RT8167B datasheet(33/38 Pages) RICHTEK

33 / 38 page

RT8167B

DS8167B-00

October 2011

www.richtek.com

Figure 11. On-Time Setting with RC Filter

(13)

≥

××

−

ONx

REFx

-12

TONSETx

REFx

1.2V)

23.33 10

(14)

−

−−

=×

−

⎡⎤

+×

−

⎣⎦

⎡⎤

+×

−

⎣⎦

S(MAX)

HS Delay

REFx(MAX)

LOAD(MAX)

ON _ LS FET

DROOP

IN(MAX)

LOAD(MAX)

ON _ LS FET

ON _ HS FET

f(kHz)

DCR R

When VREFx is larger than 1.2V, the equivalent switching

frequency may be over the maximum design range, making

it unacceptable. Therefore, the VR implements a pseudo-

constant-frequency technology to avoid this disadvantage

of CCRCOT topology. When VREFx is larger than 1.2V,

the on-time equation will be modified to :

On-time translates roughly to switching frequencies. The

on-times guaranteed in the Electrical Characteristics are

influenced by switching delays in external high side

MOSFET. Also, the dead-time effect increases the effective

on-time, reducing the switching frequency. It occurs only

in CCM during dynamic output voltage transitions when

the inductor current reverses at light or negative load

currents. With reversed inductor current, PHASEx goes

high earlier than normal, extending the on-time by a period

equal to the high side MOSFET rising dead time.

For better efficiency of the given load range, the maximum

switching frequency is suggested to be :

where fS(MAX) is the maximum switching frequency, tHS-

Delay is the turn on delay of high side MOSFET, VREFx(MAX)

is the maximum application DAC voltage of application,

VIN(MAX) is the maximum application input voltage,

ILOAD(MAX) is the maximum load of application, RON_LS-FET

is the low side MOSFET RDS(ON), RON_HS-FET is the high

side MOSFET RDS(ON), DCRL is the inductor DCR, and

RDROOP is the load line setting.

GFX/CORE

VR CCRCOT

PWM

Generator

TONSETx

RTONSETx

VIN

VREFx

On-Time

Differential Remote Sense Setting

The CORE/GFX VR includes differential, remote-sense

inputs to eliminate the effects of voltage drops along the

PC board traces, CPU internal power routes and socket

contacts. The CPU contains on-die sense pins CORE/

GFX VCC_SENSE and VSS_SENSE. Connect RGNDx to CORE/

GFX VSS_SENSE. Connect FBx to CORE/GFX VCC_SENSE

with a resistor to build the negative input path of the error

amplifier. The precision voltage reference VREFx is referred

to RGND for accurate remote sensing.

Current Sense Setting

The current sense topology of the CORE/GFX VR is

continuous inductor current sensing. Therefore, the

controller can be less noise sensitive. Low offset amplifiers

are used for loop control and over current detection. The

internal current sense amplifier gain (AI) is fixed to be 10.

The ISENxP and ISENxN denote the positive and negative

input of the current sense amplifier.

Users can either use a current sense resistor or the

inductor's DCR for current sensing. Using inductor's DCR

allows higher efficiency as shown in Figure 12. To let

then the transient performance will be optimum. For

example, choose L = 0.36

μH with 1mΩ DCR and

CX = 100nF, to yields for RX :

DCR

=×

(15)

0.36 H

R3.6k

100nF

Ω×

(16)

DCR

VOUT

(VCORE/VGFX)

CByp

ISENxP

ISENxN

PHASEx

VCSx

Figure 12. Lossless Inductor Sensing

RT8167B Datasheet(PDF) 33 Page - Richtek Technology Corporation

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