+V

S1

+V

S2

Gnd

Gnd

V

IN

V

OUT

–V

S1

±V

S1

±V

S2

–V

S2

1µF

1µF 1µF

1µF

Isolation Barrier

ISO124

19

ISO124

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SBOS074E – SEPTEMBER 1997 – REVISED JUNE 2018

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Copyright © 1997–2018, Texas Instruments Incorporated

9 Power Supply Recommendations

9.1 Signal and Supply Connections

Each power-supply pin should be bypassed with 1-µF tantalum capacitors located as close to the amplifier as

possible. The internal frequency of the modulator/demodulator is set at 500 kHz by an internal oscillator.

Therefore, if it is desired to minimize any feedthrough noise (beat frequencies) from a DC-DC converter, use a π

filter on the supplies (see Figure 10). The ISO124 output has a 500-kHz ripple of 20 mV, which can be removed

with a simple 2-pole low-pass filter with a 100-kHz cutoff using a low-cost op amp (see Figure 10).

The input to the modulator is a current (set by the 200-kΩ integrator input resistor) that makes it possible to have

an input voltage greater than the input supplies, as long as the output supply is at least ±15 V. It is therefore

possible, when using an unregulated DC-DC converter, to minimize PSR related output errors with ±5-V voltage

regulators on the isolated side and still get the full ±10-V input and output swing.

Figure 24. Basic Signal and Power Connections