L6713ATR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
L6713ATR
STMicroelectronics
'L6713ATR' PDF : 64 Pages View PDF
Oscillator
19 Oscillator
L6713A
L6713A embeds two/three phase oscillator with optimized phase-shift (180º/120º phase-
shift) in order to reduce the input rms current and optimize the output filter definition.
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 200 kHz so that the resulting switching frequency at the
load side results in being multiplied by N (number of phases).
The current delivered to the oscillator is typically 25 μA (corresponding to the free running
frequency FSW = 200 kHz) 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 1.24 V). Since the
OSC pin is fixed at 1.24 V, the frequency is varied proportionally to the current sunk (forced)
from (into) the pin considering the internal gain of 6 KHz/μA.
In particular connecting ROSC to SGND the frequency is increased (current is sunk from the
pin), while connecting ROSC to VCC = 12 V the frequency is reduced (current is forced into
the pin), according the following relationships:
ROSC vs. SGND
FSW = 200(kHz) + R-----O1---.-S-2--C-4---(-0--k-V--Ω-----) ⋅ 6k--μ--H--A---z- = 200(kHz) + -7R---.-O4----2S---2-C---(-⋅--k-1--Ω-0----3)- ⇒ ROSC(kΩ) =
6 k--μ--H--A---z-
=
200 ( k H z )
+
-7---.-4----2---2-----⋅---1---0----3-
ROSC(kΩ)
⇒
ROSC(kΩ)
=
----------------7---.--4---2----2-----⋅---1---0----3---------------- [kΩ]
FSW(kHz) – 200(kHz)
ROSC vs. +12V
FSW
=
200 ( k H z )
–
1----2----V-----–-----1---.--2---4---0----V--
ROSC(kΩ)
⋅
-8---μk----HA----z--
=
200 ( k H z ) – -8R---.-O6----0S---8-C---(-⋅--k-1--Ω-0----4)-
⇒
ROSC(kΩ)
=
2--
k--μ--H--A---z-
=
200 ( k H z ) – -6---.-4----5---6-----⋅---1---0----4-
ROSC(kΩ)
⇒
ROSC(kΩ)
=
----------------8---.--6---0----8-----⋅---1---0----4---------------- [kΩ]
200(kHz) – FSW(kHz)
Maximum programmable switching frequency per phase 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 24. ROSC vs. switching frequency
7000
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6000
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50
0
25
50
75
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125
150
175
200
Fsw [kHz] Programmed
0
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950 1050
Fsw [kHz] Programmed
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