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ADM2914-2ARQZ Folha de dados(PDF) 10 Page - Analog Devices |
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ADM2914-2ARQZ Folha de dados(HTML) 10 Page - Analog Devices |
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10 / 16 page  ADM2914 Rev. B | Page 10 of 16 THRESHOLD ACCURACY The reset threshold accuracy is fundamental, especially at lower voltage levels. Consider an FPGA application that requires a 1 V core voltage input with tolerance of ±5%, where the supply has a specified regulation, for example, ±1.5%. As shown in Figure 19, to ensure that the supply is within the FPGA input voltage require- ment range, its voltage level must be monitored for UV and OV conditions. The voltage swing on the supply itself causes the voltage band available for setting the monitoring threshold to be quite narrow. In this example, the threshold voltages, including the tolerances, must fit within a monitor region of only 0.035 V. The ADM2914 device with 0.1% resistors can achieve this level of accuracy. 1.05V TIME VOLTAGE 1.015V 1V CORE VOLTAGE 0.985V 0.95V UV +5% TOLERANCE 3.5% RANGE FOR OV MONITORING 3.5% RANGE FOR UV MONITORING +1.5% SUPPLY REGULATION –1.5% SUPPLY REGULATION –5% TOLERANCE tUOTO Figure 19. Monitoring Threshold Accuracy Example VOLTAGE MONITORING EXAMPLE To illustrate how the ADM2914 device works in a real application, consider the 1 V input example shown in Figure 19, with the addition of a −12 V rail. The first step is to choose the nominal current flow through both voltage divider circuits, for example, 5 μA. For the 1 V ± 5% input, due to the specified ±1.5% regulation of the supply, the UV and OV thresholds should be set in the middle of the voltage monitoring band. In this case, on the ±3.25% points of the supply, the UV threshold is 0.9675 V and the OV threshold is 1.0325 V. Input these values into Equation 1. ( ) () () kΩ 5 . 96 10 5 0325 . 1 1 ) 5 . 0 ( 6 ≈ × = − Z R Insert the value of RZ into Equation 2. ( ) () () kΩ 42 . 6 kΩ 5 . 96 10 5 9675 . 0 1 ) 5 . 0 ( 6 ≈ − × = − Y R Then substitute the calculated values for RZ and RY into Equation 3. kΩ 5 . 96 kΩ 42 . 6 kΩ 5 . 96 10 5 1 6 ≈ − − × = − X R This design approach meets the application specifications. As described previously, the 1 V rail is specified with an input requirement of ±5% and a supply tolerance of ±1.5%. This effectively means that the OV threshold of the monitoring device, including all the tolerance factors, must fit within the 1.015 V to 1.05 V range. Similarly, the UV threshold range must be between 0.95 V and 0.985 V. The four worst-case scenarios of minimum and maximum undervoltage and overvoltage thresholds are calculated as follows: Minimum overvoltage threshold () V 015 . 1 V 016 . 1 ) 001 . 1 )( 500 , 96 ( ) 999 . 0 )( 6420 500 , 96 ( 1 4925 . 0 % 1 . 0 %) 1 . 0 ( %) 1 . 0 ( 1 %) 5 . 1 V 5 . 0 ( _ > = ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + + = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + − + − + − = Z Y X MIN OV R R R V Maximum overvoltage threshold () V 05 . 1 V 049 . 1 % 1 . 0 %) 1 . 0 ( %) 1 . 0 ( 1 %) 5 . 1 V 5 . 0 ( _ < = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − + + + + + = Z Y X MAX OV R R R V The maximum and minimum overvoltage threshold values lie within the 1.015 V to 1.05 V range specified. The minimum and maximum undervoltage thresholds are calculated as follows: Minimum undervoltage threshold () ( ) V 95 . 0 V 953 . 0 % 1 . 0 % 1 . 0 %) 1 . 0 ( 1 %) 5 . 1 V 5 . 0 ( _ > = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + + + − + − = Z Y X MIN UV R R R V Maximum undervoltage threshold () () V 985 . 0 V 984 . 0 % 1 . 0 % 1 . 0 %) 1 . 0 ( 1 %) 5 . 1 V 5 . 0 ( _ < = ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − + − + + + = Z Y X MAX UV R R R V Again, these values fit within the specified undervoltage monitoring range. All four worst-case scenarios satisfy the tolerance requirement; therefore, the design approach is valid. ADM2914 VH1 VCC 5V 1V RAIL GND VL1 VL3 VH3 REF UV SEL OV –12V RAIL 2.49MΩ 23.4kΩ 89.8kΩ 96.5kΩ 6.42Ω 96.5kΩ Figure 20. Positive and Negative Supply Monitor Example |
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Descrição semelhante - ADM2914-2ARQZ |
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