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NCV8504 Datasheet(PDF) 9 Page - ON Semiconductor |
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NCV8504 Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 14 page NCV8504 Series http://onsemi.com 9 CIRCUIT DESCRIPTION REGULATOR CONTROL FUNCTIONS The NCV8504 contains the microprocessor compatible control function RESET (Figure 13). Figure 13. 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 1.5% of the regulated output voltage, or when VOUT drops out of regulation,and is lower than 4.0% 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 14. This lead is grounded to select the default value of 4.6 V (on the 5.0 V option). Figure 14. Adjustable RESET RADJ to µP and System Power RRST VOUT COUT RESET CDELAY DELAY NCV8504 to µP and RESET Port VR(ADJ) 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 4.0 µA) 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 Comparator A general use comparator is included whose positive input terminal is tied to the on−chip bandgap voltage reference. This provides a very temperature stable referenced comparator with versatile use in any system. The trip point can be programmed externally using a resistor divider to the input monitor (MON) (Figure 15). The typical threshold is 1.29 V on the MON pin. Figure 15. Flag/Monitor Function VBAT VIN MON VOUT COUT VCC I/O RESET µP FLAG RESET GND DELAY NCV8504 RADJ VMON Voltage Adjust Figure 16 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 (1.30 V typical). Figure 16. Adjustable Output Voltage VOUT VADJ NCV8504 15 k 5.1 k COUT ≈5.0 V 1.28 V |
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