Analog Devices’ AD215

Isolated amplifier

Galvanic insulation is God‘s gift to man – whether optocoupler or light waveguide line, being able to transfer things without creating a physical connection is extremely valuable. Sadly, most optocouplers are not particularly smart – an aspect Analog Devices seeks to change.

Given that the AD215 is quite complex, let us start out by looking at the block diagram shown in figure 1

The AD215 contains a set of largely independent parts

First of all, a supply of both positive and negative 15V is expected. The chip chops it up and hunts the signal over a power isolator, which generates an external isolated voltage supplies. It can then be used to power sundry components which can live with its maximum output of about 10mA.

Secondarily, the main modulator chain is in place. It is responsible for the actual galvanic decoupling and handles signal frequencies of up to 120kHz.

The interesting aspect of the part is that the input to the modulator chain is not a normal buffer – instead, Analog Devices provides users with a full-blown operational amplifier and its feedback pin. That way, the chip can be used to simplify signal conditioning circuits based on operational amplifiers – some can even be created without adding additional components to the system.

Small-scale sensor conditioning – think about small applications which do not demand more than an inverting or a noninverting buffer – can be created without a dedicated Opamp.

Analog Devices long design heritage leads to an excellent datasheet: the twelve pages found here provide four pages worth of schematics and implementation examples.

Return of the SIP

Our AD215 most definitely is not a cheap part – the OEMsecrets best price starts out at around €35, with significant spreads making this one component where price comparisons are really really important. However, the SIP casing, shown in the figure, is easy to integrate – due to its through-hole design, it can be soldered by hand with ease.

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