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PC87373 Datasheet(PDF) 28 Page - National Semiconductor (TI) |
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PC87373 Datasheet(HTML) 28 Page - National Semiconductor (TI) |
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28 / 174 page  2.0 Power, Reset and Clocks (Continued) 28 www.national.com Revision 1.1 Figure 1 shows the power state transitions: 2.1.3 Power Connection and Layout Guidelines The PC87373 requires a power supply voltage of 3.3V ± 10% for both the V DD3 and VSB3 supplies. The on-chip Core power converter generates a voltage below 3V for the internal logic. The device is designed to operate with a Lithium backup bat- tery supplying up to 3.6V. Therefore, it includes an internal current-limiting resistor on the VBAT input to prevent the battery from shorting, as required by the UL regulations. If the system implementation does not require backup power for the PC87373 device, the VBAT pin must be connected to VSS through an external pull-down resistor. VDD3, VSB3, VCORF and VBAT use a common ground return marked VSS. To obtain the best performance, bear in mind the following recommendations. Ground Connection. The following items must be connected to the ground layer (VSS) as close to the device as possible: • The ground return (V SS) pins • The decoupling capacitors of the Main power supply (V DD3) pins • The decoupling capacitors of the Standby power supply (V SB3) pins Table 5. Power States and Related Power Planes Power State Main (VDD3) Standby (VSB3) Core (VCORF) 1 1. VCORF is generated from VSB3; therefore, both voltages are on or off at approximately the same time. VBAT Battery Fail2 2. This power state applies only to the SWC functions powered by VBAT. On or Off On or Off On or Off Off Power Fail Off Off Off On or Off Power Off Off On On On or Off PowerOn On On On OnorOff Illegal3 3. Operation is not guaranteed and register data may be corrupted. However, at power-on/off, the device may temporarily enter this power state due to the different rise/fall times of the VDD3 and VSB3 power supplies. On Off Off On or Off VDD3, VSB3, VCORF On or Off Battery Fail VDD3, VSB3 and VCORF Off, Power Fail VDD3 Off, Power Off VDD3, VSB3, VCORF and VBAT On Power On VBAT On VBAT Power-Up Reset VSB3 On, VDD3 On, VBAT Off VSB3 Off VDD3 Off VSB3 On VBAT Off VBAT On generates VDD3 On VBAT Off VSB Power-Up Reset VDD Power-Up Reset and VBAT Off VBAT On VSB3, VCORF and VBAT On VSB3 Off VBAT On VBAT On VBAT Off Figure 1. Power State Transitions SWC functions powered by VBAT |
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