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L6711 Datasheet(PDF) 38 Page - STMicroelectronics

Part # L6711
Description  3 Phase controller with dynamic VID and selectable DACs
PDF  50 Pages
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Manufacturer  STMICROELECTRONICS [STMicroelectronics]
Direct Link  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

L6711 Datasheet(HTML) 38 Page - STMicroelectronics

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Oscillator
L6711
38/50
15
Oscillator
The internal oscillator generates the triangular waveform for the PWM charging and
discharging with a constant current an internal capacitor. The switching frequency for each
channel, FSW, is internally fixed at 150kHz so that the resulting switching frequency at the
load side results in being tripled.
The current delivered to the oscillator is typically 25
µA (corresponding to the free running
frequency Fsw=150kHz) and it may be varied using an external resistor (ROSC) connected
between the OSC pin and SGND or VCC (or a fixed voltage greater than 1.24V). Since the OSC
pin is fixed at 1.24V, the frequency is varied proportionally to the current sunk (forced) from (into)
the pin considering the internal gain of 6KHz/
µA.
In particular connecting ROSC to SGND the frequency is increased (current is sunk from the
pin), while connecting ROSC to VCC=12V the frequency is reduced (current is forced into the
pin), according to the following relationships:
Maximum programmable switching frequency depends on the Current Reading Method
selected. When reading across LS mosfet, the maximum switching frequency per phase
must be limited to 500kHz to avoid current reading errors causing, as a consequence,
current sharing errors. When reading across the inductor, higher switching frequency can be
approached (device power dissipation must be checked prior to design high switching
frequency systems).
Figure 19.
ROSC vs. switching frequency
R
OSC vs. GND: FSW
150kHz
1.237
R
OSC kΩ
()
---------------------------- 6
kHz
µA
-----------
⋅
+
150kHz
7.422 10
6
⋅
R
OSC kΩ
()
-----------------------------
+
==
R
OSC vs. 12V: FSW
150kHz
12-1.237
R
OSC kΩ
()
---------------------------- 6
kHz
µA
-----------
⋅
+
150kHz
6.457 10
7
⋅
R
OSC kΩ
()
-----------------------------
+
==
0
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25
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75
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150
0
200
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ROSC [kΩ] to SGND vs. Selected FSW [kHz]
ROSC [kΩ] to 12V vs. Selected FSW [kHz]



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