PC87373 datasheet(122/174 Pages) NSC

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9.0 Glue Functions (Continued)

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9.2.6

Power Distribution Control

This function generates the BKFD_CUT and the LATCHED_BF_CUT power distribution control signals.

An active low BKFD_CUT signal is generated when the Main power supply voltage is valid (PWRGD_PS = high) and the

system is not in one of the S3 to S5 sleep states (SLP_S3 = high).

The LATCHED_BF_CUT signal is generated from BKFD_CUT and SLP_S5 as follows:

Rising edge of BKFD_CUT while the system is not in S5 sleep state (SLP_S5 = high) sets LATCHED_BF_CUT to

high.

Falling edge of BKFD_CUT while the system is not in S5 sleep state (SLP_S5 = high) resets LATCHED_BF_CUT to

low.

When the system is in S5 sleep state (SLP_S5 = low), LATCHED_BF_CUT is reset to low.

Figure 28 shows a simplified diagram of the circuit that generates the BKFD_CUT and the LATCHED_BF_CUT signals.

Figure 28. BKFD_CUT and LATCHED_BF_CUT Generation (Simpliﬁed Diagram)

For the AC characteristics, see Power Distribution Control on page 171.

9.2.7

Main Power Supply Control

This function generates the PS_ON signal, which turns the Main power supply on and off.

The Main power supply is turned on by an active low PS_ON signal, generated when the processor is currently inserted in

its socket (CPU_PRESENT = low) and the system is not in one of the S3 to S5 sleep states (SLP_S3 = high).

Figure 29 shows a simplified diagram of the circuit that generates the PS_ON signal.

Figure 29. PS_ON Generation (Simpliﬁed Diagram)

For the AC characteristics, see Main Power Supply Control on page 172.

1 K

Ω

BKFD_CUT

VDD5

Reset

(BKFD_CUT)

SLP_S5

LATCHED_BF_CUT

SLP_S3

PWRGD_PS

R-S Flip-Flop

Set

Detector

22 K

Ω

PS_ON

VSB5

SLP_S3

CPU_PRESENT

PC87373 Datasheet(PDF) 122 Page - National Semiconductor (TI)

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