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CAT1027LI-25-T3 データシート(PDF) 7 Page - Catalyst Semiconductor |
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CAT1027LI-25-T3 データシート(HTML) 7 Page - Catalyst Semiconductor |
7 / 20 page CAT1026, CAT1027 © Catalyst Semiconductor, Inc. 7 Doc. No. MD-3010 Rev. M Characteristics subject to change without notice DEVICE OPERATION Reset Controller Description The CAT1026 and CAT1027 precision RESET controllers ensure correct system operation during brownout and power up/down conditions. They are configured with open drain RESET outputs. During power-up, the RESET outputs remain active until VCC reaches the VTH threshold and will continue driving the outputs for approximately 200ms (tPURST) after reaching VTH. After the tPURST timeout interval, the device will cease to drive the reset outputs. At this point the reset outputs will be pulled up or down by their respective pull up/down resistors. During power-down, the RESET outputs will be active when VCC falls below VTH. The RESET ¯¯¯¯¯¯ output will be valid so long as VCC is >1.0V (VRVALID). The device is designed to ignore the fast negative going VCC transi- ent pulses (glitches). Reset output timing is shown in Figure 1. Manual Reset Capability The RESET ¯¯¯¯¯¯ pin can operate as reset output and manual reset input. The input is edge triggered; that is, the RESET ¯¯¯¯¯¯ input will initiate a reset timeout after detecting a high to low transition. When RESET ¯¯¯¯¯¯ I/O is driven to the active state, the 200ms timer will begin to time the reset interval. If external reset is shorter than 200ms, Reset outputs will remain active at least 200ms. Monitoring Two Voltages The CAT1026 and CAT1027 feature a second voltage sensor, VSENSE, which drives the open drain VLOW output low whenever the input voltage is below 1.25V. The auxiliary voltage monitor timing is shown in Figure 2. By using an external resistor divider the sense circuitry can be set to monitor a second supply in the system. The circuit shown in Figure 3 provides an externally adjustable threshold voltage, VTH_ADJ to monitor the auxiliary voltage. The low leakage current at VSENSE allows the use of large value resistors, to reduce the system power consumption. The VLOW output can be externally connected to the RESET output to generate a reset condition when either of the supplies is invalid. In other applications, VLOW signal can be used to interrupt the system controller for an impending power failure notification. Data Protection The CAT1026 and CAT1027 devices have been desig- ned to solve many of the data corruption issues that have long been associated with serial EEPROMs. Data corruption occurs when incorrect data is stored in a memory location which is assumed to hold correct data. Whenever the device is in a Reset condition, the embedded EEPROM is disabled for all operations, including write operations. If the Reset output(s) are active, in progress communications to the EEPROM are aborted and no new communications are allowed. In this condition an internal write cycle to the memory can not be started, but an in progress internal non- volatile memory write cycle can not be aborted. An internal write cycle initiated before the Reset condition can be successfully finished if there is enough time (5ms) before VCC reaches the minimum value of 2 V. In addition, to avoid data corruption due to the loss of power supply voltage during the memory internal write operation, the system controller should monitor the unregulated DC power. Using the second voltage sensor, VSENSE, to monitor an unregulated power supply, the CAT1026 and CAT1027 signals an impen- ding power failure by setting VLOW low. Watchdog Timer The Watchdog Timer provides an independent protec- tion for microcontrollers. During a system failure, the CAT1027 device will provide a reset signal after a time-out interval of 1.6 seconds for a lack of activity. CAT1027 is designed with the Watchdog timer feature on the WDI pin. If WDI does not toggle within 1.6 second intervals, the reset condition will be generated on reset output. The watchdog timer is cleared by any transition on monitored line. As long as reset signal is asserted, the watchdog timer will not count and will stay cleared. |
同様の部品番号 - CAT1027LI-25-T3 |
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同様の説明 - CAT1027LI-25-T3 |
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