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LTC2909ITS8-2.5 数据表(PDF) 13 Page - Linear Technology |
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LTC2909ITS8-2.5 数据表(HTML) 13 Page - Linear Technology |
13 / 16 page LTC2909 13 2909fa APPLICATIO S I FOR ATIO If the user wishes to avoid having an external capacitor, the TMR pin should be tied to ground, switching the part to an internal 200ms timer. If the user requires a shorter timeout than 400μs, or wishes to perform application-specific processing of the reset output, the part may be put in comparator mode by tying the TMR pin to VCC. In comparator mode, the timer is bypassed and comparator outputs go straight to the reset output. The current required to hold TMR at ground or VCC is about 2μA. To force the pin from the floating state to ground or VCC may require as much as 100μA during the transition. When the part is in comparator mode, one of the two means of preventing false reset has been removed, so a small amount of one-sided hysteresis is added to the inputs to prevent oscillation as the monitored voltage passes through the threshold. This hysteresis is such that the valid-to-invalid transition threshold is unchanged, but the invalid-to-valid threshold is moved by about 0.7%. Thus, when the ADJ input polarity is positive, the threshold voltage is 500mV nominal when the in- put is above 500mV. As soon as the input drops below 500mV, the threshold moves up to 503.5mV nominal. Conversely, when configured as a negative-polarity input, the threshold is 500mV when the input is below 500mV, and switches to 496.5mV when the input goes above 500mV. The comparator mode feature should be enabled by directly shorting the TMR pin to the VCC pin. Connecting the pin to any other voltage may have unpredictable results. Selecting the Reset Timing Capacitor Connecting a capacitor, CTMR, between the TMR pin and ground sets the reset timeout, tRST. The following formula approximates the value of capacitor needed for a particular timeout: CTMR = t⎯R⎯S⎯T • 110 [pF/ms] Leaving the TMR pin open with no external capacitor generates a reset timeout of approximately 400μs. Maximum length of the reset timeout is limited by the ability of the part to charge a large capacitor on start-up. Initially, with a large (discharged) capacitor on the TMR pin, the part will assume it is in internal timer mode (since the pin voltage will be at ground). If the 2μA flowing out of the TMR pin does not charge the capacitor to the ground- sense threshold within the first 200ms after supplies become good, the internal timer cycle will complete and ⎯R⎯S⎯T will go high too soon. APPLICATIO S I FOR ATIO Table 3. Suggested Resistor Values for 5% Monitoring NOMINAL VOLTAGE 5% UV 5% OV 5% UV and OV RX1 RX2 RX1 RX2 RX4 RX5 RX6 24 232k 10.2M 102k 5.11M 82.5k 11.5k 4.12M 15 115k 3.09M 200k 6.19M 76.8k 10.7k 2.37M 12 49.9k 1.07M 102k 2.49M 76.8k 10.7k 1.87M 9 115k 1.82M 78.7k 1.43M 162k 22.6k 2.94M 5 137k 1.15M 137k 1.33M 76.8k 10.7k 732k 3.3 221k 1.15M 340k 2.05M 76.8k 10.7k 453k 2.5 115k 422k 51.1k 221k 137k 19.1k 576k 1.8 63.4k 150k 115k 324k 82.5k 11.5k 221k 1.5 59.0k 107k 137k 301k 76.8k 10.7k 158k 1.2 127k 158k 102k 158k 187k 26.1k 267k 1 200k 174k 100k 113k 107k 15.0k 105k –5 133k 1.37M 118k 1.37M 174k 20.0k 2.00M –9 97.6k 1.74M 115k 2.32M 182k 22.6k 3.65M –12 107k 2.49M 40.2k 1.07M 40.2k 5.11k 1.07M –15 107k 3.09M 309k 10.2M 309k 40.2k 10.2M Trip points are nominal voltage ±6.5%. |
类似零件编号 - LTC2909ITS8-2.5 |
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类似说明 - LTC2909ITS8-2.5 |
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