FA6A11N データシートの表示（PDF） - Fuji Electric
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FA6A11N Datasheet PDF : 7 Pages
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3
Range of frequency variation
during normal operation
Range of frequency
variation during
burst operation
2
1
+
S1
HO
P1
Vi +
VS
LO
S2
Aux
P2
0
0
50
100
150
200
Frequency (kHz)
Fig.3 Current resonant gain diagram
High
Invalid region
Region with high conversion efficiency
Region with low conversion efficiency
(1)
(2)
(3)
Low
FA5760N
FA6A00N Series
Fig.4 Frequency during burst operation
and low side duty cycle of 50% and controls the gain
by the switching frequency. Figure 3 shows the current
resonant gain diagram. The frequency variation range
is narrow in principle during normal operation and
widened during burst operation.
Figure 4 shows the frequency during burst opera-
tion. The high frequency region (1) is an invalid region
in which the gain is low and switching cannot trans-
fer energy. In the low frequency region (3), the gain
is high and excitation current is large, which makes
energy transfer inefficient; hence there is a low conver-
sion efficiency. With the FA6A00N Series, the invalid
region and the region with low conversion efficiency
have been reduced to widen the region with high con-
version efficiency (2), resulting in successful reduction
of standby power. Audible noise has also been sup-
pressed.
3.2 High-precision overload protection function
The 1st-generation product FA5760N used the pri-
mary side auxiliary winding P2 (see Fig. 5) to supply
power to the VCC terminal and realized hard switch-
ing protection and shoot-through current prevention.
The FA6A00N Series, which is the 2nd generation,
uses this auxiliary winding to integrate the high-pre-
cision overload protection function for the first time in
the world while inheriting the functions of FA5760N.
The overload protection, which is intended for
Fig.5 Schematic circuit diagram of current resonance
protecting the power management system, is a func-
tion that stops switching when a certain delay time
has elapsed after a load increases to approximately
1.5 times the rated load. Degradation of the preci-
sion of this function causes insufficient output power
or failure to limit the output power, thus the overload
protection cannot perform adequately. In addition, the
overload protection level must be maintained within
a certain range (about ± 20%) even if an input voltage
varies in a wide range.
Figure 6 shows the circuit configuration of the high-
precision overload protection function of the FA6A00N
Series. The auxiliary winding voltage is detected by
the resistor-divided voltage, VW voltage. The recom-
mended precision of this voltage-dividing resistor is
± 1%. The VW voltage exceeding the threshold voltage
Volpvw is recognized as an overload state, and when
the overload state continues for 76.8 ms, switching is
stopped. In order to improve the detection precision,
variation of Volpvw has been specified to be within ± 3%,
which is highly precise. The commercialized versions
are the auto-restart version, which restarts when the
switching stop time has reached 550 ms, and the latch
stop version that does not restart.
Figure 7 shows a waveform during overload pro-
tection operation. In overload protection operation,
switching is suspended and the output voltage drops
along with an energy transfer stop.
Figure 8 shows how the overload protection oper-
ating power depends on the input voltage. FA5760N
provides overload protection with general resonant
current detection. With this method, the overload
Aux
R1 VW
P2
R2
+
-
Volpvw
Delay circuit
Tolpdly = 76.8 ms
Delay circuit
Tolpoff = 550 ms
SQ
R
Stop
switching
Fig.6 Circuit configuration of high-precision overload protection
function
2nd Generation LLC Current Resonant Control IC, “FA6A00N Series”
247
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