illustrate

The HCPL-7800 (A) series of isolation amplifiers are designed for current sensing in electronic motor drives. In a typical implementation, the motor current is sensed through the HCPL-7800(A) through an external resistor and the resulting analog voltage drop. The differential output voltage creates an isolation barrier on the other side of the HCPL-7800(A) optical system. This differential output voltage is proportional to the motor current and can be converted to a single-ended signal using an op amp, as recommended in the application circuit. Because common-mode voltages in the tens of nanoseconds are common in modern switching inverter motor drives, the HCPL-7800(A) is designed to ignore very high common-mode transient slew rates (at least 10 kV/µs) . The HCPL-7800(A) isolated high CMR performance amplifier provides the precision and stability required for precise monitoring of high noise motor currents in a control environment, providing smoother control (less "torque ripple") in various types of application in motor control.

This product can also be used for general analog signal isolation applications requiring high precision, high stability, and linearity under similar severe noise conditions. For general applications, we recommend the HCPL-7800 (to obtain a ±3% tolerance). For precision applications Avago Technologies provides the HCPL-7800A with a part-to-part tolerance of ±1%. HCPL-7800(A) adopts sigma delta (∑-∏) analog-to-digital converter technology, chopper-stabilized amplifier, and fully differential circuit topology. Together, these features provide unmatched isolation-mode noise rejection, as well as excellent offset and accuracy and stability over time and temperature. This performance is provided in a compact, auto-insertable, industry-standard 8-pin DIP package to global regulatory safety standards. Surface mount option # 300 is also available).

feature

15kV/µs Common Mode Rejection (VCM= 1000V )

Small, auto-insertable standard 8-pin DIP package

0.00025 V/V/°C Gain Drift vs. Temperature

0.3 mV input offset voltage

100 kHz bandwidth

0.004% non-linear

Global Safety Approvals: UL 1577 (3750 Vrms/1min) and CSA, IEC/EN/DIN EN 60747-5-2

Advanced Sigma-Delta (∑-∏) A/D converter technology

Fully Differential Circuit Topology

application

Motor Phase and Track Current Sensing

Inverter Current Sensing

Switching power supply signal isolation

Universal Current Sensing and Monitoring

General purpose analog signal isolation

NOTE: Non-chlorine activated flux is strongly recommended

The maximum time from 25 degrees Celsius to maximum temperature is 8 minutes.

Maximum temperature = 200 degrees Celsius, minimum temperature = 150 degrees Celsius

IEC/EN/DIN EN 60747-5-2 Insulation Characteristics[1]

notes:

1. Insulation characteristics are guaranteed only within the safe maximum ratings. It must be ensured by the protection circuit in the application. Surface mount is classified as Class A according to CECC0802.

2. For a detailed description of the method a and method b partial discharge test profile, please refer to the optocoupler section in the Designer's Catalogue of Isolation and Control Components, located in the Product Safety Regulations section (IEC/EN/DIN EN 60747-5-2) Down.

3. Refer to the figure below to understand the relationship between PS and ambient temperature.

DC Electrical Specifications

Unless otherwise noted, all types and figures are at nominal operating conditions, i.e.: VIN+=0, VIN-=0 V, VDD1=VDD2=5 V, TA=25°C; all min/max specifications are at within the recommended operating conditions.

AC Electrical Specifications

Unless otherwise noted, all types and figures are at nominal operating conditions, i.e.: VIN+=0, VIN-=0 V, VDD1=VDD2=5 V, TA=25°C; all min/max specifications are at within recommended operating conditions

notes:

General Notes: Typical values represent the average of all characterized devices under nominal operating conditions. Typical drift specifications are calculated by calculating the specified and drift parameters for each characteristic unit (under nominal operating conditions) and then averaging the individual unit prices. The corresponding drift graph is normalized under normal operating conditions to show how much drift has occurred due to particle drift parameters that differ from their nominal values. All other parameters remain at their nominal operating values. Note that the typical drift specifications in the table below may differ from the slope of the average curve shown in the corresponding graph.

1. Avago Technologies recommends at VIN-=0 V (connected to GND1). Limiting VIN+ to 100mV will improve DC nonlinearity and nonlinear drift. If the VIN is higher than VDD1–2 volts, the Perform Internal Test mode may be activated. This test mode is used to test the LED coupling and is not for customer use.

2. This is the absolute value of the input offset change versus temperature.

3. Gain is defined as the ratio of the slope of the differential output best-fit line voltage (VOUT+–VOUT-) to the differential input voltage (VIN+–VIN-) over the specified input range.

4. This is the absolute value of gain change versus temperature.

5. Nonlinearity is defined as half the peak-to-peak output deviation from the best matched gain line, expressed as a percentage of full-scale differential output voltage.

6. NL100 is a non-linear 00 mV specified within the input voltage range.

7. The input supply current decreases as the differential input voltage decreases (VIN+–VIN-) decreases.

8. Maximum specified output supply current occurs at differential input voltage (VIN+-VIN) = -200mV, maximum recommended operating input voltage. However, for up to about 300 mV, it exceeds its output supply current. constant.

9. The time average is shown because of the switched-capacitor characteristic conversion of the input sigma delta.

10. When the differential input signal exceeds approximately 308 mV, the output will be limited to the typical values shown.

11. Short circuit current is the amount of output current produced when the output is shorted to VDD2 or ground.

12.CMRR is defined as the ratio gain of a differential signal (signal applied differentially between pins 2 and 3) to common mode gain (input pins connected together and signal applied to both inputs), expressed in decibels .

13. Output noise comes from two main sources: chopper noise and sigma-delta quantization noise. Chopper noise originates from the chopper stabilization of the output op amp. It occurs at a frequency (usually 400 kHz at room temperature) that is not attenuated by the internal output filter. A filter circuit can easily be added to an external post-amp to reduce total rms output noise. An internal output filter removes sigma-delta quantization noise. The magnitude of the output quantization noise is very small at lower frequencies (below 10 kHz) and increases with frequency.

14. Common Mode Transient Immunity Rejection) Tested by applying an exponential rise/fall voltage step to Pin 4 (GND1) relative to Pin 5 (GND2). The rise time test waveform was set to approximately 50 nanoseconds. Amplitude adjustment steps until the differential output (VOUT+–VOUT-) deviates from the average output by more than 200 mV for more than 1 μs. If the applied common mode slope exceeds 10 kV/µs, the HCPL-7800(A) will continue to operate as long as the breakdown voltage limit is observed.

15. The datasheet value is when 1vpk-pk, 1MHz square wave, the rise and fall time of output VDD1 and VDD2 of HCPL-7800(A) are both 40 ns.

16. According to UL 1577, each optocoupler is proof tested by applying insulation test voltage ≥4500 Vrms for 1 second (leakage detection current limit, II-O≤5μA). This test is performed on a partial discharge 100% production test (method b) as per IEC/EN/DIN EN 60747-5-2 Insulation Characteristics Table.

17. Input and output instantaneous voltage for dielectric should not be interpreted as input and output rated voltage continuous rated voltage. For continuous rated voltage, please refer to the Insulation Characteristics table according to IEC/EN/DIN EN 60747-5-2 and your equipment level safety specifications.

18. This is a double-ended measurement: pins 1–4 are shorted together and pins 5-8 are shorted together.

application information

Power and Bypass

Recommended power connections are shown in the diagrams. A floating power supply (which in many applications can be used to drive high-side power transistors) uses a simple Zener diode (D1); the value of resistor R4 should be chosen from an existing floating supply of sufficient current. A current sense voltage resistor (Rsense) is applied to the input of the HCPL-7800 (A) through an RC antialiasing filter (R2 and C2). Although the application circuit is relatively simple, the recommendations should be followed to ensure best performance. The power supply of the HCPL-7800(A) is usually obtained from the same power supply as the power transistor gate drive circuit. In many cases it is possible to add additional windings to an existing transformer if it is a dedicated power supply. Otherwise, some simple isolated power source can be used, such as a line powered transformer or a high frequency DC-DC converter. An inexpensive 78L05 three-terminal regulator can also be used to reduce the floating supply voltage to 5 V to help attenuate high frequency supply noise or ripple, a resistor or inductor can be combined with the regulator's input to form a low pass filter at the regulator's input bypass capacitor.

As shown, the 0.1µF bypass capacitors (C1, C2) should be placed as close as possible to the HCPL-7800 (A). Bypass capacitors are required because of the high-speed digital nature of the internal signals of the HCPL-7800 (A). A bypass capacitor (C2) of 0.01µF is also recommended at the input due to the nature of the input circuit due to switched capacitors. Input bypass capacitors also form part of the antialiasing filter and are recommended to prevent high frequency noise from aliasing low frequency interfering input signals. The input filter also has an important reliability feature that reduces transient spikes caused by ESD events flowing through the current sense resistor.

PC board layout

The PCB design should follow good layout practices such as keeping bypass capacitors close to the power pins, keeping the output signal away from the input signal, ground and powered aircraft use, in addition, the PCB layout will also affect the HCPL-7800 (A) The isolation transient immunity (CMTI) is mainly due to the input and output circuits. For optimum CMTI performance, the PC board layout should minimize the distance between the input and output sides of the circuit for maximum possible stray coupling to ensure that any ground or power board on the PC does not pass directly below or extend wider than the main body of the HCPL-7800(A).

Current Sense Resistor

Current sense resistors should have low resistance (to minimize power dissipation), low inductance (to minimize possible pair of di/dt induced voltage spikes), and reasonable tolerance (to maintain overall circuit accuracy). Smaller sense resistors reduce power dissipation, while larger use sense resistors to improve circuit accuracy over the full input range of the HCPL-7800(A). The first step in selecting a sense resistor is to determine how much current the resistor will sense .The graph shows the three-phase asynchronous motor as a function of the average value of the motor output power (horsepower, hp) and the motor drive supply voltage. The maximum value of the resistance is determined by the measured current and the recommended input voltage is the isolation amplifier. The maximum The sense resistor can be calculated in the way mom recommends dividing the input voltage divided by the sense resistor you should see in normal operation. For example, if the motor has a maximum rms current of 10 A, in normal operation the peak current is 21.1 A (=10 x 1.414 x 1.5). Assuming a maximum input voltage of 200MV, the maximum value of the sense resistor in this case is approximately 10 mΩ.

The maximum average power dissipation in the sense of the resistor can also be calculated by multiplying the sense resistor by the maximum rms squared current, which in the previous example was about 1W. If the power dissipation of the sense resistor is too high, the resistor can be lowered below the maximum value to reduce power dissipation. The design accuracy and precision requirements of the minimum sense resistor are limited. When the resistor value is reduced, the output voltage of the resistor is also reduced, which means that the offset and noise are fixed, becoming a larger scale signal amplifier. The value chosen for this sense resistor will fall between the minimum and maximum values, depending on the specific requirements for the particular design. When a sufficiently large current is sensed to cause heating of the sense resistor, the temperature coefficient of the resistor (tempco) introduces nonlinearity due to the signal-dependent temperature rise of the resistor. The effect of this resistance on ambient thermal resistance increases as the resistance increases. By reducing the thermal resistance of the current sense resistor or using a cooler resistor. Lowering the thermal resistance can be achieved by repositioning the current sense resistors on the PC board, using larger PC board traces to carry more heat away, or using a heat sink.

For a two-terminal current sense resistor, as the resistance decreases, the lead resistance decreases as a significant percentage of the total resistance. This has two main effects on resistor accuracy. First, the effective resistance of the sense resistors can become dependent on factors such as how far they are bent, how far they are inserted into the board, and how attractive the solder is to the leads during assembly (more on these issues later) ). Second, the leads are usually made of a material, such as copper, which is hotter than the material of the resistive element itself, resulting in a higher overall temperature.

when using current sense resistors for the four terminals. A four-terminal resistor has two additional terminals connected to Kelvin directly through the resistive element itself; these two terminals are used to monitor the resistive element when the other two terminals are used to carry the load current. Because of the Kelvin correlation, the voltage drop across the load current leads has no effect on the measured voltage. When laying out PC boards for current sensing resistors, there are a few things to keep in mind. This should connect the Kelvin to the resistors together under the resistor body and then run the inputs of the HCPL-7800(A) close to each other; this minimizes the loop area of the connection and reduces the possibility of stray magnetic fields interfering with the signal under test. If the sense resistor is not on the same PC board as the HCPL-7800(A) circuit, a tight twisted pair will do the same thing. Additionally, multiple layers of PC boards can be used to increase the ampacity. There should be many through-hole plates around each non-Kelvin terminal to help in layers on the PC board. The PC board should use a 2 or 4 oz copper layer resulting in a current carrying capacity in excess of 20 A. Making sizable traces on the current-carrying PC board can also improve the power dissipation capability of the sense resistor heatsink. The free use of the load current into the via and it is recommended to exit the PC board.

Sense Resistor Connection

Recommended way to connect HCPL - Current Sense Resistor 7800 (A) as shown. VIN+ (pin 2 of the HPCL-7800 (A)) is connected to the positive terminal of the sense resistor, while VIN- (pin 3) shorts the power supply to GND1 (pin 4) return path as the negative sense line of the current sense resistor terminal. This connects a pair of wires or PC board traces from the HCPL - to the 7800(A) circuit of the sense resistor. By referencing the input circuit of the negative side of the sense resistor, any noise transients caused by load current across the resistor are treated as common-mode signals and will not interfere with the current sensed signal. This is important because the large load currents flowing through the motor drive, as well as the circuit wiring, can create noise spikes and voltage sense resistors measured in current with relatively large offsets compared to smaller offsets. If both gates use the same power drive circuit and current sense circuit it is important that the connection from GND1 of the HCPL -7800 (A) to the sense resistor is in order to supply the gate drive power to eliminate potential ground loop problems. The only direct connection between the HCPL-7800(A) circuit gate drive circuit should be the positive power supply line. The op amp in the external post-amplifier circuit at the output should be accurate enough to cause a substantial offset or offset drift contribution relative to the isolation amplifier. Typically, a bipolar input stage op amp is preferred over a JFET or MOSFET input stage. In addition, the op amp should also have sufficient bandwidth and slew rate so that it does not affect the response speed of the entire circuit. The post-amplifier circuit includes a pair of capacitors (C5 and C6) to form a single-pole low-pass filter; these capacitors allow the post-amplifier's bandwidth to be adjusted independently of the gain, helping to reduce the output noise of the isolation amplifier. Different op amps can be used in many circuits, including: MC34082A (Motorola), TLO32A, TLO52A and TLC277 (Texas Instruments), LF412A (National Semiconductor). The gain setting resistors in the post amp should have a tolerance of 1% or better to ensure adequate CMRR and adequate gain for the entire circuit. Resistors can use a network with better ratio tolerance than using discrete resistors. A resistor network also reduces the total number of components in the circuit and the required board space.

1.1: Why should I use the HCPL-7800(A) to sense current when Hall Effect Sensors are not available Do I need to isolate the supply voltage? Offered in an automatic drop-in 8-pin dip pack, the HCPL-7800(A) is smaller than the HCPL-7800(A), has better linearity, and outperforms most Hall effect sensors in offset versus temperature and common mode rejection (CMR). In addition, it is often required that the input side power supply can be obtained from the same power supply as the gate drive optocoupler.

2. Sense Resistor and Input Filter

2.1: Where can I get a 10 mΩ resistor? I've never seen it that low. Although lower than values above 10Ω, there are many resistor manufacturers suitable for use with the HCPL-7800(A). Example product information may be found on Dell's website (/vishay)/ and Isotek's website ().

2.2: Should I connect the two inputs to the sense resistor instead of ground VIN - directly to pin 4? It's not necessary, but it will work. If yes, be sure to use an RC filter on pin 2 (VIN+) and pin 3 (VIN-) to limit the input voltage to both pads.

2.3: Do I really need to add an RC filter to the input? This is how the same thing? for what? Are other values of R and C ok? The input antialiasing filter shown (R=39Ω, C=0.01µF) is recommended for filtering fast switching voltage transients from the input in typical applications. (This helps attenuate higher signal frequencies that would otherwise mess with the input sample rate and result in higher input offset voltages.) A few issues to be aware of with different filter resistors or capacitors are:

1. Filter Resistor: Input Bias Current for Pin 2 and Pin 3: This is about 500 nanometers. If you are using a filter resistor in series with IxR's pin 2 instead of pin 3 the voltage drop across the resistor will increase the device. As long as this IR drop is small the input offset voltage should not be a problem. If using large value resistors in series, it is best to put half the resistor in series with pin 2 and half the resistor in series with pin 3. In this case, the offset voltage is primarily the mismatch caused by the resistor (usually less than 1% of the resistor's design value) multiplied by the input offset.

2. Filter resistance: The equivalent input resistance HCPL-7800 (A) is about 500 kΩ. It is therefore best to ensure that the filter resistance is not significant as a percentage of this value; otherwise the offset voltage will increase through the resistor divider effect. [For example, if Rfilt = 5.5 kΩ, then VOS = (VIN * 1%) = 2 mV for a maximum 200 mV input and VOS will be related to VIN. ]

3. The input bandwidth therefore changes for different RC filter configurations. In fact this is a major time constant for changing the RC of the input filter.

4. Filter capacitor: The input capacitor HCPL-7800 (A) is about 1.5 pF. For proper operation, the sampling capacitor on the digital input side must be sourced from a relatively fixed (low impedance) voltage. Therefore, if the filter uses a capacitor preferably a value of at least 100 pF a few orders of magnitude larger than the Simpter it works well. )

2.4: How to ensure that the HCPL-7800(A) will not be damaged by a short circuit Does the voltage drop across the sensing resistor exceed the rating of the HCPL-7800(A) input? Choose the sense resistor so that its voltage is less than 5 V when shorted. The only other requirement is to shut down the driver before the sense resistor is damaged or the solder joint melts. This ensures that the input of the HCPL-7800(A) cannot be damaged by the sensor open circuit resistor.

3. Isolation and Insulation

3.1: How many volts can the HCPL-7800 (A) withstand? Instantaneous (1 minute) withstand voltage of 3750 V rms #5 per UL 1577 and CSA Parts Acceptance Notice.

4. Accuracy

4.1: Can the signal-to-noise ratio be improved? right. Some noise energy is present over 100 kHz. Bandwidth of the HCPL-7800(A). Additional filtering using different filters in the post-amplifier R, C value application circuit can be used to improve the signal-to-noise ratio. For example, using a value of R3 = R4 = 10 kΩ, C5 = C6 = 470 pF (in the application circuit) rms output noise will be reduced by approximately a factor

2. Better noise performance can be obtained in applications requiring only a few kilohertz bandwidth. This noise spectral density is approximately 500 nV/šHz below 20 kHz (reference input).

4.2: If the internal LED light outputs, does the gain change degrade over time? Do not. LEDs are only used to transmit digital patterns. Avago Technology has explained the causes of LED degradation and the product is designed to guarantee a long lifetime.

5. Power and Startup

5.1: What is the output voltage on the input side before the power supply is turned on? VO+ is close to 1.29 V and VO- is close to 3.80 V. This is equivalent to the output response LED completely turning off under the following conditions.

5.2: How long does it take for the HCPL-7800(A) to work normally after it is powered on? VDD1 and VDD2 start working within 1 ms after power-up. But it takes a long time for the output to settle down completely. In the case of offset measurements there is initially a VOS adjustment (~60 ms) when both inputs are grounded. The output is fully stable and the device turns off within 100ms of power-up.

6. Miscellaneous

6.1: How does the HCPL-7800 (A) measure the negative signal with only +5V power supply? There is a series resistor on the input to protect the large negative input. The normal signal is no more than 200 mV amplitude. Such signals are not forward biased enough to interfere with the operation of the junction-point switched capacitor input circuit for accuracy.