Data Sheet

ManualsBrandsON SEMICONDUCTOR ManualsPMICsPMIC - AC/DC converter, offline switcher Half-bridge Frequency control SIP 9

FSFR1800 / FSFR1700-HS • Rev.1.0.1 11

FSFR-HS Series — Advanced Fairchild Power Switch (FPS™) for Half-Bridge Resonant Converter

The initial maximum frequency can be set up to 600 kHz,

which is given by:

][

54.0||792

min

RRp

+×

(3)

The soft-start time, t

can be calculated by:

]s[CRt

SSSSSS

⋅×=

(4)

4. Self Auto-Restart: The FSFR-HS series can restart

automatically even though any built-in protections are

triggered in case external supply voltage is applied. As

shown in Figure 22 and Figure 23; once a protection is

triggered, the power MOSFET immediately stops. The

counter starts to operate and 1008-clocks are counted,

then the V-I converter is disabled. C

starts to be naturally

discharged with the series impedance of R

and R

min

until

drops to V

RT,RESET

, typically 0.1 V. Then, all protections

are reset and the V-I converter resumes. The FSFR-HS

starts switching again with soft-start.

The counter operating time for 1008-clocks after

protection activation is set by the current out of the RT

pin until V

drops to V

RT,RESET

. Finally, the stop time of

FSFR-HS can be estimated, without considering the

counter operation time, as:

()

]s[RRCt

minSSSSSTOP

+⋅=

(5)

Figure 22. Internal Block for Auto-Restart

Figure 23. Self Auto-Restart Operation

5. Protection Circuits: The FSFR-HS series has several

self-protective functions; such as Over-Current Protection

(OCP), Abnormal Over-Current Protection (AOCP), Over-

Voltage Protection (OVP), Thermal Shutdown (TSD), and

Line Under-Voltage Lockout (LUVLO or Brownout).

These protections are Auto-Restart Mode protections, as

shown in Figure 24.

Once a fault condition is detected, switching is instantly

terminated and the MOSFETs remain off. When LV

falls

to the LV

stop voltage of 10 V and V

is lower than

RT,RESET

of 0.1 V, the protection is reset. The FSFR-HS

resumes normal operation when LV

reaches the start

voltage of 12.5 V.

Figure 24. Protection Blocks

5.1 Over-Current Protection (OCP): When the

sensing pin voltage drops below -0.58 V and its

duration becomes more than OCP blanking time of

1.5 µs, OCP is triggered and the MOSFETs remain off.

5.2 Abnormal Over-Current Protection (AOCP):

If the secondary rectifier diodes are shorted, large

current with extremely high di/dt can flow through the

MOSFET before OCP is triggered. AOCP is triggered

without shutdown delay if the sensing pin voltage drops

below -0.9 V.

5.3 Over-Voltage Protection (OVP): When the LV

reaches 23 V, OVP is triggered. This protection is used

when auxiliary winding of the transformer supplies V

to the FPS™.

5.4 Thermal Shutdown (TSD): The MOSFETs and

the control IC in one package make it easier for the

control IC to detect the abnormal over-temperature of

the MOSFETs. If the temperature exceeds

approximately 130°C, thermal shutdown triggers.

6. Line Under-Voltage Lockout (UVLO): FSFR-HS

includes precise line UVLO (or brownout) with

programmable hysteresis voltage. This function can start

or restart the IC when V

for the scale-down voltage of

the DC-link by the sensing resistors, R1 and R2, is higher

than V

LINE

of 2.5 V as the DC-link voltage increases and

vice versa. A hysteresis voltage between the start and

stop voltage of the IC is programmable by I

LINE

. In normal

operation, the comparator’s output is HIGH and I

LINE

deactivated so that a voltage on LS pin, V

LS,

can be

obtained as a divided voltage by R1 and R2. On the

contrary, I

LINE

is activated when the comparator’s output

is LOW. V

is generated by the difference between the

current through R1 and I

LINE