SSC3S910 datasheet(21/31 Pages) SANKEN

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SSC3S910

SSC3S910 - DSJ Rev.1.5

SANKEN ELECTRIC CO., LTD.

Jan. 17, 2018

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

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, and the IC stops switching operation

in protection mode. After stopping, the VCC pin voltage

decreases to VCC(OFF) = 8.8 V, the Undervoltage Lockout

(UVLO) Function is activated, and the IC reverts to the

state before startup again.

After that, the startup circuit is activated, the VCC pin

voltage increases to VCC(ON) = 14.0 V, and the IC restarts.

During the protection mode, restart and stop are repeated.

When the fault condition is removed, the IC returns to

normal operation automatically. 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

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 8-33, 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 (see Section 8.12).

Therefore, setting of ROCP and C3 should be taken

account of both OCP and the capacitive mode

operation.

(14)

● R6 and C8 are for high frequency noise reduction.

R6 is 100 Ω to 470 Ω. C6 is 100 pF to 1000 pF.

The OCP operation has two-step threshold voltage as

follows:

Step I, RC pin threshold voltage (Low), VRC(L):

This step is active first. When the absolute value of

the RC pin voltage increases to more than |VOC(L) | = 1.50

V, C6 connected to the CSS pin is discharged by

ICSS(L) = 1.8 mA. Thus, the switching frequency increases,

and the output power is limited. During discharging C6,

when the absolute value of the RC pin voltage decreases

to |VRC(L)| or less, the discharge stops.

Step II, RC pin threshold voltage (High-speed),

VRC(S):

This step is active second. When the absolute value of

the RC pin voltage increases to more than |VRC(S) | = 2.30

V, the high-speed OCP is activated, and power

MOSFETs reverse on and off. At the same time, C6 is

discharged by ICSS(S) = 20.5 mA. Thus, the switching

frequency quickly increases, and the output power is

quickly limited. This step operates as protections for

exceeding overcurrent, such as the output shorted. When

the absolute value of the RC pin voltage decreases to

|VRC(S)| or less, the operation is changed to the above

Step I.

When OLP Input Voltage Compensation is used, CL

pin voltage is needed to reach the threshold voltage of

Overload Protection (OLP), VCL(OLP), in the state that RC

pin voltage is less than VRC(L). Therefore, when output

power increases, the OLP is activated (see Section 8.17).

When the input voltage is constant like PFC output, OLP

Input Voltage Compensation is unnecessary. Therefore,

when output power increases, the above OCP operation

(Step I and Step II ) is activated.

VGL

VGH

GND

CSS

I(H)

ROCP

Q(H)

Q(L)

Figure 8-33.

RC pin peripheral circuit

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