NCL30082
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21
Figure 55. Winding Short Circuit Protection, Max. Peak Current Limit Circuits
S
R
Q
CS
Rsense
LEB1
+
−
S
R
Q
VCC
aux
Vcc
management
Vdd
grand
reset
DRV
Ipkmax
PWMreset
VCCstop
+
−
LEB2
WOD_SCP
Vcontrol
+
−
STOP
from Fault Management Block
OVP
UVLO
S
R
Q
grand
reset
OVP
8_HICC
OFF
WOD_SCP
latch
latch
8_HICC
V
ILIMIT
V
CS(stop)
Q
Q
Q
Thermal Fold−back and Over Voltage / Over
Temperature Protection
The thermal fold−back circuit reduces the current in the
LED string when the ambient temperature exceeds a set
point. The current is gradually reduced to 50% of its nominal
value if the temperature continues to rise. (Figure 56). The
thermal foldback starting temperature depends of the
Negative Coefficient Temperature (NTC) resistor chosen by
the power supply designer.
Indeed, the SD pin allows the direct connection of an NTC
to sense the ambient temperature. When the SD pin voltage
V
SD
drops below V
TF(start)
, the internal reference for the
constant current control V
REF
is decreased proportionally to
V
SD
. When V
SD
reaches V
TF(stop)
, V
REF
is clamped to
V
REF50
, corresponding to 50% of the nominal output current
(versions A, B, B1, B2, B3). For the NCL30082D, the output
current is decreased to 25% of the nominal output current.
If V
SD
drops below V
OTP
, the controller enters into the
auto−recovery fault mode for version B, B1, B2, B3 and D
meaning that the 4−s timer is activated. The controller will
re−start switching after the 4−s timer has elapsed and when
V
SD
> V
OTP(on)
to provide some temperature hysteresis.
For version A, this protection is latched: reset occurs when
V
CC
< V
CC(reset)
.
Temperature increases
Temperature decreases
Shutdown
Figure 56. Output Current Reduction vs. SD Pin
Voltage for NCL30082 Versions A, B, B1, B2, B3
V
SD
V
TF(start)
V
TF(stop)
V
OTP(off)
V
OTP(on)
I
out
I
out(nom)
50% I
out(nom)
Figure 57. Output Current Reduction vs. SD Pin
Voltage for NCL30082D
Temperature increases
Temperature decreases
Shutdown
V
SD
I
out
I
out(nom)
25% I
out(nom)
V
OTP(off)
V
TF(start)
V
TF(stop)
V
OTP(on)
