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NCV8502PDW100R2G Datasheet(PDF) 9 Page - ON Semiconductor |
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NCV8502PDW100R2G Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 15 page NCV8502 Series http://onsemi.com 9 CIRCUIT DESCRIPTION REGULATOR CONTROL FUNCTIONS The NCV8502 contains the microprocessor compatible control function RESET (Figure 12). Figure 12. Reset and Delay Circuit Wave Forms VIN VOUT RESET DELAY (VDT) Threshold DELAY Threshold RESET Td Td RESET Function A RESET signal (low voltage) is generated as the IC powers up until VOUT is within 6.0% of the regulated output voltage, or when VOUT drops out of regulation,and is lower than 8.0% below the regulated output voltage. Hysteresis is included in the function to minimize oscillations. The RESET output is an open collector NPN transistor, controlled by a low voltage detection circuit. The circuit is functionally independent of the rest of the IC thereby guaranteeing that the RESET signal is valid for VOUT as low as 1.0 V. Adjustable Reset Function The reset threshold can be made lower by connecting an external resistor divider to the RADJ lead from the VOUT lead, as displayed in Figure 13. This lead is grounded to select the default value of 4.6 V. Figure 13. Adjustable RESET RADJ to mP and System Power RRST VOUT COUT RESET CDELAY DELAY NCV8502 to mP and RESET Port DELAY Function The reset delay circuit provides a programmable (by external capacitor) delay on the RESET output lead. The DELAY lead provides source current (typically 2.5 mA) to the external DELAY capacitor during the following proceedings: 1. During Power Up (once the regulation threshold has been verified). 2. After a reset event has occurred and the device is back in regulation. The DELAY capacitor is discharged when the regulation (RESET threshold) has been violated. This is a latched incident. The capacitor will fully discharge and wait for the device to regulate before going through the delay time event again. FLAG/Monitor Function An on−chip comparator is provided to perform an early warning to the microprocessor of a possible reset signal. The reset signal typically turns the microprocessor off instantaneously. This can cause unpredictable results with the microprocessor. The signal received from the FLAG pin will allow the microprocessor time to complete its present task before shutting down. This function is performed by a comparator referenced to the bandgap reference. The actual trip point can be programmed externally using a resistor divider to the input monitor (MON) (Figure 14). The typical threshold is 1.20 V on the MON pin. Figure 14. FLAG/Monitor Function VBAT VIN MON VOUT COUT VCC I/O RESET mP FLAG RESET GND DELAY NCV8502 RADJ Voltage Adjust Figure 15 shows the device setup for a user configurable output voltage. The feedback to the VADJ pin is taken from a voltage divider referenced to the output voltage. The loop is balanced around the Unity Gain threshold (1.28 V typical). Figure 15. Adjustable Output Voltage VOUT VADJ NCV8502 15 k 5.1 k COUT ≈5.0 V 1.28 V |
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