LYT0002/0004-0006
LYTSwitch-0
Off-Line Low Power
LED Driver IC Family
Lowest Component Count, Off-Line Switcher IC
for Non-Isolated LED Lighting Applications
Product Highlights
•
•
•
•
High power factor meeting EU and USA requirements
Very low component count
Frequency jitter reduces EMI
No bias supply or transformer required
V
IN
FB
D
BP
S
LYTSwitch-0
Cost-Effective LED driver
The LYTSwitch-0 family parts are a highly integrated combination
of controller, driver and switching power MOSFET that enable low
component-count, non-isolated switching topologies for highly
cost competitive LED lighting applications.
66 kHz operation together with frequency jittering insures a very
low-cost EMI filter. Less than <50 ms start-up time turn-on
without overshoot, improves end user experience – no delay.
Power Factor Correction
Allows designs that easily meet European and North American
standards for PFC in consumer lighting applications.
Tight CC Performance
Accurate current limit with tight line and load regulation that is
stable over a wide temperature range makes the LYTSwitch-0
ideal for LED lighting applications.
Comprehensive Protection
Integrated auto-restart for short-circuit, open-circuit and open-
loop faults as well as a high threshold over-temperature
protection feature (min. 135 °C) with automatic restart provide
extensive protection at no additional cost.
LYTSwitch-0 Supports Different LED Applications
Flyback, buck, buck-boost and boost architectures are all
supported by the LYTSwitch-0 family. The 700 V switching power
MOSFET supports an input voltage range of 85 VAC to 308 VAC.
Figure 1.
(a)
PI-6810-060613
FB
BP
S
+
V
IN
D
LYTSwitch-0
(b)
PI-6819a-060613
Typical Application Schematic (a) Buck, (b) Buck-Boost.
Output Current Table
1
Product
6
LYT0002D/P
LYT0004D/P
LYT0005D/P
LYT0006D/P
Table 1.
PF
4,5
High
Low
High
Low
High
Low
High
Low
230 VAC
±15%
MDCM
45 mA
63 mA
85 mA
98 mA
100 mA
120 mA
165 mA
200 mA
2
85-308 VAC
3
CCM
MDCM
2
30 mA
63 mA
50 mA
98 mA
60 mA
120 mA
100 mA
200 mA
CCM
3
40 mA
80 mA
70 mA
139 mA
90 mA
170 mA
140 mA
280 mA
65 mA
80 mA
110 mA
139 mA
140 mA
170 mA
220 mA
280 mA
Description
The LYTSwitch™-0 family is specifically designed for low cost
LED bulb replacement applications. LYTSwitch-0 devices
integrate a 700 V power MOSFET, oscillator, simple ON/OFF
control scheme, a high-voltage switched current source,
frequency jittering, cycle-by-cycle current limit and thermal
shutdown circuitry into a monolithic IC.
The start-up and operating power are derived directly from the
voltage on the DRAIN pin. This eliminates the need for a bias
supply and associated circuitry plus allowing low-cost discrete
inductors to be used. The fully integrated auto-restart circuit in
the LYTSwitch-0 family safely limits output power during fault
conditions such as short-circuit or open-loop, reducing component
count and lower system cost. Package options for thru-hole and
surface-mount suit different manufacturing requirements.
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Output Current Table.
Notes:
1. Typical output current in a non-isolated buck converter. See Key Applications
Considerations section for more information.
2. MDCM – mostly discontinuous mode.
3. CCM – continuous conduction mode.
4. PF high: >0.7 @ 120 VAC and >0.5 @ 230 VAC.
5. PF low: for non-PF application where C
IN
>5
mF
minimum.
6. Packages: P: PDIP-8B, D: SO-8C.
SO-8C (D Package)
Figure 2.
Package Options.
PDIP-8B (P Package)
June 2015
This Product is Covered by Patents and/or Pending Patent Applications.
LYT0002/0004-0006
Topology
Basic Circuit Schematic
Key Features
FB
BP
S
High-Side
Buck –
Direct
Feedback
+
D
•
•
•
•
LYTSwitch-0
V
IN
Output referenced to input
Positive output (V
O
) with respect to -V
IN
Step down – V
O
< V
IN
Low cost direct feedback (±5% typ.)
PI-7043-053113
•
Low-Side
Buck –
Constant
Current LED
Driver;
Optocoupler
Feedback
PI-7044-060313
•
•
•
+
I
O
V
IN
V
F
+
BP
D
FB
S
LYTSwitch-0
R=
V
F
I
O
Output referenced to input
Negative output (V
O
) with respect to +V
IN
Step down – V
O
< V
IN
Optocoupler feedback
•
Low-cost non-safety rated optocoupler
•
Optional Zener provides disconnected load
protection
•
Accuracy determined by V
F
variation of
optocoupler LED
Output referenced to input
Negative output (V
O
) with respect to +V
IN
Step up/down – V
O
> V
IN
or V
O
< V
IN
Low-cost direct feedback (±5% typ.)
Fail-safe – output is not subjected to input voltage
if the internal power MOSFET fails
Ideal for driving LEDs – better accuracy and
temperature stability than low-side Buck constant
current LED driver
•
•
High-Side
Buck-Boost –
Constant
Current LED
Driver
FB
D
BP
S
R
SENSE
I
O
•
•
•
•
LYTSwitch-0
V
IN
PI-7045-060313
+
Low-Side
Boost –
Constant
Current LED
Driver
•
•
V
IN
LYTSwitch-0
S
D
FB
BP
•
•
•
Output referenced to input
Positive output (V
O
) with respect to -V
IN
Step up – V
O
> V
IN
Low-cost direct feedback (±5% typ.)
Ideal for driving high-voltage LEDs string – good
accuracy and temperature stability
PI-7046-053113
+
•
•
•
Low-Side
Flyback –
Constant
Current LED
Driver
V
IN
LYTSwitch-0
D
•
FB
BP
•
•
•
PI-7047-060313
S
Output referenced to input
Positive output (V
O
) with respect to -V
IN
Step down – V
O
< V
IN
Low-cost direct feedback (±5% typ.)
Fail-safe – output is not subjected to input voltage
if the internal power MOSFET fails
Ideal for driving very low voltage LEDs string –
good accuracy and temperature stability
Table 2.
Common Circuit Configurations Using LYTSwitch-0 for Driving LEDs.
2
Rev. B 06/15
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LYT0002/0004-0006
BYPASS
(BP)
REGULATOR
5.8 V
DRAIN
(D)
+
BYPASS PIN
UNDERVOLTAGE
CURRENT LIMIT
COMPARATOR
+
-
5.8 V
4.85 V
-
6.3 V
JITTER
CLOCK
DC
MAX
FEEDBACK
(FB)
1.65 V -V
T
S
R
Q
Q
OSCILLATOR
THERMAL
SHUTDOWN
VI
LIMIT
LEADING
EDGE
BLANKING
SOURCE
(S)
PI-3904-032213
Figure 3a. Functional Block Diagram LYT0002.
BYPASS
(BP)
REGULATOR
5.8 V
FAULT
PRESENT
AUTO-
RESTART
COUNTER
CLOCK
RESET
5.8 V
4.85 V
BYPASS PIN
UNDERVOLTAGE
CURRENT LIMIT
COMPARATOR
+
-
DRAIN
(D)
6.3 V
+
-
VI
LIMIT
JITTER
CLOCK
DC
MAX
FEEDBACK
(FB)
1.65 V -V
T
S
R
Q
Q
LEADING
EDGE
BLANKING
OSCILLATOR
THERMAL
SHUTDOWN
SOURCE
(S)
PI-2367-032213
Figure 3b. Functional Block Diagram LYT0004-0006.
3
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Rev. B 06/15
LYT0002/0004-0006
Pin Functional Description
DRAIN (D) Pin:
Power MOSFET Drain connection. Provides internal operating
current for both start-up and steady-state operation.
BYPASS (BP) Pin:
Connection point for a 0.1
mF
external bypass capacitor for the
internally generated 5.8 V supply.
FEEDBACK (FB) Pin:
During normal operation, switching of the power MOSFET is
controlled by this pin. Power MOSFET switching is terminated
when a current greater than 49
mA
is delivered into this pin.
SOURCE (S) Pin:
This pin is the power MOSFET source connection. It is also the
ground reference for the BYPASS and FEEDBACK pins.
and quasi-peak emissions. The frequency jitter should be
measured with the oscilloscope triggered at the falling edge of
the Drain waveform. The waveform in Figure 5 illustrates the
frequency jitter of the LYTSwitch-0.
Feedback Input Circuit
The feedback input circuit at the FEEDBACK pin consists of a
low impedance source follower output set at 1.65 V. When the
current delivered into this pin exceeds 49
mA,
a low logic level
(disable) is generated at the output of the feedback circuit. This
output is sampled at the beginning of each cycle on the rising
edge of the clock signal. If high, the power MOSFET is turned
on for that cycle (enabled), otherwise the power MOSFET remains
off (disabled). Since the sampling is done only at the beginning
of each cycle, subsequent changes in the FEEDBACK pin
voltage or current during the remainder of the cycle are ignored.
5.8 V Regulator and 6.3 V Shunt Voltage Clamp
The 5.8 V regulator charges the bypass capacitor connected to
the BYPASS pin to 5.8 V by drawing a current from the voltage
on the DRAIN, whenever the power MOSFET is off. The BYPASS
pin is the internal supply voltage node for the LYTSwitch-0.
When the power MOSFET is on, the LYTSwitch-0 runs off of the
energy stored in the bypass capacitor. Extremely low power
consumption of the internal circuitry allows the LYTSwitch-0 to
operate continuously from the current drawn from the DRAIN
pin. A bypass capacitor value of 0.1
mF
is sufficient for both
high frequency decoupling and energy storage.
BYPASS Pin Undervoltage
The BYPASS pin undervoltage circuitry disables the power
MOSFET when the BYPASS pin voltage drops below 4.85 V.
Once the BYPASS pin voltage drops below 4.85 V, it must rise
back to 5.8 V to enable (turn-on) the power MOSFET.
Over-Temperature Protection
The thermal shutdown circuitry senses the die temperature.
The threshold is set at 142
°C
typical with a 75
°C
hysteresis.
When the die temperature rises above this threshold (142
°C)
the power MOSFET is disabled and remains disabled until the
die temperature falls by 75
°C,
at which point it is re-enabled.
Current Limit
The current limit circuit senses the current in the power
MOSFET. When this current exceeds the internal threshold
(I
LIMIT
), the power MOSFET is turned off for the remainder of that
cycle. The leading edge blanking circuit inhibits the current limit
comparator for a short time (t
LEB
) after the power MOSFET is
turned on. This leading edge blanking time has been set so
that current spikes caused by capacitance and rectifier reverse
recovery time will not cause premature termination of the
switching pulse cycle.
Auto-Restart (LYT0004-0006)
In the event of a fault condition such as output overload, output
short, or an open loop condition, LYTSwitch-0 enters into
auto-restart operation. An internal counter clocked by the
oscillator gets reset every time the FEEDBACK pin is pulled
P Package (PDIP-8B)
S
S
BP
FB
1
2
3
4
3a
D Package (SO-8C)
1
2
8
7
6
8
7
S
S
BP
FB
S
S
S
S
5
D
D
4
5
3b
PI-6899-060613
Figure 4.
Pin Configuration.
LYTSwitch-0 Functional Description
LYTSwitch-0 combines a high-voltage power MOSFET switch
with a power supply controller in one device. Unlike conventional
PWM (pulse width modulator) controllers, LYTSwitch-0 uses a
simple ON/OFF control to regulate the output voltage. The
LYTSwitch-0 controller consists of an oscillator, feedback (sense
and logic) circuit, 5.8 V regulator, BYPASS pin undervoltage circuit,
over-temperature protection, frequency jittering, current limit
circuit, leading edge blanking and a 700 V power MOSFET. The
LYTSwitch-0 incorporates additional circuitry for auto-restart.
Oscillator
The typical oscillator frequency is internally set to an average of
66 kHz. Two signals are generated from the oscillator: the
maximum duty cycle signal (DC
MAX
) and the clock signal that
indicates the beginning of each cycle.
The LYTSwitch-0 oscillator incorporates circuitry that introduces
a small amount of frequency jitter, typically 4 kHz peak-to-peak,
to minimize EMI emission. The modulation rate of the frequency
jitter is set to 1 kHz to optimize EMI reduction for both average
4
Rev. B 06/15
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LYT0002/0004-0006
PI-3660-081303
600
500
V
DRAIN
400
300
200
100
0
68 kHz
64 kHz
while still meeting conducted EMI limits. Power factor is >0.5
at 230 VAC and >0.7 PF at 120 VAC meeting requirements for
LED lamps in Europe and USA.
The input stage comprises fusible resistor RF1, bridge rectifier
BR1, capacitors C1 and C2, and inductor L1. Resistor RF1 is a
flame proof, fusible, wire wound resistor. It accomplishes
several functions: a) Inrush current limitation to below specification
of BR1; b) Differential mode conducted EMI noise attenuation; c)
Fuse should any other component fail short-circuit; d) Higher
power factor. Capacitor C1, C2 and inductor L1 forms a
π
filter
to reduce differential mode EMI. Capacitor C2 provides local
decoupling for the switching current through U1. There is an
optional parallel resistor on the board across L1 which damps
the resonance of the pi filter.
The power processing stage is formed by the integrated
MOSFET switch within LYT0006 (U1), a free-wheeling diode
(D1), sense resistor (R2), power inductor (L2) and output
capacitor (C5). To reduce reverse recovery losses in D1 the
value of L2 was designed such that the converter operates in
mostly discontinuous conduction mode. Diode D1 is an
ultrafast diode with a reverse recovery time (t
RR
)
≈35
ns. This
recovery is recommended due to the high ambient operating
time temperature which will increase diode reverse recovery
charge. A bobbin based EE10 core size indictor was selected
for L2 in order to prevent changes in inductance value when
placed inside a metal enclosure. Lower cost drum core or dog
bone inductor types may also be used, however these have an
open magnetic path which can be shorted by a metal enclosure.
This reduces the effective inductance and requires the value to
be adjusted to take this into account when placed inside the
final enclosure.
Capacitor C5 is the output filter capacitor; its primary function is
to limit the output current ripple and ensures high frequency
currents flow within as small as a loop area as possible to
reduce EMI.
0
Time (µs)
20
Figure 5.
Frequency Jitter.
high. If the FEEDBACK pin is not pulled high for 50 ms, the
power MOSFET switching is disabled for 800 ms. The auto-
restart alternately enables and disables the switching of the
power MOSFET until the fault condition is removed.
Applications Example
A 6 W (Output) Universal Input Buck LED Driver Converter
The circuit shown in Figure 6 is a typical implementation of a
non-isolated, power factor corrected buck power supply for
LED driver applications. The simplicity and low component
count make this ideal for space constrained, cost sensitive
designs such as GU10 or A19 size lamps. This design was
optimized to drive an LED string at a voltage of 54 V with a
constant current of 110 mA, giving 6 W of output power. The
design operates over a universal input range from 90 VAC to
265 VAC and achieves an output current tolerance of <
±5%
at nominal line voltage. The input capacitance (C1 + C2) was
reduced to achieve the highest possible power factor input
R1
4.7 kΩ
FB
BP
S
C4
C3
22
µF
100 nF 16 V
25 V
5
4
54 V, 110 mA
L
RF1
4.7
Ω
BR1
MB6S
600 V
L1
4.7 mH
D
LYTSwitch-0
U1
LYT0006P
L2
R2
18.7
Ω
1%
C5
47
µF
63 V
D1
MURS160T3G
+
90 - 265
VAC
N
RV1*
275 VAC
C1
47 nF
630 V
C2
330 nF
450 V
*Optional <1 kV Surge Requirements
Figure 6.
Universal Input, 54 V, 110 mA Constant Current Power Supply using LYTSwitch-0.
PI-6998f-061313
RTN
5
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Rev. B 06/15
FPGA/CPLD
