NCL30060

www.onsemi.com

11

mA typical value. After the device is

400 mV. And the RT pin output current is switched back to

normal operation, and the RT voltage is regulated to

The timing resistor should be placed as close as possible

to the RT and GND pins with short trace lengths. Care should

to reduce noise pickup.

CURRENT SENSE, ZERO CURRENT AND

OVERVOLTAGE DETECTION

The NCL30060 uses a novel architecture combining the

current sense, the zero current detector (ZCD), output

overvoltage and shorted output detector functions in a single

terminal. Figure 6 shows the circuit schematic of the current

sense and ZCD detectors.

Figure 6. Current Sense and ZCD Detectors Schematic

Short

Winding

Comparator

CS/ZCD

Peak Current

Comparator

ZCD

Comparator

Disable

DRV

Reset

UVLO

Edge

Detector

ZCD Blanking

Time

Selector

ILIM2, OVP

GND

R

S

Q

Q

UVLO

Clamp

DRV

Counter

Reset

Count

ACTIVE

ILIM2

Re−start

Edge

Detector

HV(high)

DRV

DRV

Reset

Dominant

Latch

LEB

LEB

CURRENT SENSE

The Switch current is sensed across a sense resistor,

CS/ZCD pin. The current signal is blanked by a leading edge

blanking (LEB) circuit. The blanking period eliminates the

leading edge spike and high frequency noise during the

typically 325 ns. The Current Limit Comparator disables the

driver once the current sense signal exceeds the current

switching cycle is initiated by the ZCD or watchdog timer.

A severe overload fault like a secondary side winding

short circuit causes the switch current to increase very

rapidly during the on−time. The current sense signal

signal is blanked by the LEB circuit during the switch turn

on, the current could damage the system.

The NCL30060 protects against this fault by adding an

additional comparator, Short Circuit Comparator. The

current sense signal is blanked with a shorter LEB duration,

Circuit Comparator.

The

voltage

threshold

of

the

consecutive faults detected by the Short Circuit Comparator

causes the controller to enter a fault mode. The NCL30060B

will auto−recover from the fault state if the short is removed.

The count to 4 provides noise immunity during surge testing.

The counter is reset each time a DRV pulse occurs without

activating the Short Circuit Comparator.

1.25 ms independent of the PFC ZCD state.