L6718TR datasheet(61/71 Pages) STMICROELECTRONICS

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L6718

Main oscillator

voltage immediately after loading TDC current), change the divider at the TCOMP pin

in order to increase the TCOMP voltage.

The same procedure can be implemented with a variable resistor in place of one of the

resistors of the divider. In this case, once the compensated configuration is found,

simply replace the variable resistor with a resistor of the same value.

Main oscillator

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

discharging with a constant current internal capacitor. The switching frequency for each

channel, FSW, FSSW, is internally fixed at 200 kHz: 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

μA (corresponding to the free-running

frequency FSW= 200 kHz) and it 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 1.8 V, the frequency is varied proportionally to the current sunk from the pin

considering the internal gain of 10 kHz/

μA (see Figure 14).

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

according to the following relationships:

Equation 13

Figure 14. ROSC [KOhm] vs. switching frequency [kHz] per phase

200kHz

1.800V

OSC kΩ

()

---------------------------

kHz

μA

-----------

⋅

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