RT9206GS Ver la hoja de datos (PDF) - Richtek Technology

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componentes Descripción

Fabricante

RT9206GS

High Efficiency, Synchronous Buck with Dual Linear Controllers

Richtek Technology 

RT9206

Linear Regulator

Output Capacitor Selection

Solid tantalum capacitors are recommended for use on

the output capacitors of LDO because their typical ESR is

very close to the ideal value required for loop compensation.

Tantalums also have good temperature stability: a good

quality tantalum will typically show a capacitance value

that varies less than 10-15% across the full temperature

range of 125°C to -40°C. ESR will vary only about 2X going

from the high to low temperature limits.

Linear Regular MOSFETs Selection

The main consideration of pass MOSFETs of linear regulator

is package selection for efficient removal of heat. The power

dissipation of a linear regulator is

Plinear = (VIN - VOUT) × IOUT (W) (26)

The criterion for selection of package is the junction

temperature below the maximum desired temperature with

the maximum expected ambient temperature.

Layout Consideration

Layout is very important in high frequency switching

converter design. If designed improperly, the PCB could

radiate excessive noise and contribute to the converter

instability. First, place the PWM power stage components.

Mount all the power components and connections in the

top layer with wide copper areas. The MOSFETs of Buck,

inductor, and output capacitor should be as close to each

other as possible. This can reduce the radiation of EMI

due to the high frequency current loop. If the output

capacitors are placed in parallel to reduce the ESR of

capacitor, equal sharing ripple current should be

considered. Place the input capacitor directly to the drain

of high-side MOSFET. The MOSFETs of linear regulator

should have wide pad to dissipate the heat. In multilayer

PCB, use one layer as power ground and have a separate

control signal ground as the reference of the all signal. To

avoid the signal ground is effect by noise and have best

load regulation, it should be connected to the ground

terminal of output. Furthermore, follows below guidelines

can get better performance of IC:

(1). The IC needs a bypassing ceramic capacitor C1 as a

R-C filter to isolate the pulse current from power stage

and supply to IC, so the ceramic capacitor C1 should

be placed adjacent to the IC.

(2). Place the high frequency ceramic decoupling close

to the power MOSFETs.

(3). The feedback part should be placed as close to IC as

possible and keep away from the inductor and all noise

sources.

(4). The components of bootstraps (C8, C9 and D1) should

be closed to each other and close to MOSFETs.

(5).The PCB trace from UGATE and LGATE of controller to

MOSFETs should be as short as possible and can

carry 1A peak current.

(6). Place all of the components as close to IC as possible.

Figure 11 shows the typical PCB layout of synchronous

Buck converter with RT9206 controller

Figure 11. The PCB layout of synchronous Buck

converter with RT9206 controller

www.richtek.com

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DS9206-11 March 2007

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