PT1305 データシートの表示（PDF） - Unspecified

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PT1305

High Voltage Step-Up Converter

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PT1305

High Voltage Step-Up Converter

APPLICATION INFORMATION

z Inductor Selections

For most of the applications of the PT1305, it is

recommended to use an inductor of 22uH. Although

small size is one of the major factors in selecting an

inductor, the smaller and thinner inductors give higher

core losses at 1.25MHz and DRC, resulting in lower

efficiencies. The following tab le provides a list of

recommended inductors:

PARTNUMBER

LQH3C220

CDRH3D16-220

LB2012B220M

LEM2520-220

EJPC220KF

DCR（Ω）

0.71

0.53

1.7

5.5

4.0

CURRENT RATING (mA）

250

350

75

125

160

MANUFACTURER

MURATA

SUMIDA

TAIYO YUDEN

TAIYO YUDEN

PANASONIC

z Capacitor Selection

The small size of ceramic capacitors makes them ideal

for PT1305 applications. X5R and X7R types are

recommended because they retain their capacitance

over wider voltage and temperature ranges than other

types such as Y5V or Z5U. A 4.7　F input capacitor

and a 4.7　F output capacitor are sufficient for most

PT1305 applications.

The compensation capacitor C3 is selected as 22p in the

typical application.

z Diodes Selection

Schottky diodes, with their low forward voltage drop

and fast reverse recovery, are the ideal choices for

PT1305 applications. The forward voltage drop of a

Schottky diode represents the conduction losses in the

diode, while the diode capacitance (CT or CD)

represents the switching losses. For diode selection,

both forward voltage drop and diode capacitance need

to be considered. Schottky diodes with higher current

ratings usually have lower forward voltage drop and

larger diode capacitance, which can cause significant

switching losses at the 1.25MHz switching frequency

of the PT1305.

z Resistor Selection

The output voltage is controlled by the feedback

resistor. The feedback reference is 1.25V. The output

voltage is 1.25*(1+R2/R1). In order to have accurate

output voltage, precision resistors are preferred (1% is

recommended). The formula and table for R1 and R2

selection are shown below

VOUT = 1.25*(1+R2/R1)

VOUT

（V）

12

15

18

24

R1 Value

（KΩ）

210

90

75

100

R2 Value

（KΩ）

1800

1000

1000

1800

z Board Layout Consideration

As with all switching regulators, careful attention must

be paid to the PCB board layout and component

placement. To maximize efficiency, switch rise and fall

times are made as short as possible. To prevent

electromagnetic interference (EMI) problems, proper

layout of the high frequency switching path is essential.

The voltage signal of the SW pin has sharp rise and fall

edges. Minimize the length and area of all traces

connected to the SW pin and always use a ground plane

under the switching regulator to minimize interplane

coupling. In addition, the ground connection for the

feedback resistor R1 should be tied directly to the GND

pin and not shared with any other component, ensuring

a clean, noise-free connection.

China Resources Powtech (Shanghai) Limited

PT1305_DS Rev EN_1.0

WWW.CRPOWTECH.COM

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