Datasheet Si8931/32 (Silicon Labs) - 5

Si8931/32 Data Sheet Voltage Sense Application
3. Voltage Sense Application
A typical isolated voltage sensing application circuit is shown below. In this example, a high voltage is divided down to produce a volt- age (VIN) within the optimum input signal range of the Si8931/32. Numerous alternative inputs configurations are possible with the flexi- bility of a high impedance input isolator. The Si8931 senses the single-ended input voltage and reproduces it as a differential (or single- ended with the Si8932) output voltage across the galvanic isolation barrier. The Si8931 differential outputs (AOP, AON) can be routed directly to a differential ADC as shown below. The Si8932 senses the single-ended input voltage and reproduces it as a single-ended output voltage across the galvanic isolation barrier. The single-ended output can be routed directly to a standard ADC (not shown). If the voltage sensed is > 2.5 V, a simple voltage divider consisting of R1 and R2 can be used to scale down any voltage to fit the input range of the Si8931/32. R2 < 10 kΩ is recommended for best performance.
Figure 3.1. Voltage Sense Application
The amplifier bandwidth of the Si8931/32 is approximately 600 kHz. For applications where input filtering is required, a passive, differ- ential RC low-pass filter can be placed at the input pin. Consider the source resistance of the signal measured (or the parallel combina- tion of R1 and R2 if using a voltage divider) as it should be included in the filter calculation. Capacitor C1 should be sized to make a band limiting filter at the desired frequency. C4, the local bypass capacitor for the B-side of Si8931/32, should be placed closed to VDDB supply pin with its return close to GNDB. The output signal at AOP and AON is differential with unity gain and common mode of 1.4 V. The outputs are sampled by a differential input ADC. Depending on the sample rate of the ADC, an anti-aliasing filter may be required. A simple anti-aliasing filter can be made from the passive components, R5, C6, and R6. The characteristics of this filter are dictated by the input topology and sampling frequen- cy of the ADC. However, to ensure the Si8931/32 outputs are not overloaded, R5 = R6 > 5 kΩ and C6 can be calculated by the follow- ing equation: 1 C6 = 2 × π × (R5 + R6) × f3dB
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| Building a more connected world. Preliminary Rev. 0.5 | 5 Document Outline 1. Ordering Guide 2. System Overview 3. Voltage Sense Application 4. Electrical Specifications 4.1 Regulatory Information 4.2 Typical Operating Characteristics 5. Pin Descriptions 5.1 Si8931 Pin Descriptions 5.2 Si8932 Pin Descriptions 6. Packaging 6.1 Package Outline: 8-Pin Wide Body Stretched SOIC 6.2 Package Outline: 8-Pin Narrow Body SOIC 6.3 Land Pattern: 8-Pin Wide Body Stretched SOIC 6.4 Land Pattern: 8-Pin Narrow Body SOIC 6.5 Top Marking: 8-Pin Wide Body Stretched SOIC 6.6 Top Marking: 8-Pin Narrow Body SOIC 7. Document Revision History