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LTC2914 Datasheet(PDF) 8 Page - Linear Technology |
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LTC2914 Datasheet(HTML) 8 Page - Linear Technology |
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8 / 16 page  LTC2960 8 2960f VOLTAGE MONITORING The LTC2960 is a voltage supervisor with a wide operating voltage range up to 36V with only 850nA quiescent current. The supervisor has two outputs, RST and OUT that pro- vide voltage monitoring capabilities for system power-up, power-down and brown-out conditions. Built-in hysteresis and a reset timeout period ensure that fluctuations due to load transients or supply noise do not cause chattering of the status outputs. The LTC2960 can provide reset and voltage status signals to a microprocessor based system or can alternatively be used as an Under Voltage Lock Out (UVLO) for DC/DC switchers or LDOs for control over a battery operated system. If the monitored voltage drops below the reset threshold, RST pulls low until the ADJ input rises above 0.4V plus 2.5% hysteresis. An internal reset timer delays the return of the RST output to a high state to provide monitored voltage settling and initialization time. The RST output is typically connected to a processor reset input. If the monitored supply voltage falls to the IN+ (LTC2960-1/ LTC2960-3) threshold, the spare comparator pulls OUT low. OUT remains low until the IN+ input rises above 0.4V plus 5% hysteresis. OUT is typically used to signal preparation for controlled shutdown. For example, the OUT output may be connected to a processor nonmaskable interrupt (NMI). Upon interrupt, the processor begins shutdown procedures such as supply sequencing and/or storage/ erasure of system state in nonvolatile memory. If the monitored supply voltage rises to the IN– threshold (LTC2960-2/LTC2960-4), the spare comparator pulls OUT low. OUT remains low until the IN– falls below 0.4V minus 5% hysteresis. The LTC2960-2/LTC2960-4 operates as an undervoltage and overvoltage monitor. Few, if any, external components are necessary for reliable operation. However, a decoupling capacitor between VCC and ground is recommended (0.01μF minimum). Use a capacitor with a compatible voltage rating. APPLICATIONS INFORMATION THRESHOLD CONFIGURATION The LTC2960 monitors voltage applied to its inputs IN+/IN– and ADJ. A resistive divider connected between a monitored voltage and ground is used to bias the inputs. Figure 1 demonstrates how the inputs can be made dependent upon a single voltage (V1). Only three resistors are required. To calculate their values, specify desired falling reset (VR) and IN+ (VIN+) thresholds with VIN+ > VR. For example: VIN+ = 6.4V, VR = 6V Figure 1. Configuration for Single Voltage Monitoring ADJ IN+ RST OUT LTC2960-1/ LTC2960-3 R3 R2 V1 R1 2960 F01 The solution for R1, R2 and R3 provides three equations and three unknowns. Maximum resistor size is governed by maximum input leakage current. For the LTC2960, the maximum input leakage current below 85°C is 1nA. For a maximum error of 1% due to both input currents, the resistor divider current should be at least 100 times the sum of the leakage currents, or 0.2μA. At the reset threshold, V1 = 6V, RSUM = 8MΩ where: RSUM = R1 + R2 + R3 Both the falling reset and IN+ thresholds are 0.4V, so: R1 = VTH •RSUM VIN+ = 0.4V • 8MΩ 6.4V = 500k The closest 1% value is 499k. R2 can be determined from: R2 = VTH • RSUM VR –R1 = 0.4V • 8MΩ 6V – 499k R2 = 34.33k |
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