NCL30081ASNT1G ON Semiconductor, NCL30081ASNT1G Datasheet - Page 23

• Manufacturer Part Number: NCL30081ASNT1G
• Description: LED Lighting Drivers Step-Dimm Quasi-Res I-Mode Cntlr
• Manufacturer: ON Semiconductor

Specifications of NCL30081ASNT1G

• Rohs: yes
• Input Voltage: 18 V
• Operating Frequency: 65 kHz
• Maximum Supply Current: 1 mA
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: TSOP-6
• Minimum Operating Temperature: - 40 C

Zero Crossing Detection Block
voltage of the power MOSFET reaches a valley.
below the V
oscillations, the ZCD comparator may not be able to detect
the ZCD pin or the auxiliary winding is shorted, the
controller could continue switching leading to improper
regulation of the LED current. Moreover during an output
short circuit, the controller will strive to maintain constant
current operation.
The ZCD pin allows detecting when the drain−source
A valley is detected when the voltage on pin 1 crosses
At startup or in case of extremely damped free
Normally with this type of time−out function, in the event
high
high
high
high
low
low
low
low
ZCD(THD)
The 2nd valley is detected
By the ZCD comparator
internal threshold.
The 3rd valley
is validated
Figure 50. Time−out Chronograms
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The 3rd valley is not detected
account for the missing 3rd valley
the valleys. To avoid such a situation, the NCL30081
features a Time−Out circuit that generates pulses if the
voltage on ZCD pin stays below the V
for 6.5 ms.
detection and simulates a missing valley in case of too
damped free oscillations.
a comparator and secondary timer starts counting when the
ZCD voltage is below the V
reaches 90 ms, the controller detects a fault and shutdown.
The auto−restart version (B suffix) waits 4 seconds, then the
controller restarts switching. In the latched version
(A suffix), the controller is latched as long as V
above the V
Time−out circuit adds a pulse to
The time−out also acts as a substitute clock for the valley
To avoid these scenarios, a protection circuit consisting of
by the ZCD comp
CC(reset)
threshold.
ZCD(short)
threshold. If this timer
ZCD(THD)
14
12
15
16
17
4 3
V ZCD(THD)
2nd,
V ZCD
ZCD comp
TimeOut
Clk
3rd
threshold
CC
stays