RT9245PC datasheet(14/22 Pages) RICHTEK

14 / 22 page

RT9245

DS9245-06

March 2007

www.richtek.com

For load line design, with application circuit in Figure 13,

it can eliminate the dead zone of load line at light loads.

VCSP = VOUT +IL x DCR

if GM holds input voltages equal, then

VCSP = VCSN

For the lack of sinking capability of GM, RCSN2 should be

small enough to compensate the negative inductor valley

current especially at light loads.

VID on the Fly

With external pull up resistors tied to VID pins, RT9245

converters different VID codes from CPU into output

voltage. Figure 12 and Figure 13 show the waveforms of

VID on the fly function.

Figure 12

CSN

CSN2

CSN1

OUT

CSN2

CSN1

OUT

CSN2

CSN1

IDCR

DCR

IDCR

+×

××

CSN

CSN2

CSN1

DCR

≥

CSN2

1.3V

5A 1m

R330

−×

≥

RCSN2

≤ 85.8kΩ

Choose RCSN2 = 82k

Assume the negative inductor valley current is

−5A at no

load, then for

Figure 15

Current Balance Function

2040

6080

100

IOUT (A)

IL1

IL3

IL2

IL4

CH1:(5V/Div)

CH2:(500mV/Div)

CH3:(500mV/Div)

CH4:(1V/Div)

VID on the Fly (Falling)

Time (25

μs/Div)

VCORE

PWM

VFB

VID125

VDAC = 1.500, IOUT = 5A

Figure13. Application circuit of GM

DCR

ESR

RCSN1

GMx

RCSN2

VCSP

VCSN

RCSN1 = 330

Ω, RADJ = 160Ω, VOUT = 1.300

Figure 14

Load Line without dead zone at light loads

1.23

1.24

1.25

1.26

1.27

1.28

1.29

1.3

1.31

IOUT (A)

RCSN2 open

RCSN2 = 82k

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