ACPL-C87B, ACPL-C87A, ACPL-C870 Precision Optically Isolated Voltage Sensor Data Sheet Lead (Pb) Free RoHS 6 fully compliant RoHS 6 fully compliant options available; -xxxE denotes a lead-free product Description Features The ACPL-C87B/C87A/C870 voltage sensors are optical isolation amplifiers designed specifically for voltage sensing. Its 2 V input range and high 1 G input impedance, makes it well suited for isolated voltage sensing requirements in electronic power converters applications including motor drives and renewable energy systems. In a typical voltage sensing implementation, a resistive voltage divider is used to scale the DC-link voltage to suit the input range of the voltage sensor. A differential output voltage that is proportional to the input voltage is created on the other side of the optical isolation barrier. Advanced Sigma-Delta (-) Modulation Technology For general applications, the ACPL-C87A (±1% gain tolerance) and the ACPL-C870 (±3% gain tolerance) are recommended. For high precision requirements, the ACPL-C87B (±0.5% gain tolerance) can be used. The ACPL-C87B/C87A/C870 family operates from a single 5 V supply and provides excellent linearity. An active-high shutdown pin is available which reduces the IDD1 current to only 15 A, making them suitable for battery-powered and other power-sensitive applications. 3 V to 5.5 V Wide Supply Range for Output Side The high common-mode transient immunity (15 kV/s) of the ACPL-C87B/C87A/C870 provides the precision and stability needed to accurately monitor DC-link voltage in high noise environments. Combined with superior optical coupling technology, the ACPL-C87B/C87A/C870 implements sigma-delta (-) modulation, chopper stabilized amplifiers, and differential outputs to provide unequaled isolation-mode noise rejection, low offset, high gain accuracy and stability. This performance is delivered in a compact, auto-insertable Stretched SO-8 (SSO-8) package that meets worldwide regulatory safety standards. Unity Gain 1 V/V, ±0.5% High Gain Accuracy (ACPL-C87B) 1 G Input Impedence 0 to 2 V Nominal Input Range -35 ppm/°C Low Gain Drift 21V /°C Offset Voltage Drift 0.1% Non-Linearity Max Active-High Shutdown Pin 100 kHz Wide Bandwidth -40° C to +105° C Operating Temperature Range 15 kV/s Common-Mode Transient Immunity Compact, Auto-Insertable Stretched SO-8 Package Safety and Regulatory Approvals (pending): – IEC/EN/DIN EN 60747-5-5: 1230 Vpeak working insulation voltage – UL 1577: 5000 Vrms/1 min double protection rating – CSA: Component Acceptance Notice #5 Applications Isolated Voltage Sensing in AC and Servo Motor Drives Isolated DC-Bus Voltage Sensing in Solar Inverters, Wind Turbine Inverters Isolated Sensor Interfaces Signal Isolation in Data Acquisition Systems General Purpose Voltage Isolation CAUTION: It is advised that normal static precautions be taken in handling and assembly of this component to prevent damage and/or degradation which may be induced by ESD. Functional Diagram VDD1 1 8 VDD2 VIN 2 7 VOUT+ SHDN 3 6 VOUT– GND1 4 5 GND2 SHIELD Table 1. Pin Description Figure 1. NOTE: A 0.1 F bypass capacitor must be connected between pins 1 and 4 and between pins 5 and 8. Pin No. Symbol Description 1 VDD1 Supply voltage for input side (4.5 V to 5.5 V), relative to GND1 2 VIN Voltage input 3 SHDN Shutdown pin (Active High) 4 GND1 Input side ground 5 GND2 Output side ground 6 VOUT- Negative output 7 VOUT+ Positive output 8 VDD2 Supply voltage for output side (3 V to 5.5 V), referenced to GND2 Ordering Information ACPL-C87B/C87A/C870 is UL recognized with 5000 Vrms/1 minute rating per UL 1577 (pending). Table 2. Option Part number (RoHS Compliant) Package Surface Mount ACPL-C87B ACPL-C87A ACPL-C870 -000E Stetched SO-8 X -500E X Tape & Reel X IEC/EN/DIN EN 60747-5-5 Quantity X 80 per tube X 1000 per reel To order, choose a part number from the part number column and combine with the desired option from the option column to form an order entry. Example: ACPL-C87A-500E to order product of Surface Mount package in Tape and Reel packaging with IEC/EN/DIN EN 60747-5-5 Safety Approval and RoHS compliance. Contact your Avago sales representative or authorized distributor for information. 2 Package Outline Drawing Stretched SO-8 Package (SSO-8) RECOMMENDED LAND PATTERN 5.850 ± 0.254 (0.230 ± 0.010) PART NUMBER 8 7 6 5 C87B YWW RoHS-COMPLIANCE INDICATOR DATE CODE 12.650 (0.498) 6.807 ± 0.127 (0.268 ± 0.005) 1.905 (0.075) 1 2 3 4 0.64 (0.025) 7° 1.590 ± 0.127 (0.063 ± 0.005) 45° 0.450 (0.018) 3.180 ± 0.127 (0.125 ± 0.005) 0.750 ± 0.250 (0.0295 ± 0.010) 11.50 ± 0.250 (0.453 ± 0.010) 0.200 ± 0.100 (0.008 ± 0.004) 0.381 ± 0.127 (0.015 ± 0.005) 1.270 (0.050) BSG 0.254 ± 0.100 (0.010 ± 0.004) Dimensions in millimeters and (inches). Figure 2. SSO-8 Package Note: Lead coplanarity = 0.1 mm (0.004 inches). Floating lead protrusion = 0.25mm (10mils) max. Recommended Pb-Free IR Profile Recommended reflow condition as per JEDEC Standard, J-STD-020 (latest revision). Non-Halide Flux should be used. Regulatory Information The ACPL-C87B/C87A/C870 is pending approval by the following organizations: IEC/EN/DIN EN 60747-5-5 Approval with Maximum Working Insulation Voltage VIORM = 1230 Vpeak. UL Approval under UL 1577, component recognition program up to VISO = 5000 Vrms/1 min. File 55361. CSA Approval under CSA Component Acceptance Notice #5, File CA 88324 3 Table 3. Insulation and Safety Related Specifications Parameter Symbol Value Unit Conditions Minimum External Air Gap (External Clearance) L(101) 8.0 mm Measured from input terminals to output terminals, shortest distance through air Minimum External Tracking (External Creepage) L(102) 8.0 mm Measured from input terminals to output terminals, shortest distance path along body 0.5 mm Through insulation distance, conductor to conductor, usually the direct distance between the photoemitter and photodetector inside the optocoupler cavity > 175 V DIN IEC 112/VDE 0303 Part 1 Minimum Internal Plastic Gap (Internal Clearance) Tracking Resistance (Comparative Tracking Index) CTI Isolation Group IIIa Material Group (DIN VDE 0110, 1/89, Table 1) Table 4. IEC/EN/DIN EN 60747-5-5 Insulation Characteristics [1] Description Symbol Value Installation classification per DIN VDE 0110/1.89, Table 1 for rated mains voltage ≤ 150 Vrms for rated mains voltage ≤ 300 Vrms for rated mains voltage ≤ 450 V rms for rated mains voltage ≤ 600 Vrms for rated mains voltage ≤ 1000 Vrms I-IV I-IV I-IV I-IV I-III Climatic Classification 55/105/21 Pollution Degree (DIN VDE 0110/1.89) Units 2 Maximum Working Insulation Voltage (Pending Qualification) VIORM 1230 Vpeak Input to Output Test Voltage, Method b VIORM x 1.875 = VPR, 100% Production Test with tm = 1 sec, Partial Discharge < 5 pC VPR 2306 Vpeak Input to Output Test Voltage, Method a VIORM x 1.6 = VPR, Type and Sample Test, tm = 10 sec, Partial Discharge < 5 pC VPR 1968 Vpeak Highest Allowable Overvoltage (Transient Overvoltage, tini = 60 sec) VIOTM 8000 Vpeak Safety-limiting values (Maximum values allowed in the event of a failure) Case Temperature Input Current [2] Output Power [2] TS IS,INPUT PS,OUTPUT 175 230 600 °C mA mW Insulation Resistance at TS, VIO = 500 V RS ≥ 109 Notes: 1. Insulation characteristics are guaranteed only within the safety maximum ratings, which must be ensured by protective circuits within the application. 4 Table 5. Absolute Maximum Rating Parameter Symbol Min. Max. Units Storage Temperature TS -55 +125 °C Ambient Operating Temperature TA -40 +105 °C Supply Voltage VDD1, VDD2 -0.5 6.0 V Steady-State Input Voltage [1, 3] VIN -2 VDD1 + 0.5 V Two-Second Transient Input Voltage [2] VIN -6 VDD1 + 0.5 V Logic Input VSD -0.5 VDD1 + 0.5 V Output Voltages VOUT+, VOUT− -0.5 VDD2 + 0.5 V Lead Solder Temperature 260° C for 10 sec., 1.6 mm below seating plane Notes: 1. DC voltage of up to -2 V on the inputs does not cause latch-up or damage to the device. 2. Transient voltage of 2 seconds up to -6 V on the inputs does not cause latch-up or damage to the device. 3. Absolute maximum DC current on the inputs = 100 mA, no latch-up or device damage occurs. Table 6. Recommended Operating Conditions Parameter Symbol Min. Max. Units Ambient Operating Temperature TA -40 +105 °C VDD1 Supply Voltage VDD1 4.5 5.5 V VDD2 Supply Voltage VDD2 3.0 5.5 V Input Voltage Range[1] VIN 0 2.0 V Shutdown Enable Voltage VSD VDD1 – 0.5 VDD1 V Notes: 1. 2 V is the nominal input range. Full scale input range (FSR) is 2.46 V. 5 Table 7. Electrical Specifications Unless otherwise noted, TA = -40° C to +105° C, VDD1 = 4.5 V to 5.5 V, VDD2 = 3.3 V to 5.5 V, VIN = 0 – 2 V, and VSD = 0 V. Parameter Symbol Min. Typ.[1] Max. -9.9 -0.3 9.9 Unit Test Conditions/Notes Fig. DC CHARACTERISTICS Input Offset Voltage VOS Magnitude of Input Offset Change vs. Temperature |dVOS/dTA| Gain (ACPL-C87B, ±0.5%) G0 21 mV TA = 25° C 3, 4 V/°C TA = –40° C to +105° C ; Direct short across inputs. 5 0.995 1 1.005 V/V TA = 25° C; VDD2 = 5 V; Note 2. 6, 7 0.994 0.999 1.004 V/V TA = 25° C; VDD2 = 3.3 V; Note 2. 6, 7 Gain (ACPL-C87A, ±1%) G1 0.99 1 1.01 V/V TA = 25° C; Note 2. 6, 7 Gain (ACPL-C870, ±3%) G3 0.97 1 1.03 V/V TA = 25° C; Note 2. 6, 7 Magnitude of Gain Change vs. Temperature dG/dTA -35 ppm/°C TA = -40° C to +105° C 8 Nonlinearity NL 0.05 % VIN = 0 to 2 V, TA = 25° C 9, 10 Magnitude of NL Change vs. Temperature |dNL/dTA| 0.0002 %/°C TA = -40° C to +105° C 11 Recommended Input Range VINR 2 V Referenced to GND1 Full-Scale Differential Voltage Input Range FSR 2.46 V Referenced to GND1 Shutdown Logic Low Input Voltage VIL 0.8 Shutdown Logic High Input Voltage VIH VDD – 0.5 5 Input Bias Current IIN -0.1 Magnitude of IIN Change vs. Temperature 0.1 INPUTS AND OUTPUTS TA = 25° C TA = 25° C -0.0015 A dIIN/dTA 1 nA/°C Equivalent Input Impedance RIN 1000 M Output Common-Mode Voltage VOCM 1.23 V VOUT+ or VOUT– Output Voltage Range VOUTR Vocm ± 1.23 V VSD = 0 V. Note 4. Output Short-Circuit Current |IOSC| 30 mA VOUT+ or VOUT–, shorted to GND2 or VDD2 Output Resistance ROUT 36 VOUT+ or VOUT– 6 VIN = 0 V 13 Table 7. Electrical Specifications (continued) Unless otherwise noted, TA = -40° C to +105° C, VDD1 = 4.5 V to 5.5 V, VDD2 = 3.3 V to 5.5 V, VIN = 0 – 2 V, and VSD = 0 V. Parameter Symbol Typ.[1] Min. Max. Unit Test Conditions/Notes Fig. mVrms Vin = 0 V; Output low-pass filtered to 180 KHz. Note 3. 12 AC CHARACTERISTICS Vout Noise Nout 0.013 Small-Signal Bandwidth (-3 dB) f–3 dB kHz Guaranteed by design Input to Output Propagation Delay 50%-10% tPD10 70 100 2.2 3.0 s Step input. 18 50%-50% tPD50 3.7 5.5 s Step input. 18 18 tPD90 5.3 6.5 s Step input. Output Rise/Fall Time (10%-90%) tR/F 2.7 4.0 s Step input (tPD90 - tPD10) Shutdown Delay tSD 25 40 s Vin = 2 V Enable Delay tON 150 200 s 50%-90% Common Mode Transient Immunity CMTI 15 kV/s VCM = 1 kV, TA = 25° C Power Supply Rejection PSR -78 dB 1 Vpp 1 kHz sine wave ripple on VDD1, differential output IDD1 10.5 mA VSD = 0 V A VSD = 5 V 10 17 POWER SUPPLIES Input Side Supply Current 15 15 IDD2 6.5 12 mA 5 V supply 6.1 11 mA 3.3 V supply Notes: 1. All Typical values are under Typical Operating Conditions at TA = 25° C, VDD1 = 5 V, VDD2 = 5 V. 2. Gain is defined as the slope of the best-fit line of differential output voltage (VOUT+ – VOUT-) versus input voltage over the nominal range, with offset error adjusted. 3. Noise is measured at the output of the differential to single ended post amplifier. 4. When is VSD = 5 V or when shutdown is enabled, Vout+ is close to 0V and Vout- is at close to 2.46 V. This is similar to when VDD1 is not supplied. Table 8. Package Characteristics Parameter Symbol Min Input-Output Momentary Withstand Voltage VISO 5000 Resistance (Input-Output) RI-O Capacitance (Input-Output) CI-O Typ Max Units Test Conditions Note Vrms RH < 50%, t = 1 min., TA = 25° C 1, 2 > 1012 VI-O = 500 VDC 3 0.5 pF f = 1 MHz 3 Notes: 1. In accordance with UL 1577, each optocoupler is proof tested by applying an insulation test voltage ≥ 6000 Vrms for 1 second (leakage detection current limit, II-O ≤ 5 mA). This test is performed before the 100% production test for partial discharge (method b) shown in IEC/EN/DIN EN 607475-5 Insulation Characteristic Table. 2. The Input-Output Momentary Withstand Voltage is a dielectric voltage rating that should not be interpreted as an input-output continuous voltage rating. For the continuous voltage rating, refer to the IEC/EN/DIN EN 60747-5-5 insulation characteristics table and your equipment level safety specification. 3. This is a two-terminal measurement: pins 1–4 are shorted together and pins 5–8 are shorted together. 7 Typical Performance Plots 5 4 3 2 1 0 -1 -2 -3 -4 -5 2 1.5 1 Offset (mV) Offset (mV) All ±3(sigma symbol) plots are based on characterization test result at the point of product release. For guaranteed specification, refer to the respective Electrical Specifications section. -0.5 -1.5 -2 5 Vdd1(V) 5.5 3.5 4 5 5.5 1.003 M+3 Mean 1.002 M- 3 1.001 1.000 0.999 0.998 0.997 -55 -35 -15 5 25 45 Temp (qC) 65 85 105 4.5 125 Figure 5. Input Offset vs Temperature 5 Vdd1 (V) 5.5 Figure 6. Gain vs Supply VDD1 1.00300 1.002 1.00200 1.001 1.00100 Gain (V/V) 1.003 1.000 1.00000 0.999 0.99900 0.998 0.99800 0.99700 0.997 3 3.5 4 4.5 5 5.5 -55 -35 -15 Vdd2 (V) Figure 7. Gain vs Supply VDD2 8 4.5 Figure 4. Input Offset vs Supply VDD2 Gain (V/V) 10 8 6 4 2 0 -2 -4 -6 -8 - 10 3 Vdd2 (V) Figure 3. Input Offset vs Supply VDD1 Offset (mV) 0 -1 4.5 Gain (V/V) 0.5 Figure 8. Gain vs Temperature 5 25 45 Temp (qC) 65 85 105 125 0.1 0.08 0.08 0.06 0.06 NL (%) NL (%) 0.1 0.04 0.02 0.04 0.02 0 0 4.5 5 Vdd1 (V) 4.5 5 5.5 17 Vin = 0 V Vin = 1 V Vin = 2 V 15 AC Noise (Vrms) 13 11 9 7 5 3 1 -1 -35 -15 5 25 45 Temp (qC) 65 85 105 0 125 Figure 11. Non-Linearity vs Temperature 20 40 60 80 100 Freq Filter (khz) 120 140 Figure 12. AC noise vs Filter Freq vs Vin 3 1 VOUT+ VOUT– 2.5 0 -1 2 Gain (dB) VOUT+, VOUT– 4 Figure 10. Non-Linearity vs Supply VDD2 0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 -55 1.5 1 -2 -3 -4 0.5 -5 0 0 0.5 Figure 13 VIN vs VOUT+, VOUT- 9 3.5 Vdd2 (V) Figure 9. Non-Linearity vs Supply VDD1 NL (%) 3 5.5 1 1.5 VIN 2 2.5 3 -6 1000 Figure 14. Frequency Response 10000 Bandwidth (Hz) 100000 160 5 Prog Delay (PS) Phase (deg) 6 200 180 160 140 120 100 80 60 40 20 0 1000 4 3 2 TPLH 50-10 TPLH 50-50 TPLH 50-90 1 0 10000 Bandwidth (Hz) -55 100000 Figure 15. Phase Response 0V 2V Vin 0V +2 V VOut Diff tSD tON 0V -2.46 V Figure 17. Shutdown And Wakeup Input To Output Timing Diagram. VOut Diff = VOut+ - VOut- 2V VIN 0V 2V VOut Diff 0V TPLH50-10 TPLH50-50 TPLH50-90 Figure 18. Input to Output Propagation Delay Timing Diagram. VOut Diff = VOut+ - VOut- 10 -15 5 25 45 Temp (qC) Figure 16. Propagation Delay vs Temperature 5V VSD -35 65 85 105 125 Definitions Application Information Gain Application Circuit Gain is defined as the slope of the best-fit line of differential output voltage (VOUT+ – VOUT-) over the nominal input range, with offset error adjusted out. The typical application circuit is shown in Figure 19. The ACPL-C87X voltage sensor is often used in photovoltaic (PV) panel voltage measurement and tracking in PV inverters, and DC bus voltage monitoring in motor drivers. The high voltage across rails needs to be scaled down to fit the input range of the iso-amp by choosing R1 and R2 values according to appropriate ratio. Nonlinearity Nonlinearity is defined as half of the peak-to-peak output deviation from the best-fit gain line, expressed as a percentage of the full-scale differential output voltage. The ACPL-C87X senses the single-ended input signal and produces differential outputs across the galvanic isolation barrier. The differential outputs (Vout+, Vout-) can be connected to an op-amp to convert to a singleended signal or directly to two ADCs. The op-amp used in the external post-amplifier circuit should be of sufficiently high precision so that it does not contribute a significant amount of offset or offset drift relative to the contribution from the isolation amplifier. Generally, op-amps with bipolar input stages exhibit better offset performance than op-amps with JFET or MOSFET input stages. Common Mode Transient Immunity, CMTI, also known as Common Mode Rejection CMTI is tested by applying an exponentially rising/falling voltage step on pin 4 (GND1) with respect to pin 5 (GND2). The rise time of the test waveform is set to approximately 50 ns. The amplitude of the step is adjusted until the differential output (VOUT+ – VOUT-) exhibits more than a 200 mV deviation from the average output voltage for more than 1μs. The ACPL-C87x will continue to function if more than 10 kV/s common mode slopes are applied, as long as the breakdown voltage limitations are observed. In addition, the op-amp should also have enough bandwidth and slew rate so that it does not adversely affect the response speed of the overall circuit. The postamplifier circuit includes a pair of capacitors (C4 and C5) that form a single-pole low-pass filter; these capacitors allow the bandwidth of the post-amp to be adjusted independently of the gain and are useful for reducing the output noise from the isolation amplifier. Power Supply Rejection, PSR PSRR is the ratio of differential amplitude of the ripple outputs over power supply ripple voltage, referred to the input, expressed in dB. The gain-setting resistors in the post-amp should have a tolerance of 1% or better to ensure adequate CMRR and adequate gain tolerance for the overall circuit. Resistor networks can be used that have much better ratio tolerances than can be achieved using discrete resistors. A resistor network also reduces the total number of components for the circuit as well as the required board space. C5 100 pF L1 1 U1 VDD1 VDD2 8 2 VIN VOUT+ 7 3 SHDN VOUT- 6 4 GND1 GND2 5 VDD1 R1 R2 10K C1 100 pF C2 100 nF GND1 VDD2 ACPL-C87X R6 10K, 1% R3 10K,1% C3 100 nF GND2 Vout R4 10K,1% C4 100 pF U2 OPA237 R5 10K, 1% L2 GND2 Figure 19. Typical application circuit. 11 V+ V- Measurement Accuracy and Power Dissipation of the Resistive Divider The input stage of the typical application circuit in Figure 19 can be simplified as the diagram shown in Figure 20. R2 and RIN, input resistance of the ACPL-C87X, create a current divider that results in an additional measurement error component that will add on to the tot on top of the device gain error. With the assumption that R1 and RIN have a much higher value than R2, the resulting error can be estimated to be R2/RIN. With RIN of 1 GW for the ACPL-C87X, this additional measurement error is negligible with R2 up to 1 M, where the error is approximately 0.1%. Though small, it can be further reduced by reducing the R2 to 100 k (error of 0.01% approximately), or 10 k (error of 0.001% approximately). However with lower R2, a drawback of higher power dissipation in the resistive divider string needs to be considered, especially in higher voltage sensing applications. For example, with 600 V DC across L1 and L2 and R2 of 100 k for 0.01% measurement error, the resistive divider string R1 RIN + +– R2 GND ACPL-C87x Figure 20. Simplified Input Stage. consumes about 12 mW, assuming VIN is set at 2 V. If the R2 is reduced to 10 k to reduce error to 0.001%, the power consumption will increase to about 120 mW. In energy efficiency critical applications such as PV inverters and battery-powered applications, this trade-off between measurement accuracy and power dissipation in the resistive string provides flexibility in design priority. Isolated Temperature Sensing using Thermistor IGBTs are an integral part of a motor or servo drive system and because of the high power that they usually handle, it is essential that they have proper thermal management and are sufficiently cooled. Long term overload conditions could raise the IGBT module temperature permanently or failure of the thermal management system could subject the module to package overstress and lead to catastrophic failures. One common way to monitor the temperature of the module is through using a NTC type thermistor mounted onto the IGBT module. Some IGBT module manufacturers also have IGBTs that comes with the thermistor integrated inside the module. In some cases, it is necessary to isolate this thermistor to provide added isolation and insulation due to the high power nature of the IGBTs. The ACPL-C87x voltage sensor can be used to easily meet such a requirement, while providing good accuracy and non-linearity. Figure. 21 shows an example of such an implementation. The ACPL-C87x is used to isolate the thermistor voltage which is later fed by the post amp stage to an ADC onboard the microcontroller (MCU) to determine the module temperature. The thermistor needs to be biased in way that its voltage output will optimize the 2 V input range of the ACPL-C87x across the intended temperature measurement range. HV+ U V W Vdd +– + GND HVNTC Thermistor IGBT Module Figure 21. Thermistor sensing in IGBT Module 12 ACPL-C87x Post Amp ADC MCU Power Supplies and Bypassing A power supply of 5 V is required to power the ACPL-C87x input side VDD1. In many motor drive DC bus voltage sensing applications, this 5 V supply is most often obtained from the same supply used to power the power transistor gate drive circuit using an inexpensive 78L05 three-terminal regulator. To help attenuate high frequency power supply noise or ripple, a resistor or inductor can be used in series with the input of the regulator to form a low-pass filter with the regulator’s input bypass capacitor. In some other applications a dedicated supply might be required to supply the VDD1. These applications include photovoltaic (PV) inverter voltage tracking and measurement, temperature sensor signal isolation. In these cases it is possible to add an additional winding on an existing transformer. Otherwise, some sort of simple isolated supply can be used, such as a line powered transformer or a high-frequency DC-DC converter module. As shown in Figure 22, 100 nF bypass capacitors (C2, C3) should be located as close as possible to the pins of the isolation amplifier. The bypass capacitors are required because of the high-speed digital nature of the signals inside the isolation amplifier. A 100 pF bypass capacitor (Cin) is also recommended at the input pins due to the switched-capacitor nature of the input circuit. The input bypass capacitor Cin also forms part of the anti-aliasing filter, which is recommended to prevent high-frequency noise from aliasing down to lower frequencies and interfering with the input signal. When R1 is far greater than R2, the low-pass anti-aliasing filter corner frequency can be calculated by 1/(2R2Cin). The input filter also performs an important reliability function – it reduces transient spikes from ESD events flowing through the high voltage rails. HV+ R1 Floating Positive Supply IN 78L05 C2 0.1μF C1 0.1μF Gate Drive Circuit 5V VDD2 VDD1 VOUT+ VIN R2 HVFigure 22. Recommended Power Supply and Bypassing 13 OUT Cin 0.1nF ACPL-C87A SHDN VOUT- GND1 GND2 C3 0.1μF PC Board Layout The design of the printed circuit board (PCB) should follow good layout practices, such as keeping bypass capacitors close to the supply pins, keeping output signals away from input signals, the use of ground and power planes, etc. In addition, the layout of the PCB can also affect the isolation transient immunity (CMTI) of the ACPLC87x, primarily due to stray capacitive coupling between the input and the output circuits. To obtain optimal CMTI performance, the layout of the PC board should minimize For product information and a complete list of distributors, please go to our web site: any stray coupling by maintaining the maximum possible distance between the input and output sides of the circuit and ensuring that any ground or power plane on the PC board does not pass directly below or extend much wider than the body of the ACPL-C87A. The placement of the input capacitor which forms part of the anti-aliasing filter together with the resistor network should also be placed as close as possible to the Vin pin. www.avagotech.com Avago, Avago Technologies, and the A logo are trademarks of Avago Technologies in the United States and other countries. Data subject to change. Copyright © 2005-2012 Avago Technologies. All rights reserved. AV02-3563EN - July 24, 2012