iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 1/12 FEATURES APPLICATIONS ♦ Laser diode driver for continuous and pulsed operation (CW to 300 kHz) up to 250 mA ♦ Averaging control of laser power ♦ Simple adjustment of the laser power via external resistor ♦ Adjustable watchdog at the switching input to protect the laser diode ♦ Soft-start after power-on ♦ Driver shutdown with overtemperature and undervoltage ♦ Single 5 V supply ♦ Simple circuitry ♦ iC-WJ for laser diodes with 50 to 500 µA monitor current ♦ iC-WJZ for laser diodes with 0.15 to 1.5 mA monitor current ♦ General purpose laser diode driver PACKAGES SO8 MSOP8 BLOCK DIAGRAM DRIVER STAGE 3 REF VCC 5 +5 V C1 1 100 µF REFERENCE C3 THERMAL ISET RSET 10 kΩ 2 nF SHUTDOWN KLD 4 6 INPUT VCC IN 8 LD MD R1 12Ω POWER DOWN REF AMD 7 74HCxx 2 4 1:1 iC−WJ 1:3 iC−WJZ WATCHDOG iC−WJ/WJZ CWD 2 CWD CI 3 GND 1 CI 100 nF..470 nF usable LD models Copyright © 2006 iC-Haus http://www.ichaus.com iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 2/12 DESCRIPTION The iC-WJ and iC-WJZ devices are driver ICs for laser diodes in continuous and pulsed operation up to 300 kHz. The laser diode is activated via switching input IN. A control to the mean value of the optical laser power 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 for the laser diode driver to protect the laser diode when switching on the supply voltage. An external resistor at ISET is utilised to adapt the power control to the laser diode being used. The capacitor at CI determines the recovery time constants and the start-up 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 power control 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, MSOP8 to JEDEC Standard PIN CONFIGURATION SO8 (top view) PIN FUNCTIONS No. Name Function 8 1 KLD GND 2 7 AMD CWD CI 4 ISET WJ Code... ...yymm 3 6 IN 5 VCC PIN CONFIGURATION MSOP8 (top view) 1 CWD CI ISET iC−WJ Code GND KLD AMD IN 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 5 V Supply Voltage Input Anode Monitor Diode Cathode Laser Diode iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 3/12 ABSOLUTE MAXIMUM RATINGS Beyond these values damage may occur; device operation is not guaranteed. Item No. Symbol Parameter Conditions Fig. Unit Min. Max. G001 VCC Supply Voltage 0 6 V G002 I(CI) Current in CI -4 4 mA G003 V(KLD) Voltage at KLD IN = lo 0 6 V G004 I(KLD) G005 I(AMD) Current in KLD IN = hi -4 600 mA Current in AMD iC-WJ iC-WJZ -4 -6 4 6 mA mA G006 I(IN) Current in IN -10 2 mA G007 I(ISET) Current in ISET -2 2 mA G008 I(CWD) Current in CWD IN = lo -2 2 mA G009 Vd() ESD Susceptibility at CWD, CI, ISET, IN, AMD, KLD MIL-STD-883, HBM 100 pF discharged through 1.5 kΩ 1.5 kV G010 Tj Junction Temperature -40 150 °C G011 Ts Storage Temperature -40 150 °C THERMAL DATA Operating Conditions: VCC = 5 V ±10 % Item No. Symbol Parameter Conditions Fig. Unit Min. T01 Ta Operating Ambient Temperature Range (extended temperature range on request) T02 Rthja Thermal Resistance Chip to Ambient -25 surface mounted on PCB, without special cooling All voltages are referenced to ground unless otherwise stated. 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-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 4/12 ELECTRICAL CHARACTERISTICS Operating Conditions: VCC = 5 V ±10 %, RSET = 2.7...27 kΩ, iC-WJ: I(AMD) = 50...500 µA, iC-WJZ: I(AMD) = 0.15...1.5 mA, Tj = -25...125 °C, unless otherwise noted. Item No. Symbol Parameter Conditions Tj °C Fig. Unit Min. Typ. Max. Total Device 001 VCC Permissible Supply Voltage Range 4.5 002 Iav(VCC) Supply Current in VCC (average Iav(KLD) = 100 mA, value) f(IN) = 200 kHz ±20 % 003 tp(IN-KLD) Delay Time Pulse Edge V(IN) to I(KLD) IN(hi ↔ lo), V(50 %) : I(50 %) 004 Vc()lo Clamp Voltage lo at VCC, IN, AMD, KLD, CI, CWD, ISET I() = -2 mA, other pins open 005 Vc()hi Clamp Voltage hi at IN, AMD, KLD, GND, CI, CWD, ISET Vc()hi = V() − VCC; I() = 2 mA, other pins open 101 Vs(KLD) Saturation Voltage at KLD IN = hi, I(KLD) = 200 mA 102 103 I0(KLD) Leakage Current in KLD IN = lo, V(KLD) = VCC I(KLD) Current in KLD IN = hi, I(AMD) = 0 104 V(AMD) Voltage at AMD iC-WJ: I(AMD) = 500 µA iC-WJZ: I(AMD) = 1.5 mA 105 tr Current Rise Time in KLD 106 tf 107 CR1() 5.5 V 15 mA 135 ns -1.5 -0.3 V 0.3 1.5 V 1.3 V Driver 108 CR2() Input IN 201 Vt()hi 10 -25 27 70 125 225 250 250 250 Vt()lo V V Imax(KLD) = 20...250 mA, Ip(): 10 → 90 % 100 ns Current Fall Time in KLD Imax(KLD) = 20...250 mA, Ip(): 90 % → 10 % 100 ns Current Ratio I(AMD) / I(ISET) I(CI) = 0, closed control loop; iC-WJ iC-WJZ 0.8 2.4 1 3 1.2 3.6 V(CI) = 1...3.5 V, ISET open; iC-WJ iC-WJZ 0.9 2.7 1 3 1.1 3.3 Threshold hi 1.60 Threshold lo Vt()hys 1.50 Hysteresis 10 Rin Pull-Down Resistor V(IN) = -0.3...VCC + 0.3 V 205 206 V0() Open-loop Voltage I(IN) = 0 Vtwd() Threshold for Watchdog Reference und Thermal Shutdown 301 V(ISET) Voltage at ISET 2.4 2.0 1.5 1.0 1.17 27 302 CR() Current Ratio I(CI) / I(ISET) V(CI) = 1...3.5 V, I(AMD) = 0 2.20 V V V V V 190 mV mV mV mV mV 80 90 90 100 4 -25 27 70 125 V V V V V 1.76 1.78 1.79 1.81 -25 27 70 125 204 2.40 1.84 1.87 1.88 1.91 -25 27 70 125 203 µA mA mA mA mA 1.5 1.5 Current Ratio I(AMD) / I(CI) 0.5 0.4 -25 27 70 125 202 250 16 kΩ 0.1 V 3.2 2.8 2.3 1.8 V V V V 1.28 V V 1.22 0.9 1 1.1 iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 5/12 ELECTRICAL CHARACTERISTICS Operating Conditions: VCC = 5 V ±10 %, RSET = 2.7...27 kΩ, iC-WJ: I(AMD) = 50...500 µA, iC-WJZ: I(AMD) = 0.15...1.5 mA, Tj = -25...125 °C, unless otherwise noted. Item No. Symbol Parameter Conditions Tj °C Fig. Unit Min. Max. 303 RSET Permissible Resistor at ISET (Control Set-up Range) 2.7 50 kΩ 304 Toff Thermal Shutdown Threshold 125 150 °C 305 Thys Thermal Shutdown Hysteresis 10 40 °C 4.3 V V Power-Down and Watchdog 401 VCCon Turn-on Threshold VCC 3.5 27 402 403 VCCoff Undervoltage Threshold at VCC VCChys Hysteresis VCChys = VCCon − VCCoff 3.8 3.2 3.8 V 300 450 mV mV 27 (*) Typ. 400 404 Vs(CI)off Saturation Voltage at CI with undervoltage I(CI) = 300 µA, VCC < VCCoff 1.6 V 405 Vs(CI)wd Saturation Voltage at CI with IN = lo I(CI) = 300 µA, t(IN = lo) > tp (*) 1.5 V 406 Ipu(CWD) Pull-Up Current at CWD V(CWD) = 0, IN = lo -15 -3 µA 407 tpmin Min. Activation Time for Watchdog IN = lo, CWD open 10 45 µs 408 Kwd (*) Constant for Calculating the Watchdog Activation Time IN = lo 0.57 µs/pF tp = (C(CWD) ∗ Kwd) + tpmin (see Applications Information) 0.19 0.38 iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 6/12 APPLICATIONS INFORMATION Laser Power Adjustment The iC-WJ and iC-WJZ devices can be adapted to CW laser diodes from approximately 2 to 40 mW. N- and M-type models can 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. VCC DRIVER 3 REF +5 V 5 C1 100 uF 1 REFERENCE C3 2 nF THERMAL 4 ISET SHUTDOWN KLD MD 8 RSET LD R1 12 Ω VCC INPUT 6 IN POWER DOWN REF AMD 7 74HCxx 2 4 1:1 iC−WJ 1:3 iC−WJZ WATCHDOG iC−WJ/WJZ CWD CI GND 2 3 1 CI 470 nF Figure 1: Operation of a laser diode according to the example To calculate the current required at ISET, the average optical laser power is to determine: Pav Example iC-WJ Laser diode with 5 mW maximum optical output, monitor diode with 0.13 mA/mW, pulse duty factor set to 20 % with Ppeak = 5 mW: The resulting average optical power is 1 mW and the average monitor diode current is 0.13 mA. The resistor RSET is calculated as: t = Ppeak ∗ whi T RSET = CR1 ∗ V (ISET ) 1 ∗ 1.22 V = = 9.4 k Ω Iav (AMD) 0.13 mA with peak value Ppeak and pulse/period duration twhi /T . twlo T Figure 2: Duty cycle Ppeak twhi with the Electrical Characteristics No. 301 for V(ISET) and No. 108 for current ratio CR1. Example iC-WJZ Laser diode with 5 mW maximum optical output, monitor diode with 0.75 mA at 3 mW, CW operation (pulse duty factor 100 %) with Pcw = 1 mW: iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 7/12 For the monitor diode current of 0.25 mA the resistor RSET is calculated as: RSET = CR1 ∗ V (ISET ) 3 ∗ 1.22 V = = 14.6 k Ω Iav (AMD) 0.25 mA with Electrical Characteristics No. 301 for V(ISET) and No. 108 (iC-WJZ) for current ratio CR1. Averaging control 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: Figure 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 possible. 5.0 V V(IN) 0V 3.120 V V(CI) 3.118 V 600 uA I(AMD) 440 ∗ I(ISET ) 440 CI ≥ = f ∗ V (ISET ) f ∗ RSET 0A Example Pulse repetition frequency 100 kHz, RSET = 10 kΩ: CI = 440 nF, chosen 470 nF. 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 overshots following the rising edge. Time Figure 4: Steady-state averaging, f(IN) = 100 kHz (1:4), CI = 470 nF, RSET = 10 kΩ 3.0 V 2.0 V V(CI) 1.0 V 0V I(KLD) 5.0 V V(IN) 0A 0s 0V 2.552 V 2 ms 4 ms 6 ms 8 ms 10 ms 12 ms Figure 5: Turn-on behavior, f(IN) = 100 kHz (1:1), CI = 470 nF, RSET = 10 kΩ V(CI) 2.550 V 250 uA 0A I(AMD) Time Figure 3: Steady-state averaging control, f(IN) = 100 kHz (1:1), CI = 470 nF, RSET = 10 kΩ In steady-state condition and for a pulse duty factor of 50 % (pulse/pause 1:1), signals as shown in Figure 3 are present at the IC pins. Turn-on and turn-off behavior Capacitor CI also determines the starting time from switching on the supply voltage VCC to steady-state laser pulse operation or after a discharge of CI by the watchdog. The following applies to estimating the starting time (Figure 5): Ton = 2.5 V ∗ CI 2.5 V ∗ CI ∗ RSET = I(ISET ) 1.22 V iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 8/12 Example CI = 470 nF, RSET = 10 kΩ: Ton = 9.6 ms 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. 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 applies: CWD = 2.55 V V(CI) tp − tpmin Kwd 2.45 V with tpmin and Kwd from Electrical Characteristics No. 407, 408. I(KLD) V(IN) 5.0 V 0A Time 0V 5V Figure 6: Turn-on behavior, detailed view f(IN) = 100 kHz (1:1), CI = 470 nF, RSET = 10 kΩ V(CWD) 0V 3V V(CI) 5.0 V 2V VCC I(AMD) 300 uA 0V 3.0 V 0A V(CI) Time Figure 8: Watchdog, CWD open, f(IN) = 100 kHz (1:1), CI = 470 nF, RSET = 10 kΩ 0V I(KLD) 0A V(IN) 5.0 V Time Figure 7: Turn-off behavior, f(IN) = 100 kHz (1:1), CI = 470 nF, RSET = 10 kΩ 0V 5.0 V V(CWD) 0V Watchdog In order for the watchdog to function correctly, the input IN must be activated with a CMOS output (e.g. with an HCMOS gate: see Figure 1). 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 (Figure 3): 3.0 V V(CI) 2.0 V 300 uA I(AMD) 0A Time Figure 9: Watchdog, CWD open, f(IN) = 100 kHz → 10 kHz (1:1), CI = 470 nF, RSET = 10 kΩ I(ISET ) ∗ twlo ∆V = CI Figure 8 shows the signals during normal operation, without the watchdog being activated. The potential at CWD rises during pulse pauses but does not reach the watchdog activation threshold. 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. Figure 9 shows the watchdog behavior when the input frequency is reduced from 100 kHz to 10 kHz. The pulse pauses are longer than the watchdog’s response iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 9/12 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 introduction of the watchdog permits long pulse pauses and activation of the laser diode with pulse packets. C1 10 uF 1 GND KLD 8 C3 5 nF R1 12 Ω LD MD AMD 2 7 CWD CI 100 nF RSET 10 kΩ 3 4 CI WDOG IN 6 REF ISET VCC iC−WJ/WJZ 5 +5 V C2 100 nF Figure 10: CW operation via cable CW Operation In case of CW operation, the input IN can be connected to the power supply VCC. The pin CWD may be left open, because the capacitor for the watchdog is not necessary. The capacitor CI for the averaging control can be reduced to 100 nF. Operation of laser diode via cable It is recommended to connect a capacitor of 1 to 10 nF across the laser diode in order to protect the laser diode against destruction due to ESD or transients. This capacitor should be placed close to the laser diode and not at the beginning of the LD supply line. An approx. 12 Ω 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. On a PCB the forward path VCC to the laser diode should be arranged in parallel with the return path to KLD even when the line is only a few centimeters in length. iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 10/12 +5 V C1 100 uF C3 2 nF 1 GND LD KLD 8 MD R1 12Ω AMD 2 CI 22 nF VMOD 0..1.5 V R2 10 kΩ WDOG 3 7 CWD CI IN 6 +5 V REF 4 ISET iC−WJ/WJZ RSET 10 kΩ VCC 5 C2 100 nF Figure 11: Analogue modulation during CW operation Analogue 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 = 100 nF and RSET = R2 = 10 kΩ the cut-off frequency is approx. 40 kHz, with CI = 22 nF and the same resitor value of about 230 kHz. 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, RSET should be connected to the OTA output (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. DEMO BOARD For the devices iC-WJ/WJZ/WJB a Demo Board is available for test purposes. The following figures show the schematic diagram and the component side of the test PCB. iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 11/12 ALD J1 VCC LD C1 C3 2 nF 100 uF MONITOR IN LASER IC1 GND 1 GND KLD 8 R1 12Ω KLD AMD 2 AMD 7 CWD WDOG 3 IMOD RMOD 10 kΩ (15 kΩ ) 6 VCC 5 I II REF 4 CWD ... AGND IN CI ISET iC−WJ/WJZ/WJB CI 470 nF RSET 10 kΩ (15 kΩ ) C2 100nF Figure 12: Schematic diagram of the Demo Board Figure 13: Demo Board (components side) This specification is for a newly developed product. iC-Haus therefore reserves the right to change or update, without notice, any information contained herein, design and specification; and to discontinue or limit production or distribution of any product versions. Please contact iC-Haus to ascertain the current data. Copying – even as an excerpt – is only permitted with iC-Haus approval in writing and precise reference to source. iC-Haus does not warrant the accuracy, completeness or timeliness of the specification on this site and does not assume liability for any errors or omissions in the materials. The data specified is intended solely for the purpose of product description. No representations or warranties, either express or implied, of merchantability, fitness for a particular purpose or of any other nature are made hereunder with respect to information/specification or the products to which information refers and no guarantee with respect to compliance to the intended use is given. In particular, this also applies to the stated possible applications or areas of applications of the product. iC-Haus conveys no patent, copyright, mask work right or other trade mark right to this product. iC-Haus assumes no liability for any patent and/or other trade mark rights of a third party resulting from processing or handling of the product and/or any other use of the product. iC-WJ, iC-WJZ LASER DIODE DRIVER Rev C1, Page 12/12 ORDERING INFORMATION Type Package Order Designation iC-WJ SO8 MSOP8 iC-WJ SO8 iC-WJ MSOP8 iC-WJ EVAL WJ1D SO8 MSOP8 iC-WJZ SO8 iC-WJZ MSOP8 iC-WJZ EVAL WJ1D WJ Evaluation Board iC-WJZ WJZ Evaluation Board For information about prices, terms of delivery, other packaging options etc. please contact: iC-Haus GmbH Am Kuemmerling 18 D-55294 Bodenheim GERMANY Tel.: +49 (61 35) 92 92-0 Fax: +49 (61 35) 92 92-192 Web: http://www.ichaus.com E-Mail: [email protected]