LYT5216-5228
LYTSwitch-5
Family
Single-Stage LED Driver IC with Combined PFC and Constant Current
Output in Isolated and Non-Isolated Topologies
Product Highlights
Combined Single-Stage PFC + Accurate CC Output
•
•
•
•
•
Accurate CC, better than ±3%
Power Factor >0.9
Low THD, <10% with typical input and output conditions
>90% efficient in optimized designs
High switching frequency and DCM allow compact magnetics
LYTSwitch-5
DS
DO
FB
L
D
Design Flexibility
CONTROL
•
Supports buck, buck-boost, tapped-buck, boost, isolated and
BP
OC
S
non-isolated flyback topologies
•
2 MOSFET voltage options and 3 power levels for optimum device
selection
PI-7711-121015
Highest Reliability
Figure 1a. Typical Application Schematic: Isolated Flyback.
•
No electrolytic bulk capacitors or optoisolators for increased lifetime
•
Comprehensive protection features
•
Input and output overvoltage
•
Open-loop protection
•
Advanced thermal control
•
Thermal foldback allows output light delivery at abnormally high
ambient temperatures
•
Hysteretic shutdown provides protection during fault conditions
Description
The LYTSwitch™-5 family is ideal for single-stage power
factor
corrected constant current LED applications – bulbs, tubes and
ballasts.
Each device incorporates a high-voltage power MOSFET and discon-
tinuous mode, variable frequency, variable on-time controller. The
controller also provides fast (cycle-by-cycle) current limit, input and
output OVP, plus advanced thermal management circuitry.
The combination of a low-side switching topology, cooling via electroni-
cally quiet SOURCE pins and frequency jitter ensures extremely low EMI.
This reduces the size of the input filter components – greatly reducing
audible noise.
The part numbers shown in Table 1 describe 3 different power levels and
two MOSFET voltage options to cost-optimize designs, while EcoSmart™
switching technology ensures maximum efficiency for each device size
and load condition.
LYTSwitch-5
DS
DO
FB
L
D
CONTROL
BP
OC
S
PI-7799-121015
Figure 1b. Typical Application Schematic: Non-Isolated Buck.
Output Power Table
Product
2
LYT5225D
LYT5216D, LYT5226D
LYT5218D, LYT5228D
Output Power
1
90-308 VAC
9W
16 W
25 W
Table 1. Output Power Table.
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.
Figure 2.
SO-16B (D Package).
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March 2016
This Product is Covered by Patents and/or Pending Patent Applications.
LYT5216-5228
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
ZC
V
FB
V
FB(SK)
UPDATE
+
+
R
V
ZC
FREQUENCY AND
DUTY CYCLE CONTROL
V
FB
V
FB(AR)
FEEDBACK
(FB)
OUTPUT
COMPENSATION
(OC)
MULTIPLIER
DRIVER CURRENT
SENSING
(DS)
I
FB
FAULT
HANDLING
Enable
(EN)
AUTO-RESTART
S
R
Q
Q
DATA
OUTPUT
(DO)
PI-7753-110215
SOURCE
(S)
Figure 3.
Block Diagram.
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Rev. C 03/16
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LYT5216-5228
Pin Functional Description
LINE SENSE (L) Pin
The LINE-SENSE pin measures input voltage. Input OVP is activated
when LINE-SENSE pin current exceeds the predetermined threshold.
DATA OUTPUT (DO) Pin
Describes auto-restart events.
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.
R
DS
(W)
6 k
–
12 K
24 k
Table 2.
Topology Selection Resistor.
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.
Topology
Buck, Buck-Boost, Isolated Flyback
Non-Isolated Flyback
D Package (SO-16B)
OC BP S S S S S S
16 15 14 13 12 11 10 9
FEEDBACK (FB) Pin
In normal operation the preset threshold on the FEEDBACK pin is
300 mV.
Cycle skipping is triggered when voltage on this pin exceeds 600 mV.
Auto-Restart is triggered when voltage on this pin exceeds 2 V.
BYPASS (BP) Pin
5.25 V supply rail.
1 2 3 4 5
FB L DO DS NC
8
D
PI-7712-091015
Figure 4.
Pin Configuration.
3
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LYT5216-5228
Applications Example
12 W Tube Lamp Driver Accurate Regulation, High
Power Factor, Low ATHD Design Example (DER-515)
L1
3.3 mH
Optional RCD Clamp
R1
10 kΩ
D5
RS1K
R2
680 kΩ
C3
2.2
µF
450 V
T1
EFD15
RTN
R3
2 MΩ
1%
C8
100
µF
100 V
R11
180 kΩ
L
F1
5A
BR1
B10S-G
1000 V
C1
100 nF
450 V
C2
150 nF
450 V
R4
2 MΩ
1%
LYTSwitch-5
U1
LYT5226D
DS
DO
FB
BP
OC
75 V, 160 mA
D7
MURS160T3G
90 - 308
RV1
VAC
320 VAC
R7
6.04 kΩ
1%
R8
6.04 kΩ
1%
R9
40.2 kΩ
1%
L
D
N
CONTROL
R5
100 kΩ
1%
S
D6
BAV21W-7-F
C7
10
µF
25 V
PI-7763-120315 HLBB
C4
10
µF
10 V
C6
150 nF
25 V
R6
6.2 kΩ
C5
1
µF
10 V
T1
EFD15
R10
3
Ω
1%
Figure 5.
12 W, 75 V, 160 mA Non-Isolated Tube Lamp Driver for Wide Input Range of 90 VAC to 308 VAC using LYT5526D.
The circuit shown in Figure 5 is configured as a buck-boost power
supply utilizing the LYT5526D from the LYTSwitch-5 family of ICs.
This type of LED driver configuration is common for tube lamp
applications where 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 70 V to 80 V
with a constant output current of 160 mA ±3% across input range of
90 VAC to 308 VAC and can operate in a maximum ambient tempera-
ture of 100 ºC with good margin below the thermal foldback
protection point. It has an efficiency of greater than 89%, very low
ATHD% (less than 10%) and high power factor of greater than 0.95
measured at nominal input voltages (115 VAC and 230 VAC).
LYTSwitch-5 also can be configured in a buck topology, and has
advantages where low ATHD is not a critical requirement. Buck
designs can realize between 15% to 33% ATHD. Advantages of buck
over buck-boost configuration are:
•
Lower stress voltage on the driver MOSFET.
•
Higher system efficiency.
•
Potentially smaller EMI filter – dependent on power, shape and size
voltage into a single package, greatly reducing component count.
The integrated 725 V power MOSFET provides a large drain voltage
margin in universal input AC applications thus increasing reliability.
A 625 V MOSFET option is also offered to reduce cost in applications
where the voltage stress on the 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 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. 1000 V voltage rating is
recommended (the maximum clamp voltage for a typical 320 V
varistor is 850 V). The rectified DC is filtered by the input capacitors
C1 and C2. 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,
C1 and C2 form a π (pi) filter, which attenuates conducted differential
and common mode EMI currents. Resistor R1 across L1 damps the
Q of the filter inductor to improve filtering without reducing low
frequency attenuation. F1 provides input protection against
catastrophic failure such as short-circuit after the fuse. For cost
of system.
Circuit Description
The LYTSwitch-5 device (U1- LYT5526D) combines a high-voltage
power MOSFET, variable frequency and on-time control engine, fast
start-up, and protection functions including line and output over-
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Rev. C 03/16
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LYT5216-5228
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 (F1) type and rating is dependent on input surge
requirements. Typical minimum requirement for tube application is
500 V differential surges. This design meets a 3 kV surge specifica-
tion, so a 5-ampere slow blow fuse was used. A fast-blow fuse with
a high ampere energy (I
2
T) rating could also be used.
An optional RCD surge clamp circuit (D5, R2 and C3) can be
employed
for differential surge voltage requirement of 3 kV. Capacitor C3 can
also be increased to help meet a higher surge voltage requirement.
Input Range
90 to 264 VAC
90 to 308 VAC
Table 3.
It is important to note that for accurate output current regulation the
use of 1% tolerance for LINE SENSE pin resistors (R3 and R4) is
recommended. This recommendation also applies to OUTPUT
COMPENSATION pin resistor R5, FEEDBACK pin resistor R9 (capacitor
C6 at least X7R type), and DRIVER CURRENT SENSE pin resistor R7
and R10.
Diode D6 and C7 provides a bias supply for U1 from an auxiliary
winding on the transformer. Bias supply recommended voltage level
is 12 V. Filter capacitor C7 should be sized to ensure a low ripple
voltage. Capacitor C5 serves as local decoupling for the BYPASS pin
of U1 which is the supply pin for the internal controller. Current via
R6 is typically limited to 1 mA. During start-up, C5 is charged to
~5.25 V from an internal high-voltage current source internally fed
from the DRAIN pin. This allows U1 to start switching. After start-up
the operating supply current is provided from the bias supply via R6.
The recommended value for the BYPASS pin capacitor C5 is 1
mF.
The voltage rating for the capacitor should be greater than 7 V. The
capacitor can be a ceramic or electrolytic type, but tolerance should
be less than 50%. The capacitor must be physically located close to
BYPASS and SOURCE pins for effective noise decoupling.
Output Rectification
During the switching off-state the output from the transformer main
winding is rectified by D7 and filtered by C8. An ultrafast 1 A, 600 V
with 35 ns reverse recovery time (trr) diode was selected for efficiency.
The value of the output capacitor C8 was selected to give peak-to-
peak LED ripple current equal to 30% of the mean value. For designs
where lower ripple is desirable the output capacitance value can be
increased unlike traditional power supplies, low ESR capacitors are
not required for the output stage of LED designs.
A small output pre-load resistor R11 discharges the output capacitor
when the driver is turned off, giving a relatively quick and smooth
decay of the LED light. Recommended pre-load power dissipation is
≤0.5% of the output power.
Typical Line Surge
Requirement
500 V Differential Surge /
2.5 kV Ring Wave
1 kV to 3 kV Differential
Surge / 2.5 kV Ring Wave
Protection
275 VAC MOV
320 VAC MOV,
RCD Clamp
Recommended Surge Protection.
LYTSwitch-5 Output Regulation
In order to maintain very accurate output current regulation – within
±3%, the FEEDBACK (FB) pin voltage (with an appropriately selected
low-pass filter comprising R9 and C6) is compared to a preset
average feedback voltage (V
FB
) of 300 mV. When the detected signal
is above or below the preset average V
FB
threshold voltage, the
onboard averaging-engine will adjust the frequency and/or on-time to
maintain regulation.
The bias winding voltage is proportional to the output voltage
(controlled by the turns-ratio between the bias supply and output-
main winding). This allows the output voltage to be monitored
without the need for output-side feedback components. Resistor R5
converts the bias voltage into a current which is fed into the OUTPUT
COMPENSATION (OC) pin of U1. The OUTPUT COMPENSATION pin
current is also used to detect output overvoltage which is set to 30%
above the nominal output voltage. Once the current exceeds the
I
LOV+
threshold the IC will trigger a latch which disables switching
which prevents the output from rising further. An AC recycle is
needed to reset this protection mode once triggered.
In order to provide line input voltage information to U1 the rectified
input AC voltage is fed into the LINE SENSE (L) pin of U1 as a current
via R3 and R4 (4 MW
total resistance). This sensed current is also
used by U1 to detect input zero-crossing and set the input line
overvoltage protection threshold. In a line overvoltage condition
once this current exceeds the I
OOV
threshold, the IC will instanta-
neously disable switching to protect the MOSFET from further voltage
stress. The IC will start switching as soon the line voltage drops to
safe levels indicated by the L pin current dropping by 5
mA.
The primary switched current is sensed via R10 and filtered with C4.
The signal is fed into the DRIVER CURRENT SENSE (DS) pin. A low ESR
ceramic capacitor of at least 10
mF
is recommended for capacitor C4.
The internal frequency/on-time engine inside LYTSwitch-5 combines
the OUTPUT COMPENSATION pin current, the LINE SENSE pin current
and the DRIVER CURRENT SENSE pin current information to deduce
the FB signal. This is compared to an internal V
FB
threshold to
maintain accurate constant output current.
Key Design Considerations
Device Selection
The data sheet power table (Table 1) represents the maximum
practical continuous output power that can be delivered in an open
frame design with adequate heat sinking.
Output Power Table
Product
LYT5225D
LYT5216D, LYT5226D
LYT5218D, LYT5228D
Table 4.
Output Power Table.
2
Output Power
1
90-308 VAC
9W
16 W
25 W
DER-515 is a 12 W driver. The LYT5226D IC was chosen for its higher
voltage MOSFET rating of 725 V because the topology chosen was a
buck-boost and the specification called for a maximum input voltage
of 308 VAC. In other applications where surge and line voltage
conditions allow, it may be possible to use the 650 V MOSFET option
to reduce design cost without impacting reliability.
Magnetics Design
The core type selected was a low profile EFD15 with ferrite core
material and a wide winding window that allowed better convection
cooling for the winding.
5
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