D1

Q1

V

~-7V/20mA

GL

T1

BC857B

-V

S

D3

D4

R14

5.6kW

D2

BZX84C

7V5

C16

1

F/

16V

m

C17

470nF

C18

470nF

V

S

13.6V/500mA

V

2.5Vto6V

IN

BAT54S

Components Selection

f

p

´

´

´

C

1

X

=

2

C

(6)

TPS65148

Figure 21. Partially Regulated External Negative

Capacitors (Charge Pumps)

For best output voltage filtering a low ESR output capacitor is recommended. Ceramic capacitors have a low

ESR value but depending on the application tantalum capacitors can be used as well. For every capacitor, the

reactance value has to be calculated as follows:

This value should be as low as possible in order to reduce the voltage drop due to the current flowing through it.

The rated voltage of the capacitor has to be able to withstand the voltage across it. Capacitors rated at 50 V are

enough for most of the applications. Typically a 470-nF capacitance is sufficient for the flying capacitors whereas

bigger values like 1 µF or more can be used for the output capacitors to reduce the output voltage ripple.

CAPACITOR

COMPONENT SUPPLIER

COMPONENT CODE

COMMENTS

100 nF/0603

Taiyo Yuden

UMK107 BJ 104KA

Flying Cap

470 nF/0805

Taiyo Yuden

UMK212 BJ 474KG

Output Cap 1

1

µF/1210

Taiyo Yuden

UMK325 BJ 105KH

Output Cap 2

Diodes (Charge Pumps)

For high efficiency, one has to minimize the forward voltage drop of the diodes. Schottky diodes are

Usually a Schottky diode with 200 mA average forward rectified current is suitable for most of the applications.

CURRENT

COMPONENT

COMPONENT

PACKAGE

SUPPLIER

CODE

TYPE

200 mA

30 V

0.5V / 30mA

International Rectifier

BAT54S

SOT 23

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