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SSL21081T
Compact non-dimmable LED driver IC
1. General description
The SSL21081T is a high-voltage Integrated Circuit (IC) for driving LED lamps in general
mains non-dimmable lighting applications.
The main benefits are: Small Printed-Circuit Board (PCB) footprint; compact solution High efficiency (up to 95 %) Ease of integration Low electronic Bill Of Material (BOM)
The IC incorporates a 300 V MOSFET.
The IC works as boundary conduction mode converters, typically in buck configuration. It
has been designed to start up directly from the HV supply by an internal high-voltage
current source. Thereafter, the dV/dt supply is used with capacitive coupling from the drain
or any other auxiliary supply. This function provides full flexibility in the application design.
The IC consumes 1.3 mA of supply current with an internal clamp limiting the supply
voltage.
The IC provides accurate output current control with LED current accuracy within 5 %. It
can be operated using Pulse-Width Modulation (PWM) current regulation. It has many
protection features including easy LED temperature feedback.
2. Features and benefits LED driver ICs for driving LED strings from a rectified mains supply High-efficiency switch mode buck driver product family: driver with integrated 300 V (DC) power switches Controller with power-efficient boundary conduction mode of operation with: No reverse recovery losses in freewheel diode Zero Current Switching (ZCS) for turn-on of switch Zero voltage or valley switching for turn-on of switch Minimal required inductance value and size Direct PWM current regulation possible Fast transient response through cycle-by-cycle current control: Negligible AC mains ripple at LED current and minimal total capacitor value No over or undershoots in the LED current
SSL21081T
Compact non-dimmable LED driver IC
Rev. 6 — 3 October 2013 Product data sheet
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC Internal protections: UnderVoltage LockOut (UVLO) Leading-Edge Blanking (LEB) OverCurrent Protection (OCP) Short-Winding Protection (SWP) Internal OverTemperature Protection (OTP) Brownout protection Output Short Protection (OSP) Low component count LED driver solution (see Figure 3): No Schottky diode required due to ZCS Easy external temperature protection with a single NTC resistor Option for soft-start function Compatible with wall switches with built-in indication light during standby1 IC lifetime easily matches or surpasses LED lamp lifetime
3. Applications
SSL21081T products are intended for compact mains non-dimmable LED lighting
applications with accurate fixed current output for single mains input voltages. Mains input
voltages include 100 V (AC), 120 V (AC). The output signal can be modulated using a
PWM signal. The Hotaru switch is a well-known wall switch with built-in light
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC
4. Quick reference data
[1] An internal clamp sets the supply voltage. The current into the VCC pin must not exceed the maximum IDD
value (see Table 5).
5. Ordering information
5.1 Ordering options
Remark: All voltages are in V (AC) unless otherwise specified.
Table 1. Quick reference data
VCC supply voltage operating range [1]8 - 16 V
RDSon drain-source on-state
resistance
Tj = 25 C 2.05 2.3 2.55 
Tj = 125 C 3.05 3.45 3.85 
fconv conversion frequency - 100- kHz
IDRAIN current on pin DRAIN 2 - +2 A
VDRAIN voltage on pin DRAIN 0.4 - +300 V
Table 2. Ordering information
SSL21081T SO8 plastic small package outline body; 8 leads; body width
3.9 mm
SOT96-1
Table 3. Ordering options
SSL21081T 100 V; 120 V 300 V (DC); 2.3  SO8
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC
6. Block diagram
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC
7. Pinning information
7.1 Pinning
7.2 Pin description
Table 4. Pin description 1 high-voltage supply pin
SOURCE 2 low-side internal switch
VCC 3 supply voltage
NTC 4 LED temperature protection input
DVDT 5 AC supply pin
GND 6, 7 ground
DRAIN 8 high-side internal switch
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC
8. Functional description
8.1 Converter operation
The converter in the SSL21081T is a Boundary Conduction Mode (BCM), peak current
controlled system. Figure 3 shows the basic application diagram. Figure 4 shows the
waveforms. This converter type operates at the boundary between continuous and
discontinuous mode. Energy is stored in inductor L each period that the switch is on. The
inductor current IL is zero when the internal MOSFET switch is switched on. Thereafter,
the amplitude of the current build-up in L is proportional to VIN VOUT and the time that
the internal MOSFET switch is on. When the internal MOSFET switch is switched off, the
current continues to flow through the freewheel diode and the output capacitor. The
current then falls at a rate proportional to the value of VOUT. The LED current ILED is
almost equal to half the peak switch current. As soon as the inductor current IL is zero, a
new cycle is started.
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC
8.2 Valley detection
A new cycle is started when the primary switch is switched on (see Figure 4). Following
time t1, when the peak current is detected on the SOURCE pin, the switch is turned off
and the secondary stroke starts (3). When the secondary stroke is complete and the coil
current at t3 equals zero, the drain voltage starts to oscillate around the VIN  VOUT level.
The amplitude equals VOUT. A special feature, called valley detection is an integrated part
of the SSL21081T circuitry. Dedicated built-in circuitry connected to the DRAIN pin,
senses when the voltage on the drain of the switch has reached its lowest value. The next
cycle is then started and as a result the capacitive switching losses are reduced.
If both the frequency of the oscillations and the voltage swing are within the range
specified (fring and ∆Vvrec(min)) for detection, a valley is detected and accepted. If a valid
valley is not detected, the secondary stroke is continued until the maximum off-time
(toff(high)) is reached. Then the next cycle is started.
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC
8.3 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 Short-Winding Protection (SWP) Output Short Protection (OSP) LED overtemperature control and protection
The SWP and the OSP are latched protections. These protections cause the IC to halt
until a reset (a result of power cycling) is executed. When VCC drops to below VCC(rst), the
IC resets the latch protection mode. The internal OTP and LED over temperature
protections are safe-restart protections. The IC halts, causing VCC to drop to below
VCC(stop), triggering a start-up. When VCC drops to below VCC(rst), the IC resets the latch
protection mode. Switching starts only when a no fault condition exists.
8.3.1 UnderVoltage LockOut (UVLO)
When the voltage on the VCC pin drops to below VCC(stop), the IC stops switching. An
attempt is made to restart by supplying VCC from the HV pin voltage.
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 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 (tleb), the spike is
disregarded.
8.3.3 OverCurrent Protection (OCP)
The SSL21081T contain a highly accurate built-in peak current detector. It triggers when
the voltage at the SOURCE pin reaches the peak-level Vth(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 tleb. 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 (td(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.
8.3.4 OverTemperature Protection (OTP)
When the internal OTP function is triggered at a certain IC temperature (Tth(act)otp), the
converter stops operating. The safe-restart protection is triggered and the IC restarts with
switching resuming when the IC temperature drops lower than Tth(rel)otp.
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC
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
SSL21081T, there is a maximum limit on the on-time ton(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 ton(high). As a result
the average output current to the LEDs is reduced.
8.3.6 Short-Winding Protection (SWP)
SWP activates if there is a steep rising current through the MOSFET and thus through the
external resistor connected to the SOURCE pin. This current can occur when there is a
short from the freewheel diode. Additionally, it occurs due to a small/shorted inductor
between the input voltage and the DRAIN pin. If the voltage on the SOURCE pin is
> 1.5 V, latched protection is triggered following LEB time tleb. In addition, if VCC drops to
below VCC(rst) the IC resets the latched protection mode.
8.3.7 Output Short-circuit Protection (OSP)
During the secondary stroke (switch-off time), if a valley is not detected within the off-time
limit (toff(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 tdet(sc) is started when toff(high) is detected. Timer tdet(sc) is reset when a valid valley
detection occurs in one of the subsequent cycles or when VCC drops to below VCC(stop).
The timer can also be reset if the maximum limit on the on-time of the switch (ton(high)) is
reached, which is usually the case at start-up (brownout protection). If no valley is
detected and (ton(high)) is not reached before tdet(sc), then it is concluded that a real
short-circuit exists. The IC enters latched protection. If VCC drops to below VCC(rst), the IC
resets the latched protection mode (see Figure 5).
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC
8.4 VCC supply
The SSL21081T is supplied using three methods: Under normal operation, the voltage swing on the DVDT pin is rectified within the IC
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 either the dV/dt supply or 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 VCC(startup). The IC locks out
(stops switching) when the voltage at the VCC pin is < VCC(stop). The hysteresis between
the start and stop levels allows the IC to be supplied by a buffer capacitor until the dV/dt
supply is settled. The SSL21081T has an internal VCC 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 VCC. If the maximum current of the dV/dt supply minus the
current consumption of the IC (determined by the load on the gate drivers), is lower than
the maximum value of IDD no external Zener diode is required in the dV/dt supply circuit.
8.5 DVDT pin supply (dV/dt)
The DVDT pin is connected to an internal single-sided rectification stage. When a different
voltage with sufficient amplitude is supplied to the pin, the IC can be powered without any
other external power connection. This provides an effective method to prevent additional
high power losses, which are the result if a regulator were used for continuously powering
the IC. Unlike an auxiliary supply, additional inductor windings are not required.
8.6 VCC regulator
During supply dips, the input voltage can drop so much that it can no longer supply the
required IC current through the DVDT pin. Under these conditions, if the VCC voltage
drops to below VCC(swon)reg level, another regulator with a current capability of up to
Isup(high)HV is started. The job of the regulator is to fill in the required supply current, which
the dV/dt supply does not deliver, thus preventing that the IC enters UVLO. When the
VCC voltage exceeds the VCC(swon)reg level, the regulator is turned off.
8.7 NTC functionality and PWM regulation
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
regulation). The pin has an internal current source that generates the current of Ioffset(NTC).
An NTC resistor to monitor the LED temperature can be connected directly 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 VCC reaches VCC(startup) the voltage on the NTC pin must be less
than the minimum value of Vact(tmr)NTC. This is valid when the voltage on the NTC pin is
derived from the VCC using a resistive divider and a PTC in series with the resistor
between pins VCC and NTC.
NXP Semiconductors SSL21081T
Compact non-dimmable LED driver IC
If an NTC resistor is connected between the NTC pin and ground, the voltage on the NTC
pin is 0 V when VCC reaches VCC(startup).
When the voltage on the NTC pin exceeds Vth(high)NTC (see Figure 6 (4)), the converter
delivers nominal output current. When the voltage is lower than this level, the peak current
is gradually reduced until Vth(low)NTC is reached (see Figure 6 (3)). The peak current is
now half the peak current of nominal operation. When Vact(tmr)NTC is passed
(see Figure 6 (2)), a timer starts to run to distinguish between the following situations: If the low-level Vdeact(tmr)NTC is not reached within time tto(deact)NTC (see Figure 6 (1)),
LED overtemperature is detected. The IC stops switching and attempts to restart from
the HV pin voltage. The converter restarts from an NTC protection shutdown when the
voltage on the NTC pin exceeds Vth(high)NTC (see Figure 6 (4)). It is assumed that the
reduction in peak current does not result in a lower NTC temperature and LED OTP is
activated. If the low-level Vdeact(tmr)NTC is reached within the time tto(deact)NTC (see Figure 6 (1)) it
is assumed that the pin is pulled down externally. The restart function is not triggered.
Instead, the output current is reduced to zero. PWM regulation and consequently LED
output current regulation can be implemented this way. The output current rises again
when the voltage exceeds Vth(low)NTC.
8.7.1 Soft-start function
The NTC pin can be used to make a soft start function. During switch-on, the level on the
NTC pin is low. By connecting a capacitor (in parallel with the NTC resistor), a time
constant can be defined. The time constant causes the level on the NTC pin to increase
slowly. When passing level Vth(low)NTC (see Figure 6 (3)), the converter starts with half of
the maximum current. The output current slowly increases to maximum when Vth(high)NTC
(see Figure 6 (4)) is reached.

Partno	Mfg	Dc	Qty	Available	Descript
SSL21081T	NXP	N/a	10000	avai	Compact non-dimmable LED driver IC