FA5527 FUJI [Fuji Electric], FA5527 Datasheet - Page 18

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

(5) Minimum ON pulse width
(6) Slope compensation
IS pin is ignored during a blanking period right after
turn-on. Consequently, the sum of blanking time and
output delay time (100ns) is the minimum ON pulse
width at the OUT pin of the IC. The minimum ON pulse
width for FA5526/36, FA5527/37 and FA5528/38 are
300ns, 500ns and 700ns, respectively.
to generate pulses at no load.
is below 0.68V, the output of the comparator is inverted
and a clear signal “CLR” is input to the blanking circuit.
Then, the blanking circuit will not output a set signal and
no set signals will be input to PMW latch (F.F.), keeping
the output voltage low.
(See “9-(14) Timing chart.”)
may occur at a continuous current mode operation with
a duty cycle of 50% or more.
have built-in slope compensation circuits.
and slope compensation effect, see p.32.
a input of FB pin voltage to the current comparator (IS
comp.), which subtracted ramp signal generated from
oscillator passing through slope generator.
gradually decreases with time within each switching
cycle as shown in Fig.10 even when voltages at the FB
pin and CS pin are constant.
(See “9-(14) Timing chart.”)
AN-087E Rev.1.0
April-2011
As described in “(4) Blanking,” the input voltage at the
In addition, a dedicated comparator is incorporated not
When FB pin voltage is below 0.28V or CS pin voltage
In the current mode control, subharmonic oscillation
To avoid this, FA5526/36, FA5527/37 and FA5528/38
For details of subharmonic oscillation phenomenon
As shown in Fig.9, slope compensation is achieved by
Therefore, the threshold voltage at the FB pin
Fuji Electric Co., Ltd.
FA5526/5527/5528/5536/5537/5538
FB
18
2
5V Reg.
60k
20k
7.4k
Fig.10 Slope compensation
Fig.9 Slope compensation circuit
1Meg
5pF
GENERATOR
Ramp Signal
http://www.fujielectric.co.jp/products/semiconductor/
+
SLOPE
-
Σ
VCO
OSC
IS
( CS pin voltage ) / 4
Q
3
0.52V
IS comp.
Rs