Datasheet

Device description L6730 - L6730B
14/52 Doc ID 11938 Rev 3
5 Device description
5.1 Oscillator
The switching frequency is internally fixed to 400 kHz. The internal oscillator generates the
triangular waveform for the PWM charging and discharging an internal capacitor (F
SW
= 400
kHz). This current can be varied using an external resistor (R
T
) connected between OSC pin
and GND or V
CCDR
in order to change the switching frequency. Since the OSC pin is
maintained at fixed voltage (typ. 1.2 V), the frequency is increased (or decreased)
proportionally to the current sunk (sourced) from (into) the pin. In particular by connecting
R
T
versus GND the frequency is increased (current is sunk from the pin), according to the
following relationship:
Connecting R
T
to V
CCDR
reduces the frequency (current is sourced into the pin), according
to the following relationship:
Switching frequency variation vs. R
T
is shown in Figure 4.
Figure 4. Switching frequency variation versus RT
)(
1088.9
400
6
Ω
⋅
+=
KR
KHzFsw
OSC
(1)
)(
1001.3
400
7
Ω
⋅
−=
KR
KHzFsw
OSC
(2)
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
0 100 200 300 400 500 600 700 800 900 1000
Rosc (KOHM)
Fsw (KHz)
Rosc connected to GND
Rosc connected to Vccdr