With this choice the core losses are approximately 280mW. The temperature increasing of the core is

12°C approximately.

Output Capacitor

The selection of Cout is driven by the output ripple voltage required, 1% of Vo. This is defined by the

ESR of the output capacitance and by the maximum ripple current (0.525A).

The maximum ESR is:

ESR =

∆Vo/∆Io = 0.051/0.525 = 97mΩ

The selected capacitance is 220

µF/35V FA Panasonic with ESR = 90mW and the ripple voltage is

0.92% of Vo (47mV).

Bill of Material

C1, C3

680

µF / 35V FA PANASONIC 16x15 Irms=1690mA

C2

1.2nF/35V SMD 1206

C4

22nF SMD 1206

C16

4.7nF SMD 1206

C13

100nF/35V SMD 1206

C5,C15

15nF/35V SMD 1206

C6,C7,C12,C17,C18,C23

220nF/50V SMD 10% Kemet 1206 X7R

C8,C21

220

µF/35V FA PANASONIC 8x15

C10,C20

1

µF/10V electrolitic (not SMD)

C11,C22

not used

C14

10nF/35V SMD 1206

C9,C19

220pF SMD 1206

U1,U2

L4973D3.3

R1

22k SMD 1% 1206, 0.25W

R2

9.1k SMD 1% 1206, 0.25W

R3,R10

2.7k SMD 1% 1206, 0.25W

R4,R12

4.7k SMD 1% 1206, 0.25W

R6,R9

0.025 Ohm 1W 1% DALE WSL-2512

R7

0 SMD 1206

R11,R5,R8

10K SMD 1% 1206, 0.25W

D1

STPS640CB (DPAK)

D2

STPS640CB (DPAK)

U3

LM358 SO8 ST

Z1

Diodo Zener 25V SOT23

L1,L2

43

µH KoolMu Magnetics core 77120 34 Turns d(mm)=0.91 AWG19

Stability Analysis of the Current Loop.

In the current sharing configuration the U1 regulator acts as a master in order to regulate the output

voltage. The second section U2 works as current follower. Its task is to deliver an output current equal to

the current delivered from the first section. For the analysis of the stability, see Fig. 21, the current loop

of the U2 section can be considered as a separated loop from the voltage loop of the U1 section, consid-

ering that the current loop is quite faster than the voltage one.

AN1126 APPLICATION NOTE

11/16