RT8113 datasheet(15/21 Pages) RICHTEK

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RT8113

DS8113-02 April 2011

www.richtek.com

Figure 5. Circuit for VOUT Differential Sensing and No Load Offset

Load Transient Quick Response

In steady state, the voltage of VFB is controlled to be very

close to VEAP. However While a load step transient from

light load to heavy load could cause VFB to be lower than

VEAP by several tens of mV. In conventional buck converter

design (without non-linear control) for CPU VR application,

due to limited control bandwidth, it is hard for the VR to

prevent VOUT undershoot during quick load transient from

light load to heavy load. Hence, the RT8113 builds in a

state-of-the-art quick response function which detects load

Figure 6. Load Transient Quick Response

VEAP = VDAC - VADJ

VOUT

COMP

RFB

CFB

QR Circuit

IOUT

VOUT

VDAC

EAP

COMP

FBRTN

RADJ

ADJ

IOFSP

CFB

RFB

(Positive Remote

Sense Pin of CPU)

VCC_SNS

VSS_SNS

(Negative Remote

Sense Pin of CPU)

transient by comparing VFB and VEAP. If VFB suddenly

drops below “VEAP

− VQR”where VQR is a predetermined

voltage (~40mV), the quick response indicator QR rises

up. When QR = high, the RT8113 turns on all high side

MOSFETs and turns off all low side MOSFETs. The

sensitivity of quick response can be adjusted by varying

the values of CFB and RFB. Smaller RFB and/or larger CFB

will make QR easier to be triggered. Figure 6 is the circuit

and typical waveforms.

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