RT7263B datasheet(12/15 Pages) RICHTEK

12 / 15 page

RT7263B

DS7263B-01

September 2012

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

OUT

RMS

OUT(MAX)

OUT

= I

−

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, one 22

μF low ESR ceramic

capacitors are recommended. For the recommended

capacitor, please refer to table 3 for more detail.

Table 3. Suggested Capacitors for CIN and COUT

Input and Output Capacitors Selection

The input capacitance, CIN, is needed to filter the

trapezoidal current at the source of the high side MOSFET.

To prevent large ripple current, a low ESR input capacitor

sized for the maximum RMS current should be used. The

RMS current is given by :

Location

Component Supplier

Part No.

Capacitance (

μF)

Case Size

CIN

MURATA

GRM32ER71C226M

1210

CIN

TDK

C3225X5R1C226M

1210

COUT

MURATA

GRM31CR60J476M

1206

COUT

TDK

C3225X5R0J476M

1210

COUT

MURATA

GRM32ER71C226M

1210

COUT

TDK

C3225X5R1C226M

1210

The inductor's current rating (caused a 40

°C temperature

rising from 25

°C ambient) should be greater than the

maximum load current and its saturation current should

be greater than the short circuit peak current limit. Please

see Table 2 for the inductor selection reference and it is

highly recommended to keep inductor value as close as

possible to the recommended inductor values for each

VOUT as shown in Table 1.

Component Supplier

Series

Dimensions (mm)

TDK

VLF10045

10 x 9.7 x 4.5

TDK

SLF12565

12.5 x 12.5 x 6.5

TAIYO YUDEN

NR8040

8 x 8 x 4

Table 2. Suggested Inductors for Typical

Application Circuit

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.

The output ripple,

ΔVOUT, is determined by :

OUT

ESR

8fC

⎡⎤

Δ≤ Δ

⎢⎥

⎣⎦

Higher values, lower cost ceramic capacitors are now

becoming available in smaller case sizes. Their high ripple

OUT

L(MAX)

IN(MAX)

L =

⎡⎤ ⎡

⎤

×−

⎢⎥ ⎢

⎥

×Δ

⎣⎦ ⎣

⎦

For the ripple current selection, the value of

ΔIL= 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 a specified maximum, the inductor

value should be chosen according to the following

equation :

current, high voltage rating and low ESR make them ideal

for switching regulator 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.

RT7263B Datenblatt(PDF) 12 Page - Richtek Technology Corporation

RT7263B Datenblatt(HTML) 12 Page - Richtek Technology Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Datenblatt Download

Link URL