SSL5015TE All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
Product data sheet Rev. 2 — 26 February 2014 7 of 20
NXP Semiconductors
SSL5015TE
Compact non-dimmable LED driver IC
8.3.2 Leading-Edge Blanking (LEB)
To prevent false detection of the short-winding or overcurrent, a blanking time following
switch-on is implemented. When the internal MOSFET switch turns on there can be a
short current spike due to capacitive discharge of voltage over the drain and source.
During the LEB time (t
leb
), the spike is disregarded.
8.3.3 OverCurrent Protection (OCP)
The SSL5015TE contains a highly accurate built-in peak current detector. It triggers when
the voltage at the SOURCE pin reaches the peak-level V
th(ocp)SOURCE
. The current
through the switch is sensed using a resistor connected to the SOURCE pin. The sense
circuit is activated following LEB time (t
leb
). As the LED current is half the peak current (by
design), it automatically provides protection for maximum LED current during operation.
There is a propagation delay (t
d(ocp-swoff)
) between overcurrent detection and the actual
MOSFET switch-off. Due to the delay, the actual peak current is slightly higher than the
OCP level set by the resistor in series with the SOURCE pin.
8.3.4 OverTemperature Protection (OTP)
When the internal OTP function is triggered at a certain IC temperature (T
th(act)otp
), the
converter stops operating. The safe-restart protection is triggered and the IC restarts with
switching resuming when the IC temperature drops to lower than T
th(rel)otp
.
8.3.5 Brownout protection
Brownout protection is designed to limit the lamp power when the input voltage drops
close to the output voltage level. The input power has to remain constant. The input
current would otherwise increase to a level that is too high for the input circuitry. For the
SSL5015TE, there is a maximum limit on the on-time t
on(high)
. The rate of current rise in
the coil during the on-phase is proportional to the difference between input voltage and
output voltage. Therefore, the peak current cannot be reached before t
on(high)
. As a result
the average output current to the LEDs is reduced.
8.3.6 Output Short Protection (OSP)
During the switch-off time, if a valley is not detected within the maximum off-time limit
(t
off(high)
), the output voltage is less than the minimum limit allowed in the application. This
condition can occur either during start-up or due to a short-circuit. A timer is started when
t
off(high)
is detected, and is stopped only if a valid valley-detection occurs in one of the
subsequent cycles. The timer can also be reset if the maximum limit on the on-time of the
switch (t
on(high)
) is reached, which is usually the case at start-up (brownout protection).
The timer can also be reset if the maximum limit on the on-time of the switch (t
on(high)
) is
reached, which is usually the case at start-up (brownout protection).
If no valley is detected and t
on(high)
is not reached before t
det(sc)
, then it is concluded that a
real short-circuit exists. The IC enters latched protection. If V
CC
drops to lower than
V
CC(rst)
, the IC resets the latched protection. During PWM current regulation, the OSP
timer is paused during the off-cycle of the PWM signal.
