HCPL-788J Isolation Amplifier with Short Circuit and Overload Detection Data Sheet Description Features (continued) Avago’s Isolation Amplifier with Short Circuit and Overload Detection makes motor phase current sensing compact, affordable and easy-to-implement while satisfying worldwide safety and regulatory requirements.
Description The HCPL-788J isolation amplifier is designed for current sensing in electronic motor drives. In a typical implementation, motor currents flow through an external resistor and the resulting analog voltage drop is sensed by the HCPL-788J. A larger analog output voltage is created on the other side of the HCPL-788J’s optical isolation barrier. The output voltage is proportional to the motor current and can be connected directly to a single-supply A/D converter.
Ordering Information HCPL-788J is UL Recognized with 3750 Vrms for 1 minute per UL1577. Part Number HCPL-788J Option RoHS non RoHS Compliant Compliant -000E no option -500E #500 Package SO-16 Surface Mount X X Tape & Reel X IEC/EN/DIN EN 60747-5-2 X X Quantity 45 per tube 850 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.
Package Outline Drawings 16-Lead Surface Mount 0.018 (0.457) Dimensions in inches (millimeters) LAND PATTERN RECOMMENDATION 16 15 14 13 12 11 10 9 TYPE NUMBER DATE CODE A 788J YYWW Note: Initial and continued variation in the color of the HCPL788J’s white mold compound is normal and does not affect device performance or reliability. Note: Floating lead protrusion is 0.25 mm (10 mils) max. 0.050 (1.270) 0.458 (11.63) 0.295 ± 0.010 (7.493 ± 0.254) 0.085 (2.16) 1 2 3 4 5 6 7 8 0.406 ± 0.10 (10.
Solder Reflow Thermal Profile 300 TEMPERATURE (°C) PREHEATING RATE 3°C + 1°C/–0.5°C/SEC. REFLOW HEATING RATE 2.5°C ± 0.5°C/SEC. PEAK TEMP. 245°C PEAK TEMP. 240°C PEAK TEMP. 230°C 200 2.5°C ± 0.5°C/SEC. SOLDERING TIME 200°C 30 SEC. 160°C 150°C 140°C 30 SEC. 3°C + 1°C/–0.5°C 100 PREHEATING TIME 150°C, 90 + 30 SEC. 50 SEC. TIGHT TYPICAL LOOSE ROOM TEMPERATURE 0 0 50 100 150 200 TIME (SECONDS) Note: Non-halide flux should be used.
Regulatory Information The HCPL-788J has been approved by the following organizations: IEC/EN/DIN EN 60747-5-2 Approved under: IEC 60747-5-2:1997 + A1:2002 EN 60747-5-2:2001 + A1:2002 DIN EN 60747-5-2 (VDE 0884 Teil 2):2003-01. UL Recognized under UL 1577, component recognition program, File E55361. CSA Approved under CSA Component Acceptance Notice #5, File CA 88324. IEC/EN/DIN EN 60747-5-2 Insulation Characteristics* Description Installation classification per DIN VDE 0110/1.
Insulation and Safety Related Specifications Parameter Symbol Min. Max. Conditions Minimum External Air Gap (Clearance) L(101) 8.3 mm Measured from input terminals to output terminals, shortest distance through air. Minimum External Tracking (Creepage) L(102) 8.3 mm Measured from input terminals to output terminals, shortest distance path along body. 0.5 mm Through insulation distance conductor to conductor, usually the straight line distance thickness between the emitter and detector.
DC Electrical Specifications Unless otherwise noted, all typicals and figures are at the nominal operating conditions of VIN+ = 0, VIN- = 0 V, VREF = 4.0 V, VDD1 = VDD2 = 5 V and TA = 25°C; all Minimum/Maximum specifications are within the Recommended Operating Conditions. Parameter Symbol Min. Typ. Max. Units Test Conditions Input Offset Voltage VOS -3 0 3 mV VIN+ = 0 V Magnitude of Input Offset Change vs.
AC Electrical Specifications Unless otherwise noted, all typicals and figures are at the nominal operating conditions of VIN+ = 0, VIN- = 0 V, VREF = 4.0 V, VDD1 = VDD2 = 5 V and TA = 25°C; all Minimum/Maximum specifications are within the Recommended Operating Conditions. Parameter Symbol Min. Typ. VOUT Bandwidth (-3dB) BW 20 30 VOUT Noise NOUT 2.2 VIN to VOUT Signal Delay (50 - 50%) tDSIG VOUT Rise/Fall Time (10–90) Units Test Conditions Fig. kHz VIN+ = 200 mVpk-pk sine wave.
Notes: 01. In accordance with UL1577, each optocoupler is proof tested by applying an insulation test voltage ≥ 4500 Vrms for 1 second (leakage detection current limit, II-O ≤ 5 µA). This test is performed before the 100% production test for partial discharge (method b) shown in IEC/EN/DIN EN 60747-5-2 Insulation Characteristic Table, if applicable. 02. The Input-Output Momentary Withstand Voltage is a dielectric voltage rating that should not be interpreted as an input-output continuous voltage rating.
600.0 400.0 200.0 0 -200.0 -400.0 -600.0 -800.0 -40 -20 0 20 40 60 800 800 600 600 400 200 0 -200 -400 -600 -800 4.5 80 Figure 3. Input offset voltage change vs. temperature. 5.25 1.5 3.0 1.0 2.5 2.0 1.5 1.0 0.5 0 100 200 1.0 0.5 0 -0.5 -1.0 -1.5 5.25 5.5 OUTPUT SUPPLY VOLTAGE – VDD2 – V Figure 9. Gain change vs. VDD2. 5.0 5.25 5.5 -0.5 -1.0 1.0 0.5 0 -0.5 -1.0 -1.5 -20 0 20 40 60 -2.0 4.5 80 4.75 5.0 5.25 Figure 7. Gain change vs. temperature. Figure 8.
35 3.5 FAULT DETECTION DELAY – µs 34 BANDWIDTH – kHz 33 32 31 30 29 28 27 26 25 -40 -20 0 20 40 60 80 300 mV 0 mV 3.25 VIN 300 mV/D -300 mV 5V 2.5 V 3.0 VOUT (PIN 12) 2.5 V/D 0V 5V 2.75 2.5 V ABSVAL (PIN 13) 2.5 V/D 0V 2.5 -40 TEMPERATURE – °C -20 0 20 40 60 80 TEMPERATURE – °C 5V 2.5 V FAULT (PIN 14) 2.5 V/D 0V 5.00 µs/DIV Figure 12. Bandwidth vs. temperature. 300 mV 0 mV Figure 13. FAULT detection delay vs. temperature.
5V 4.7 kΩ 50 Ω VIN+ 14 1 10 Ω FAULT 13 0.01 µF ABSVAL 12 3 VOUT 11 VREF 0.1 µF 4 HCPL-788J 0.1 µF 6 5, 7 VDD1 0.1 µF 2, 8 10,15 9, 16 VDD2 0.1 µF Figure 20. AC test circuit. HCPL-788J 1 2 VIN+ VIN- FAULT DETECT Σ∆ MODULATOR DECODER 3 CH 4 CL 6 VLED+ VREF 11 VOUT 12 ABSVAL 13 FAULT 14 VDD2 15 VDD2 10 GND2 9 GND2 16 ENCODER D/A LPF 256 mV REFERENCE RECTIFIER 5 VDD1 7 VDD1 8 GND1 Figure 21. Internal block diagram.
Applications Information rectified output (ABSVAL) is essentially a DC signal representing the rms motor current. This single DC signal and a threshold comparator can indicate motor overload conditions before damage to the motor or drive occur. Figure 22 shows the ABSVAL output when 3 HCPL-788Js are used to monitor a sinusoidal 60 Hz current. Figures 23 and 24 show the ABSVAL output when only 2 or 1 of the 3 phases are monitored, respectively.
R2 39 Ω + INPUT CURRENT R SHUNT 0.02 Ω R1 HCPL-788J .01 µF 1 VIN+ GND2 16 2 VIN- VDD2 15 3 CH FAULT 14 4 CL ABSVAL 13 5 VDD1 VOUT 12 A/D 6 VLED1+ VREF 11 VREF 7 VDD1 VDD2 10 8 GND1 GND2 9 C6 0.1 µF C2 C3 0.1 µF ISOLATED +5 V C1 0.1 µF R3 4.7 kΩ µC TO OTHER PHASE OUTPUTS C8 C4 C7 C5 GND +5 V C5 = C7 = C8 = 470 pF C4 = 0.1 µF Figure 25. Recommended applications circuit. + HV+ FLOATING POWER SUPPLY GATE DRIVE CIRCUIT – R4 R2 39 Ω D1 5.1 V C2 0.
line powered transformer or a high-frequency DC-DC converter. An inexpensive 78L05 threeterminal regulator can also be used to reduce the floating supply voltage to 5 V. 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. As shown in Figure 25, 0.
Current Sensing Resistors The current sensing resistor should have low resistance (to minimize power dissipation), low inductance (to minimize di/ dt induced voltage spikes which could adversely affect operation), and reasonable tolerance (to maintain overall circuit accuracy). Choosing a particular value for the resistor is usually a compromise between minimizing power dissipation and maximizing accuracy.
Both of these effects are eliminated when a four-terminal current sensing resistor is used. A four-terminal resistor has two additional terminals that are Kelvin-connected directly across the resistive element itself; these two terminals are used to monitor the voltage across the resistive element while the other two terminals are used to carry the load current. Because of the Kelvin connection, any voltage drops across the leads carrying the load current should have no impact on the measured voltage.
Frequently Asked Questions about the HCPL-788J 1. The Basics 1.1: Why should I use the HCPL-788J for sensing current when Hall-effect sensors are available which don’t need an isolated supply voltage? Historically, motor control current sense designs have required trade-offs between signal accuracy, response time, and the use of discrete components to detect short circuit and overload conditions.
2.4: Do I really need an RC filter on the input? What is it for? Are other values of R and C okay? This filter prevents damage from input spikes which may go beyond the absolute maximum ratings of the HCPL-788J inputs during ESD and other transient events. The filter also prevents aliasing of high frequency (above 3 MHz) noise at the sampled input.
4.2: Can the signal to noise ratio be improved? Yes. Some noise energy exists beyond the 30 kHz bandwidth of the HCPL-788J. An external RC low pass filter can be used to improve the signal to noise ratio. For example, a 680 Ω, 4700 pF RC filter will cut the rms output noise roughly by a factor of 2. This filter reduces the -3dB signal bandwidth only by about 10%. In applications needing only a few kHz bandwidth even better noise performance can be obtained.
5. Power Supplies and Start-Up 5.1: What are the output voltages before the input side power supply is turned on? VOUT (pin 12) is close to zero volts, ABSVAL (pin 13) is close to VREF and FAULT (pin 14) is in the high (inactive) state when power to the input side is off. In fact, a self test can be performed using this information. In a motor drive, it is possible to turn off all the power transistors and thus cause all the sense resistor voltages to be zero.
