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L4949DR2G Datasheet(PDF) 8 Page - ON Semiconductor |
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L4949DR2G Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 10 page L4949, NCV4949 http://onsemi.com 8 Reset Circuit The block circuit diagram of the reset circuit is shown in Figure 16. The reset circuit supervises the output voltage. The reset threshold of 4.5 V is defined with the internal reference voltage and standby output divider. The reset pulse delay time tRD, is defined with the charge time of an external capacitor CT: t RD + C T x2.0 V 2.0 mA The reaction time of the reset circuit originates from the discharge time limitation of the reset capacitor CT and is proportional to the value of CT. The reaction time of the reset circuit increases the noise immunity. 1.23 V Vref 22 k Out Reg 2.0 mA CT 2.0 V + − Reset Figure 16. Reset Circuit Standby output voltage drops below the reset threshold only a bit longer than the reaction time results in a shorter reset delay time. The nominal reset delay time will be generated for standby output voltage drops longer than approximately 50 ms. The typical reset output waveforms are shown in Figure 17. VRT + 0.1 V 5.0 V UKT Vout 3.0 V Reset Vout1 Vin 40 V t tR tRD tRD tRR Switch On Input Drop Dump Output Overload Switch Off Figure 17. Typical Reset Output Waveforms Sense Comparator The sense comparator compares an input signal with an internal voltage reference of typical 1.23 V. The use of an external voltage divider makes this comparator very flexible in the application. It can be used to supervise the input voltage either before or after the protection diode and to give additional information to the microprocessor like low voltage warnings. ORDERING INFORMATION Device Operating Temperature Range Package Shipping† L4949N TJ = −40°C to +125°C PDIP−8 50 Units / Rail L4949NG PDIP−8 (Pb−Free) 50 Units / Rail L4949D SOIC−8 98 Units / Rail L4949DG SOIC−8 (Pb−Free) 98 Units / Rail L4949DR2 SOIC−8 2500 Units / Tape & Reel L4949DR2G SOIC−8 (Pb−Free) 2500 Units / Tape & Reel NCV4949DG* SOIC−8 (Pb−Free) 98 Units / Rail NCV4949DR2* SOIC−8 2500 Units / Tape & Reel NCV4949DR2G* SOIC−8 (Pb−Free) 2500 Units / Tape & Reel NCV4949DWR2* SOIC−20W 1000 Units / Tape & Reel NCV4949DWR2G* SOIC−20W (Pb−Free) 1000 Units / Tape & Reel †For information on tape and reel specifications,including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. *NCV4949: Tlow = −40°C, Thigh = +125°C. Guaranteed by design. NCV prefix is for automotive and other applications requiring site and change control. |
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