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In a typical implementation, and motor currents flow through an external resistor and the resulting analog voltage drop is sensed by the ACPLT. A differential output voltage is created on the other side of the ACPLT optical isolation barrier.
This differential output voltage is proportional to the motor current and can be converted to a single-ended signal by using an op-amp as shown in the recommended application circuit.
The product can also be used for general analog signal isolation applications requiring high accuracy, stability, and linearity under similarly severe noise conditions.
The ACPLT utilizes sigma delta 6′ analog-to-digital converter technology, chopper stabilized amplifiers, and a fully differential circuit topology. Together, these features deliver unequaled isolationmode noise rejection, as well as excellent offset and gain accuracy and stability over time and temperature.
This performance is delivered in a compact, auto-insertable, industry standard 8-pin DIP package that meets worldwide regulatory safety standards.
ACPL-782T problem understanding datasheet
A gull-wing surface mount option E is also available. Avago R2Coupler isolation products provide the reinforced insulation and reliability needed for critical in automotive and high temperature industrial applications. Option datasheets are available. Contact your Avago sales representative or authorized distributor for information. Floating lead protrusion is 0. Tolerances unless otherwise specified: 782y Flux should be used.
Insulation characteristics are guaranteed only within the safety maximum ratings which must be ensured by protective circuits within the application.
Refer to the following figure for dependence of PS and IS on ambient temperature. Minimum External Tracking Creepage L 8. Specifications are within the Recommended Operating Conditions. Units Test Conditions Fig. Note 13 4,15 Typical values represent the mean value of all characterization units at the nominal operating conditions. Typical drift specifications are determined by calculating the rate of change of the specified parameter versus the drift parameter at nominal operating conditions for each characterization unit, and then averaging the individual unit rates.
The corresponding drift figures are normalized to the nominal operating conditions and show how much drift occurs as the par-ticular drift parameter is varied from its nominal value, with all other parameters held at their nominal operating values. Note that the typical drift specifications in the tables below may differ from the slopes of the mean curves shown in the corresponding figures. This test mode is for testing LED coupling and is not intended for customer use.
This is the Absolute Value of Gain Change vs. Temperature in PPM level. 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.
However, the output supply current will continue to rise for differential input voltages up to approximately mV, beyond which the output supply current remains constant. Because of the switched-capacitor nature of the input sigma-delta converter, time-averaged values are shown. When the differential input signal exceeds approximately mV, the outputs will limit at the typical values shown.
Short circuit current is the amount of output current generated when either output is shorted to VDD2 or ground. CMRR is defined as the ratio of the differential signal gain signal applied differentially between pins 2 and 3 to the common-mode gain input pins tied together and the signal applied to both inputs at the same timeexpressed in dB. Output noise comes from two primary sources: Chopper noise results from chopper stabilization of the output op-amps.
It occurs at a specific frequency typically kHz at room temperatureand is not attenuated by the internal output filter. A filter circuit can be easily added to the external post-amplifier to reduce the total RMS output noise. The internal output filter does eliminate most, but not all, of the sigmadelta quantization noise. The magnitude of the output quantization noise is very small at lower frequencies below 10kHz and increases with increasing frequency.
The rise time of the test waveform is set to approximately 50 ns. The Input-Output Momentary Withstand Voltage is a dielectric voltage rating that should not be interpreted as an input-output continuous voltage rating.
This is a two-terminal measurement: Input Offset Voltage Test Circuit. Input Offset Voltage vs.
Gain and Nonlinearity Test Circuit. Propagation Delay Test Circuits. A floating power supply which in many applications could be the same supply that is used to drive 78t2 high-side power transistor is regulated to 5 V using a simple zener diode D1 ; the value of resistor R4 should be chosen to supply sufficient current from the existing floating supply.
Although the application circuit is relatively simple, a few recommendations should be followed to ensure optimal performance. An inexpensive 78L05 three-terminal regulator can also be used to reduce the floating supply voltage to 5 V. As shown in Figure 18, 0. The bypass capacitors are required because of the high-speed digital nature of the signals inside the ACPLT. The input bypass capacitor also forms part of the anti-aliasing filter, which is recommended to prevent high-frequency noise from 78t2 down to lower frequencies and interfering with the input signal.
The input filter also performs an important reliability function—it reduces transient spikes from ESD events flowing through the current sensing resistor. The power supply for the ACPL T is most often obtained from the same supply used to power the power transistor gate drive circuit.
If a dedicated supply is required, in many cases it is possible to add an additional winding on adpl 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. Recommended Supply and Sense Resistor Connections. PC Board Layout Acpk 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.
To obtain optimal CMTI performance, the layout of the PC board should minimize 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 ACPLT. Example Printed Circuit Board Layout. Choosing a particular value for the resistor is usually a compromise between minimizing power dissipation afpl maximizing accuracy.
Smaller sense resistance decreases power dissipation, while larger sense resistance can improve circuit accuracy by utilizing the full input range of the ACPL T. The first step in selecting a sense resistor is determining how much current the resistor will be sensing.
The graph in Figure 20 shows the RMS current in each phase of a threephase induction motor as a function of average motor output power in horsepower, hp and motor drive supply voltage. The maximum value of the sense resistor is determined by the current being measured and the maximum recommended input voltage of the isolation amplifier.
The maximum sense resistance can be calculated by taking the maximum recommended input voltage and dividing by the peak current that the sense resistor should see during normal operation. Assuming a maximum 728t voltage of mV, the maximum value of sense resistance in this case would be about 10 m:. The maximum average power dissipation in the sense resistor can also be easily calculated by multiplying the sense resistance times the square of the maximum RMS current, which is about 1 W in the previous example.
If the power dissipation in the sense resistor is too high, the resistance can be decreased below the maximum value to decrease power dissipation.
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Motor Output Horsepower vs. Motor Phase Current and Supply Voltage. As the resistance value is reduced, the output voltage across the resistor is also reduced, which means that the offset and noise, which are fixed, become a larger percentage of the signal amplitude. The selected value of the sense resistor will fall somewhere between the minimum and maximum values, depending on the particular requirements of a specific design.
When sensing currents large enough to cause significant heating of the sense resistor, the temperature coefficient tempco of the resistor can introduce nonlinearity due to the signal dependent temperature rise of the resistor. The effect increases as the resistor-to-ambient thermal resistance increases. This effect can be minimized by reducing the thermal resistance of the current sensing resistor or by using a resistor with a lower tempco.
Lowering the thermal resistance can be accomplished by repositioning the current sensing resistor on the PC board, by using larger PC board traces to carry away more heat, or by using a heat sink. For a two-terminal current sensing resistor, as the value of resistance decreases, the resistance of the leads become a significant percentage of the total resistance.
This has two primary effects on resistor accuracy. First, the effective resistance of the sense resistor can become dependent on factors such as how long the leads are, how they are bent, how far they are inserted into the board, and how far solder wicks up the leads during assembly these issues will be discussed in more detail shortly.
Second, the leads are typically made from a material, such as copper, which has a much higher tempco than the material from which the resistive element itself is made, resulting in a higher tempco overall. 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. When laying out a PC board for the current sensing resistors, a couple of points should be kept in mind. The Kelvin connections to the resistor should be brought together under the body of the resistor and then run very close to each other to the input of the ACPLT; this minimizes the loop area of the connection and reduces the possibility of stray magnetic fields from interfering with the measured signal.
If the sense resistor is not located on the same PC board as the ACPLT circuit, a tightly twisted pair of wires can accomplish the same thing. The only direct connection between the ACPLT circuit and the gate drive circuit should be the positive power supply line. Also, multiple layers of the PC board can be used to increase current carrying capacity. Numerous platedthrough vias should surround each non-Kelvin terminal of the sense resistor to help distribute the current between the layers of the PC board.
The PC board should use 2 or 4 oz. Output Side 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.
By referencing the input circuit to the negative side of the sense resistor, any load current induced noise transients on the resistor are seen as a common-mode signal and will not interfere with the current-sense signal.
This is important because the large load currents flowing through the motor drive, along with the parasitic inductances inherent in the wiring of the circuit, can generate both noise spikes and offsets that are relatively large compared to the small voltages that are being measured across the current sensing resistor.
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 C5 and C6 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.
Many different op-amps could be used in the circuit, including: 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.