Electronic Components Datasheet Search |
|
LTC1727 Datasheet(PDF) 11 Page - Linear Technology |
|
LTC1727 Datasheet(HTML) 11 Page - Linear Technology |
11 / 16 page LTC2917/LTC2918 11 29178f The reference input of the comparator is controlled by the tolerance pin. The external resistive divider should make the voltage at VM = 0.5V when the supply is at nominal value. The actual threshold of VM accounts for the sup- ply tolerance of ±1.5% guaranteed over the full operating temperature range. The resulting tolerances are –6.5%, –11.5%, –16.5% which correspond to 0.468V, 0.443V, 0.418V respectively. Typically, the user will pick a value of R1 based on accept- able current draw. Current used by the resistor divider will be approximately: R V I 1 05 = ⎛ ⎝⎜ ⎞ ⎠⎟ . Recommended range of R1 is 1k—1M. Higher values of resistance exacerbate the degradation of threshold ac- curacy due to leakage currents. If the nominal value of the supply being monitored is VNOM, then R2 = R1(2VNOM – 1) Resistor tolerances must be taken into account when determining the overall accuracy. Selecting the Reset Timing Capacitor The reset timeout period can be set to one of two fixed internal timers or set with a capacitor in order to accom- modate a variety of applications. Connecting a capacitor, CRT, between the RT pin and ground sets the reset timeout period, tRST. The following formula approximates the value of capacitor needed for a particular timeout: CRT = tRST • 110 [pF/ms] For example, using a standard capacitor value of 2.2nF would give a 20ms timeout. Figure 2 shows the desired reset timeout period as a function of the value of the timer capacitor. Leaving RT open with no external capacitor generates a reset timeout of approximately 400μs. Shorting RT to VCC generates a reset timeout of approximately 200ms. ⎯R⎯S⎯T Output Characteristics The DC characteristics of the ⎯R⎯S⎯T pull-down strength are shown in the Typical Performance Characteristics section. ⎯R⎯S⎯T is an open-drain pin and thus requires an external pull-up resistor to the logic supply. ⎯R⎯S⎯T may be pulled above VCC, providing the voltage limits of the pin are observed. The open-drain of the ⎯R⎯S⎯T pin allows for wired-OR con- nection of several LTC2917/LTC2918’s. Watchdog LTC2917-A/LTC2918-A A standard watchdog function is used to ensure that the system is in a valid state by continuously monitoring the microprocessor’s activity. The microprocessor must toggle the logic state of the WDI pin periodically (within upper boundary) in order to clear the watchdog timer. If timeout occurs, the LTC2917-A/LTC2918-A asserts ⎯R⎯S⎯T low for the reset timeout period, issuing a system reset. Once the reset timeout completes, ⎯R⎯S⎯T is released to go high and the watchdog timer starts again. During power-up, the watchdog timer remains cleared while ⎯R⎯S⎯T is asserted low. As soon as the reset timer times out, ⎯R⎯S⎯T goes high and the watchdog timer is started. APPLICATIONS INFORMATION Figure 2. Reset Timeout Period vs RT Capacitance RT PIN CAPACITANCE, CRT (nF) 0.001 0.1 10 10000 0.1 0.01 1 10 100 1000 29178 F02 1 100 1000 |
Similar Part No. - LTC1727 |
|
Similar Description - LTC1727 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |