SSC3S902 datasheet(21/32 Pages) SANKEN

21 / 32 page

SSC3S900 Series

SSC3S900 - DSJ Rev.2.4

SANKEN ELECTRIC CO.,LTD.

Apr. 01, 2016

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

8.15 Overvoltage Protection (OVP)

When the voltage between the VCC pin and the GND

applied

the

OVP

threshold

voltage,

VCC(OVP) = 32.0 V, or more, the Overvoltage Protection

(OVP) is activated.

The IC has two operation types of OVP. One is the

auto restart. The other is latched shutdown.

When the auxiliary winding supplies the VCC pin

voltage, the OVP is able to detect an excessive output

voltage, such as when the detection circuit for output

control is open in the secondary-side circuit because the

VCC pin voltage is proportional to the output voltage.

The output voltage of the secondary-side circuit at

OVP operation, VOUT(OVP), is approximately given as

below:

(13)

where,

VOUT(NORMAL) : Output voltage in normal operation

VCC(NORMAL): VCC pin voltage in normal operation

● Auto Restart Type: SSC3S901

Figure 8-33 shows the OVP operation waveforms of

auto restart type.

When the OVP is activated, the IC stops switching

operation and VCC pin voltage decreases. When VCC

pin voltage decreases to VCC(P.OFF) = 9.8 V, the OVP

operation is released and the startup circuit is

activated. When VCC pin voltage is increased to

VCC(ON) = 14.0 V by startup current, the IC starts the

switching operation. During the OVP operation, the

intermittent operation by UVLO is repeated.

When the fault condition is removed, the IC returns to

normal operation automatically.

VCC pin voltage

VGH/VGL

VCC(P.OFF)

VCC(ON)

VCC(OVP)

Figure 8-33 Auto restart type

OVP operation waveforms

● Latched Shutdown Type: SSC3S902

Figure 8-34 shows the OVP operation waveforms of

latched shutdown type.

When the OVP is activated, the IC stops switching

operation at the latched state and VCC pin voltage

decreases.

When VCC pin voltage decreases to VCC(OFF) = 9.8 V,

the startup circuit is activated. When VCC pin voltage

is increased to VCC(ON) = 14.0 V by startup current, the

startup circuit is turned off and VCC pin voltage

decreases. During the OVP operation, the latch state is

kept by turning on/off of the startup circuit.

The latched state is released by following condition:

VCC pin voltage is decreased to VCC(L.OFF) = 7.8 V or

less by turning off the input voltage,

or VSEN pin voltage is decreased to VSEN(OFF) = 1.0 V

or less.

VCC pin voltage

VGH/VGL

VCC(OFF)

VCC(ON)

VCC(OVP)

VCC(L.OFF)

Input voltage

turn off

Release

Latch mode

Figure 8-34 Latched shutdown type

OVP operation waveforms

8.16 Overcurrent Protection (OCP)

The Overcurrent Protection (OCP) detects the drain

current, ID, on pulse-by-pulse basis, and limits output

power. In Figure 8-35, this circuit enables the value of

C3 for shunt capacitor to be smaller than the value of Ci

for current resonant capacitor, and the detection current

through C3 is small. Thus, the loss of the detection

resistor, ROCP, is reduced, and ROCP is a small-sized one

available. There is no convenient method to calculate the

accurate resonant current value according to the mains

input and output conditions, and others. Thus, ROCP, C3,

and C6 should be adjusted based on actual operation in

the application. The following is a reference adjusting

method of ROCP, C3, R6, and C8:

● C3 and R

OCP

C3 is 100pF to 330pF (around 1 % of Ci value).

ROCP is around 100 Ω.

Given the current of the high side power MOSFET at

ON state as ID(H). ROCP is calculated Equation (14).

The detection voltage of ROCP is used the detection of

the capacitive mode operation (refer to Section 8.12).

Therefore, setting of ROCP and C3 should be taken

account of both OCP and the capacitive mode

operation.

(14)

SSC3S902 Datasheet(PDF) 21 Page - Sanken electric

SSC3S902 Datasheet(HTML) 21 Page - Sanken electric

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL