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NCP803SN308T1G Datasheet(PDF) 7 Page - ON Semiconductor |
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NCP803SN308T1G Datasheet(HTML) 7 Page - ON Semiconductor |
7 / 10 page MAX803 Series, NCP803 Series www.onsemi.com 7 APPLICATIONS INFORMATION VCC Transient Rejection The MAX803/NCP803 series provides accurate VCC monitoring and reset timing during power−up, power−down, and brownout/sag conditions, and rejects negative−going transients (glitches) on the power supply line. Figure 13 shows the maximum transient duration vs. maximum negative excursion (overdrive) for glitch rejection. Any combination of duration and overdrive which lies under the curve will not generate a reset signal. Combinations above the curve are detected as a brownout or power−down. Typically, transient that goes 100 mV below the reset threshold and lasts 5.0 ms or less will not cause a reset pulse. Transient immunity can be improved by adding a capacitor in close proximity to the VCC pin of the MAX803. Figure 13. Maximum Transient Duration vs. Overdrive for Glitch Rejection at 25 °C Duration VTH Overdrive VCC 10 250 200 110 60 50 RESET COMPARATOR OVERDRIVE (mV) 0 410 150 100 VTH = 1.2 V 160 210 260 310 360 VTH = 4.63 V RESET Signal Integrity During Power−Down The MAX803/NCP803 RESET output is valid to VCC = 1.0 V. Below this voltage the output becomes an “open circuit” and does not sink current. This means CMOS logic inputs to the Microprocessor will be floating at an undetermined voltage. Most digital systems are completely shutdown well above this voltage. However, in situations where RESET must be maintained valid to VCC = 0 V, since the NCP803/MAX803 has Open−Drain and active−low output, it typically uses a pullup resistor. With this device, RESET will most likely not maintain an active condition, but will drift to a non−active level due to the pullup resistor and the reduced sinking capability of the open−drain device. Therefore, this device is not recommended for applications where the RESET pin is required to be valid down to VCC = 0 V. VCC VCC R1 100 k* MAX809 NCP803 GND Figure 14. RESET Signal Integrity RESET *Assume High−Z Reset Input to Microprocessor MAX803 RESET Output Allows Use With Two Power Supplies In numerous applications the pullup resistor place on the RESET output is connected to the supply voltage monitored by the IC. Nevertheless, a different supply voltage can also power this output and so level−shift from the monitored supply to reset the microprocessor. However, if the NCP803/MAX803’s supply goes blew 1 V, the RESET output ability to sink current will decrease and the result is a high state on the pin even though the supply’s IC is under the threshold level. This occurs at a VCC level that depends on the Rpullup value and the voltage which is connected. VCC VCC2 Microprocessor RESET MAX803 NCP803 GND GND Rpullup Figure 15. MAX803 RESET Output with Two Supplies RESET VCC VCC1 |
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