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POWER MANAGEMENT

SC2516

Application information

Description

The SEMTECH SC2516 DDR power supply controller is

the latest and most complete, Three in One switching

and linear regulator controller, providing the necessary

functions to comply with S3 and S5 sleep state signals

generated by the Desktop Computer Motherboards. The

SC2516 uses the Latched BF_CUT input signal which is

to comply with the power sequencing requirements.

Logically, the BF_CUT signal can be represented as:

OK

P

S

CUT

BF

_

3

_

•

=

(For details of the Latched BF_CUT signal definition, refer

to Intel documentation).

Where S3 is the input to the Silver-box Supply for Suspend

to RAM, (S3=1 for Suspend to RAM) and P_OK is a signal

generated by the Silver-box supply, indicating that all rails

are within specification.

S3 and S5 States

S3 and S5 States

S3 and S5 States

S3 and S5 States

S3 and S5 States

During S3 and S5 sleep states, The operation of the

VDDQ and VTT is governed by the intelR specifications

with regards to the BF_CUT signal. The timing diagram

demonstrates the state of the controller and each of

the VDDQ, VTT and GMCH supplies during S3 and S5

transitions

VDDQ Power Section

SC2516 architecture eliminates the need for the Back-

Feed Cut MOSFET, since the VDDQ is always supplied

from the same input voltage bus (5V dual). The SC2516

is capable of driving a 4000pf capacitor in 25ns (typical,

top gate). This drive capability allows 15-20A DC load on

the VDDQ supply from the 5V main input rail.

Power Sequencing

Power Sequencing

Power Sequencing

Power Sequencing

Power Sequencing

Once BF_CUT signal low and P_OK signal goes high, The

VDDQ supply will be activated with S0 as well. The SS/

EN pin voltage is charged by internal constant current

source. When SS/EN voltage reaches to 0.3V (typical),

High side driver begins chopping and main power is

activated as an asynchronous Buck converter. When SS/

EN voltage reaches to 1.25V (typical), Low side driver

begins chopping and main power is activated as a

synchronous Buck converter.

When BF_CUT signal goes high (S3 state), the VDDQ

switcher is always on and is sourced by 5VSTBY rail during

this time.

When both BF_CUT and P_OK signals are low, The VDDQ

supply be disabled with S5 as well. Both high side and

low side drivers are pulled low.

Short Circuit Protection

Short Circuit Protection

Short Circuit Protection

Short Circuit Protection

Short Circuit Protection

Short circuit protection is implemented by sensing the

VDDQ output voltage. If it falls to 75% (typical) of its

nominal voltage, as sensed by the FB pin, the TG and BG

pins are latched off and the VDDQ switcher is shutdown.

It will shutdown the VTT also, since the VTT regulator is

fed from the VDDQ bus. To recover from the short circuit

protection mode, either the 5VSBY rail has to be recycled,

or the SS/EN pin must be pulled below 0.3V and

released to restart VDDQ switcher operation.

GMCH Power Section

The SC2516 Switching controller supplies a 1.5V or 1.

25V GMCH (Graphic Memory Control Hub) voltage via a

standard synchronous BUCK converter typically

connected to the 5VCC or 3.3VCC power rail from Silver-

box supply. Base on the basic advantage of switching

mode controller, The GMCH output current can support

up to 20A.

Power Sequencing

Power Sequencing

Power Sequencing

Power Sequencing

Power Sequencing

Since the Chip-Set supply should come up before the

Active Memory cycle, the GMCH supply is sequenced with

the rising edge of the P_OK signal from Sliver-box supply.

Thus the GMCH regulator drivers are on when P_OK signal

is greater than its respective threshold. The external

MOSFET gates are pulled low when P_OK signal is lower

than its threshold. Thus the GMCH is disabled during S3

and S5 (See timing diagram).

VTT Rail

The VTT termination voltage is supplied via an internal

sink/source linear regulator when BF_CUT is low, and

the P_OK signal has met its threshold voltage and SS/

EN voltage reaches to 1V. When BF_CUT is high, the VTT

termination voltage is not needed and is thus tri-stated.

The VTT linear regulator is capable of sourcing and sinking

1.8 Amps (Minimum). It is recommended that one should

use at least 470uF low ESR capacitor and 1uF ceramic

capacitor (from VTT pin to Ground with short distance)

to ensure the stable operation.

Short Circuit Protection

Short Circuit Protection

Short Circuit Protection

Short Circuit Protection

Short Circuit Protection

The VTT regulator has two internal current limit circuits,

one for the sink and one for the source regulators. Both

current limits are set at 3Amp (typical). If maintained at

current limit, the internal regulators act like constant

current sources, and supply the max current until the

device temperature raises above thermal shutdown

thresholds, at which point that regulator shuts down.