RT9199GS datasheet(9/13 Pages) RICHTEK

9 / 13 page

RT9199

DS9199-07

September 2007

www.richtek.com

General Regulator

The RT9199 could also serves as a general linear regulator.

The RT9199 accepts an external reference voltage at

REFEN pin and provides output voltage regulated to this

reference voltage as shown in Figure 6, where

VOUT = VREFEN x R2/(R1+R2)

As other linear regulator, dropout voltage and thermal issue

should be specially considered. Figure 7 shows the RDS(ON)

over temperature of RT9199. 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.

Application Information

Consideration while designing the resistance of

voltage divider

Refer to the “Typical Application Circuit”.Make sure the

current sinking capability of pull-down NMOS is enough

for the chosen voltage divider to pull-down the voltage at

REFEN pin below 0.15V to shutdown the device.

In addition, the capacitor CSS 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.

Distributed Bus Terminating Topology

R(2N)

R(2N+1)

RT9199

VOUT

REFEN

BUS(0)

BUS(1)

BUS(2)

BUS(3)

BUS(4)

BUS(5)

BUS(6)

BUS(7)

BUS(8)

BUS(9)

BUS(2N)

BUS(2N+1)

Terminator Resistor

Input Capacitor and Layout Consideration

Place the input bypass capacitor as close as possible to

the RT9199. A low ESR capacitor larger than 470uF is

recommended for the input capacitor. Use short and wide

traces to minimize parasitic resistance and inductance.

Inappropriate layout may result in large parasitic inductance

and cause undesired oscillation between RT9199 and the

preceding power converter.

Thermal Consideration

RT9199 regulators have internal thermal limiting circuitry

designed to protect the device during overload conditions.

For continued operation, do not exceed absolute maximum

operation junction temperature 125

°C. The power

dissipation definition in device is:

PD = (VIN - VOUT) x IOUT + VIN x IQ

Figure 6

VCNTL

REFEN

GND

VIN

VOUT

RT9199

REFEN

Figure 7

RDS(ON) vs. Temperature

0.28

0.3

0.32

0.34

0.36

0.38

0.4

0.42

0.44

0.46

0.48

-50

-25

255075

100

125

Temperature

VCNTL = 5V, VREFEN = 1V

(

°C)

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