l6706 STMicroelectronics, l6706 Datasheet - Page 38

• Manufacturer Part Number: l6706
• Description: Vr11.1 Single Phase Controller With Integrated Driver
• Manufacturer: STMicroelectronics

Oscillator
16
38/47
F
SW
F
SW
=
=
200 kHz
200 kHz
Oscillator
The internal oscillator generates the triangular waveform for the PWM charging and
discharging with a constant current an internal capacitor. The current delivered to the
oscillator is typically 25 μA (corresponding to the free running frequency F
and it may be varied using an external resistor (R
pin and SGND or VCC (or a fixed voltage greater than 1.24 V). Since the OSC/FAULT pin is
fixed at 1.240 V, the frequency is varied proportionally to the current sunk (forced) from (into)
the pin considering the internal gain of 10 kHz/μA.
In particular connecting R
pin), while connecting R
the pin), according the following relationships:
R
R
Maximum programmable switching frequency must be limited to 1 MHz to avoid minimum
Ton limitation. Anyway, device power dissipation must be checked prior to design high
switching frequency systems.
Figure 22. R
(
OSC
OSC
(
vs. SGND
vs. +12V
)
–
)
+
12V 1.240V
----------------------------------- - 10 kHz
R
--------------------------- - 10
R
OSC
1.240V
OSC
–
OSC
(
(
kΩ
kΩ
)
)
vs. switching frequency
⋅
⋅
kHz
---------- -
μA
OSC
---------- -
μA
OSC
=
to VCC = 12 V the frequency is reduced (current is forced into
=
200 kHz
to SGND the frequency is increased (current is sunk from the
200 kHz
Doc ID 15698 Rev 1
(
(
)
) 10.76 10
+
–
12.40 10
---------------------------- -
R
---------------------------- -
R
OSC
OSC
(
⋅
(
⋅
kΩ
kΩ
OSC
3
)
4
)
⇒
⇒
) connected between the OSC/FAULT
R
R
OSC
OSC
(
(
kΩ
kΩ
)
)
=
=
----------------------------------------------------------- -
F
----------------------------------------------------------- -
200 kHz
SW
(
(
kHz
12.40 10
10.76 10
SW
) F
) 200 kHz
–
–
⋅
⋅
= 200 kHz)
SW
3
4
(
(
kHz
L6706
)
)
[
[
kΩ
kΩ
]
]