PC87414 datasheet(33/257 Pages) NSC

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2.0 Power, Reset and Clocks (Continued)

Revision 1.2

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Figure 1 shows the power state transitions:

Figure 1. Power State Transitions

2.1.3

Power Connection and Layout Guidelines

The PC8741x requires a power supply voltage of 3.3V

± 10% for both the V

DD and the VSB supplies. The device is designed

to operate with a Lithium backup battery 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.

VDD, VSB 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 five ground return (V

SS) pins.

• The decoupling capacitors of the Main power supply (V

DD) pins.

• The decoupling capacitors of the Standby power supply (V

SB) pins.

• The decoupling capacitor of the Backup battery (V

BAT) pin.

Note that a low-impedance ground layer also improves noise isolation.

Decoupling Capacitors. The following decoupling capacitors must be used in order to reduce EMI and ground bounce:

• Main power supply (V

DD): Place one capacitor of 0.1 µFon each VDD-VSS pin pair as close to the pin as possible. In

addition, place one 10

−47 µF tantalum capacitor on the common net as close to the chip as possible.

• Standby power supply (V

SB): Place one capacitor of 0.1 µFon each VSB-VSS pin pair as close to the pin as possible. In

addition, place one 10

−47 µF tantalum capacitor on the common net as close to the chip as possible.

• Backup battery (V

BAT): Place one capacitor of 0.1 µF on the VBAT pin as close to the pin as possible. In addition, place

one 4.7

−10 µF ceramic capacitor on the common net as close to the chip as possible.

VDD, VSB and VBAT Off

Battery Fail

VDD and VSB Off, VBAT On

Power Fail

VDD Off, VSB On

Power Off

VDD and VSB On

Power On

VBAT On,

VPP Power-Up Reset

VSB On,

VDD On,

VBAT Off

VSB Off

VDD Off

VSB On (VBAT Off),

Cold Reset +

VPP Power-Up Reset

VBAT On

VBAT Off

VSB Off (VBAT Off)

VBAT On

VBAT Off

VSB Power-Up Reset

VDD Power-Up Reset

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