L6751C datasheet(44/57 Pages) STMICROELECTRONICS

44 / 57 page

Main oscillator

L6751C

44/57

DocID025037 Rev 1

Main oscillator

The internal oscillator generates the triangular waveform for the PWM charging and

discharging, with a constant current, on the internal capacitor. The switching frequency for

each channel is internally fixed at 200 kHz (FSW) and at 230 kHz (FSSW): the resulting

switching frequency at the load side for the multi-phase section results in being multiplied by

N (number of configured phases).

The current delivered to the oscillator is typically 20

A and may be varied using an external

resistor (ROSC, RSOSC) typically connected between the OSC/SOSC pins and GND. Since

the OSC/SOSC pins are fixed at 1.02 V, the frequency is varied proportionally to the current

sunk from the pin considering the internal gain of 10 KHz/

A for the multi-phase section and

of 11.5 kHz/

A for the single-phase section, see Figure 14.

Connecting ROSC/RSOSC to SGND, the frequency is increased (current is sunk from the pin),

according to the following relationships:

Equation 17

Equation 18

Connecting ROSC/RSOSC to a positive voltage Vbias, the frequency is reduced (current is

injected into the pin), according to the following relationships:

Equation 19

Equation 20

Figure 14. ROSC vs. FSW per phase (ROSC to GND - left; ROSC to 3.3 V - right)

FSW

200kHz

1.02V

ROSC k



---------------------------- 10

kHz

A

-----------



FSSW

250kHz

1.02V

RSOSC k



-------------------------------- 11.5

kHz

A

-----------



FSW

200kHz

Vbias 1.02V

–

ROSC k



-------------------------------------- 10

kHz

A

-----------



–

FSSW

250kHz

Vbias 1.02V

–

RSOSC k



-------------------------------------- 11.5

kHz

A

-----------



–

100

1000

200

300

400

500

600

700

800

900

1000

Multi Phase section

SinglePhase section

100

1000

100

125

150

175

200

225

Multi Phase section

SinglePhase section

AM14820v1

L6751C датащи(PDF) 44 Page - STMicroelectronics

L6751C датащи(HTML) 44 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

датащи скачать

ссылки URL