Main oscillator

L6738

18/32

Doc ID 18133 Rev 1

7

Main oscillator

The controller embeds a programmable oscillator. The internal oscillator generates the

sawtooth waveform for the PWM charging with a constant current and resetting an internal

The current delivered to the oscillator is typically 20 µA (corresponding to the free running

connected between the OSC pin and GND. As the OSC pin is fixed at 1.240 V, the

frequency is varied proportionally to the current sunk from the pin considering the internal

gain of 10 KHz/µA (see

Figure 7).

according to the following relationships:

pin), according to the following relationships:

Figure 7.

F

SW

200kHz

1.240V

R

OSC

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

10

kHz

µA

-----------

⋅

+

=

F

SW

200kHz

+V

1.240

–

R

OSC

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

10

kHz

µA

-----------

⋅

–

=