RT3612EB datasheet(25/47 Pages) RICHTEK

25 / 47 page

RT3612EB

DS3612EB-02 December 2019

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Per Phase Current Sense

To achieve higher efficiency, the RT3612EB adopts

inductor DCR current sensing to get each phase current

signal, as illustrated in Figure 6. An external low-pass

filter RX1 and CX reconstruct the current signal. The low-

pass filter time constant RX1 x CX should match time

constant

DCR of Inductance and DCR. It's fine to fine tune

RX1 and CXfor transient performance and current reporting.

If RC network time constant matches inductor time

constant

DCR , an ideal load transient waveform can be

designed. If RC network time constant is larger than

inductor time constant

DCR , VCORE waveform has a

sluggish droop during load transient. If RC network is

smaller than inductor time constant

DCR ,VCORE

waveform sags to create an undershooting to fail the

specification and mis-trigger over current protections (sum

OCP and per phase OCP). Figure 7 shows the output

waveforms according to the RC network time constant.

The resistance of RCSx is restricted to 680

Ω and the

accuracy is within 1%. RX1 is highly recommended as

two 0603 size resistors in series to enhance the Iout

reporting accuracy. X7R type capacitor is suggested for

CX in the application.

CSIN

CS PERx

DCR

680







RX2 is optional for prevent VCSIN exceeding current sense

amplifier input range. The time constant of (RX1//RX2)*C

should match

DCR

CSIN

CS,PERx

DCR

/ =

680

R +R





The current signal ICS,PERx is mirrored for loadline control/

current reporting, current balance, zero current detection

and over current protection. The mirrored current to IMON

pin is one time of ICS,PER.





IMON

MIRROR

CS PERx

MIRROR

, A





The current sense lines must be routed as differential pair

from the inductor to the controller on the same layer.

Figure 6. Inductor DCR Current Sensing Method

ISENxP

ISENxN

DCR

RX1

VCORE

RCSx=680ohm

ILx

ICS,PERx

ICBx

IZDx

IOCx

VCSIN

IMONx

RX2

Option

Figure 7. All Kinds of RC Network Time Constant

RC =

DCR



RC <

DCR



RC >

DCR



Sluggish droop

Undershoot created in VCORE

VCORE

VIMON

OUT

x R



OUT



Ideal load transient waveform

VCORE

VIMON

OUT

x R



OUT



VCORE

VIMON

OUT

x R



OUT



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