L6910G データシートの表示（PDF） - STMicroelectronics

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L6910G

ADJUSTABLE STEP DOWN CONTROLLER WITH SYNCHRONOUS RECTIFICATION

STMicroelectronics 

L6910G

Figure 16. Efficiency vs Output Current

100

95

90

85

80

75

70

65

60

55

50

1

Vo=5V

Vo=3.3V

Vo=1.5V

Vo=1.8V

Vo=2.5V

Vo=1.2V

Vo=0.9V

Vin=Vcc=12V

Fsw.=200KHZ

3

5

7Output Cur9rent (A) 11

13

15

17

Output Current (A)

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 40mΩ each.

Therefore, the resultant ESR is of 20mΩ. Considering a current ripple of 4A, the output voltage ripple is:

∆Vout = 4 · 0.02 = 80mV

6.3 Input Capacitors

For IOUT = 15A and D = 0.5 (worst case for input current ripple), the RMS current of the input capacitor is equal

to 7.5A.

Two OSCON electrolytic capacitors 6SP680M, with a maximum ESR equal to 13mΩ, have been chosen to sus-

tain the ripple. Therefore, the resultant ESR is equal to 13mΩ/2 = 6.5mΩ. The losses, in worst case, are:

P = ESR · I2rms = 366mW

6.4 Over-Current Protection

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

ship reported in the relative section, (IOSCMIN =170µA; IP = 20A; RDSONMAX = 9mΩ / 2=4.5mΩ) it results

that ROCS = 510Ω

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