NCL30088
www.onsemi.com
24
Figure 67. Output Current Reduction versus SD
Pin Voltage
At startup, when V
CC
reaches V
CC(on)
, the OTP
comparator is blanked for at least 250 ms in order to allow the
SD pin voltage to reach its nominal value if a filtering
capacitor is connected to the SD pin. This avoids flickering
of the LED light during turn on.
Brown−Out Protection
The NCL30088 prevents operation when the line voltage
is too low for proper operation. As illustrated in Figure 68,
the circuit detects a brown−out situation if the V
S
pin
remains below the V
BO(off)
threshold (0.9 V typical) for
more than the 25−ms blanking time. In this case, the
controller stops operating. Operation resumes as soon as the
V
S
pin voltage exceeds V
BO(on)
(1.0 V typical) and V
CC
is
higher than V
CC(on)
. To ease recovery, the circuit overrides
the V
CC
normal sequence (no need for V
CC
cycling down
below V
CC(off)
). Instead, its consumption immediately
reduces to I
CC(start)
so that V
CC
rapidly charges up to
V
CC(on)
. Once done, the circuit re−starts operating.
Figure 68. Brown−out Circuit
Die Over Temperature (TSD)
The circuit stops operating if the junction temperature (T
J
)
exceeds 150°C typically. The controller remains off until T
J
goes below nearly 100°C.
Pin Connection Faults
The circuit addresses most pin connection fault cases:
• CS pin short to ground
The circuit senses the CS pin impedance every time it
starts−up and after DRV pulses terminated by the 36−ms
maximum on−time. If the measured impedance does
not exceed 120 ohm typically, the circuit stops
operating. In practice, it is recommended to place a
minimum of 250−ohm in series between the CS pin and
the current sense resistor to take into account possible
parametric deviations.
• Fault of the GND connection
If the GND pin is properly connected, the supply
current drawn from the positive terminal of the V
CC
capacitor, flows out of the GND pin to return to the
negative terminal of the V
CC
capacitor. If the GND pin
is not connected, the circuit ESD diodes offer another
return path. The accidental non−connection of the GND
pin is monitored by detecting that one of the ESD diode
is conducting. Practically, the ESD diode of CS pin is
monitored. If such a fault is detected for 200 ms, the
circuit stops generating DRV pulses.
More generally, incorrect pin connection situations
(open, grounded, shorted to adjacent pin) are covered by
AND9204/D
.
