AN614

6

Rev. 0.2

3. Application Examples

The electrocardiograph (ECG) application shown in Figure 6 requires safety isolation to protect the patient from

dangerous leakage currents. Medical applications of this type typically use conductive gels at sensor sites, which

lower human body impedance to the extent that a few milliamps of leakage current can cause injury or death. To

mitigate this issue, ECGs typically have multiple stages of isolation to prevent downstream leakage current from

flowing into the patient. The ECG of Figure 6 shows the patient connected to an instrumentation amplifier powered

by a low-current floating supply, V1. The ISOlinear circuit (shown as a functional block in the center of the diagram)

galvanically isolates the instrumentation amplifier input side from potential down-stream leakage currents

generated by the voltage source, V2. The lower voltage, higher-current DSP circuit is also isolated from the ADC/

filter circuit by a separate Si86xx digital isolator, again to ensure no leakage current paths into the ECG inputs.

Figure 6. ECG (Safety Isolation) Application

V2

Filter(s)

Si86xx

Isolator

Instrumentation 

Amplifier

ADC

To DSP

Right Leg Driver

V1

ISOlinear 

Reference Design

FG

FG

V3