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MCP6544-I/ST Datasheet(PDF) 17 Page - Microchip Technology |
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MCP6544-I/ST Datasheet(HTML) 17 Page - Microchip Technology |
17 / 34 page © 2006 Microchip Technology Inc. DS21696E-page 17 MCP6541/1R/1U/2/3/4 4.8 PCB Surface Leakage In applications where low input bias current is critical, PCB (Printed Circuit Board) surface leakage effects need to be considered. Surface leakage is caused by humidity, dust or other contamination on the board. Under low humidity conditions, a typical resistance between nearby traces is 1012 Ω. A 5V difference would cause 5 pA of current to flow. This is greater than the MCP6541/1R/1U/2/3/4 family’s bias current at 25°C (1 pA, typ.). The easiest way to reduce surface leakage is to use a guard ring around sensitive pins (or traces). The guard ring is biased at the same voltage as the sensitive pin. An example of this type of layout is shown in Figure 4-9. FIGURE 4-9: Example Guard Ring Layout for Inverting Circuit. 1. Inverting Configuration (Figures 4-6 and 4-9): a. Connect the guard ring to the non-inverting input pin (VIN+). This biases the guard ring to the same reference voltage as the comparator (e.g., VDD/2 or ground). b. Connect the inverting pin (VIN–) to the input pad without touching the guard ring. 2. Non-inverting Configuration (Figure 4-4): a. Connect the non-inverting pin (VIN+) to the input pad without touching the guard ring. b. Connect the guard ring to the inverting input pin (VIN–). 4.9 Unused Comparators An unused amplifier in a quad package (MCP6544) should be configured as shown in Figure 4-10. This circuit prevents the output from toggling and causing crosstalk. It uses the minimum number of components and draws minimal current (see Figure 2-15 and Figure 2-18). FIGURE 4-10: Unused Comparators. Guard Ring V SS VIN-VIN+ ¼ MCP6544 VDD – + |
Similar Part No. - MCP6544-I/ST |
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Similar Description - MCP6544-I/ST |
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