SSC2005SC datasheet(11/19 Pages) SANKEN

11 / 19 page

SSC2005SC

SSC2005SC-DS Rev.1.1

SANKEN ELECTRIC CO.,LTD.

Feb. 06, 2015

Figure 8-10 tDLY as a function of and RDLY (IC design)

tDLY

Free oscillation

Delay time is short.

Make RDLY value larger.

Delay time is Long.

Make RDLY value smaller.

Ideal delay time

Bottom on

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

OUT pin

voltage

VOVP

VOVPHYS

Figure 8-12 Overvoltage protection waveforms

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.

Error AMP

VFB

= 2.50V

VOUT

RVS1

RVS2

VOSC

PWM COMP

OVP

VOVP

= 1.090×VFB

VOVP(HYS)

= 90mV

GND

UVP

VUVP

= 300mV

VUVP(HYS)

= 120mV

IFB

Figure 8-13 The FB pin peripheral circuit and

internal circuit.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

DLY (kΩ)

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