SSC2016S datasheet(13/22 Pages) SANKEN

13 / 22 page

SSC2016S

SSC2016S - DSJ Rev.1.3

SANKEN ELECTRIC CO.,LTD.

Jul. 22, 2016

http://www.sanken-ele.co.jp/en/

8.8

Overvoltage Protection (OVP)

Figure 8-13 shows the waveforms of Overvoltage

Protection (OVP) operation. 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 1.060 times the

Feedback Voltage Reference, VREF = 2.500 V. When the

cause of the overvoltage is removed and FB pin voltage

decreases to VOVP

− V

OVP(HYS) the switching operation

restarts.

FB pin voltage

OUT pin

voltage

VOVP

VOVP(HYS)

Figure 8-13.

OVP Waveforms

8.9

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,

the short of RVS2, or the open of FB pin.

Figure 8-14 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.

Error AMP

VREF

= 2.500V

VOUT

RVS1

RVS2

VOSC

PWM COMP

OVP

VOVP

= 1.060×VREF

VOVP(HYS)

= 60mV

GND

UVP

VUVP

= 300mV

VUVP(HYS)

= 110mV

IFB

Figure 8-14.

The FB Pin Peripheral Circuit and

Internal Circuit.

8.10 Thermal Shutdown (TSD)

< Using External Power Supply >

When the temperature of control circuit increases to

Tj(TSD) = 150 °C or more, Thermal Shutdown (TSD) is

activated and the IC stops switching operation.

When the fault condition is removed and the

temperature decreases to less than Tj(TSD) – Tj(TSDHYS), the

IC returns to normal operation automatically.

< Using Auxiliary Winding D for VCC supply >

When TSD is activated and the IC stops switching

operation, VCC pin voltage decreases to VCC(OFF) and the

control circuit stops operation. After that, the IC reverts

to the initial state by UVLO circuit, and the IC starts

operation when VCC pin voltage increases to VCC(ON) by

startup current. Thus the intermittent operation by

UVLO is repeated in TSD state.

When the fault condition is removed and the

temperature decreases to less than Tj(TSD) – Tj(TSDHYS), the

IC returns to normal operation automatically.

Design Notes

9.1

Inductor Design

Inductor T1 consists of a boost winding P and

auxiliary winding D. The winding P is used for boosting

the voltage and winding D is used for off-timing

detection.

The calculation methods of winding P and winding D

are as shown below. Since the following calculating

formulas are approximated, the peak current and the

frequency of operational waveforms may be different

from the setting value at calculating. Eventually, the

inductance value should be adjusted in actual operation.

Apply proper design margin to temperature rise by

core loss and copper loss.

9.1.1

Boost winding, P

Inductance LP of PFC in CRM mode is calculated as

follows:

1) Output Voltage, VOUT

The output voltage VOUT of boost-converter should be

set higher than peak value of input voltage as

following equation:

VOUT≥√2×VACRMS(MAX)×VDIF(V) (3)

where

VACRMS(MAX): Maximum AC input voltage rms value (V)

VDIF: Boost voltage (about 10V) (V)

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