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Fabricante

RT9173C

Cost-Effective, 2A Sink/Source Bus Termination Regulator

Richtek Technology 

RT9173C

Application Information

Consideration while designs the resistance of voltage

divider

Make sure the sinking current capability of pull-down NMOS

if the lower resistance was chosen so that the voltage on

VREFEN is below 0.2V.

In addition, the capacitor and voltage divider form the low-

pass filter. There are two reasons doing this design; one is

for output voltage soft-start while another is for noise

immunity.

How to reduce power dissipation on Notebook PC or

the dual channel DDR SDRAM application?

In notebook application, using RichTek's Patent

“Distributed Bus Terminator Topology” with choosing

RichTek's product is encouraged.

REFEN

Distributed Bus Terminating Topology

Terminator Resistor

R0

R1

VOUT

R2

RT9173C

R3

R4

R5

R6

VOUT

R7

RT9173C

R8

R9

BUS(0)

BUS(1)

BUS(2)

BUS(3)

BUS(4)

BUS(5)

BUS(6)

BUS(7)

BUS(8)

BUS(9)

VEXT

Figure 2

R(2N)

R(2N+1)

BUS(2N)

BUS(2N+1)

R1

VCNTL

VIN

RT9173C

REFEN

VOUT

R2

GND

VOUT

Figure 3

General Regulator

The RT9173C could also serves as a general linear

regulator. The RT9173C accepts an external reference

voltage at REFEN pin and provides output voltage regulated

to this reference voltage as shown in Figure 3, where

VOUT = VEXT x R2/(R1+R2)

For sourcing 2A output applications, the RT9173C could

works with low-ESR ceramic capacitors as a general linear

regulator. It offers significant cost and space savings for

power applications, especially for hand-held wireless

devices and notebooks application. The recommended

input and output capacitors must be 10μF or greater X7R/

X5R ceramic capacitors. The input and output capacitors

should be located as close as possible to the IC.

It’ s not recommended for sinking application while using

ceramic capacitors. When the sinking function is used with

ceramic capacitors, the system may be unstable. If the

current sinking function is necessary for this regulator,

please refer to the RT9173C Typical Application Circuit as

shown on page 2 for component selection.

As other linear regulator, dropout voltage and thermal issue

should be specially considered. Figure 4 and 5 show the

RDS(ON) over-temperature of RT9173C in PSOP-8 (Exposed

Pad) package. The minimum dropout voltage could be

obtained by the product of RDS(ON) and output current. For

thermal consideration, please refer to the relative sections.

RDS(ON) vs. Temperature

0.40

VCNTL = 3.3V

0.35

0.30

0.25

0.20

0.15

0.10

-50 -25

0

25 50 75

Temperature (°C)

100 125

Figure 4

www.richtek.com

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DS9173C-12 September 2007

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