SSC2005SC 查看數據表（PDF） - Sanken Electric co.,ltd.
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SSC2005SC Datasheet PDF : 19 Pages
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SSC2005SC
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
15 20 25 30 35 40 45 50 55 60
RDLY (kΩ)
Figure 8-10 tDLY as a function of and RDLY (IC design)
tDLY
Bottom on
Free oscillation
Ideal delay time
Delay time is short.
Make RDLY value larger.
Delay time is Long.
Make RDLY value smaller.
Figure 8-11 Turn-on timing of VDS
8.6 Minimum Off-time Limit Function
In order to prevent the rise of operation frequency at
light load, the IC have the Minimum Off-Time
tOFF(MIN) = 1.95 μs. If this Minimum Off-Time is shorter
than the freewheeling time of inductor, the IC operates
in discontinuous condition mode (DCM).
8.7 Overvoltage Protection (OVP)
Figure 8-12 shows the waveforms of Overvoltage
Protection (OVP) operation.
FB pin voltage
VOVP
OUT pin
voltage
VOVPHYS
When the FB pin voltage increase to Overvoltage
Protection Threshold Voltage, VOVP, OUT pin voltage
become Low immediately and the switching operation
stops. As a result, the rise of output voltage is prevented.
VOVP is 1.090 times the Feedback Control Voltage,
VFB = 2.50 V. When the cause of the overvoltage is
removed and FB pin voltage decreases to VOVP −
VOVP(HYS), the switching operation restarts.
8.8 FB pin Under Voltage Protection
(FB_UVP)
FB pin Under Voltage Protection (FB_UVP) is
activated when the FB pin voltage is decreased by the
malfunctions in feedback loop such as the open of RVS1
or the short of RVS2.
Figure 8-13 shows the FB pin peripheral circuit and
internal circuit. When the FB pin voltage is decreased to
VUVP = 300 mV or less, the OUT pin output is turned-off
immediately and switching operation stops. This
prevents the rise of output voltage. When the cause of
malfunction is removed and the FB pin voltage rises to
VUVP + VUVP(HYS), the switching operation restarts.
In case the FB pin is open, the FB pin voltage is
increase and Overvoltage Protection (OVP) is activated
as described in Section 8.7.
When the cause of malfunction is removed and the IC
becomes nomal control, the switching operation rstarts.
U1
PWM COMP Error AMP
VOSC
IFB
FB
1
VFB
= 2.50V
C6
OVP
VOVP
= 1.090×VFB
VOVP(HYS)
= 90mV
GND
6
UVP
VUVP
= 300mV
VUVP(HYS)
= 120mV
VOUT
RVS1
RVS2
Figure 8-13 The FB pin peripheral circuit and
internal circuit.
Figure 8-12 Overvoltage protection waveforms
SSC2005SC-DS Rev.1.1
SANKEN ELECTRIC CO.,LTD.
11
Feb. 06, 2015
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