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NCV4263-2C Datasheet(PDF) 11 Page - ON Semiconductor |
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NCV4263-2C Datasheet(HTML) 11 Page - ON Semiconductor |
11 / 14 page NCV4263−2C www.onsemi.com 11 APPLICATIONS INFORMATION The NCV4263−2C regulator is self−protected with internal thermal shutdown and internal current limit. Typical characteristics are shown in Figures 4 to 22. Input Decoupling (Cin) A ceramic or tantalum 0.1 mF capacitor is recommended and should be connected close to the NCV4263−2C package. Higher capacitance and lower ESR will improve the overall line and load transient response. If extremely fast input voltage transients are expected then appropriate input filter is recommended to use in order to decrease rising and/or falling edges below 50 V/ ms for proper operation. The filter can be composed of several capacitors in parallel. Output Decoupling (Cout) The NCV4263−2C is a stable component and requires a minimum Equivalent Series Resistance (ESR) for the output capacitor. Stability region of ESR versus Output Current is shown in Figure 13. The minimum output decoupling value is 22 mF and can be augmented to fulfill stringent load transient requirements. Larger values improve noise rejection and load transient response. Enable Operation The Enable pin will turn the regulator on or off. The threshold limits are covered in the electrical characteristics table in this data sheet. Delay Timing The Delay Timing pin is current source. Current from Delay Timing pin charges connected capacitor. The value of this capacitor determines the Reset Delay Time by Equation 1 and Watchdog Trigger Time by Equation 4. C D + t RD_des t RD 100 nF (eq. 1) where: CD is capacitance of Delay capacitor tRD_des is desired Reset Delay Time tRD is Reset Delay Time specified in datasheet Reset Operation A reset signal is provided on the Reset Output pin to provide feedback to the microprocessor of an out of regulation condition. The timing diagram of reset function is shown in Figure 21. This is in the form of a logic signal on Reset Output. Output voltage conditions below the Reset Threshold causes Reset Output to go low. The Reset Output integrity is maintained down to Vout = 1.0 V. The Reset Output circuitry is open collector output with internal 30 k W pull−up resistor. Leave open this output if the Reset function is not needed else an external pull−up resistor (5.6 k W) connect to the output (Vout). Reset Threshold is default set to 93% of nominal Output Voltage (VRADJ = 0 V). Reset Threshold can be varied in range of Output Voltage 70% ≤ Vout < VRT by external resistor output voltage divider, see schematic on Figure 23 and specification of Reset Output. NCV4263−2C GND 100 nF RADJ RO WDI D I/O ON OFF EN 100 nF Figure 23. Application Schematic with Adjustable Reset Threshold Microprocessor Vin Vout Cin RRADJ1 RRADJ2 RESET RRO 5.6 k W CD Cout 22 mF VDD Desired Reset Threshold is given by Equation 2. V RT_des + R RADJ1 ) RRADJ2 R RADJ2 V th(RADJ) (eq. 2) where: VRT_des is desired Reset Threshold RRADJ1, RRADJ2 are resistance of resistor divider Vth(RADJ) is Reset Adjust Threshold specified in datasheet Use RRADJ2 ≤ 50 kW to avoid significant Reset Threshold error due to RADJ bias current. Watchdog Operation Watchdog Input monitors a signal from microprocessor. This input is positive edge sensitive. The timing diagram of watchdog function is shown in Figure 22. When watchdog signal is not received during Watchdog Trigger Time, Reset Output goes low for a Watchdog Input Low Time and is periodically generated with period given by Equation 3. Capacitance of Delay capacitor for setting the desired Watchdog Trigger Time is given by Equation 4. t WP + tWL ) tWTT (eq. 3) C D + t WTT_des t WTT 100 nF (eq. 4) where: CD is capacitance of Delay capacitor tWTT_des is desired Watchdog Trigger Time tWTT is Watchdog Trigger Time specified in datasheet tWL is Watchdog Input Low Time tWP is Watchdog Input Period Thermal Considerations As power in the NCV4263−2C increases, it might become necessary to provide some thermal relief. The maximum power dissipation supported by the device is dependent |
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