded unless we are guilty of premeditation or gross negligence. We do not assume any guarantee that the specified circuits or procedures are free of copyrights of third parties. Copying - even as an excerpt - is only permitted with the approval of the publisher and precise reference to source.