feature

Isolation Voltage Rating: 1500 V rms; Broadband: 120 kHz, Full Power (–3 dB); Fast Slew Rate: 6 V/ms; Fast Settling Time: 9ms; Low Harmonic Distortion: –80 dB@1 kHz; Low nonlinearity: 60.005%; wide output range: 610 V, min (buffered); built-in isolated power supply: 615V dc@610mA; performance level between -408C to +858C.

Applications include: high-speed data acquisition systems; power line and transient monitors; multi-channel, multiple-input isolation; waveform recording instrumentation; power control; vibration analysis.

General Instructions

The AD215 is a high-speed input isolation amplifier for isolating and amplifying wideband analog signals. The innovative circuit and transformer design of the AD215 ensures wideband dynamic characteristics while retaining critical DC performance specifications.

The AD215 provides complete galvanic isolation between the input and output of the device, including a user-available front-end isolated power supply. A fully functional design powered by ±15V DC power without the need for a user-supplied isolated dc/dc converter. This allows designers to minimize circuit overhead and reduce overall system design complexity and component cost.

The AD215 is designed to emphasize maximum flexibility and ease of use in a wide range of applications where high analog signals must be measured at high common mode voltage (CMV). The AD215 features a ±10 V input/output range, a specified gain range of 1 V/V to 10 V/V, a buffered output with offset trim, and a user-available isolated front-end power supply that generates ±15 V DC at ±10 mA .

Product Highlights

High-speed dynamics: The AD215 has a typical full-power bandwidth of 120 kHz (100 kHz min), a rise time of 3 μs, and a settling time of 9 μs. The high-speed performance of the AD215 allows unmatched galvanic isolation of virtually any wideband dynamic signal.

Flexible Input and Buffered Output Stages: An uncommitted op amp is provided on the input stage of the AD215 to allow input buffering or amplification and signal conditioning. The AD215 also features a buffered output stage for driving low impedance loads and output voltage trim for zeroing the output offset when needed.

High Accuracy: The AD215 has a typical nonlinearity of ±0.005% of full-scale range (Class B) and a typical total harmonic distortion of -80 dB at 1 kHz. The AD215 provides the designer with complete isolation of the desired signal without loss of signal integrity or quality.

Excellent Common Mode Performance: The AD215BY (AD215AY) provides 1500 V rms ( 750 V rms) common mode voltage protection from input to output. Both grades feature low common-mode capacitance of 4.5 pF, including dc/dc power isolation. This results in a typical common mode rejection specification of 105db with a low leakage current of 2.0µa rms max (240v rms, 60hz).

Isolated Power: The isolated input port of the AD215 provides ±15 V dc@±10 mA of unregulated isolated power. This allows the use of auxiliary isolated front-end amplifiers or signal conditioning components without the need for a separate dc/dc power supply. Even sensor excitation can be implemented in most applications.

Rated Performance Over -40C to +85C Temperature Range: With an extended industrial temperature range rating, the 88AD215 is an ideal isolation solution for use in many industrial environments.

AD215 internal

The AD215 is a completely self-contained analog signal and power isolation solution. It uses double-balanced amplitude pairs for frequencies ranging from true DC values to frequencies up to 120 kHz. To generate the power supply circuit for the isolated front end, the internal clock oscillator drives T2 of the main winding across the DC/DC power transformer. This resultant voltage generated through the secondary winding is then rectified and filtered for use as an isolated power supply.

This built-in isolated dc/dc converter provides sufficient power for the two internal isolated circuit components of the AD215 as well as any auxiliary components provided by the user. It saves onboard space and component costs that require additional amplification or signal conditioning. After the input signal is amplified by an uncommitted op amp, it is modulated at a carrier frequency of approximately 430 kHz. Primary winding transformer T1 for signal isolation. The signal generated on the secondary winding is then demodulated and filtered on the transformer using a low-pass Bessel response filter set at a frequency of 150 kHz. The function of the filter is to reconstruct what is present at the input.

The design and construction of the signal transformer allows the nonlinearity to be independent of the specified temperature and to obtain a range. After full reconstruction, the signal goes through an offset trim stage and a final output buffer. The trimming circuit allows the designer to adjust any offset as needed.

Performance Characteristics - AD215

Powering the AD215

The AD215 is powered by a bipolar ±15V DC power supply, as shown in Figure 11. External bypass capacitors should be provided in bus applications. Note that a small current (50mA/V) associated with the signal will flow from the out LO pin (pin 37). Therefore, the OUT LO terminals should be bus-connected together and referenced to a ±15 V dc common supply at a single "analog star ground" as shown in Figure 11.

Power Supply Voltage Considerations

The rated performance of the AD215 is not affected when the supply voltage is in the range of ±14.5 V dc to ±16.5 V dc. Voltages below ±14.25 V dc may cause the AD215 to stop functioning properly.

Note: Supply voltages greater than ±17.5 V dc may damage internal components and should not be used.

Using AD215

Unity Gain Input Configuration

Figure 12 shows the basic unity-gain configuration for input signals up to ±10 V.

Non-vertical configuration with gain greater than unity Figure 13 shows how a gain greater than 1 can be achieved while maintaining a very high input impedance. The recommended PC board layout for multi-channel applications is shown in Figure 20b.

In this circuit, the gain equation is as follows:

Where: VO=output voltage (V); VSIG=input signal voltage (V); RF=feedback resistor value (Ω) RG=gain resistor value (Ω); the values of resistors RF and RG are subject to the following restrictions:

(1) The total impedance of the gain network should be less than 10 kiloohms.

(2) At ±10 V, the RF current is less than 1 mA. Note that the power supply drive capability is reduced by 1 mA for each mA drawn for the feedback resistor.

(3) The amplifier gain is set by the feedback (RF) and gain resistors (right).

A 47 pF capacitor is recommended to bypass the RF display.

Note: A 2 kΩ input resistor (RIN) in series with the input is recommended to use the source and input + terminals in Figures 12 and 13 to limit the current at the input terminals of the AD215 to 5.0 mA when unpowered.

Compensate for uncommitted input op amps

Figure 14 shows the open-loop gain and phase versus frequency for an uncommitted input op amp. These curves can be used to determine appropriate values for the feedback resistor (RF) and compensation capacitor (CF) to ensure frequency stability when reactive or nonlinear components are used.

Invert, sum or current input configuration

Figure 14 shows how the AD215 measures current or the sum of current or voltage.

For this circuit, the output voltage equation is:

Where: V=output voltage (V); VS1=input voltage signal 1 (V); VS2=input voltage signal 2 (V); IS=input current source (A); RF=feedback resistance (Ω) (10 kΩ, Typical value); RS1 = input signal 1 source resistance (Ω) RS2 = input signal 2 source resistance (Ω).

The circuit of Figure 15 can also be used when the input signal is greater than the ±10V input range of the isolator. For example, in Figure 15, if only VS1, RS1, and RF are connected with solid lines as shown, the input voltage span of VS1 can accommodate up to ±50 V when RF = 10 kΩ and RS1 = 50 kΩ.

Gains and Offset Adjustments General Comments

The AD215 features an output stage trim pin that can be used to zero the output offset voltage using user-supplied circuitry.

When gain and offset adjustments are required, the actual compensation circuit that is ultimately used depends on the following:

(1) The input configuration mode of the isolation amplifier (non-inverting or inverting).

(2), the position of any adjustment potentiometer (on the input or output side of the isolator).

Generally speaking:

(1) The gain adjustment should be done on the gain setting resistor network at the input end of the isolator.

(2) To ensure the stability of gain adjustment, the potentiometer should be as close as possible to the input of the isolator, and its impedance should be kept low. The adjustment range should also be kept to a minimum, as its resolution and stability depend on the actual potentiometer used.

(3) If during the adjustment process, due to the existence of high common-mode voltage, adjusting the potentiometer placed near the input end will cause harm to the user, output adjustment may be required.

(4) It is recommended to perform input offset adjustment before obtaining adjustment.

The AD215 should be allowed to warm up for about 10 minutes before making gain or offset adjustments.

Input Gain Adjustment for Non-Vertical Mode Figure 16 shows the proposed non-rotational gain adjustment circuit. Note that the gain adjustment potentiometer RP is incorporated into the gain setting resistor network.

Gain adjustment for non-vertical configurations within ±1% trim:

Input Gain Adjustment for Inverted Mode

Figure 17 shows the proposed reverse gain adjustment circuit.

In this circuit, gain adjustment is achieved by using a potentiometer (RP) in the feedback loop. These adjustments are valid for all gains in the 1 to 10 V/V range.

For approximately ±1% gain trim range,

Then choose:

Although:

Note: RF and RIN should have matched temperature coefficient drift characteristics.

Output offset adjustment

Figure 18 illustrates one method of adjusting the output offset voltage. Since the AD215 has a nominal output offset of –35 mV, the circuit shown was chosen to produce an offset correction of 0 mV to +73 mV. This results in a total output offset range of approximately 35 mV to +38 mV.

output gain adjustment

Since the output amplifier stage of the AD215 is fixed at unity gain, any adjustments can only be made in subsequent stages.

Use isolated power

Each AD215 provides an unregulated, isolated, bipolar supply of ±15 VDC at ±10 mA, called the input common. This power supply can be used to power various auxiliary components such as signal conditioning and/or conditioning circuits, references, operational amplifiers or remote sensors. Figure 19 shows a typical connection.

PCB layout for multi-channel applications

The pins of the AD215 are designed to facilitate multi-channel applications. Figure 20a shows the recommended board layout for a unity gain configuration.

be careful

The AD215 is not designed to provide short-circuit protection for isolated power supplies. A current limiting resistor should be placed in series with the power terminals and the load to prevent accidental short circuits.

When using gain setting resistors, the 0.325" channel center can still be achieved, as shown in Figure 20b.

Application Example Motor Control

Figure 21 shows the AD215 used in a DC motor control application. Its excellent phase characteristics and wide frequency band are ideal for this type of application.

Multiplex data acquisition

The current drive capability of the AD215 bipolar ±15V DC isolated power supply is sufficient to meet the modest ±800µA supply current requirement of the AD7502 multiplexer. The enable (EN), A0, and A1 logic control signals should be isolated using digital isolation techniques.

AC Sensor Applications

In applications such as vibration analysis, where the user must acquire and process the spectral content of the sensor signal, rather than its "DC" level, the wideband nature of the AD215 proves to be most useful. Key specifications for AC drive applications include bandwidth, slew rate, and harmonic distortion. Since sensors may be mechanically attached or soldered to the object under test, isolation is often required to eliminate ground loops and protect the electronics used in the data acquisition system. Figure 23 shows an isolated strain gauge circuit using the AD215 and a high-speed op amp (AD744).

To reduce the need for instrumentation amplifiers, the bridge is powered by a bipolar excitation source. Under this approach, the common-mode voltage is ±VSPAN, typically only a few millivolts, instead of the VEXC42 implemented with a unipolar excitation source and a Wheatstone bridge structure.

Using two strain gauges with a measurement factor of 3 mV/V and an excitation signal of ±1.2 V will produce an output signal of ±6.6 mV. A gain setting of 454 will amplify this low-level signal to ±3V, which can then be digitized by a high-speed, 100kHz sampling ADC such as the AD7870.

Low-voltage excitation is used to allow the front-end circuitry to be powered by the isolated power supply of the AD215, which can provide up to ±10mA of isolated power at ±15V. The bridge consumes only 3.5mA, leaving enough current to power the micropower bimodal amplifier (400µA quiescent current) and the high-speed AD744 bimodal amplifier (4mA quiescent current).

Dimensions

Dimensions are in inches and (mm).