LYTSwitch-6
Family
Flyback CV/CC LED Driver IC with Integrated
650 V / 725 V MOSFET and FluxLink Feedback
Product Highlights
Highly Integrated, Compact Footprint
•
Up to 94% efficiency across full load range
•
Incorporates a multi-mode Quasi-Resonant (QR) / CCM / DCM flyback
SR FET
controller, 650 V or 725 V MOSFET, secondary-side control and
synchronous rectification driver
•
Integrated FluxLink™, HIPOT-isolated, feedback link
•
Exceptional CV/CC accuracy, independent of transformer design or
external components
•
Adjustable accurate output current sense using external sense resistor
FWD
GND
BPS
SR
LYTSwitch-6
Primary FET
and Controller
D
V
FB
VOUT
EcoSmart™ – Energy Efficient
•
Less than 15 mW no-load including line sense (without PF front end)
•
Designs using LYTSwitch-6 easily meet Energy Star and all global
•
Low heat dissipation
Optional
Current
Sense
S
BPP
IS
Secondary
Control IC
PI-8375-072817
lighting energy efficiency regulations
Advanced Protection / Safety Features
•
•
•
•
•
Figure 1.
Typical Application/Performance.
Input line OV with auto-restart
Output fault OVP/UVP with auto-restart
Open SR FET gate detection
Input voltage monitor with accurate brown-in
Thermal foldback ensures that power continues to be delivered
(lower level) at elevated temperatures
Full Safety and Regulatory Compliance
•
•
•
•
Reinforced insulation
Isolation voltage >4000 VAC
100% production HIPOT compliance testing
UL1577 and TUV (EN60950) safety approved
Figure 2.
High Creepage, Safety-Compliant InSOP-24D Package.
Green Package
•
Halogen free and RoHS compliant
Output Power Table
Product
3
277 VAC ± 15%
Open Frame
1
LYT6063C/6073C
LYT6065C/6075C
LYT6067C/6077C
LYT6068C
15 W
30 W
50 W
65 W
85-305 VAC
380 VDC /
450 VDC
2
Applications
•
Isolated off-line LED driver
•
Smart LED lighting
•
High-voltage flyback post regulator
Open Frame
1
Open Frame
1
12 W
25 W
45 W
55 W
25 W
40 W
60 W
Description
The LYTSwitch™-6 series family of ICs dramatically simplifies the
development and manufacturing of off-line LED drivers, particularly
those in compact enclosures or with high efficiency requirements.
The LYTSwitch-6 architecture is revolutionary in that the devices
incorporate both primary and secondary controllers, with sense
elements and a safety-rated feedback mechanism into a single IC.
Close component proximity and innovative use of the integrated
communication link, FluxLink, permit accurate control of a secondary-
side synchronous rectification MOSFET with Quasi-Resonant switching
of primary integrated high-voltage MOSFET to maintain high efficiency
across the entire load range.
Table 1. Output Power Table.
Notes:
1. Minimum continuous power in a typical non-ventilated and PCB size measured
at 40 °C ambient. Max output power is dependent on the design. With
condition that package temperature must be < 125 °C.
2. With 725 V FET only.
3. Package: InSOP-24D.
www.power.com
June 2018
This Product is Covered by Patents and/or Pending Patent Applications.
LYTSwitch-6
DRAIN
(D)
INPUT
OVERVOLTAGE (V)
PRIMARY BYPASS
REGULATOR
ENABLE
ENABLE
LINE
INTERFACE
BPP/UV
OV
GATE
OSCILLATOR/
TIMERS
JITTER
AUTO-RESTART
COUNTER
RESET
PRIMARY BYPASS
(BPP)
FAULT
BPP/UV
PRIMARY
BYPASS PIN
UNDERVOLTAGE
+
-
GATE
PRIM-CLK
PRIMARY
BYPASS PIN
CAPACITOR
SELECT AND
CURRENT
LIMIT
V
ILIM
V
SHUNT
V
BP+
t
ON(MAX)
THERMAL
SHUTDOWN
GATE
SenseFET
BPP
OV
t
OFF(BLOCK)
GATE
FAULT
AUTO-RESTART
Q
S
R
SecREQ
PRIM/SEC
SecPulse
PRIM/SEC
Power
MOSFET
From
Secondary
Controller
RECEIVER
CONTROLLER
DRIVER
I
S
LEB
BPP/UV
ILIM
Q
Sec-
FAULT
t
OFF(BLOCK)
PRIM-CLK
+
V
ILIM
-
AUTO-RESTART
t
ON(MAX)
PRIMARY OVP
PI-8388-020618
SOURCE
(S)
Figure 3.
Primary Controller Block Diagram.
FORWARD
(FWD)
SYNCRONOUS RECTIFIER DRIVE
(SR)
OUTPUT VOLTAGE
(VOUT)
SR CONTROL
REGULATOR
4.4 V
SECONDARY
BYPASS
(BPS)
INH
VOUT
FORWARD
ENABLE
SR
BPS
UV
+
-
DETECTOR
+
S
R
Q
Q
4.4 V
3.8 V
SR
THRESHOLD
QR
HANDSHAKE/
FAULT DETECTION
CONTROL
INH
DCM
SECONDARY
OVP
FEEDBACK
(FB)
VREF
To
Primary
Receiver
FEEDBACK
DRIVER
INH
QR
+
-
FEEDBACK
COMPENSATION
Ts
MAX
t
OFF(MIN)
OSCILLATOR/
TIMER
t
SS(RAMP)
+
-
t
SECINH(MAX)
THERMAL
FOLDBACK
SECONDARY
GROUND
(GND)
ISENSE
(IS)
PI-8045e-020618
Figure 4.
Secondary Controller Block Diagram.
2
Rev. E 06/18
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LYTSwitch-6
Pin Functional Description
ISENSE (IS) Pin (Pin 1)
Connection to the power supply output terminals. An external
current sense resistor should be connected between this and the
GND pin. If current regulation is not required, this pin should be tied
to the GND pin.
SECONDARY GROUND (GND) (Pin 2)
GND for the secondary IC. Note this is not the power supply output
GND due to the presence of the sense resistor between this and the
ISENSE pin.
FEEDBACK (FB) Pin (Pin 3)
Connection to an external resistor divider to set the power supply
output voltage.
SECONDARY BYPASS (BPS) Pin (Pin 4)
Connection point for an external bypass capacitor for the secondary
IC supply.
SYNCHRONOUS RECTIFIER DRIVE (SR) Pin (Pin 5)
Gate driver for external SR FET.
OUTPUT VOLTAGE (VOUT) Pin (Pin 6)
Connected directly to the output voltage to provide current for the
controller on the secondary-side.
FORWARD (FWD) Pin (Pin 7)
The connection point to the switching node of the transformer output
winding providing information on the primary switch timing. Provides
power for the secondary-side controller when V
OUT
is below a threshold.
NC Pin (Pin 8-12)
Leave open. Should not be connected to any other pins.
Input Overvoltage (V) Pin (Pin 13)
A high-voltage pin connected to the AC or DC side of the input bridge
for detecting overvoltage conditions at the power supply input. This
pin should be tied to Source to disable OV protection.
PRIMARY BYPASS (BPP) Pin (Pin 14)
The connection point for an external bypass capacitor for the
primary-side supply. This is also the ILIM selection pin for choosing
standard ILIM or ILIM+1.
NC Pin (Pin 15)
Leave open. Should not be connected to any other pins.
SOURCE (S) Pin (Pin 16-19)
These pins are the power MOSFET source connection. It is also
ground reference for primary BYPASS pin.
DRAIN (D) Pin (Pin 24)
Power MOSFET drain connection.
Figure 5.
Pin Configuration.
V 13
BPP 14
NC 15
S 16-19
D 24
12 NC
11 NC
10 NC
9 NC
8 NC
7 FWD
6 VOUT
5 SR
4 BPS
3 FB
2 GND
1 IS
PI-7877-022216
LYTSwitch-6 Functional Description
The LYTSwitch-6 combines a high-voltage power MOSFET switch,
along with both primary-side and secondary-side controllers in one
device.
The architecture incorporates a novel inductive coupling feedback
scheme using the package lead frame and bond wires to provide a
safe, reliable, and low-cost means to communicate accurate direct
sensing of the output voltage and output current on the secondary
controller to the primary controller.
The primary controller on LYTSwitch-6 is a Quasi-Resonant (QR)
flyback controller that has the ability to operate in continuous
conduction mode (CCM). The controller uses both variable frequency
and variable current control schemes. The primary controller consists
of a frequency jitter oscillator; a receiver circuit magnetically coupled
to the secondary controller, a current limit controller, 5 V regulator on
the PRIMARY BYPASS pin, audible noise reduction engine for light load
operation, bypass overvoltage detection circuit, a lossless input line
sensing circuit, current limit selection circuitry, over-temperature
protection, leading edge blanking, and a 650 V / 725 V power MOSFET.
The LYTSwitch-6 secondary controller consists of a transmitter circuit
that is magnetically coupled to the primary receiver, a constant
voltage (CV) and a constant current (CC) control circuit, a 4.4 V
regulator on the secondary SECONDARY BYPASS pin, synchronous
rectifier MOSFET driver, QR mode circuit, oscillator and timing
functions, thermal foldback control and a host of integrated
protection features.
Figure 3 and Figure 4 show the functional block diagrams of the
primary and secondary controller with the most important features.
3
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Rev. E 06/18
LYTSwitch-6
Primary Controller
The LYTSwitch-6 features variable frequency QR controller + CCM
operation for enhanced efficiency and extended output power
capability.
PRIMARY BYPASS Pin Regulator
The PRIMARY BYPASS pin has an internal regulator that charges the
PRIMARY BYPASS pin capacitor to V
BPP
by drawing current from the
voltage on the DRAIN pin whenever the power MOSFET is off. The
PRIMARY BYPASS pin is the internal supply voltage node. When the
power MOSFET is on, the device operates from the energy stored in
the PRIMARY BYPASS pin capacitor.
In addition, there is a shunt regulator clamping the PRIMARY BYPASS
pin voltage to V
SHUNT
when the current is provided to the PRIMARY
BYPASS pin through an external resistor. This facilitates powering the
LYTSwitch-6 externally through a bias winding to decrease the
no-load consumption to less than 15 mW.
Primary Bypass ILIM Programming
LYTSwitch-6 has user programmable current limit (ILIM) settings
through the selection of PRIMARY BYPASS pin capacitor value. The
PRIMARY BYPASS pin can use a ceramic capacitor for decoupling the
internal supply of the device.
There are (2) programmable settings using 0.47
mF
and 4.7
mF
for
standard and increased ILIM settings respectively.
1.05
1.0
0.95
0.9
0.85
0.8
0.75
Normalized I
LIM
(A)
30
40
50
60
70
80
90
100
Steady-State Switching Frequency (kHz)
Figure 6.
Normalized Primary Current vs. Frequency.
Current Limit Operation
The primary-side controller has a current limit threshold ramp that is
inversely proportional to time from the end of the last primary
switching cycle (i.e. from the time the primary FET turns off at the
end of a switching cycle).
The characteristic produces a primary current limit that increases as
the load increases (Figure 6).
This algorithm enables the most efficient use of the primary switch
with immediate response when a feedback switching cycle request is
received.
At high load, switching cycle have a maximum current approaching
100% ILIM gradually reduced to 30% of the full current limit as the
load reduces. Once 30% current limit is reached, there is no further
reduction in current limit (since this is low enough to avoid audible
noise) but the time between switching cycles will continue to reduce
as load reduces.
Jitter
The normalized current limit is modulated between 100% and 95% at
a modulation frequency of f
M
this results in a frequency jitter of ~7 kHz
with average frequency of ~100 kHz.
Auto-Restart
In the event a fault condition occurs such as an output overload,
output short-circuit, or external component/pin fault, the LYTSwitch-6
enters into auto-restart (AR) operation. In auto-restart the power
MOSFET switching is disabled for t
AR(OFF)
. There are 2 ways to enter
auto-restart:
Primary Bypass Undervoltage Threshold
The PRIMARY BYPASS pin undervoltage circuitry disables the power
MOSFET when the PRIMARY BYPASS pin voltage drops below ~4.5 V
(V
BPP
- V
BP(H)
) in steady-state operation. Once the PRIMARY BYPASS
pin voltage falls below this threshold, it must rise back to V
SHUNT
to
re-enable turn-on of the power MOSFET.
Primary Bypass Output Overvoltage Auto-Restart Function
The PRIMARY BYPASS pin has an OV protection non-latching feature.
A Zener diode in parallel to the resistor in series with the PRIMARY
BYPASS pin capacitor is typically used to detect an overvoltage on the
primary bias winding to activate this protection mechanism. In the
event the current into the PRIMARY BYPASS pin exceeds I
SD
, the
device will disable the power MOSFET switching for a time t
AR(OFF)
.
After this time the controller will restart operation and attempt to
return to regulation.
This VOUT OV protection is also available as an integrated feature on
the secondary controller.
Over-Temperature Protection
The thermal shutdown circuitry senses the primary MOSFET die
temperature. The threshold is typically set to T
SD
with T
SD(H)
hysteresis. When the die temperature rises above this threshold the
power MOSFET is disabled and remains disabled until the die
temperature falls by T
SD(H)
at which point it is re-enabled. A large
hysteresis of T
SD(H)
is provided to prevent over-heating of the PCB due
to continuous fault condition.
1.
Continuous secondary requests at above the overload detection
2.
No requests for switching cycles from the secondary for > t
AR(SK)
.
frequency (~110 kHz) for longer than 80 ms.
4
Rev. E 06/18
www.power.com
PI-8205-120516
LYTSwitch-6
The second was included to ensure that if communication is lost, the
primary tries to restart again. Although this should never be the case
in normal operation, this can be useful in the case of system ESD
events for example where a loss of communication due to noise
disturbing the secondary controller, the issue is resolved when the
primary restarts after an auto-restart off time.
The very first auto-restart off-time is short. This short auto-restart
timer is to provide a quick recovery under fast reset conditions. The
short auto-restart off-time allows the controller to quickly check to
determine whether the auto-restart condition is maintained beyond
t
AR(OFF)SH
. If so will resort to full auto-restart off timing.
The auto-restart is reset as soon as an AC reset occurs.
SOA Protection
In the event there are two consecutive cycles where the ILIM is
reached within the blanking time and current limit delay time
(~500 ns), the controller will skip approximately 2.5 cycles or ~25
ms
(based on full frequency of 100 kHz). This provides sufficient time for
reset of the transformer during start-up into large capacitive loads
without extending the start-up time.
Input Line Voltage Monitoring
The INPUT OVERVOLTAGE pin is used for input overvoltage sensing
and protection.
A 4 MΩ resistor is tied between the high-voltage DC bulk capacitor
after the bridge (or to the AC side of the bridge rectifier for fast AC
reset) and the INPUT OVERVOLTAGE pin to enable this functionality.
This pin functionality can be disabled by shorting INPUT
OVERVOLTAGE pin to primary Source.
Primary/Secondary-Side Handshake
At start-up, the primary-side initially switches without any feedback
information (this is very similar to the operation of a standard
TOPSwitch™, TinySwitch™ or LinkSwitch™ controllers).
If no feedback signals are received during the auto-restart on-time
(t
AR
), the primary goes into auto-restart mode. Under normal
conditions, the secondary controller will power-up via the FORWARD
pin or from OUTPUT VOLTAGE pin and take over control. From this
point onwards the secondary controls switching.
If the primary stops switching or does not respond to cycle requests
from the secondary during normal operation (when the secondary
has control), the handshake protocol is initiated to ensure that the
secondary is ready to assume control once the primary begins to
switch again. An additional handshake is also triggered if the
secondary detects that the primary is providing more cycles than
were requested.
The most likely event that could require an additional handshake is
when the primary stops switching as the result of a momentary line
brown-out event. When the primary resumes operation, it will default
into a start-up condition and attempt to detect handshake pulses
from the secondary.
If the secondary does not detect that the primary responds to
switching requests for 8 consecutive cycles, or if the secondary
detects that the primary is switching without cycle requests for 4
or more consecutive cycles, the secondary controller will initiate a
S: Has powered
up within t
AR
No
P: Goes to Auto-Restart Off
S: Bypass Discharging
Start
P: Powered Up, Switching
S: Powering Up
P: Primary Chip
S: Secondary Chip
P: Auto-Restart
S: Powering Up
2s
Yes
P: Switching
S: Sends Handshaking Pulses
64 ms
P: Has Received
Handshaking
Pulses
Yes
P: Stops Switching, Hands
Over Control to Secondary
No
P: Continuous Switching
S: Doesn’t Take Control
S: Has Taken
Control?
No
P: Not Switching
S: Doesn’t Take Control
Yes
End of Handshaking,
Secondary Control Mode
PI-8437-092017
Figure 7.
Primary-Secondary Handshake Flow Chart.
second handshake sequence. This provides additional protection
against cross-conduction of SF FET while the primary is switching.
This protection mode also prevents an output overvoltage condition
in the event that the primary is reset while the secondary is still in
control.
Wait and Listen
When the primary resumes switching after initial power-up recovery
from input line voltage fault or an auto-restart event, it will assume
control and require a successful handshake to relinquish control to
the secondary controller.
5
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Rev. E 06/18
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