PC87372 datasheet(24/144 Pages) NSC

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Revision 1.2

2.0

Power, Reset and Clocks

2.1 POWER

2.1.1

Power Planes

The PC87372 device has three power planes (wells), as shown in the table below:

For correct operation, VSB3 must be applied before VDD3.

2.1.2

Power States

The PC87372 device has three power states:

• Power Fail - Main, Standby and Core power planes are powered off (V

DD3, VSB3 and VCORF are inactive).

• Power Off - Main power plane is powered off; the Standby and Core power planes are on (V

DD3 is inactive; VSB3 and

VCORF are active).

• Power On - Main, Standby and Core power planes are powered on (V

DD3, VSB3 and VCORF are active).

The following power state is illegal:

• The Main power plane is powered on and the Standby and Core power planes are off (i.e., V

DD3 is active; VSB and VCORF

are inactive). Operation is not guaranteed; 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.

Table 5 summarizes the power states described above.

Table 4. Power Planes

Power Plane

Description

Power Pins

Ground Pins

Main

Powers the I/O buffers for the external signals1 of the

Legacy modules (Serial Port, Parallel Port, FDC, KBC),

on-chip High-Frequency Clock Generator, FSM and the

LPC interface, including the buffered reset outputs

1. See the tables in Section 1.4 (pages 14

−22), speciﬁcally the Power Well column.

VDD3

VSS

Standby

Powers the I/O buffers for the external signals1 of the

GPIO ports, SWC, Glue Functions and the on-chip Core

power converter

VSB3

VSS

Core

Powers the internal (core) logic of all the device modules

VCORF

2. VCORF is generated from VSB3 by an on-chip power converter.

VSS

Table 5. Power States and Related Power Planes

Power State

Main (VDD3)

Standby (VSB3)

Core (VCORF)

1. VCORF is generated from VSB3; therefore both voltages are on or off at

approximately the same time.

Power Fail

Off

Power Off

Off

Power On

OnOnOn

Illegal2

2. Operation is not guaranteed and register data may be corrupted.

On Off

Off

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