RT3624LE datasheet(33/48 Pages) RICHTEK

33 / 48 page

RT3624LE

is a registered trademark of Richtek Technology Corporation

DS3624LE-00

April

2022

www.richtek.com

Load

Inductor

current

ΔV1

ΔV3

Short-term voltage target

VID Target

Output Voltage

Inductor

current

Loading Current ΔIcc

Figure 8. Zero Load-line with AC-droop Control

Per Phase Current Sense

To achieve higher efficiency, the RT3624LE adopts

inductor DCR current sensing to get each phase

current signal, as illustrated in Figure 9. An external

low-pass filter RX1 and CX reconstruct the current

signal. The low-pass filter time constant RX1×CX

should match time constant

DCR

of Inductance and

DCR. It’s necessary to fine tune RX1 and CX for

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

, VGTUS waveform has a sluggish droop

during load transient. If RC network is smaller than

inductor time constant

DCR

, VGTUS waveform sags to

create

undershooting

failing

meet

the

specification and mis-trigger over-current protections

(sum OCP). Figure 11 shows the output waveforms

according to the RC network time constant.

The RX1 is highly recommended as two 0603 size

resistors in series to enhance the Iout reporting

accuracy. CX is suggested to be 0.1

µF X7R/0603 for

low de-rating value at high frequency.

ICS,PERx=

VCSIN

680

ILx×DCR

680

RX2 is optional for preventing VCSIN from exceeding

current sense amplifier input range. The time constant

of (RX1//RX2) x CX should match

DCR

ICS,PERx=

VCSIN

680Ω

ILx×DCR

680Ω

RX2

RX1+R

The current signal ICS,PERx is mirrored for load-line

control/current reporting, current balance and zero

current. The mirrored current to IMON pin is one time of

ICS,PER. (IIMON=AMIRROR×ICS,PERx, AMIRROR=1)

The current sense lines must be routed as differential

pair from the inductor to the controller on the same

layer.

The AUX current sense is demonstrated in Figure 10.

In this design, the RCS is 1k

Ω and the mirror-gain is

1.25 (IIMON_AUX =AMIRROR×ICS_AUX, AMIRROR=1.25)

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