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TS9002 数据表(PDF) 9 Page - Silicon Laboratories |
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TS9002 数据表(HTML) 9 Page - Silicon Laboratories |
9 / 12 page TS9002 TS9002 Rev. 1.0 Page 9 R1 = VHB 2 x IREF R2 = 1.182 - VHB 2 IREF where IREF is the primary source of current out of the reference pin and should be maintained within the maximum current the reference can source. It is safe to maintain the current within 20µA. It is also important to ensure that the current from reference is much larger than the HYST pin input current. Given R2 = 2.4M Ω, the current sourced by the reference is 0.5 μA. This allows the hysteresis band and R1 to be approximated as follows: R1(k Ω) = VHB(mv) Note the hysteresis is the same for both comparators. Board Layout and Bypassing While power-supply bypass capacitors are not typically required, it is good engineering practice to use 0.1 μF bypass capacitors close to the device’s power supply pins when the power supply impedance is high, the power supply leads are long, or there is excessive noise on the power supply traces. To reduce stray capacitance, it is also good engineering practice to make signal trace lengths as short as possible. Also recommended are a ground plane and surface mount resistors and capacitors. Window Detector The schematic shown in Figure 3 is for a 4.5V undervoltage threshold detector and a 5.5V overvoltage threshold detector using the TS9002. Resistor components R1, R2, and R3 can be selected based on the threshold voltage desired while resistors R4 and R5 can be selected based on the hysteresis desired. Adding hysteresis to the circuit will minimize chattering on the output when the input voltage is close to the trip point. OUTA and OUTB generate the active low undervoltage indication and active-low overvoltage indication, respectively. If both OUTA and OUTB signals are ANDed together, the resulting output of the AND gate is an active-high, power-good signal. To design the circuit, the following procedure needs to be followed: 1. As described below, determine the desired hysteresis and select resistors R4 and R5 accordingly. This circuit has ±5mV of hysteresis at the input where the input voltage VIN will appear larger due to the input resistor divider. 2. Choosing R1. As the leakage current at the INB- pin is less than 1nA, the current through R1 should be at least 100nA to minimize offset voltage errors caused by the input leakage current. Values within 100k Ω and 1M Ω are recommended. In this example, a 294k Ω, 1% standard value resistor is selected for R1. 3. Calculating R2 + R3. As the input voltage VIN rises, the overvoltage threshold should be 5.5V. Choose R2 + R3 as follows: R1 + R3 = R1 x VOTH VREF+VHYS - 1 = 294k Ω x 5.5V 1.182V + 5mV - 1 = 1.068M Ω 4. Calculating R2. As the input voltage VIN falls, the undervoltage threshold should be 4.5V. Choose R2 as follows: R2 = (R1 + R2+ R3) x VREF-VHYS VUTH - 294k = (294k Ω + 1.068MΩ) x 1.182V-5mV 4.5 - 294k = 62.2k Ω Figure 3. Window Detector |
类似零件编号 - TS9002 |
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类似说明 - TS9002 |
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