PC87373 datasheet(116/174 Pages) NSC

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Revision 1.1

9.0

Glue Functions

This chapter describes the glue functions integrated in the PC87373 device.

9.1 OVERVIEW

This module contains 11 glue functions. Most of them operate independently of the other functions and of the other modules

in the PC87373 device.

The 11 glue functions are divided into three groups:

• Power-related functions:

— Highest active Main supply reference (REF5V)

— Highest active Standby supply reference (REF5V_STBY)

— Resume reset (RSMRST)

— Main power good (PWRGD_3V)

— Rambus SCK clock gate control (SCK_BJT_GATE)

— Power distribution control (BKFD_CUT, LATCHED_BF_CUT)

— Main power supply control (PS_ON)

• Miscellaneous functions:

— CNR downstream codec dynamic control (CDC_DWN_RST)

— Hard-disk LED indicator control (HD_LED)

• SMBus support functions:

— SMBus voltage translation (3V_DDCSCL, 3V_DDCSDA, 5V_DDCSCL, 5V_DDCSDA)

— SMBus isolation (SMB1_SCL, SMB1_SDA, SMB2_SCL, SMB2_SDA)

Each function is described in the following sections.

9.2 FUNCTIONAL DESCRIPTION

9.2.1

Highest Active Main Supply Reference

This function generates the REF5V analog output signal (see specification in Section 13.2.10 on page 155). When the Main

power supply is turned on or off, the REF5V signal tracks either the VDD3 or VDD5 power supplies, whichever has a higher

voltage.

The circuit that generates the REF5V output is composed of two parts:

One part tracks the VDD3 supply voltage and is implemented in the PC87373 device.

One part tracks the VDD5 supply voltage and is implemented by an external resistor connected to the VDD5 power

supply.

Figure 21 shows a simplified diagram of the circuit that generates the REF5V analog output signal

Figure 21. REF5 Generation (Simpliﬁed Diagram)

VDD5

1 K

Ω

VDD3

REF5V

Comp

0.1-1

µF

PC87373

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