L6910 - L6910A

14/29

Figure 16. Efficiency vs Output Current

6

COMPONENTS SELECTION

6.1 Inductor Selection

To select the right inductor value, the application conditions must be fixed. For example we can consider:

Vin=12V Vout =3.3V Iout=15A

Considering a ripple of approximately 25% to 30% of Iout, the inductor value will be L=3

µH.

An iron powder core (TO50-52B) with 7 windings has been chosen.

6.2 Output Capacitors

2 POSCAP capacitors, model 6TPB330M, have been chosen, with a maximum ERS equal to 40m

Ω each.

Therefore, the resultant ESR is of 20m

Ω. Considering a current ripple of 4A, the output voltage ripple is:

∆Vout = 4 · 0.02 = 80mV

6.3 Input Capacitors

to 7.5A.

Two OSCON electrolytic capacitors 6SP680M, with a maximum ESR equal to 13m

Ω, have been chosen to sus-

tain the ripple. Therefore, the resultant ESR is equal to 13m

Ω/2 = 6.5mΩ. The losses, in worst case, are:

6.4 Over-Current Protection

The current limit can be set to approximately 20A. Substituting the demo board parameters in the relation-

Ω

Output Current (A)

50

55

60

65

70

75

80

85

90

95

100

13

579

11

13

15

17

Vin=Vcc=12V

Fsw.=200KHZ

Vo=1.2V

Vo=1.8V

Vo=3.3V

Vo=5V

Vo=0.9V

Vin=Vcc=12V

Fsw.=200KHZ

Vo=1.2V

Vo=1.8V

Vo=3.3V

Vo=5V

Vo=0.9V

Vo=1.5V

Vo=2.5V

Vo=1.5V

Vo=2.5V

Output Current (A)