Isolating Amplifiers, Analog Devices
Small Size: 4 Channels/lnch
Low Power: 35 mW (AD204)
High Accuracy: 0.025% Max Nonlinearity (K Grade)
High CMR: 130 dB (Gain = 100 V/V)
Wide Bandwidth: 5 kHz Full-Power (AD204)
High CMV Isolation: 2000 V pk Continuous (K Grade)
(Signal and Power)
Isolated Power Outputs
Uncommitted Input Amplifier
Multichannel Data Acquisition
Current Shunt Measurements
Process Signal Isolation
High Voltage Instrumentation Amplifier
The AD202 and AD204 are general purpose, two-port, transformer-coupled isolation amplifiers that may be used in a broad range of applications where input signals must be measured, processed, and/or transmitted without a galvanic connection. These industry standard isolation amplifiers offer a complete isolation function, with both signal and power isolation provided for in a single compact plastic SIP or DIP style package. The primary distinction between the AD202 and the AD204 is that the AD202 is powered directly from a 15 V dc supply while the AD204 is powered by an externally supplied clock, such as the
recommended AD246 Clock Driver. The AD202 and AD204 provide total galvanic isolation between the input and output stages of the isolation amplifier through the use of internal transformer-coupling. The functionally complete AD202 and AD204 eliminate the need for an external, user-supplied dc-to-dc converter. This permits the designer to minimize the necessary circuit overhead and consequently reduce the overall design and component costs.
The design of the AD202 and AD204 emphasizes maximum flexibility and ease of use, including the availability of an uncommitted op amp on the input stage. They feature a bipolar ±5 V output range, an djustable gain range of from 1V/V to 100 V/V, ± 0.025% max nonlinearity (K grade), 130 dB of CMR, and the AD204 consumes a low 35 mW of power. The functional block diagrams can be seen in Figures 1a and 1b.
The AD202 and AD204 are full-featured isolators offering numerous benefits to the user:
Small Size: The AD202 and AD204 are available in SIP and DIP form packages. The SIP package is just 0.25″ wide, giving
the user a channel density of four channels per inch. The isolation barrier is positioned to maximize input to output spacing. For applications requiring a low profile, the DIP package provides a height of just 0.350″.
High Accuracy: With a maximum nonlinearity of ±0.025% for the AD202K/AD204K (±0.05% for the AD202J/AD204J) and low drift over temperature, the AD202 and AD204 provide high isolation without loss of signal integrity.
Low Power: Power consumption of 35 mW (AD204) and 75 mW (AD202) over the full signal range makes these isolators ideal for use in applications with large channel counts or tight power budgets.
Wide Bandwidth: The AD204’s full-power bandwidth of 5 kHz makes it useful for wideband signals. It is also effective in applications like control loops, where limited bandwidth could result in instability.
Excellent Common-Mode Performance: The AD202K/ AD204K provide ±2000 V pk continuous common-mode isolation, while the AD202J/AD204J provide ±1000 V pk continuous common-mode isolation. All models have a total common-mode input capacitance of less than 5 pF inclusive of power isolation. This results in CMR ranging from 130 dB at a gain of 100 dB to 104 dB (minimum at unity gain) and very low leakage current (2 mA maximum).
Flexible Input: An uncommitted op amp is provided at the input of all models. This provides buffering and gain as required, and facilitates many alternative input functions including filtering, summing, high voltage ranges, and current (transimpedance) input.
Isolated Power: The AD204 can supply isolated power of ±7.5 V at 2 mA. This is sufficient to operate a low-drift input preamp, provide excitation to a semiconductor strain gage, or power any of a wide range of user-supplied ancillary circuits. The AD202 can supply ±7.5 V at 0.4 mA, which is sufficient to operate adjustment networks or low power references and op amps, or to provide an open-input alarm.