Agilent ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 Laser Mouse Sensor Eye Safety Calculations Application Note 5088 Introduction The eye safety calculations presented in this application note apply to the Agilent Laser mouse sensor bundles ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012. The Agilent laser sensor bundles are made up of the following parts: laser mouse sensor (ADNS-6000 or ADNS-6010), optical lens (ADNS-6120 or ADNS-6130-001), lens clip (ADNS-6230-001) and VCSEL (ADNV-6330). As the Agilent ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 laser mouse sensor bundles contain a laser, eye safety analysis and hazard classification is important. The manufacturer of the final system, not the manufacturer of the individual pieces, holds the responsibility of product classification. Since Agilent Technologies, Inc. manufactures the above components and not the final product sold to consumers, Agilent is not responsible for final classification. This document is provided as a convenience to aid the final manufacturer in product classification. The International Electrotechnical Commission (IEC) governs standardization for electrical and electronic fields. Optical radiation (eye) safety limits and classification levels are specified in IEC 60825-1, Edition 1.2, 2001-08. This will be referred to as the IEC document in the rest of this document. To determine the eye safety limits for the optical output of the VCSEL (laser) mounted in an assembly including a lens, several factors need to be known. 1. The apparent source size (or equivalent angular subtense of the source) of ADNB6001, ADNB-6002, ADNB-6011 and ADNB6012. 2. The wavelength of the VCSEL. 3. The appropriate emission or exposure time. ) or Apparent Source Source Angular Subtense Angle ( Size Measurement The source angular subtense for the spectral range of interest is specified in the IEC document (page 31) as: "For the determination of the AEL retinal thermal hazard limits (400 nm to 1400 nm), the value of the angular subtense of a rectangular or linear source is determined by the arithmetic mean of the two angular dimensions of the source. Any angular dimension that is greater than max or less than min shall be limited to max o r min respectively, prior to calculating the mean" In the optical design of the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012, the emitted beam size is collimated with approximately 2mm diameter beam (see section "Measuring the Beam size"). Since the beam is collimated, the optical equivalent is an extended source of approximately 2.0 mm at a very large (theoretically infinite) distance. The angular subtense of such a source is infinitesimally small. Therefore, the source is considered to be a small source (IEC document, clause 3.79, definition of small source). For such a source, the angular subtense is taken to be 1.5 mrad (milliradians), equivalent to a source of 150 mm in linear extent. The derived value of the C6 parameter is 1.0. (IEC document, Table 4 Note 2, page 40) For further determination of the AEL and MPE, min will be used to determine which equations to use; yet the actual value is independent of and therefore no measurements for the exact apparent source size need to be performed. Calculating the Accessible Exposure Limits (AEL) Since the VCSEL wavelength range is specified in the ADNV-6330 datasheet as 832 to 865nm, only the thermal limits apply for this VCSEL, not the photochemical. To determine which set of equations to use, t (appropriate exposure time for MPE; appropriate emission time for AEL) must also be known. The IEC document (Section 8.4e, page 31) specifically discusses the time base for these calculations. For wavelengths of greater than 400nm with Class 1 intention, 100 seconds is used for t, exposure time. From Table 1, page 37 of the IEC document, "Accessible emission limits for Class 1 and Class 1M laser products", there are three different formulas for the allowed thermal energy when the exposure time is greater than 10 seconds and the illumination wavelength is between 700 and 1050 nm: 3.9 x 10 -4 C 4 C 7 W If t > T2 and 1.5mrad -4 7 x 10 C 4 C 6 C 7 T -0.25 2 (1) W If t > T2 and >1.5 mrad (4) T2 = 10 x 10[(-min)/98.5] s (5) T2 = 100 s (6) As discussed, is less than 1.5 mrad, so equation 4 then determines T2 to be 10 seconds. 2 (7) Substituting into the equation 1 above, the Accessible Emission Limit (AEL) allowed for the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 bundles to meet Class 1 is: AEL = 716 W * * Compliance to this value must be finetuned and tested per Agilent's guidelines for manufacturing of the ADNB-6001 , ADNB-6002, ADNB-6011 and ADNB-6012, located in the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 datasheets. T2 = 10 s If > 100 mrad C4 = 100.002(-700) = 100.002(832-700) = 1.8365 (3) Since the value for t defaults to 100 seconds, T2 must be calculated to determine which formula (1, 2, or 3 above) is to be used. From the IEC document (page 40, Note 2a) for the wavelength range of 400 to 1400 nm: If 1.5 mrad < < 100 mrad To continue with the calculation of the AEL, C4 and C7 need to be determined. C7 for the range of 700 to 1150 nm is set to 1 (IEC document, page 40, Note 2). An equation defines C4 for the spectral region from 700 to 1050nm (IEC document, page 40, note 2). Using = 832 nm, the minimum and therefore worst case value in the range from the VCSEL datasheet, the value of C4 is calculated: This value therefore is the limit and for the device to be Class 1, its emission must be less than or equal to this value (IEC document, 9.2g, page 33). 7 x 10 -4 t 0.75 C 4 C 6 C 7 J If < 1.5 mrad 3.9 x 10-4C4C7 W (2) Or If t T2 Since the measurement time t is greater than 10 seconds, and therefore T2 is less than t, formula 1 is used to determine the AEL. Class 1M is another level of classification that under acceptable conditions, might allow for a greater emission limit. This classification does not apply to the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 design. Two options are given per the standard (IEC document, section 8.2, page 28). One option is for a diverging beam, which does not apply. The second valid option applies to collimated beams where the diameter is larger than the stated 50 mm aperture stop determined from IEC document, Table 10, page 35. This also does not apply in the given case; therefore Class 1M is not an applicable standard for ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012. Determining the Maximum Permissible Exposure (MPE) The Maximum Permissible Exposure value is a critical value that relates to injury studies that have been done on the eye. "Maximum permissible exposure values are for the users and are set below known hazard levels, and are based on the best available information from experimental studies. The MPE values should be used as guides in the control of exposures " (IEC document, page 49). To calculate this guideline for ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012, refer to the MPE Table 6 (IEC document, page 53). As with calculating the AEL, 832 nm is used as the wavelength when referring to the equation table. Exposure time, t, is also necessary again to find the appropriate equations to calculate the MPE from Table 6. Given the same variable options, the equation (labeled 8 below) for 1.5 mrad is once again chosen: 10 x C4C7 W * m-2 Measuring the Beam Size The ADNS-6120 or ADNS-6130-001 lens, ADNS-6230-001 clip and the ADNV-6330 VCSEL were assembled and measured at a 100 mm standard distance to confirm that min is an accurate value for the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 setup. If the diameter of the laser at this distance is significantly less than 7 mm (fully dilated human eye) then it can be claimed with confidence that < min and Class 1M does not apply to the ADNB-6001, ADNB6002, ADNB-6011 and ADNB-6012 optical setup. Below are the measurement details and results. For the beam diameter measurement, the Pulnix Model P-TM7 camera and VCSEL fixture were placed in line with a distance of 100 mm from the camera's imaging surface to the lens surface (see Figures 1 and 2). Measurements and photos were taken of the VCSEL beam using Coherent's Beam View Analyzer TM software. (8) which results in an MPE of 18.37 W.m- 2. Assuming a 7 mm diameter aperture (fully dilated human eye), the power through the aperture is 707W. Given the limited precision (one or two decimal places) of the constants in the formulas, the value of 707W is essentially the same as the value of 716W determined through the Class 1 calculation. This is as it should be, since for a product to have a Class 1 classification, a person must not be subjected to an exposure exceeding the MPE. Figure 1. BeamView Analyzer setup with camera and ADNB-6001 under test 3 Figure 2. Zoomed photo of measurement setup used to verify beam diameter (distance =100mm) Figure 3. Beam Profile of a representative VCSEL, set at 100mm from the camera at ~700uW 4 Figure 4. 3D plot of same representative beam Data gathered from the BeamView Analyzer software (Figures 3 & 4) reports the effective diameter along with several other characteristics of this single VCSEL beam. The effective diameter at 100 mm measurement distance as specified in the IEC document was measured to be << 7 mm and therefore it can confidently be said that < min as well as Class 1M does not apply to the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 optical setup (IEC document, page 31). Factors contributing to overall system Class 1 AEL Figure 5. Typical Light Output for the VCSEL (ADNV-6320) All factors that contribute to a variance in the light output (LOP) of the VCSEL (ADNV-6330) must be considered; therefore a target LOP must be set and then a worst-case analysis of the LOP of the VCSEL (ADNV-6330) must be guard-banded. This analysis must prove that the system for ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012, under worst-case conditions, as defined by the datasheet, is still within the Class 1 AEL limit. The factors that contribute to a change in the LOP of the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 are discussed below. VCSEL (ADNV-6330) Light output power (LOP) vs. current The VCSEL (ADNV-6330) has a light output (LOP) curve similar to the typical unit data shown below in Figure 5. From this curve it is apparent that the Class 1 AEL limit could be exceeded if the current is not controlled below the necessary limit to make it safe. Agilent Technologies, Inc. provides a manufacturing guideline on how to confirm the outgoing product is meeting the eye safety limit. This information is included in the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 datasheet. Following the guidelines in the datasheet is critical to correctly manufacture a Class 1 eye safe product. 5 All tolerances in the current control must be factored into a targeted LOP to ensure that the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 will remain within the Class 1 AEL limit. Light Output vs. Temperature As discussed in the above section, the LOP is dependant upon the current driving the VCSEL (ADNV-6330). Temperature is another variable that affects the LOP. In manufacturing, Agilent performs tests on the VCSELs (ADNV-6330) and sensors (ADNS6000 or ADNS-6010), which ensure that the change from room temperature to the operating temperature extremes is acceptable. Agilent has designed the laser system to be safe within the operating temperature range of 5 to 45 C for the components that make up the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012. It is likely that the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 will exceed the maximum Eye Safety limit on some units if operated outside these temperatures. Since the temperature of the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 is a function of the system (mouse) design, and the thermal properties of the material that makeup that system, Agilent recommends that manufacturers perform testing at the system level to determine the need for any special safety circuitry, or warnings. Single Fault Considerations The IEC document specifies that products must be single fault tolerant. "The above tests shall be made under each and every reasonably foreseeable single-fault condition; however, faults which result in the emission of radiation in excess of the AEL for a limited period only, and for which it is not reasonably foreseeable that human access to the radiation will occur before the product is taken out of service, need not be considered." (IEC document, section 9.1, page 32) This requirement does not apply to components, but rather to the final product. Listed below are some theoretical single faults for the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 bundles. This is not intended to be a complete list, rather a representation of foreseeable faults and their results.The application schematic found in the datasheet for this product will be used as a reference for this discussion. Below is a list of foreseeable faults and associated results. All results described assume the latest released version of downloadable programming (SROM) has previously been correctly loaded into the sensor's memory. Because the program is held in volatile memory, some faults will result in the loss of downloaded programming. The micro-controller in the final product should be programmed to detect this situation and reload the SROM program automatically. All below references to "VCSEL" are specifically referring to the ADNV-6330 part. 1. Broken wire on any USB/PS2 cable pin (Power, Ground, Data lines): This fault will not increase the VCSEL LOP. 2. A shorted wire between any USB/PS2 cable pins (Power, Ground, Data lines): This fault will not increase the VCSEL LOP. 3. VDD3 power supply voltage increase of greater than 50mV above the voltage used during LOP calibration. The lifetime of the mouse bundle may be shortened and the VCSEL drive current may increase; therefore, Agilent advises the manufacturer to take necessary steps to prevent such a voltage increase. 4. Resistive path or short circuit between adjacent ADNS-6000 or ADNS-6010 sensor pins as detailed in Table 1 on Page 7. 6 5. Open or short to ground or short to VDD at each sensor pin (pins 1-20). See Table 2 on Page 8. 6. ESD event: tests of the sensor to 2kV (per the human body model MIL 883 Method 3015) all resulted in safe LOP levels. Agilent recommends that the manufacturer: a. follow ESD-safe handling manufacturing processes b. warn end-users that the mouse is not to be opened or tampered with c. provide safety precautions such that if a mouse is opened, the laser current drive is disabled. d. design the mouse case and PC board to prevent ESD exposure above 2kV to the RBIN and XY_LASER pins. 7. Defective PNP pass transistor: (XY_LASER current continues to limit current to correct value). 8. Noise event on VDD or clock corrupts internal memory values: an event such as this can in concept affect the laser current. The current adjustment settings are kept in two memory locations in different forms. In each frame, the sensor checks for corruption and reduces to the minimum laser power if found therefore minimizes the "foreseeable" chance that this event would result in unsafe LOP levels. 9. Fault detection relies on proper operation of the ADNS-6000 and ADNS-6010 sensors. Proper operation should be confirmed by periodically reading the Product ID register and its inverse as documented in the ADNS-6000 and ADNS-6010 datasheets. Once proper operation is assured, the Fault bit and LP_Valid bit in the Motion register should be read to detect a fault condition. Conclusion Analysis of the ADNB-6001, ADNB-6002, ADNB-6011 and ADNB-6012 for eye safety per IEC 60825-1, Edition 1.2, 2001-08 shows that given proper current control of the VCSEL and detailed adherence to the manufacture instructions in the sensor datasheet, this product has the ability to meet product classification standards with a rating of Class 1. Table 1. Pin #s Pin Names Explanation 1 to 2 NCS to MISO Will not affect VCSEL power since these are serial port digital pins 2 to 3 MISO to SCLK Will not affect VCSEL power since these are serial port digital pins 3 to 4 SCLK to MOSI Will not affect VCSEL power since these are serial port digital pins 4 to 5 MOSI to N/C Will not affect VCSEL power since these are serial port digital pins 5 to 6 N/C to RESET This fault may reset the ADNS-6000 sensor. While the RESET pin is active (high state), the laser is turned off. After the RESET pin is brought low the sensor will drive the laser at the minimum programmable drive current. In both cases the VCSEL power can only decrease or remain the same as the pre-fault level. 6 to 7 RESET to NPD Same result as pins 5 to 6 if the sensor is reset. If it is put into the power down mode (NPD pin held low), the laser is turned off. Upon removal of the fault and exit of the power down mode, the laser will return to the previously programmed power level. 7 to 8 NPD to OSC-OUT Will not affect VCSEL power since these are clock and serial port pins 8 to 9 GUARD TO OSC-OUT Will not affect VCSEL power since these are clock and ground pins 9 to 10 GUARD to OSC-IN Will not affect VCSEL power since these are clock and ground pins. 11 to 12 REFC to REFB This event may cause the collapse of the internal analog supply, which would result in a reduction in the VCSEL output 12 to 13 REFB to RBIN A comparator in the RBIN circuit detects a short circuit between these pins and will turn off the laser. Resistive paths may increase the laser current. Agilent recommends the mouse manufacturer include features in the PCB design to counter this result. The PCB features include adding a guard trace devoid of solder mask surrounding the entire Rbin node and connected to VDD3. With this design, resistive leakage between RBIN and the guard trace will reduce the laser power. Conformal coating of these pins, traces, and the Rbin resistor is an alternative. 13 to 14 RBIN to XY_LASER The sensor will latch in a state with zero laser current. 14 to 15 XY_LASER to GND The sensor detects short circuits between the XY_LASER pin and ground. When detected, the external PNP pass transistor is turned off. 15 to 16 GND to VDD3 A short or resistive path would either: a) waste supply current but leave laser power unaffected or b) collapse the supply voltage and then turn off or reduce laser power 16 to 17 VDD3 to GND Same as pins 15 to 16 17 to 18 GND to VDD3 Same as pins 15 to 16 18 to 19 VDD3 to GND Same as pins 15 to 16 19 to 20 GND to LASER_NEN A short or resistive path failure here does not alter the VCSEL on power. 7 Table 2. # NAME OPEN SHORT TO VDD SHORT TO GND 1 NCS No effect on laser No effect on laser No effect on laser 2 MISO No effect on laser No effect on laser No effect on laser 3 SCLK No effect on laser No effect on laser No effect on laser 4 MOSI No effect on laser No effect on laser No effect on laser 5 N/C No effect on laser No effect on laser No effect on laser 6 RESET Laser remains at safe power Laser always off Laser remains at safe power 7 NPD No effect on laser No effect on laser No effect on laser 8 OSC_OUT No effect on laser No effect on laser No effect on laser 9 GUARD No effect on laser VDD may collapse, laser power remains safe No effect on laser 10 OSC_IN No effect on laser No effect on laser No effect on laser 11 REFC May cause oscillation at internal supply, but Laser remains at safe power No effect on laser VDD may collapse, laser power remains safe 12 REFB No effect on laser VDD may collapse, laser power remains safe No effect on laser 13 RBIN Laser power drops to 0 as drive circuit programming current becomes 0 Laser power drops to 0 as drive circuit programming current reverses Laser shut off by internal detection circuit 14 XY_LASER Laser power drops to 0 (no current can flow) Laser power drops to 0 (both ends tied to VDD) Laser turned off via LASER_NEN output by internal detection circuit 15 GND No effect on laser - other GND pins exist VDD may collapse, laser power remains safe No effect on laser 16 VDD3 No effect on laser - other VDD pins exist No effect on laser VDD may collapse, laser power remains safe 17 GND No effect on laser - other GND pins exist VDD may collapse, laser power remains safe No effect on laser 18 VDD3 No effect on laser - other VDD pins exist No effect on laser VDD may collapse, laser power remains safe 19 GND No effect on laser - other GND pins exist VDD may collapse, laser power remains safe No effect on laser 20 LASER_NEN Laser turns off or has greatly reduced power since pass transistor is not driven on Laser turns off since pass transistor off No effect on laser XY_LASER current source remains correct www.agilent.com/ semiconductors For product information and a complete list of distributors, please go to our web site. Data subject to change. Copyright (c) 2004-2005 Agilent Technologies, Inc. May 19, 2005 5989-1584EN