NCP1254ASN65T1G View Datasheet(PDF) - ON Semiconductor

Part Name

Description

MFG CO.

NCP1254ASN65T1G

Current-Mode PWM Controller for Off-line Power Supplies featuring Peak Power Excursion

ON Semiconductor 

NCP1254

Frequency

Peak current setpoint

Fsw

130 kHz

FB

65 kHz

VCS

max

0.8 V

max

26 kHz

min skip

VFB

400 mV 1.9 V 4 V

1.5 V 3.2 V

Vfold,end Vfold

≈0.47 V

min

≈0.25 V

Vskip Vfreeze

0.4 V 1 V

Vfold

VFB

3.2 V

1.9 V

Figure 34. By observing the voltage on the feedback pin, the controller reduces its

switching frequency for an improved performance at light load.

Auto−Recovery Short−Circuit Protection

In case of output short−circuit or if the power supply

experiences a severe overloading situation, an internal error

flag is raised and starts a countdown timer. If the flag is

asserted longer than its internal value, the driving pulses are

stopped and Vcc falls down as the auxiliary pulses are

missing. When it crosses VCC(min), the controller

consumption is down to a few mA and the Vcc slowly builds

up again thanks to the resistive starting network. When Vcc

reaches VCCON, the controller purposely ignores the

re−start and waits for another Vcc cycle: this is the so−called

double hiccup. By lowering the duty ratio in fault condition,

it naturally reduces the average input power and the rms

current in the output cable. Illustration of such principle

appears in Figure 35. Please note that soft−start is activated

upon re−start attempt.

18 V

VCC(t)

8.8 V

No pulse

area

VDRV(t)

Figure 35. An auto−recovery hiccup mode is entered in case a faulty

event is acknowledged by the controller.

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