FA5590 FUJI [Fuji Electric], FA5590 Datasheet - Page 15

• Manufacturer Part Number: FA5590
• Description: FUJI Power Supply Control IC
• Manufacturer: FUJI [Fuji Electric]

MOSFET turn on.
(6-2) Overcurrent detection protective circuit
current and protects MOSFET by turning off the OUT output when it
becomes higher than a set current level. With the overcurrent detection,
the voltage across the current detection resistance Rs connected to the
GND is fed to the IS terminal, and when the IS terminal voltage
compared by the overcurrent detection comparator becomes lower than
-0.6V, it is regarded as overcurrent state.
When the overcurrent is detected, the F/F for OUT output is reset to
make MOSFET turn off.
oscillating through resonance of L1 and the parasitic capacitor
component on the circuit just before the MOSFET turns on.
adjusted at the bottom of the voltage oscillation. This makes it possible
to minimize the switching loss and the surge current generated at the
turn-on. (Fig. 13)
vice versa. (Fig. 14)
circuit and input/output conditions, tuning up is required so as to achieve
an optimum state while evaluating the operation with actual circuit.
frequency, and in the steady operation, it turns on MOSFET with a signal
from the zero current detector.
starting up or stable operation.
continues turn off for 20μs or more, the trigger signal is automatically
generated.
load is light.
drops.
(typ.) for FA5590 and 13V (typ.) for FA5591.
When the supply voltage decreases after the operation starts, either part
number stops the operation at 9V (typ.).
When UVLO is on and IC stops operation the OUT terminal becomes
LOW and cuts off the output. The current consumption of the IC
decreases to 80μA or less.
MOSFET. The peak current of the output portion is 1.0A maximum for
sink and 0.5A maximum for source.
But in start up or light load condition, a trigger signal is required for
AN-016E Rev.1.2
April-2011
UVLO is equipped to prevent circuit malfunction when supply voltage
When the supply voltage rises from zero, the operation starts at 9.6V
This IC utilizes self oscillation instead of the oscillator with fixed
The overcurrent detection protective circuit detects the inductor
Vds between the drain and the sources of the MOSFET starts
When the proper value of Rtzc, the turn on timing of MOSFET can be
When the Rtzc is smaller, the turn-on timing becomes earlier, and
This IC is provided with a restart timer, and when the output of IC
This signal can realize stable operation even when starting up or the
The output portion is of push-pull circuit and can directly drive the
(7) Zero cross delay time setting circuit
(8) Restart timer
(9) Under Voltage Lock out (UVLO)
(10) Output circuit portion
Since the optimum value of this Rtzc changes depending on the
Fuji Electric Co., Ltd.
FA5590N,FA5591N
15
MOSFET
のVds
Vds
http://www.fujielectric.co.jp/products/semiconductor/
インダクタ電流
Fig.11 when the switching frequency is
lower than the maximum frequency Fmax
インダクタ電流
inductor
current
MOSFET の Vds
MOSFET の Vds
inductor
current
Vds
Vds
Fig.12 when the switching frequency is
limited to the maximum frequency Fmax
(Rtzc is too small)
Tzcd（Rtzcが小さい）
MOSFET
Vds
のVds
Tzcd
Fig.13 Vds waveform at turn on
(with adequate Rtzc)
Fig.14 Vds waveform at turn on
(with inadequate Rtzc)
(with adequate Rtzc)
Tzcd(Rtzc最適）
T= 1/Fmax
T＜ 1/Fmax
Tzcd
Tzcd
Tzcd(Rtzcが大きい）
(Rtzc is too large)
Tzcd
Tzcd