FA5527 FUJI [Fuji Electric], FA5527 Datasheet - Page 19

• Manufacturer Part Number: FA5527
• Description: Fuji Switching Power Control IC
• Manufacturer: FUJI [Fuji Electric]

(7) Soft start circuit
(8) Overload protection of FA5526/27/28
source. The current for soft start is 11uA.
charged by the constant current source, gradually
increasing CS pin voltage.
because CS pin voltage is input to the current
comparator (IS comp.), realizing soft start.
CS pin voltage increases from 0V to 3V is given by the
following equation.
approximately 4V by a zener diode in the IC.
pulses when CS pin voltage is 0.68V or less, same as
FB pin.
(See “9-(14) Timing chart.”)
type overload protection. Fig.12 shows its block diagram
and Fig.13 its Timing chart.
CS pin voltage is clamped at 4V by a zener diode in the
IC.
overload or short-circuit on the load side, FB pin voltage
increases. If FB pin voltage exceeds the 3.6V threshold
voltage for overload protection, output voltage of a
comparator for overload detection (Overload) is inverted
and 4V clamp of the CS pin is canceled, increasing CS
pin voltage again due to a built-in constant current
source. The current supplied from the CS pin becomes
4µA.
CS pin voltage reaches the threshold voltage (8.5V) of
the comparator (Latch), the output of the comparator
(Latch) is inverted, turning off a 5V circuit in the IC and
forcing OUT pin voltage to be low.
AN-087E Rev.1.0
April-2011
mode, the start-up circuit resumes operation to supply
current to Vcc and to hold the latch mode.
The CS pin is connected to a built-in constant current
The capacitor externally connected to the CS pin is
MOSFET current gradually increases at start-up
As a guide for soft start time, the time tss taken until
Here, Cs is a capacitance connected to CS pin [ uF ].
In steady operation, CS pin voltage is clamped at
The CS pin is provided with a built-in circuit to stop
FA5526, FA5527 and FA5528 have built-in time-latch
In steady operation, FB pin voltage is 3V or less and
When power supply voltage drops on account of
If the power supply voltage continues to decrease and
This status is the latch mode of the IC. In the latch
tss [ s ] = 0.27 * Cs [ uF ] ( typical value )
Fuji Electric Co., Ltd.
FA5526/5527/5528/5536/5537/5538
19
FB
FB
2
2
60k
20k
Fig.12 Overload protection circuit
5V
5V Reg.
5V
5V Reg.
UVLO
Fig.11 Soft start circuit
2.8V
3R
VCC
R
ENB
Overload
Cs
http://www.fujielectric.co.jp/products/semiconductor/
Buf
x1
0.52V
1
3
Latch
UVLO
CS
4.8V
IS
8.5V/7.7V
11µA
Cs
S
R
F.F.
Q
IS comp.
VCC
1
11uA/4uA
CS
ENB
6
5
VCC
OUT