LYT3314-3328
LYTSwitch-3
Family
Single-Stage LED Driver IC with Combined PFC and
Constant Current Output for Outstanding TRIAC Dimming
in Isolated and Non-Isolated Topologies
Product Highlights
Combined Single-Stage PFC + Accurate CC Output
•
•
•
•
Less than ±3% CC regulation over line and load
Power Factor >0.9
Ensures monotonic VA reduction with TRIAC phase angle
Low THD, 15% typical for dimmable bulbs, as low as 7% in
optimized designs
Detects leading-edge and trailing-edge TRIAC dimmers
High-efficiency mode when no dimmer is present
Selectable dimming profile increases design flexibility
Fast turn-on (<500 ms)
Low pop-on and dead-travel
Active bleeder drive for widest dimmer compatibility
L
T
LYTSwitch-3
BL
L
D
N
BS
DS
FB
CONTROL
Advanced Integrated TRIAC Dimmer Detection
•
•
•
•
•
•
BP
OC
S
T
PI-7549a-020316 HLBB
Figure 1.
Simplified Schematic (Buck).
Design Flexibility
•
Supports buck, buck-boost, tapped buck-boost, boost, isolated and
non-isolated flyback
•
Up to 20 W output
Output Power Table
Product
2
Highest Reliability
Output Power
1
85-132 VAC or 185-265 VAC
5.7 W
8.8 W
12.6 W
20.4 W
•
No electrolytic bulk capacitors or optoisolators for increased lifetime
•
Comprehensive protection features
•
Input and output overvoltage
•
Output short-circuit and open-loop protection
•
Advanced thermal control
•
Thermal foldback ensures that light continues to be delivered at
LYT33x4D
3
LYT33x5D
LYT33x6D
LYT33x8D
elevated temperatures
•
End-stop shutdown provides protection during fault conditions
Description
The LYTSwitch™-3 family is ideal for single-stage power factor
corrected constant current LED bulbs and downlighters.
Each device incorporates a high-voltage power MOSFET and discon-
tinuous mode, variable frequency variable on-time controller. The
controller also provides cycle-by-cycle current limit, output OVP, line
overvoltage, comprehensive protection features, plus advanced
thermal management circuitry.
All LYTSwitch-3 ICs have a built-in TRIAC detector that discriminates
between leading-edge and trailing-edge dimmers. This capability
together with load monitoring circuitry regulates bleeder current during
each switching cycle. The controller disables the bleeder circuit
completely if no dimmer is detected, significantly increasing efficiency.
The combination of a low-side switching topology, cooling via electroni-
cally quiet SOURCE pins and frequency jitter ensure extremely low EMI.
This reduces the size of the input filter components – greatly reducing
audible noise during dimming.
The part numbers shown in Table 1 describe 4 different power levels and
two MOSFET voltage options to cost-optimize designs while EcoSmart
TM
switching technology insures maximum efficiency for each device size
and load condition.
Table 1. Output Power Table (Buck Topology).
Notes:
1. Maximum practical continuous power in an open frame design with adequate
heat sinking, measured at 50˚C ambient (see Key Applications Considerations
for more information).
2. Package: D: SO-16B.
3. ”x” digit describes V
DSON(MAX)
of the integrated switching MOSFET,
650 V = 1, 725 V = 2.
Figure 2.
SO-16B (D Package).
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March 2016
This Product is Covered by Patents and/or Pending Patent Applications.
LYT3314-3328
BYPASS
(BP)
UV
LINE-SENSE
(L)
4.7 V
V
LOV
REGULATOR
5.25 V
DRAIN
(D)
LOV
I
LIM
I
LIM
V_I
LIM
CURRENT LIMIT
SOA
SOA
S
Q
Q
LOV
UV
DIMMER TYPE
AND EDGE
DETECTION
V
FB
V
FB(SK)
+
R
ZC
V
ZC
UPDATE
CLxx
+
LATCH
FAULT
PHASE
MEASUREMENT
FREQUENCY AND
DUTY CYCLE CONTROL
I
OOV
FEEDBACK
(FB)
V
FB
V
FB(AR)
I
OUV
Enable
(EN)
AUTO-RESTART
OUTPUT
COMPENSATION
(OC)
MULTIPLIER
DRIVER CURRENT
SENSING
(DS)
I
FB
FAULT
HANDLING
BLEEDING CURRENT
SENSING
(BS)
S
Q
Q
I
BS
- I
DS
V
REF
(T)
R
SOURCE
(S)
BLEEDER
CONTROL
(BL)
PI-7747-020316
Figure 3.
Block Diagram.
2
Rev. D 03/16
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LYT3314-3328
Pin Functional Description
LINE-SENSE (L) Pin
LINE-SENSE pin implements input voltage waveform detection:
conduction angle is detected accurately since SOURCE pin is referenced
to bulk capacitor ground. Input OVP is activated when LINE-SENSE pin
current exceeds the predetermined threshold.
BLEEDER CURRENT SENSE (BS) Pin
BLEEDER CURRENT SENSE pin measures the total input current –
active bleeder current plus switch current. This current is sensed in
order to keep TRIAC current above its holding level. This is achieved by
modulating the bleeder dissipation.
R
BS
(W)
6k
12 k
24 k
Table 2.
FEEDBACK (FB) Pin
In normal operation and full conduction the preset threshold on the
FEEDBACK pin is 300 mV. This threshold gets reduced linearly with
conduction angle until a minimum level is reached.
Cycle skipping is triggered when voltage on this pin exceeds 600 mV.
BYPASS (BP) Pin
5.25 V supply rail.
OUTPUT COMPENSATION (OC) Pin
Output OVP for all topologies. Output voltage compensation for indirect
output current sense topologies.
DRAIN (D) Pin
High-voltage internal MOSFET (725 V or 650 V).
SOURCE (S) Pin:
Power and signal ground.
Dim Curve
Max. Dim Curve
Min. Dim Curve
Min. Dim Curve
Load Shut Down (LSD)
No
No
Yes
BS Pin Resistor Programming.
DRIVER CURRENT SENSE (DS) Pin
DRIVER CURRENT SENSE pin senses the driver current. This current is
used to deduce output current: it is multiplied by the input voltage and
the result is then divided by the output voltage to obtain output current.
D Package (SO-16B)
OC BP S S S S S S
16 15 14 13 12 11 10 9
R
DS
(W)
6k
24 k
Table 3.
Topology Selection Resistor.
Topology
Buck, Buck-Boost, Isolated Flyback
Non-Isolated Flyback
1 2 3 4 5
FB L BS DS BL
8
D
BLEEDER CONTROL (BL) Pin
BLEEDER CONTROL pin drives the external bleeder transistor in order to
maintain the driver input current above the holding current of the
dimmer TRIAC.
Figure 4.
Pin Configuration.
PI-7456-051815
3
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Rev. D 03/16
LYT3314-3328
R
DP
D
1
L
1
D
FW
C
OUT
T
R
O
R
B
C
1
C
2
R
L
L
R
F
D
B1
Q
1
MOV
Q
2
N
R
BS
R
DS
R
D
C
BL
C
DC
R
BC
R
DC
R
FB
C
FB
LYTSwitch-3
BS
DS
FB
BP
OC
S
BL
L
D
CONTROL
D
B
T
R
OC
R
BP
C
BP
C
B
PI-7872-020216 LLB
Figure 5.
Typical Schematic Buck (Low-Line).
R
DP
L
1
T
R
B1
C
1
R
B2
L
R
F
D
B1
C
P
C
2
R
P
R
L1
C
OUT
D
FW
R
O
R
L2
Q
1
MOV
Q
2
N
R
BS
R
DS
R
D
C
BL
C
DC
R
BC
R
DC
R
FB
C
FB
LYTSwitch-3
BS
DS
FB
BP
OC
S
BL
L
D
CONTROL
D
B
T
R
OC
R
BP
C
BP
C
B
PI-7873-020216 HLBB
Figure 6.
Typical Schematic Buck-Boost (High-Line).
4
Rev. D 03/16
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LYT3314-3328
Applications Example
DER-524 8 W A19 LED Bulb Driver Dimmable, Tight
Regulation, High Power factor, Low ATHD Design
Example
RTN
R7
150
Ω
2W
C4
47 nF
400 V
R9
2 kΩ
2W
L1
1 mH
R8
1 kΩ
1W
C3
47 nF
400 V
R20
2 MΩ
1%
R18
2 MΩ
1%
2
T1
1
R32
3 kΩ
2W
C5
100 nF
400 V
C10
120
µF
80 V
R19
82 kΩ
L
RF1
47
Ω
2W
BR1
B10S-G
1000 V
+V
D3
STTH1R06A
600 V
Q2
PN222A
Q1
STX13003-AP
RV1
275 VAC
N
R11
24 kΩ
LYTSwitch-3
U1
LYT3325D
BS
DS
FB
BL
L
D
CONTROL
R4
20
Ω
R1
3.9
Ω
C2
8.2 nF
50 V
R13
6.04 kΩ
1%
C6
R15
10
µF
39.2 kΩ
10 V
1%
BP
OC
S
D2
BAV21W-7-F
8 T1
C8
150 nF
25 V
R16
178 kΩ
1%
R14
6.2 kΩ
C7
22
µF
16 V
C11
22
µF
50 V
7
PI-7779-021016 HLBB
R12
4.3
Ω
1%
Figure 7.
DER-524 8 W, 72 V, 115 mA Non-Isolated Dimmable A19 LED Bulb Driver using LYT3325D.
The circuit shown in Figure 7 is configured as a buck-boost power
supply utilizing the LYT3325D from the LYTSwitch-3 family of ICs.
This type of LED driver configuration is common for dimmable bulb
applications where high dimmer compatibility, accurate regulation,
high efficiency, high power factor and low ATHD are required along
with low component count for high reliability. The output can drive
an LED load from 68 V to 76 V with a constant output current of
115 mA ±3% across an input range of 195 VAC to 264 VAC and can
operate in maximum ambient temperature of 100 ºC with good margin
below the thermal foldback protection point. It has an efficiency of
greater than 86%, very low ATHD% (less than 20%) and high power
factor of greater than 0.9 measured across the input range.
Circuit Description
The LYTSwitch-3 device (U1 - LYT3325D) combines a high-voltage
power MOSFET, variable frequency and on-time control engine, fast
start-up, selectable dimming curves with load shutdown at deep
dimming and protection functions including line and output overvolt-
age into a single package, greatly reducing component count. The
integrated 725 V power MOSFET provides a large drain voltage
margin in high-line input AC applications thus increasing reliability.
A 625 V power MOSFET option is also offered to reduce cost in
applications where the voltage stress on the power MOSFET is lower.
Configured to operate as a discontinuous conduction mode buck-
boost converter, U1 provides high power factor and very low ATHD
via its internal control algorithm (the design also features low input
capacitance to further reduce THD and increase PF). Discontinuous
conduction mode inherently eliminates reverse current from the
output diode when the power MOSFET is in the OFF-state reducing
high frequency noise and allowing the use of a simpler, smaller EMI
filter which also improves efficiency.
Input Filter
AC input power is rectified by bridge BR1. A 1000 V voltage rating is
recommended (the maximum clamp voltage for a typical 275 V
varistor is 720 V). The rectified DC is filtered by the input capacitors
C4 and C5. Too much capacitance degrades power factor and ATHD,
so the values of the input capacitors were adjusted to the minimum
values necessary to meet EMI with a suitable margin. Inductor L1,
C4 and C5 form a
π
(pi) filter, which attenuates conducted differential
and common mode EMI currents. Optional resistor R10 across L1
damps the Q of the filter inductor to improve filtering without
reducing low frequency attenuation. Fuse RF1 in Figure 7 provides
protection against catastrophic failures such as short-circuit at the
input. For cost reduction, this can be replaced by a fusible resistor
(typically a flame proof wire-wound type) which would need to be
rated to withstand the instantaneous dissipation induced when
charging the input capacitance when first connected to the input line.
Selection of fuse RF1 in Figure 7 type and rating is dependent on input
surge requirements. Typical minimum requirement for bulb applica-
tion is 500 V differential surges. This design meets a 1 kV surge
specification, so a 47
W
fusible resistor in Figure 7 was used. A fast-
blow fuse with high ampere energy (I
2
T) rating could also be used.
5
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Rev. D 03/16
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