HCPL 7850 PDF

Hermetically Sealed Analog Isolation Amplifier. Data Sheet. When used with a shunt resistor to monitor the motor. These devices consist of a sigma-delta analog-to-. The products.

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Dt Sheet. When used with a shunt resistor to monitor the motor phase current in a high speed motor drive, the device will offer superior reliability compared with the traditional solutions such as current transformers and Hall-effect sensors. The products are capable of operation and storage over the full military temperature range and can be purchased as either commercial product or with full MIL-PRF Class H testing or from the appropriate DSCC drawing.

Hermetic Optocoupler Options Option Description Surface mountable hermetic optocoupler with leads trimmed for butt joint assembly. This option is available on commercial and hi-rel product in 8 pin DIP see drawings below for details. This option is available on commercial and hi-rel product in 8 pin DIP. DSCC Drawing part numbers contain provisions for lead finish.

This option has solder dipped leads. VOS 1,2,3 —1. Units Test Conditions Fig. Symbol Group A[12] Subgroups Min. Units 8 Test Conditions Fig. Notes: 1. This test mode is not intended for customer use. Exact offset value is dependent on layout of external bypass capacitors. 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.

CMRRIN is defined as the ratio of the gain for differential inputs applied between pins 2 and 3 to the gain for both common mode inputs applied to both pins 2 and 3 with respect to pin 4. 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. Agilent does not recommend operations under these conditions.

CMR also known as IMR or Isolation Mode Rejection specifies the minimum rate of rise of a common mode signal applied across the isolation boundary at which small output perturbations begin to occur. These output perturbations can occur with both the rising and falling edges of the common mode waveform and may be of either polarity. A CMR failure is defined as a perturbation exceeding mV at the output of the recommended application circuit Figure See Applications section for more information on CMR.

Output noise comes from two primary sources: chopper noise and sigma-delta quantization noise. Chopper noise results from chopper stabilization of the output op-amps. It occurs at a specific frequency typically kHz and is not attenuated by the on-chip output filter. The on-chip filter does eliminate most, but not all, of the sigma-delta quantization noise. An external filter circuit may be easily added to the external post-amplifier to reduce the total RMS output noise.

See Applications section for more information. Device considered a two-terminal device: Pins 1, 2, 3, and 4 are shorted together and pins 5, 6, 7, and 8 are shorted together. Parameters are tested as part of device initial characterization and after design and process changes only.

Parameters are guaranteed to limits specified for all lots not specifically tested. Input Offset Change vs. Input Offset Voltage Test Circuit. Output Voltages vs. Input Voltage.

Gain and Nonlinearity Test Circuit. Gain Change vs. Nonlinearity Error Plot vs. Nonlinearity vs. Full-Scale Input Voltage. Input Current vs. Input Supply Current vs. Output Supply Current vs. Figure Common Mode Rejection Test Circuit. Input and Output Supply Current vs. Amplitude Response vs. Recommended Application Circuit Bandwidth. Recommended Application Circuit. R4 A floating power supply which in many applications could be the same supply that is used to drive the high-side power transistor is regulated to 5 V using a simple three-terminal voltage regulator U1.

And finally, the differential output of the isolation amplifier is converted to a ground-referenced Applications Information Functional Description Figure 23 shows the primary functional blocks of the HCPL In operation, the sigmadelta modulator converts the analog input signal into a highspeed serial bit stream.

The time average of this bit stream is directly proportional to the input signal. This stream of digital data is encoded and optically transmitted to the detector circuit. The detected signal is decoded and converted back into an analog signal, which is filtered to obtain the final output signal.

Although the application circuit is relatively simple, a few recommendations should be followed to ensure optimal performance. Supplies and Bypassing As mentioned above, an inexpensive three-terminal regulator can be used to reduce the gate-drive power supply voltage to 5 V.

VOUT Single-Supply Post-Amplifier Circuit. VDD 5. As shown in Figure 24, a 0. The bypass capacitors are required because of the highspeed digital nature of the signals inside the isolation amplifier.

The input bypass capacitor should be at least pF to maintain gain accuracy of the isolation amplifier. Inductive coupling between the input power-supply capacitor and the input circuit, including the input bypass capacitor and the input leads of the HCPL, can introduce additional DC offset in the circuit. Several steps can be taken to minimize the mutual coupling between the two parts of the circuit, thereby improving the offset performance of the design.

Separate the two bypass capacitors C2 and C3 as much as possible even putting them on opposite sides of the PC board , while keeping the total lead lengths, including traces, of each bypass capacitor less than 20 mm. PC board traces should be made as short as possible and placed close together or over ground plane to minimize loop area and pickup of stray magnetic fields.

Avoid using sockets, as they will typically increase both loop area and inductance. And finally, using capacitors with small body size and orienting them perpendicular to each other on the PC board can also help. The value of the shunt should be chosen as a compromise between minimizing power dissipation by making the shunt resistance smaller and improving circuit accuracy by making it larger and utilizing the full input range of the HCPL Agilent Technologies recommends four different shunts which can be used to sense average currents in motor drives up to 35 A and 35 hp.

Table 1 shows the maximum current and horsepower range for each of the LVR-series shunts from Dale. Even higher currents can be sensed with lower value shunts available from vendors such as Dale, IRC, and Isotek Isabellenhuette. When sensing currents large enough to cause significant heating of the shunt, the temperature coefficient of the shunt can introduce nonlinearity due to the signal dependent temperature rise of the shunt. Using a heat sink for the shunt or using a shunt with a lower tempco can help minimize this effect.

The Application Note , Designing with Agilent Technologies Isolation Amplifiers, contains additional information on designing with current shunts. The recommended method for connecting the isolation amplifier to the shunt resistor is shown in Figure This allows a single pair of wires or PC board traces to connect the isolation amplifier circuit to the shunt resistor. In some applications, however, supply currents flowing through the power-supply return path may cause offset or noise problems.

In this case, better performance may be obtained by connecting pin 3 to the negative terminal of the shunt resistor separate from the power supply return path. When connected this way, both input pins should be bypassed.

Whether two or three wires are used, it is recommended that twisted-pair wire or very close PC board traces be used to connect the current shunt to the isolation amplifier circuit to minimize electromagnetic interference to the sense signal. The resistor performs another important function as well; it dampens any ringing which might be present in the circuit formed by the shunt, the input bypass capacitor, and the wires or traces connecting the two.

Undampened ringing of the input circuit near the input sampling frequency can alias into the baseband producing what might appear to be noise at the output of the device.

PC Board Layout In addition to affecting offset, the layout of the PC board can also affect the common mode rejection CMR performance of the isolation amplifier, due primarily to stray capacitive coupling between the input and the output circuits.

To obtain optimal CMR performance, the layout of the printed circuit board PCB 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 plane on the PCB does not pass directly below the HCPL Using surface mount components can help achieve many of the PCB objectives discussed in the preceding paragraphs.

An example throughhole PCB layout illustrating some of the more important layout recommendations is shown in Figures 26 and To maintain overall circuit bandwidth, the post-amplifier circuit should have a bandwidth at least twice the minimum bandwidth of the isolation amplifier, or about kHz. To obtain a bandwidth of kHz with a gain of 5, the op-amp should have a gain-bandwidth greater than 1 mHz.

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 doubling the capacitor values halves the circuit bandwidth. The component values shown in Figure 24 form a differential amplifier with a gain of 5 and a cutoff frequency of approximately kHz, and were chosen as a compromise between low noise and fast response times.

The overall recommended application circuit has a bandwidth of 66 kHz, a rise time of 5. Post-Amplifier Circuit The recommended application circuit Figure 24 includes a post-amplifier circuit that serves three functions: to reference the output signal to the desired level usually ground , to amplify the signal to appropriate levels, and to help filter output noise.

The particular op-amp used in the post-amp is not critical; however, it should have low enough offset and high enough bandwidth and slew rate so that it does not adversely affect circuit performance.

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HCPL 7850 PDF

Learn more — opens in new window or tab. Redeem your points Conditions for uk nectar points — opens in a new window or tab. Add to Watch list Watching. Learn more — opens in a new window or tab. Notes: 1. This test mode is not intended for customer use. Exact offset value is dependent on layout of external bypass capacitors.

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