FA5527 FUJI [Fuji Electric], FA5527 Datasheet - Page 20

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

abrupt load change and FB pin voltage restores to the
voltage at steady state before CS pin voltage reaches 8.5V,
the 4V clamp circuit restarts, producing no latch mode.
voltage or through forcibly decreasing CS pin voltage to
7.4V or less.
supplying no current to the VCC pin. Thereafter, the latch
mode is reset when Vcc drops below the OFF threshold
voltage, 8.0Vmin.
the latch mode comparator is re-inverted and the IC
re-starts switching operation.
overload detection to the latch mode, is given by the
following equation.
charging current and proportional to the difference
between CS pin clamp voltage “4V” at steady condition and
latch-mode threshold voltage “8.5V”. Pay attention to
variations in delay time resulting from variations in
numerical values.
after rectification, it takes rather long time, approximately
several minutes, before the latch mode is reset.
(9) Overload protection of FA5536/37/38
type overload protection. Fig.14 shows VCC pin voltage
and the drain voltage of power MOSFET “Q1” in the circuit
on page 33 at “6A” overload when 90Vac input is applied
and Fig.15 shows same parameters mentioned above at
“7A” overload when 264Vac input is applied.
period are calculated as follows.
Here,
When the output voltage momentarily drops due to
The latch mode can be reset through cutting off input
Cutting off the input voltage decreases VH pin voltage,
In addition, when CS pin voltage is forcibly decreased,
In the case of typical IC, delay time td
td1
Here, Cs is a capacitance connected to CS pin [ uF ].
Delay time td
In addition, be aware that when the VH pin is connected
(See “9-(1) Start-up circuit.”)
FA5536, FA5537 and FA5538 have built-in auto-recovery
Switching period after the overload occurs and stop
Steady State to Overload : td2
After overload starts : td2
stop period t (stop) [ s ] = Cvcc [ uF ] *
Vcc(sw/OL) : Vcc in switching period at overload [ V ]
Vccoff : OFF threshold voltage of U.V.L.O ( 9V (typ.))
I
AN-087E Rev.1.0
April-2011
CCL
(OLP)
Fuji Electric Co., Ltd.
: Consumption current in latch mode ( 290uA (typ.))
[ s ] = 0.93 * Cs [ uF ] ( typical value )
(OLP)
is inversely proportional to CS
[ Vcc(sw/OL) – Vccoff ] / ( I
(OLP)
(OLP)
[ s ] = 1.65* Cs [ uF ],
[ s ] = td1
FA5526/5527/5528/5536/5537/5538
(OLP),
the time from
(OLP)
,
CCL )
Secondary
Side DC
Output
Voltage
FB pin
Voltage
CS pin
Voltage
Vcc
(20V
Vds
(100V
Vcc
(20V
Vds
(100V
OUT pin
Voltage
20
/div)
/div)
/div)
/div)
Fig.13 Overload protection timing chart
Fig.14 Overload protection waveform
Fig.15 Overload protection waveform
of FA5538 as Auto-Recovery ( 90Vac )
Short time
Overload
of FA5538 as Auto-Recovery
http://www.fujielectric.co.jp/products/semiconductor/
( 264Vac )
Overload Latch Off
3.6V
8.8V
8.5V