LNK458 Datasheet PDF - Power Integrations


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LNK458
Power Integrations

Part Number LNK458
Description LED Driver IC with TRIAC Dimming Single-Stage PFC and Constant Current Control
Page 12 Pages

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LNK454/456-458/460
LinkSwitch®-PL Family
LED Driver IC with TRIAC Dimming, Single-Stage PFC and
Constant Current Control for Non-Isolated Applications
www.DataSheet4U.com
Product Highlights
Dramatically Simplifies Off-line LED Drivers
Single stage power factor correction and accurate constant
current (CC) output
Flicker-free phase-controlled TRIAC dimming
Very low component count with small non-electrolytic bulk
capacitor, for compact replacement lamp designs
Compact SO8 package
Completely eliminates control loop compensation
Advanced Performance Features
Optimized for non-isolated flyback designs
Frequency jitter greatly reduces EMI filter size and costs
Low dissipation direct sensing of LED current
Advanced Protection and Safety Features
725 V integrated MOSFET allows small bulk capacitance and
maximizes power capability
Latching shutdown protection for short-circuit / open feedback
and output overvoltage
Auto-restart for overload condition
Hysteretic thermal shutdown
Meets high-voltage creepage between DRAIN and all other pins
both on PCB and at package
EcoSmart® - Energy Efficient
High power factor optimizes system lumen per watt by
reducing input VA
Control algorithm balances switching and conduction losses
over line and load to maintain optimum efficiency
Cycle skipping regulation for abnormally low output power to
clamp peak output current delivered
Description
The LinkSwitch-PL family enables a very small and low cost
single-stage power factor corrected constant current driver for
solid state lighting. Optimized for direct LED current sensing, the
LinkSwitch-PL operates over a wide input voltage range
delivering an output power of up to 16 W. The LinkSwitch-PL
control algorithm provides flicker-free TRIAC dimming with minimal
external components.
Each device incorporates a 725 V rated power MOSFET, a novel
discontinuous mode variable frequency variable on-time controller,
frequency jitter, cycle by cycle current limit and hysteretic thermal
shutdown in a monolithic 4-pin IC, available in SO-8C and
eDIP-12 packages.
AC
IN D LinkSwitch-PL
CONTROL
BP
S FB
Figure 1. Basic Application Schematic.
PI-5835-060710
Output Power Table
Product 2
LNK454D
LNK456D
LNK457D/V
LNK458V
LNK460V
85-265 VAC
Minimum Output
Power1
Maximum Output
Power1
1.5 W
3W
3W 6W
4W 8W
6 W 11.5 W
8 W 16 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. Packages: D: SO-8C, V: eDIP-12.
Output Current
Number of
Serial LEDs
1
2
3
4
5
6
7
8
9
10
11
12
350 mA
LNK454
LNK454
LNK456
LNK456
LNK457
LNK457
LNK458
LNK458
LNK458
LNK460
LNK460
LNK460
500 mA
LNK454
LNK456
LNK456
LNK457
LNK458
LNK458
LNK460
LNK460
LNK460
700 mA
LNK454
LNK456
LNK457
LNK458
LNK460
LNK460
1000 mA
LNK456
LNK457
LNK458
LNK460
Figure 2. Device Selection based on Length of Output LED Series String and
Current. A Typical Voltage Drop of 3.5 V per LED is Assumed.
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PRELIMINARY
This document contains information on a new product. Specifications and information herein
are subject to change without notice.
June 2010



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LNK454/456-458/460
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BYPASS (BP)
VFB(SK)
+
UV
ILIM
Q SET S
Q CLR R
4.9 V
SOA
UV
REGULATOR
5.85 V
CURRENT LIMIT
SOA
STATE MACHINE
DRAIN (D)
ILIM +
V_ILIM
VFB(LO)
+
IFB
1 µA
FEEDBACK (FB)
+
VREF DAC
FILTER
PHASE
MEASUREMENT
Zero Crossing
DIGITAL
INTEGRATOR
Update
CLK
INC/DEC
VARIABLE FREQUENCY/
DUTY CONTROLLER
ON-TIME
EXTENSION
AUTO-RESTART
S SET Q
R CLR Q
+
V_ZLIM
Figure 2. Functional Block Diagram.
Pin Functional Description
DRAIN (D) Pin:
High-voltage power MOSFET drain connection. The internal
start-up bias current is drawn from this pin through a switched
high-voltage current source. Drain current sensing and
associated controller functions are also performed using this pin.
SOURCE (S) Pin:
Power MOSFET source connection. Ground reference for
BYPASS and FEEDBACK pins.
BYPASS (BP) Pin:
Connection point for the external bypass capacitor for the
internally generated 5.85 V supply.
FEEDBACK (FB) Pin:
LED current sensing pin. During normal operation the 290 mV
threshold determines the average value of the current flowing
through the load sense resistor.
A second higher threshold clamps excessive output current ripple.
An additional higher threshold is used to protect against output
short-circuit and overvoltage conditions.
PI-5893-060210
D Package (SO-8C)
FB 1
BP 2
D4
8S
7S
6S
5S
Exposed Pad Internally
Connected to SOURCE Pin
V Package (eDIP-12)
S 12
S 11
S 10
S9
S8
S7
Figure 3. Pin Configuration (Top View).
SOURCE (S)
1 NC
2 FB
3 BP
4 NC
5 NC
6D
PI-5836a-0526–10
2
Rev. A 06/10
PRELIMINARY
This document contains information on a new product. Specifications and information herein
are subject to change without notice.
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LNK454/456-458/460
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DES
DZOV
AC
IN
D LinkSwitch-PL
RES
ROV
CONTROL
BP
S FB
CF RSENSE RF
PI-5837-060710
Figure 4. Typical Application Schematic.
Functional Description
The LinkSwitch-PL combines a high-voltage power MOSFET
switch with a power supply controller in one device. The IC
provides a single stage power factor correction plus LED
current control. The LinkSwitch-PL controller consists of an
oscillator, feedback (sense and logic) circuit, 5.85 V regulator,
hysteretic over-temperature protection, frequency jittering,
cycle-by-cycle current limit, loop compensation circuitry, auto-
restart, switching on-time extension, power factor and constant
current control.
In a direct LED current sensing configuration, the average
FEEDBACK pin voltage is a replica of the LED current, scaled
by the sense resistor (RSENSE in Figure 4). A small low-pass filter
(RF and CF in Figure 4) reduces high frequency noise at the
FEEDBACK pin.
Figure 5 illustrates the operating regions of the FEEDBACK pin
voltage. The LinkSwitch-PL sets its operating point such that
the average FEEDBACK pin voltage in steady-state operation is
290 mV. This threshold is low to minimize the sensing resistor
dissipation. The internal MOSFET switching frequency and
on-time are updated once every input AC half-cycle to regulate
the output current and maintain high power factor.
If the FEEDBACK pin peak voltage exceeds 520 mV, cycle
skipping mode is triggered and the power processed by the
integrated MOSFET is clamped on a cycle-by-cycle basis.
Switching frequency may vary during an input voltage half-cycle
to reduce thermal stress on the output LEDs.
Latching shutdown protection is triggered by a FEEDBACK pin
voltage in excess of 2 V. This feature can be used to provide
output overvoltage protection (via DZOV and ROV, in Figure 4),
which triggers the IC to latch off. This condition is reset when
the BYPASS pin voltage drops below 4.9 V, after removal of the
AC input.
Latch Off
2V
Cycle Skipping
Mode
Normal Operation
290 mV
520 mV
PI-5838-041910
Figure 5. FEEDBACK Pin Operation Voltage Thresholds.
www.powerint.com
PRELIMINARY
This document contains information on a new product. Specifications and information herein
are subject to change without notice.
3
Rev. A 06/10



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LNK454/456-458/460
VFB
ϕOS
VFB(ϕ)
ϕOL
ϕOL
VFB(ϕ)
VLINE
VTRIAC
180°
Phase
Angle
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ϕOS
180°
Phase
Angle
ϕ
0° Phase
Angle
TRIAC
Conduction
Leading Edge
TRIAC Dimmers
Phase
Angle
0° TRIAC
Conduction
ϕ
Phase
Angle
Phase
Angle
Trailing Edge
TRIAC Dimmers
PI-5894a-052610
Figure 6. Feedback Voltage vs. Phase Angle Dimming Characteristics.
TRIAC (Phase-Controlled) Dimming
The LinkSwitch-PL integrates several features to improve
dimming range and reduce external circuit complexity when
using a phase-controlled TRIAC dimmer. The output LED
current is controlled by the FEEDBACK pin voltage which
changes proportionally to the TRIAC dimmer conduction angle.
The conduction angle decreases, the voltage at the FEEDBACK
pin decreases causing the average LED current to decrease.
The FEEDBACK pin voltage adjustment is initiated at approxi-
mately 20% of the main half-cycle duration. When this (jOS)
threshold is exceeded,
reduced until a second
VpFhBaasnedatnhgeleotuhtrpeusthLoEldDiscurerraecnhteadr.e
When this happens, with the TRIAC conduction angle being
very limited, the IC runs open loop (jOL region) and the
integrated MOSFET processes as much power as the heavily
chopped input voltage will allow creating a light output that is
deeply dimmed.
The 520 mV clamping feedback threshold is also linearly reduced
during dimming to control LED current ripple.
To help maintain the holding current of the TRIAC in the dimmer,
LinkSwitch-PL extends the MOSFET on-time towards the zero
crossings of the AC input voltage providing an active bleed or
holding current function. This on-time extension is carefully
limited to avoid deterioration of input current harmonic content
and limit total harmonic distortion (THD).
4
Rev. A 06/10
PRELIMINARY
This document contains information on a new product. Specifications and information herein
are subject to change without notice.
www.powerint.com




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