RT7252B datasheet(13/14 Pages) RICHTEK

13 / 14 page

RT7252A/B

DS7252A/B-01 April 2012

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

For recommended operating condition specifications, the

maximum junction temperature is 125

°C. The junction to

ambient thermal resistance,

θJA, is layout dependent. For

SOP-8 (Exposed Pad) package, the thermal resistance,

θJA, is 75°C/W on a standard JEDEC 51-7 four-layer

thermal test board. The maximum power dissipation at

TA = 25

°C can be calculated by the following formula :

PD(MAX) = (125

°C − 25°C) / (75°C/W) = 1.333W for

SOP-8 (Exposed Pad) package

The maximum power dissipation depends on the operating

ambient temperature for fixed TJ(MAX) and thermal

resistance,

θJA. The derating curve in Figure 3 allows the

designer to see the effect of rising ambient temperature

on the maximum power dissipation.

Figure 3. Derating Curve of Maximum Power Dissipation

Layout Consideration

Follow the PCB layout guidelines for optimal performance

of the RT7252A/B

Keep the traces of the main current paths as short and

wide as possible.

Put the input capacitor as close as possible to the device

pins (VIN and GND).

SW node is with high frequency voltage swing and should

be kept at small area. Keep sensitive components away

from the SW node to prevent stray capacitive noise

pickup.

Place the feedback components to the FB pin as close

as possible.

The GND and Exposed Pad should be connected to a

strong ground plane for heat sinking and noise protection.

Figure 4. PCB Layout Guide

Table 3. Suggested Capacitors for CIN and COUT

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

100

125

Ambient Temperature (°C)

Four-Layer PCB

VOUT

COUT

CIN

CBOOT

GND

Input capacitor must

be placed as close

to the IC as possible.

SW should be connected to

inductor by wide and short trace.

Keep sensitive components

away from this trace.

The resistor divider must be

connected as close to the

device as possible.

VIN

BOOT

GND

PGOOD

GND

Location

Component Supplier

Part No.

Capacitance (

μF)

Case Size

CIN

MURATA

GRM31CR61E106K

1206

CIN

TDK

C3225X5R1E106K

1206

CIN

TAIYO YUDEN

TMK316BJ106ML

1206

COUT

MURATA

GRM32ER61E226M

1210

COUT

MURATA

GRM21BR60J226M

0805

COUT

TDK

C3225X5R0J226M

1210

COUT

TAIYO YUDEN

EMK325BJ226MM

1210

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