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X5001 Datasheet(PDF) 3 Page - Intersil Corporation |
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X5001 Datasheet(HTML) 3 Page - Intersil Corporation |
3 / 18 page 3 FN8125.0 April 6, 2005 PRINCIPLES OF OPERATION Power-on Reset Application of power to the X5001 activates a power- on reset circuit. This circuit goes active at 1V and pulls the RESET/RESET pin active. This signal prevents the system microprocessor from starting to operate with insufficient voltage or prior to stabilization of the oscillator. When VCC exceeds the device VTRIP value for 200ms (nominal) the circuit releases RESET, allowing the processor to begin executing code. Low Voltage Monitoring During operation, the X5001 monitors the VCC level and asserts RESET if supply voltage falls below a pre- set minimum VTRIP. The RESET signal prevents the microprocessor from operating in a power fail or brownout condition. The RESET signal remains active until the voltage drops below 1V. It also remains active until Vcc returns and exceeds VTRIP for 200ms. Watchdog Timer The watchdog timer circuit monitors the microprocessor activity by monitoring the WDI input. The microproces- sor must toggle the CS/WDI pin periodically to prevent a RESET signal. The CS/WDI pin must be toggled from HIGH to LOW prior to the expiration of the watch- dog time out period. The state of two nonvolatile control bits in the watchdog register determine the watchdog timer period. Vcc Threshold Reset Procedure The X5001 is shipped with a standard VCC threshold (VTRIP) voltage. This value will not change over normal operating and storage conditions. However, in applica- tions where the standard VTRIP is not exactly right, or if higher precision is needed in the VTRIP value, the X5001 threshold may be adjusted. The procedure is described below, and requires the application of a high voltage control signal. Setting the VTRIP Voltage This procedure is used to set the VTRIP to a higher voltage value. For example, if the current VTRIP is 4.4V and the new VTRIP is 4.6V, this procedure will directly make the change. If the new setting is to be lower than the current setting, then it is necessary to reset the trip point before setting the new value. To set the new VTRIP voltage, apply the desired VTRIP threshold voltage to the VCC pin and tie the WPE pin to the programming voltage VP. Then a VTRIP programming command sequence is sent to the device over the SPI interface. This VTRIP programming sequence consists of pulling CS LOW, then clocking in data 03h, 00h and 01h. This is followed by bringing CS HIGH then LOW and clocking in data 02h, 00h, and 01h (in order) and bringing CS HIGH. This initiates the VTRIP programming sequence. VP is brought LOW to end the operation. Resetting the VTRIP Voltage This procedure is used to set the VTRIP to a “native” voltage level. For example, if the current VTRIP is 4.4V and the new VTRIP must be 4.0V, then the VTRIP must be reset. When VTRIP is reset, the new VTRIP is some- thing less than 1.7V. This procedure must be used to set the voltage to a lower value. To reset the VTRIP voltage, apply greater than 3V to the VCC pin and tie the WPE pin to the programming voltage VP. Then a VTRIP command sequence is sent to the device over the SPI interface. This VTRIP pro- gramming sequence consists of pulling CS LOW, then clocking in data 03h, 00h and 01h. This is followed by bringing CS HIGH then LOW and clocking in data 02h, 00h, and 03h (in order) and bringing CS HIGH. This initiates the VTRIP programming sequence. VP is brought LOW to end the operation. X5001 |
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