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SSL2129AT/1J

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P19
SSL2129AT All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 4 — 3 October 2013 7 of 19
NXP Semiconductors
SSL2129AT
Dimmable LED driver IC
8.5 Protective features
The IC has the following protective features:
• UnderVoltage LockOut (UVLO)
• Leading-Edge Blanking (LEB)
• OverCurrent Protection (OCP)
• Internal OverTemperature Protection (OTP)
• Brownout protection
• Output Short Protection (OSP)
• LED overtemperature control and protection
• An optional output OverVoltage Protection circuit is implemented using external
components and the NTC pin.
The internal OTP and LED over temperature prot
ections are safe-restart protections. The
IC halts, causing V
CC
to drop to below V
CC(stop)
, and triggers a start-up. When V
CC
drops
to below V
CC(rst)
, the IC resets the latch protection mode. Switching starts only when no
fault condition exists.
8.5.1 UnderVoltage LockOut (UVLO)
When the voltage on the VCC pin < V
CC(stop)
, the IC stops switching. An attempt is then
made to restart by supplying V
CC
from the HV pin voltage.
8.5.2 Leading-Edge Blanking (LEB)
To prevent false detection of the short-winding or overcurrent, a blanking time following
switch-on is implemented. When the MOSFET switch switches on there can be a short
current spike due to capacitive discharge of voltage over the drain and source and the
charging of the gate to source capacitance. During the LEB time (t
leb
), the spike is
disregarded.
8.5.3 OverCurrent Protection (OCP)
The SSL2129AT contains a highly accurate peak current detector. It triggers when the
voltage on 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 the overcurrent detection and the actual switching
off of the switch. Due to the delay, the actual peak current is slightly higher than the OCP
level set by the resistor in series to the SOURCE pin.
8.5.4 OverTemperature Protection (OTP)
When the internal OTP function is triggered at a certain IC temperature (T
th(act)otp
), the
converter stops operating. The OTP safe-restart protection and the IC restarts again with
switching resuming when the IC temperature drops below T
th(rel)otp
.
SSL2129AT All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 4 — 3 October 2013 8 of 19
NXP Semiconductors
SSL2129AT
Dimmable LED driver IC
8.5.5 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. In the
SSL2129AT, there is a maximum limit on the on-time of switch t
on(high)
.
In buck mode, the rate of current rise in the coil during the on-phase is proportional to the
di
fference between input voltage and output voltage. Therefore, the peak current cannot
be reached before t
on(high)
and as a result the average output current to the LEDs is
reduced.
8.6 t
on
control
The t
on(high)
can be lowered by connecting a capacitor to the TONMOD pin. The external
capacitor is charged during the primary stroke with I
offset(TONMOD)
. If the V
th(TONMOD)
level
is reached before the t
on(high)
time, the switch is turned off and the secondary stroke starts.
When a capacitor is not connected to the pin, V
th(TONMOD)
is reached quickly. Shorter than
the minimum limit of 1 s. In this case or when the TONMOD pin
is grounded, the internal
time constant, t
on(high)
determines the maximum on-time.
8.7 Output Short-circuit Protection (OSP)
During the secondary stroke (switch-off time), if a valley is not detected within the off-time
limit (t
off(high)
), then typically 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 t
det(sc)
is started when t
off(high)
is detected. Timer t
det(sc)
is reset when a valid valley
detection occurs in one of the subsequent cycles or when V
CC
drops to below V
CC(stop)
.
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 below V
CC(rst)
, the IC
resets the latched protection mode (see Figure
5). During PWM dimming, the OSP timer
is paused during the off cycle.
The value of t
on(high)
depends on the capacitor connected to the TONMOD pin. An open or
shorted TONMOD pin sets t
on(high)
to 15 s (see Section 8.6 and Table 6).
Fig 5. OSP logic diagram
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9
&&VWRS
64
5
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6
263
4
5
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SSL2129AT All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 4 — 3 October 2013 9 of 19
NXP Semiconductors
SSL2129AT
Dimmable LED driver IC
8.8 VCC supply
The SSL2129AT can be supplied using three methods:
• Under normal operation, the voltage swing on the DRAIN pin is rectified using
external components providing current towards the VCC pin
• At start-up, there is an internal current source connected to the HV pin. The current
source provides internal power until an external current on the VCC pin provides the
supply.
• Using an auxiliary winding, the voltage can be rectified and connected to the VCC pin
via a series resistor.
The IC starts up when the voltage at the VCC pin
exceeds V
CC(startup)
. The IC locks out
(stops switching) when the voltage at the VCC pin is lower than V
CC(stop)
. The hysteresis
between the start and stop levels allows the IC to be supplied by a buffer capacitor until
the external supply is settled. The SSL2129AT has an internal V
CC
clamp, which is an
internal active Zener (or shunt regulator). This internal active Zener limits the voltage on
the supply VCC pin to the maximum value of V
CC
. If the maximum current of the supply
minus the current consumption of the IC (determined by the load on the gate drivers), is
lower than the maximum value of I
DD
no external Zener diode is needed in the supply
circuit.
8.8.1 VCC regulator
During supply dips, the input voltage can drop too low to supply the required IC current.
Under these conditions, if the VCC voltage drops lower than V
CC(swon)reg
level, a second
regulator is started. Its function is to fill in the required supply current which the external
supply does not deliver. It prevents the IC going into UVLO. When the VCC voltage
exceeds V
CC(swon)reg
level, the regulator is turned off.
8.9 NTC functionality and PWM dimming
The NTC pin can be used as a control method for LED thermal protection. Alternatively,
the pin can be used as an input to disable/enable light output using a digital signal (PWM
dimming). The pin has an internal current source that generates the current of I
offset(NTC)
.
An NTC resistor to monitor the LED temperature can be directly connected to the NTC
pin. Depending on the resistance value and the corresponding voltage on the NTC pin,
the converter reacts as shown in Figure
6.
During start-up, before V
CC
reaches V
CC(startup)
the voltage on the NTC pin must be less
than the minimum value of V
act(tmr)NTC
. This is valid when the voltage on the NTC pin is
derived from the V
CC
using a resistive divider and a PTC in series with the resistor
between pins VCC and NTC.
If an NTC resistor is connected between the NTC pin and ground, the voltage on the NTC
pin is
0 V when V
CC
reaches V
CC(startup)
.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P19

SSL2129AT/1J

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Manufacturer:
NXP Semiconductors
Description:
IC LED DRIVER OFFLINE DIM 8SO
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