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LTC2930CDD-TRPBF Datasheet(PDF) 7 Page - Linear Technology |
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LTC2930CDD-TRPBF Datasheet(HTML) 7 Page - Linear Technology |
7 / 12 page LTC2930 7 2930fa APPLICATIONS INFORMATION Supply Monitoring The LTC2930 is a low power, high accuracy configurable six supply monitoring circuit with a common reset output. An external capacitor sets the reset timeout period. An external resistive divider between VREF, VPG and GND selects 1 of 16 possible input voltage monitor combinations. All six volt- age inputs must be above their predetermined thresholds for the reset not to be activated. The LTC2930 asserts the reset output during power-up, power-down and brownout conditions on any one of the voltage inputs. Power-Up The greater of V1 and V2 serves as the internal supply voltage (VCC). On power-up, VCC powers the drive circuits for the RST pin. This ensures that the RST output will be low as soon as either V1 or V2 reaches 1V. The RST output remains low until the part is configured. Once voltage thresholds are set, if any of the supply monitor inputs is below its configured threshold, RST will be a logic low. Once all the monitor inputs rise above their thresholds, an internal timer is started and RST is released after the delay time. If VCC < (V3 – 1.0V) and VCC < 2.4V, the V3 input impedance will be low (10kΩ typical). Threshold Accuracy Consider a 5V system with ±5% tolerance. The 5V supply may vary between 4.75V to 5.25V. System ICs powered by this supply must operate reliably within this band (and a little more as explained below). A perfectly accurate su- Table 1. Voltage Threshold Modes* MODE V1 (V) V2 (V) V3 (V) V4 (V) R1 (kΩ) R2 (kΩ) VPG VREF 0 5.0 3.3 ADJ ADJ Open Short 0.000 1 5.0 3.3 ADJ –ADJ 93.1 9.53 0.094 2 3.3 2.5 ADJ ADJ 86.6 16.2 0.156 3 3.3 2.5 ADJ –ADJ 78.7 22.1 0.219 4 3.3 2.5 1.5 ADJ 71.5 28.0 0.281 5 5.0 3.3 2.5 ADJ 66.5 34.8 0.344 6 5.0 3.3 2.5 1.8 59.0 40.2 0.406 7 5.0 3.3 2.5 1.5 53.6 47.5 0.469 8 5.0 3.0 2.5 ADJ 47.5 53.6 0.531 9 5.0 3.0 ADJ ADJ 40.2 59.0 0.594 10 3.3 2.5 1.8 1.5 34.8 66.5 0.656 11 3.3 2.5 1.8 ADJ 28.0 71.5 0.719 12 3.3 2.5 1.8 –ADJ 22.1 78.7 0.781 13 5.0 3.3 1.8 –ADJ 16.2 86.6 0.844 14 5.0 3.3 1.8 ADJ 9.53 93.1 0.906 15 5.0 3.0 1.8 ADJ Short Open 1.000 *V5 and V6 are always adjustable (ADJ). pervisor for this supply generates a reset at exactly 4.75V, however no supervisor is this perfect. The actual reset threshold of a supervisor varies over a specified band; the LTC2930 varies ±1.5% around its nominal threshold voltage (see Figure 1) over temperature. The reset threshold band and the power supply tolerance bands should not overlap. This prevents false or nuisance resets when the power supply is actually within its speci- fied tolerance band. The LTC2930 has a ±1.5% reset threshold accuracy, so a “5%” threshold is typically set to 6.5% below the nominal input voltage. Therefore, a typical 5V, “5%” threshold is 4.675V. The threshold is guaranteed to lie in the band be- tween 4.750V and 4.600V over temperature. The powered system must work reliably down to the low end of the threshold band, or risk malfunction before a reset signal is properly issued. A less accurate supervisor increases the required system voltage margin and increases the probability of system malfunction. The LTC2930 ±1.5% specification improves the reliability of the system over supervisors with wider threshold tolerances. 5V 4.75V 4.675V ±1.5% THRESHOLD BAND 4.6V NOMINAL SUPPLY VOLTAGE SUPPLY TOLERANCE MINIMUM RELIABLE SYSTEM VOLTAGE IDEAL SUPERVISOR THRESHOLD REGION OF POTENTIAL MALFUNCTION –5% –6.5% –8% Figure 1. 1.5% Threshold Accuracy Improves System Reliability |
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