l6730cqtr STMicroelectronics, l6730cqtr Datasheet - Page 13

• Manufacturer Part Number: l6730cqtr
• Description: Adjustable Step-down Controller With Synchronous Rectification
• Manufacturer: STMicroelectronics

L6730C - L6730D
5
5.1
Figure 3.
Device description
Oscillator
The switching frequency is internally fixed to 400KHz. The internal oscillator generates the
triangular waveform for the PWM charging and discharging an internal capacitor (F
400KHz). This current can be varied using an external resistor (R
pin and GND or V
maintained at fixed voltage (typ. 1.2V), the frequency is increased (decreased) proportionally to
the current sunk (sourced) from (into) the pin. In particular, connecting R
frequency is increased (current is sunk from the pin), according to the following relationship:
Connecting R
the following relationship:
Switching frequency variation vs. R
Switching frequency variation versus R
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
T
to V
Rosc connected to GND
CCDR
100
CCDR
in order to change the switching frequency. Since the OSC pin is
Fsw
Fsw
200
the frequency is reduced (current is sourced into the pin), according to
400
300
400
T
KHz
KHz
is shown in
Rosc connected to Vccdr
400
Rosc (KOHM)
R
. 9
R
. 3
OSC
500
T
OSC
88
.
01
(
(
Figure
K
10
K
10
600
6
7
)
)
3..
(1)
(2)
700
800
T
) connected between OSC
900 1000
T
versus GND the
Device description
SW
=
13/50