Richtek Rt7297b User manual

RT7297B

DS7297B-02 September 2012 www.richtek.com

Ordering Information

Note :

Richtek products are :

`RoHS compliant and compatible with the current require-

ments of IPC/JEDEC J-STD-020.

`Suitable for use in SnPb or Pb-free soldering processes.

Pin Configurations

(TOPVIEW)

Applications

WirelessAP/Router

Set-Top-Box

Industrial and Commercial Low Power Systems

LCDMonitorsandTVs

GreenElectronics/Appliances

PointofLoadRegulationof High-PerformanceDSPs

SOP-8 (Exposed Pad)

3A, 18V, 1.2MHz Synchronous Step-Down Converter

General Description

TheRT7297Bisahighefficiency,monolithicsynchronous

step-down DC/DC converter that can deliver up to 3A

output current from a 4.5V to 18V input supply. The

RT7297B's current mode architecture and external

compensation allow the transient response to be

optimizedoverawideinputvoltagerangeandloads.Cycle-

by-cyclecurrentlimitprovides protection against shorted

outputs,andsoft-starteliminatesinputcurrentsurgeduring

start-up. The RT7297B also provides under voltage

protection and thermal shutdown protection. The low

current (<3μA) shutdown mode provides output

disconnection, enabling easy power management in

battery-powered systems. The RT7297B is available in

an SOP-8 (Exposed Pad) package.

Features



±±

±±

±1.5% High Accuracy Reference Voltage



4.5V to 18V Input Voltage Range



3A Output Current



Integrated N-MOSFET Switches



Current Mode Control



Fixed Frequency Operation : 1.2MHz



Output Adjustable from 0.8V to 12V



Up to 95% Efficiency



Programmable Soft-Start



Stable with Low ESR Ceramic Output Capacitors



Cycle-by-Cycle Over Current Protection



Input Under Voltage Lockout



Output Under Voltage Protection



Thermal Shutdown Protection



RoHS Compliant and Halogen Free

BOOT

VIN

GND

COMP

GND

Package Type

SP : SOP-8 (Exposed Pad-Option 1)

RT7297B

Lead Plating System

Z : ECO (Ecological Element with

Halogen Free and Pb free)

H : UVP Hiccup

L : UVP Latch-Off

Marking Information

RT7297BxZSP : Product Number

x : H or L

YMDNN : Date Code

RT7297Bx

ZSPYMDNN

RT7297B

2DS7297B-02 September 2012www.richtek.com

Functional Pin Description

Pin No. Pin Name Pin Function

1 BOOT

Bootstrap for High Side Gate Driver. Connect a 0.1μF or greater ceramic

capacitor from BOOT to SW pins.

2 VIN

Input Supply Voltage, 4.5V to 18V. Must bypass with a suitable large ceramic

capacitor.

3 SW Switch Node. Connect this pin to an external L-C filter.

9 (Exposed Pad) GND Ground. The exposed pad must be soldered to a large PCB and connected to

GND for maximum power dissipation.

5 FB Feedback Input. It is used to regulate the output of the converter to a set value

via an external resistive voltage divider.

6 COMP

Compensation Node. COMP is used to compensate the regulation control

loop. Connect a series RC network from COMP to GND. In some cases, an

additional capacitor from COMP to GND is required.

7 EN

Enable Input Pin. A logic high enables the converter; a logic low forces the IC

into shutdown mode reducing the supply current to less than 3μA. Attach this

pin to VIN with a 100kΩpull up resistor for automatic startup.

8 SS Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor

from SS to GND to set the soft-start period. A 0.1μF capacitor sets the

soft-start period to 13.5ms.

Typical Application Circuit

VOUT (V) R1 (kΩ) R2 (kΩ) RC(kΩ) CC(nF) L (μH) COUT (μF)

8 27 3 51 2.2 10 22 x 2

5 62 11.8 33 2.2 6.8 22 x 2

3.3 75 24 22 2.2 3.6 22 x 2

2.5 25.5 12 16 2.2 3.6 22 x 2

1.5 10.5 12 10 2.2 2 22 x 2

1.2 12 24 8.2 2.2 2 22 x 2

1 3 12 6.8 2.2 2 22 x 2

Table 1. Suggested Components Selection

VIN

GND

BOOT

3.6µH

0.1µF

22µF x 2

75k

24k

VOUT

3.3V

10µF x 2

VIN

4.5V to 18V RT7297B

CSS

COMP

2.2nF RC

22k

Open

4, 9 (Exposed Pad)

CBOOT

CIN

0.1µF

COUT

REN 100k

RT7297B

DS7297B-02 September 2012 www.richtek.com

Function Block Diagram

Comparator

Oscillator

Foldback

Control

0.4V

Internal

Regulator

Shutdown

Comparator

Current Sense

Amplifier

BOOT

VIN

GND

COMP

VCC

6µA

Slope Comp

Current

Comparator

-EA

0.8V

1.2V

Lockout

Comparator

VCC

Ω90m

Ω110m

2.5V

VARSENSE

5kΩ

RT7297B

4DS7297B-02 September 2012www.richtek.com

Electrical Characteristics

(VIN = 12V, TA= 25°C, unless otherwise specified)

Absolute Maximum Ratings (Note 1)

Supply InputVoltage, VIN ----------------------------------------------------------------------------------------- −0.3V to 20V

Switch Voltage, SW ------------------------------------------------------------------------------------------------ −0.3Vto (VIN + 0.3V)

VBOOT −VSW ---------------------------------------------------------------------------------------------------------- −0.3V to 6V

Other Pins Voltage -------------------------------------------------------------------------------------------------- −0.3V to 20V

Power Dissipation, PD@ TA= 25°C

SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------- 1.333W

 Package Thermal Resistance (Note 2)

SOP-8 (Exposed Pad), θJA ---------------------------------------------------------------------------------------- 75°C/W

SOP-8 (Exposed Pad), θJC --------------------------------------------------------------------------------------- 15°C/W

LeadTemperature(Soldering,10sec.)------------------------------------------------------------------------- 260°C

JunctionTemperature----------------------------------------------------------------------------------------------- 150°C

StorageTemperatureRange -------------------------------------------------------------------------------------- −65°Cto150°C

ESD Susceptibility (Note 3)

HBM(HumanBodyModel)---------------------------------------------------------------------------------------- 2kV

Recommended Operating Conditions (Note 4)

Supply InputVoltage, VIN ----------------------------------------------------------------------------------------- 4.5V to 18V

JunctionTemperatureRange-------------------------------------------------------------------------------------- −40°C to125°C

AmbientTemperatureRange-------------------------------------------------------------------------------------- −40°C to 85°C

Parameter Symbol Test Conditions Min Typ Max Unit

Shutdown Supply Current VEN = 0V -- 0.5 3 μA

Supply Current VEN = 3V, VFB = 0.9V -- 0.8 1.2 mA

Reference Voltage VREF 4.5V ≤ VIN ≤ 18V 0.788 0.8 0.812 V

Error Amplifier

Transconductance GEA ΔIC= ±10μA -- 940 -- μA/V

High Side Switch

On-Resistance RDS(ON)1 -- 110 -- mΩ

Low Side Switch

On-Resistance RDS(ON)2 -- 90 -- mΩ

High Side Switch Leakage

Current V

EN = 0V, VSW = 0V -- 0 10 μA

Upper Switch Current Limit Min. Duty Cycle, VBOOT − VSW = 4.8V -- 5.1 -- A

COMP to Current Sense

Transconductance GCS -- 4.7 -- A/V

Oscillation Frequency fOSC1 1 1.2 1.4 MHz

Short Circuit Oscillation

Frequency fOSC2 V

FB = 0V -- 270 -- kHz

Maximum Duty Cycle DMAX V

FB = 0.7V -- 78 -- %

Minimum On Time tON -- 100 -- ns

RT7297B

DS7297B-02 September 2012 www.richtek.com

Parameter Symbol Test Conditions Min Typ Max Unit

Logic-High VIH 2.7 -- 18

EN Input Threshold

Voltage Logic-Low VIL -- -- 0.4

Input Under Voltage Lockout

Threshold VUVLO V

IN Rising 3.8 4.2 4.5 V

Input Under Voltage Lockout

Hysteresis ΔVUVLO -- 320 -- mV

Soft-Start Current ISS V

SS = 0V -- 6 -- μA

Soft-Start Period tSS C

SS = 0.1μF -- 13.5 -- ms

Thermal Shutdown TSD -- 150 -- °C

Note 1. Stresses beyond those listed “Absolute Maximum Ratings”may cause permanent damage to the device. These are

stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in

the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may

affect device reliability.

Note 2. θJA is measured at TA= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is

measured at the exposed pad of the package.

Note 3. Devices are ESD sensitive. Handling precaution is recommended.

Note 4. The device is not guaranteed to function outside its operating conditions.

RT7297B

6DS7297B-02 September 2012www.richtek.com

Typical Operating Characteristics

Efficiency vs. Load Current

100

00.511.522.53

Load Current (A)

Efficiency (%)

VOUT = 3.3V

VIN = 12V

VIN = 17V

Output Voltage vs. Temperature

3.26

3.27

3.28

3.29

3.30

3.31

3.32

3.33

3.34

-50 -25 0 25 50 75 100 125

Temperature (°C)

Output Voltage (V)

VIN = 12V, VOUT = 3.3V

Output Voltage vs. Load Current

3.20

3.22

3.24

3.26

3.28

3.30

3.32

3.34

3.36

3.38

3.40

0 0.5 1 1.5 2 2.5 3

Load Current (A)

Output Voltage (V)

VOUT = 3.3V

VIN = 12V

VIN = 17V

Switching Frequency vs. Temperature

1.10

1.11

1.12

1.13

1.14

1.15

1.16

1.17

1.18

1.19

1.20

1.21

1.22

1.23

1.24

-50 -25 0 25 50 75 100 125

Temperature (°C)

Switching Frequency (kHz)1

VOUT = 3.3V, IOUT = 0A

VIN = 17V

VIN = 12V

Switching Frequency vs. Input Voltage

1.16

1.17

1.18

1.19

1.20

1.21

1.22

1.23

1.24

1.25

1.26

4.5 7 9.5 12 14.5 17

Input Voltage (V)

Switching Frequency (MHz)1

VIN = 4.5V to 17V, VOUT = 3.3V, IOUT = 0A

Output Voltage vs. Input Voltage

3.26

3.27

3.28

3.29

3.30

3.31

3.32

3.33

3.34

4 6 8 1012141618

Input Voltage (V)

Output Voltage (V)

VIN = 4.5V to 17V

RT7297B

DS7297B-02 September 2012 www.richtek.com

Current Limit vs. Temperature

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

-50-25 0 25 50 75100125

Temperature (°C)

Current Limit (A)

VIN = 12V, VOUT = 3.3V

Current Limit vs. Input Voltage

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

4.5 7 9.5 12 14.5 17

Input Voltage (V)

Current Limit (A)

VIN = 4.5V to 17V, VOUT = 3.3V

Time (100μs/Div)

Load Transient Response

VOUT

(100mV/Div)

IOUT

(2A/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 0A to 3A

Time (100μs/Div)

Load Transient Response

VOUT

(100mV/Div)

IOUT

(2A/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A

Time (500ns/Div)

Switching

VSW

(10V/Div)

VOUT

(5mV/Div)

(2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 1.5A

Time (500ns/Div)

Switching

VIN = 12V, VOUT = 3.3V, IOUT = 3A

VSW

(10V/Div)

VOUT

(5mV/Div)

(2A/Div)

RT7297B

8DS7297B-02 September 2012www.richtek.com

Power On from VIN

Time (10ms/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 3A

(2A/Div)

VOUT

(2V/Div)

VIN

(5V/Div)

Power Off from VIN

Time (10ms/Div)

(2A/Div)

VOUT

(2V/Div)

VIN

(5V/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 3A

Power On from EN

Time (10ms/Div)

VOUT

(2V/Div)

VEN

(5V/Div)

(2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A

Power Off from EN

Time (10ms/Div)

VIN = 12V, VOUT = 3.3V, IOUT = 3A

VOUT

(2V/Div)

VEN

(5V/Div)

(2A/Div)

RT7297B

DS7297B-02 September 2012 www.richtek.com

Application Information

Output Voltage Setting

TheresistivedividerallowstheFBpin to sense the output

voltage as shown in Figure 1.

Figure 1. Output Voltage Setting

The output voltage is set by an external resistive voltage

divideraccordingto the followingequation:

OUT REF R1

V =V 1

⎛⎞

⎜⎟

⎝⎠

Where VREF is the reference voltage (0.8V typ.).

External Bootstrap Diode

Connect a 100nF low ESR ceramic capacitor between

the BOOT pin and SW pin. This capacitor provides the

gatedrivervoltage forthehighsideMOSFET.

It is recommended to add an external bootstrap diode

between an external 5V and BOOT pin for efficiency

improvementwheninputvoltageislowerthan5.5Vorduty

ratio is higher than 65% .The bootstrap diode can be a

low cost one such as IN4148 or BAT54. The external 5V

can be a 5V fixed input from system or a 5V output of the

RT7297B. Note that the external boot voltage must be

lowerthan 5.5V

Figure 2. External BootstrapDiode

Chip Enable Operation

The EN pin is the chip enable input. Pulling the EN pin

low (<0.4V) will shutdown the device. During shutdown

mode,theRT7297B quiescentcurrentdropstolower than

3μA. Driving the EN pin high (>2.7V, <18V) will turn on

the device again. For external timing control, the EN pin

canalsobeexternallypulled highbyaddingaREN resistor

and CEN capacitor from the VINpin (see Figure 3).

BOOT

RT7297B 0.1µF

RT7297B

GND

VOUT

Soft-Start

The RT7297B provides soft-start function. The soft-start

function is used to prevent large inrush current while

converter is being powered-up. The soft-start timing can

beprogrammedbytheexternalcapacitorbetweenSS and

GND. An internal current source ISS (6μA) charges an

external capacitor to build a soft-start ramp voltage. The

VFB voltagewilltrackthe internalramp voltage duringsoft-

start interval. The typical soft-start time is calculated as

follows :

RT7297B

GND

VIN REN

CEN

An external MOSFET can be added to implement digital

controlontheENpin when nosystemvoltageabove1.8V

is available, as shown in Figure 4. In this case, a 100kΩ

pull-up resistor, REN, is connected between VIN and the

EN pin. MOSFET Q1 will be under logic control to pull

down the EN pin.

RT7297B

GND

100k

VIN

REN

Figure3.EnableTimingControl

Figure 4.Digital Enable Control Circuit

SS SS

0.8 C

Soft-Start time t = , if C capacitor

I0.8 0.1

is 0.1 F, then soft-start time = 13.5ms

μμ

× ≒

RT7297B

10 DS7297B-02 September 2012www.richtek.com

OUT OUT

LIN

I = 1

fL V

⎡⎤⎡ ⎤

Δ×−

⎢⎥⎢ ⎥

⎣⎦⎣ ⎦

Under Voltage Protection

Hiccup Mode

FortheRT7297BH,itprovidesHiccupMode UnderVoltage

Protection (UVP). When the VFB voltage drops below

0.4V, the UVP function will be triggered to shut down

switching operation. If the UVP condition remains for a

period, the RT7297BH will retry automatically. When the

UVP condition is removed, the converter will resume

operation. The UVP is disabled during Soft-Start period.

Having a lower ripple current reduces not only the ESR

lossesintheoutputcapacitors butalsotheoutputvoltage

ripple.Highfrequencywithsmall ripplecurrent canachieve

the highest efficiency operation. However, it requires a

large inductor to achieve this goal.

Fortheripplecurrentselection,the valueofΔIL=0.24(IMAX)

will be a reasonable starting point. The largest ripple

current occurs at the highest VIN. To guarantee that the

ripple current stays below the specified maximum, the

inductorvalueshould bechosenaccordingto thefollowing

equation :

Table 2. Suggested Inductors for Typical

Application Circuit

Component

Supplier Series Dimensions

(mm)

TDK VLF10045 10 x 9.7 x 4.5

TDK SLF12565 12.5 x 12.5x 6.5

TAIYO

YUDEN NR8040 8 x 8 x 4

OUT OUT

L(MAX) IN(MAX)

L = 1

fI V

⎡⎤⎡ ⎤

×−

⎢⎥⎢ ⎥

×Δ

⎣⎦⎣ ⎦

Theinductor'scurrentrating(causeda40°Ctemperature

rising from 25°C ambient) should be greater than the

maximum load current and its saturation current should

begreaterthanthe short circuit peak current limit.Please

see Table 2 for the inductor selection reference.

Figure 5. Hiccup Mode Under Voltage Protection

Figure6.Latch-OffModeUnderVoltageProtection

Latch-Off Mode

For the RT7297BL, it provides Latch-Off Mode Under

Voltage Protection (UVP). When the FB voltage drops

below half of the feedback reference voltage, VFB, UVP

willbetriggered andtheRT7297BLwillshutdownin Latch-

Off Mode. In shutdown condition, the RT7297BL can be

reset by EN pin or power input VIN.

Over Temperature Protection

The RT7297B features an Over Temperature Protection

(OTP) circuitry to prevent from overheating due to

excessive power dissipation. The OTP will shut down

switching operation when junction temperature exceeds

150°C. Once the junction temperature cools down by

approximately20°C,theconverterwillresumeoperation.

Tomaintaincontinuousoperation,themaximumjunction

temperatureshouldbelowerthan125°C.

Inductor Selection

Theinductorvalueandoperating frequencydeterminethe

ripple current according to a specific input and output

voltage. The ripple current ΔILincreases with higher VIN

anddecreases with higher inductance.

Time (50ms/Div)

Hiccup Mode

VOUT

(2V/Div)

ILX

(2A/Div)

IOUT = Short

Time (250μs/Div)

Latch-Off Mode

VOUT

(2V/Div)

ILX

(2A/Div)

IOUT = Short

RT7297B

DS7297B-02 September 2012 www.richtek.com

OUT IN

RMS OUT(MAX) IN OUT

I =I 1

−

CIN and COUT Selection

The input capacitance, CIN, is needed to filter the

trapezoidalcurrentatthesourceofthehighsideMOSFET.

Topreventlargeripplecurrent, alowESRinputcapacitor

sizedforthemaximumRMScurrentshouldbeused.The

approximate RMS current is given :

This formula has a maximum at VIN = 2VOUT, where

IRMS = IOUT / 2. This simple worst case condition is

commonly used for design because even significant

deviations do not offer much relief. Choose a capacitor

rated at a higher temperature than required. Several

capacitors may also be paralleled to meet size or height

requirements in the design. For the input capacitor, two

10μFlowESRceramic capacitorsaresuggested.Forthe

suggested

capacitor, please refer to Table 3 for more details. The

selection of COUT is determined by the required ESR to

minimize voltage ripple. Moreover, the amount of bulk

capacitance is also a key for COUT selection to ensure

that the control loop is stable. Loop stability can be

checked by viewing the load transient response as

described in a later section.

The output ripple, ΔVOUT, is determined by :

OUT L OUT

VIESR

8fC

⎡⎤

Δ≤Δ +

⎢⎥

⎣⎦

Theoutputripplewillbethehighest at the maximum input

voltage since ΔILincreases with input voltage. Multiple

capacitors placed in parallel may be needed to meet the

ESRandRMScurrenthandlingrequirement.Highervalues,

lowercostceramiccapacitorsarenowbecomingavailable

insmallercasesizes.Theirhighripplecurrent,highvoltage

ratingandlow ESRmakethemidealforswitchingregulator

applications. However, care must be taken when these

capacitors are used at input and output. When a ceramic

capacitor is used at the input and the power is supplied

by a wall adapter through long wires, a load step at the

output can induce ringing at the input, VIN. At best, this

ringing can couple to the output and be mistaken as loop

instability. At worst, a sudden inrush of current through

the long wires can potentially cause a voltage spike at

VIN large enough to damage the part.

Thermal Considerations

For continuous operation, do not exceed the maximum

operation junction temperature 125°C. The maximum

power dissipation depends on the thermal resistance of

IC package, PCB layout, the rate of surroundings airflow

andtemperature differencebetweenjunctiontoambient.

The maximum power dissipation can be calculated by

followingformula:

PD(MAX) = (TJ(MAX) − TA ) / θJA

Where TJ(MAX) is the maximum operation junction

temperature,TAis theambient temperatureandthe θJAis

the junction to ambient thermal resistance.

For recommended operating conditions specification of

RT7297B, the maximum junction temperature is 125°C.

The junction to ambient thermal resistance θJA is layout

dependent. For SOP-8 (Exposed Pad) package, the

thermalresistance θJA is75°C/WonthestandardJEDEC

51-7four-layersthermaltestboard.Themaximumpower

dissipation at TA= 25°C can be calculated by following

formula :

PD(MAX) = (125°C −25°C) / (75°C/W) = 1.333W

(min.copper area PCB layout)

PD(MAX) = (125°C −25°C) / (49°C/W) = 2.04W

(70mm2copperareaPCBlayout)

The thermal resistance θJA of SOP-8 (Exposed Pad) is

determined by the package architecture design and the

PCB layout design. However, the package architecture

design had been designed. If possible, it's useful to

increase thermal performance by the PCB layout copper

design. The thermal resistance θJA can be decreased by

adding copper area under the exposed pad of SOP-8

(ExposedPad)package.

AsshowninFigure7,theamountofcopperareatowhich

the SOP-8 (Exposed Pad) is mounted affects thermal

performance. When mounted to the standard

SOP-8 (Exposed Pad) pad (Figure 7.a), θJA is 75°C/W.

Adding copper area of pad under the SOP-8 (Exposed

Pad) (Figure7.b)reducestheθJA to64°C/W.Evenfurther,

increasing the copper area of pad to 70mm2(Figure 7.e)

reduces the θJA to 49°C/W.

RT7297B

12 DS7297B-02 September 2012www.richtek.com

(d) CopperArea = 50mm2,θJA = 51°C/W

(e) CopperArea = 70mm2,θJA = 49°C/W

Figure7.ThermalResistancevs.CopperArea Layout

Design

Figure8.DeratingCurveofMaximumPowerDissipation

(a) Copper Area = (2.3 x 2.3) mm2,θJA = 75°C/W

(b) CopperArea = 10mm2,θJA = 64°C/W

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

0 25 50 75 100 125

Ambient Temperature (°C)

Power Dissipation (W)

Copper Area

70mm2

50mm2

30mm2

10mm2

Min.Layout

Four-Layer PCB

Themaximumpowerdissipationdependsontheoperating

ambient temperature for fixed TJ(MAX) and thermal

resistance, θJA.ThederatingcurveinFigure8ofderating

curves allows the designer to see the effect of rising

ambient temperature on the maximum power dissipation

allowed.

RT7297B

DS7297B-02 September 2012 www.richtek.com

Layout Consideration

FollowthePCBlayoutguidelinesforoptimalperformance

oftheRT7297B.

`Keep the traces of the main current paths as short and

wide as possible.

`Puttheinputcapacitorascloseaspossibletothedevice

pins(VINandGND).

Figure 9. PCB LayoutGuide

Table 3. Suggested Capacitors for CIN and COUT

Location Component Supplier Part No. Capacitance (μF) Case Size

CIN MURATA GRM31CR61E106K 10 1206

CIN TDK C3225X5R1E106K 10 1206

CIN TAIYO YUDEN TMK316BJ106ML 10 1206

COUT MURATA GRM31CR60J476M 47 1206

COUT TDK C3225X5R0J476M 47 1210

COUT MURATA GRM32ER71C226M 22 1210

COUT TDK C3225X5R1C22M 22 1210

`SW node is with high frequency voltage swing and

shouldbekeptatsmallarea.Keepanalogcomponents

away from the SW node to prevent stray capacitive

noise pick-up.

`Connectfeedbacknetworkbehindtheoutputcapacitors.

Keep the loop area small. Place the feedback

components nearthe RT7297B.

`An example of PCB layout guide is shown in Figure 9

forreference.

VIN

VOUT

GND

CIN

GND

VOUT

COUT

Input capacitor must

be placed as close

to the IC as possible.

SW nods is with high frequency voltage swing and should

be kept at small area. Keep analog components away from

the SW node to prevent stray capacitive noise pick-up

The feedback components

must be connected as close

to the device as possible.

BOOT

VIN

GND

COMP

GND

CSS

GND VIN

REN

CBOOT

RT7297B

14 DS7297B-02 September 2012www.richtek.com

Richtek Technology Corporation

5F, No. 20, Taiyuen Street, Chupei City

Hsinchu, Taiwan, R.O.C.

Tel: (8863)5526789

Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should

obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot

assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be

accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third

parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.

Outline Dimension

EXPOSED THERMAL PAD

(Bottom of Package)

8-Lead SOP (Exposed Pad) Plastic Package