Dialog IW3614 Ac/dc digital power controller Datasheet

iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
1.0 Features
●● Isolated AC/DC offline 100 VAC / 230 VAC LED driver
●● Meets harmonic requirements, high power factor
(power factor > 0.9 without dimmer)
●● Line frequency ranges from 45Hz to 66Hz
●● Intelligent wall dimmer detection
xx Leading-edge dimmer
xx Trailing-edge dimmer
xx No-dimmer detected
xx Unsupported dimmer
●● Hybrid dimming scheme
●● Wide dimming range from 1% up to 100%
●● No visible flicker
●● Resonant control to achieve high efficiency, 85% without
dimmer
●● Temperature compensated LED current
●● Small size design
xx Small size input bulk capacitor
xx Small size output capacitor
xx Small transformer
●● Primary-side sensing eliminates the need for optoisolator feedback and simplifies design
●● Tight LED current regulation ± 5%
●● Fast start-up, typically 10µA start-up current
2.0 Description
The iW3614 is a high performance AC/DC offline power
supply controller for dimmable LED luminaires, which uses
advanced digital control technology to detect the dimmer
type and phase. The dimmer conduction phase controls
the LED brightness. The LED brightness is modulated by
PWM-dimming. iW3614’s unique digital control technology
eliminates visible flicker.
iW3614 can operate with all dimmer schemes including:
leading-edge dimmer, trailing-edge dimmer, as well as
other dimmer configurations such as R-type, R-C type or
R-L type. When a dimmer is not present, the controller can
automatically detect that there is no dimmer.
iW3614 operates in quasi-resonant mode to provide high
efficiency. The iW3614 provides a number of key builtin features. The iW3614 uses iWatt’s advanced primaryside sensing technology to achieve excellent line and load
regulation without secondary feedback circuitry. In addition,
iW3614’s pulse-by-pulse waveform analysis technology
allows accurate LED current regulation. The iW3614
maintains stability over all operating conditions without the
need for loop compensation components. Therefore, the
iW3614 minimizes external component count, simplifies EMI
design and lowers overall bill of materials cost.
3.0 Applications
●● Dimmable LED luminaires
●● Optimized for 3W - 15W output power
●● Capable of higher output power with enhanced external
driver
●● Hot-plug LED module support
●● Multiple protection features:
xx LED open circuit protection
xx Single-fault protection
iW3614
xx Over-current protection
xx LED short circuit protection
xx Current sense resistor short circuit protection
xx Over-temperature protection
xx Input over-voltage protection
Rev. 0.7
iW3614
Preliminary
Page 1
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
Chopping
Circuit
Isolated Flyback
Converter
AC Input
From Dimmer
VOUT
+
+
RTN
U1
iW3614
VCC 8
1
OUTPUT(TR)
2
VSENSE
3
VIN
ISENSE 6
4
VT
GND 5
OUTPUT 7
+
NTC
Thermistor
Figure 3.1 : Typical Application Circuit
4.0 Pinout Description
iW3614
VCC 8
1 OUTPUT(TR)
2 V
SENSE
OUTPUT 7
3 V
IN
4 V
T
ISENSE 6
GND 5
Pin #
Name
Type
Pin Description
1
OUTPUT(TR)
Output
Gate drive for chopping MOSFET switch
2
VSENSE
3
VIN
Analog Input Rectified AC line voltage sense
4
VT
Analog Input External power limit and shutdown control
5
GND
6
ISENSE
7
OUTPUT
Output
8
VCC
Power Input
Analog Input Auxiliary voltage sense (used for primary side regulation and ZVS)
Ground
Ground
Analog Input Primary current sense (used for cycle-by-cycle peak current control and limit)
Gate drive for main MOSFET switch
Power supply for control logic and voltage sense for power-on reset circuitry
Rev. 0.7
iW3614
Preliminary
Page 2
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
5.0 Absolute Maximum Ratings
Absolute maximum ratings are the parameter values or ranges which can cause permanent damage if exceeded. For
maximum safe operating conditions, refer to Electrical Characteristics in Section 6.0.
Parameter
Symbol
Value
Units
DC supply voltage range (pin 8, ICC = 20mA max)
VCC
-0.3 to 18
V
DC supply current at VCC pin
ICC
20
mA
OUTPUT (pin 7)
-0.3 to 18
V
OUTPUT(TR) (pin 1)
-0.3 to 18
V
VSENSE input (pin 2, IVsense ≤ 10mA)
-0.7 to 4.0
V
VIN input (pin 3)
-0.3 to 18
V
ISENSE input (pin 6)
-0.3 to 4.0
V
VT input (pin 4)
-0.3 to 4.0
V
Power dissipation at TA ≤ 25°C
PD
526
mW
Maximum junction temperature
TJ MAX
150
°C
TSTG
–65 to 150
°C
ψJB (Note 1)
70
°C/W
ESD rating per JEDEC JESD22-A114
2,000
V
Latch-Up test per JEDEC 78
±100
mA
Storage temperature
Thermal Resistance Junction-to-PCB Board Surface Temperature
Notes:
Note 1. ψJB [Psi Junction to Board] provides an estimation of the die junction temperature relative to the PCB [Board]
surface temperature. This data is measured at the ground pin (pin 5) without using any thermal adhesives. See
Section 9.13 for more information.
Rev. 0.7
iW3614
Preliminary
Page 3
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
6.0 Electrical Characteristics
VCC = 12 V, -40°C ≤ TA ≤ 85°C, unless otherwise specified (Note 1)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
15
µA
VIN SECTION (Pin 3)
Start-up current
IINST
VIN = 10 V, CVCC = 10 µF
10
Input impedance
ZIN
TA = 25°C
2.5
VIN Range
VIN
0
kW
1.8
V
1
μA
VSENSE SECTION (Pin 2)
Input leakage current
IIN(Vsense)
VSENSE = 2V
Nominal voltage threshold
VSENSE(NOM)
TA = 25°C, negative edge
1.523
1.538
1.553
V
Output OVP threshold
VSENSE(MAX)
TA = 25°C, negative edge
1.65
1.7
1.75
V
OUTPUT SECTION (Pin 7)
Output low level ON-resistance
RDS(ON)LO
ISINK = 5mA
30
W
Output high level ON-resistance
RDS(ON)HI
ISOURCE = 5mA
50
W
Rise time (Note 2)
tR
TA = 25°C, CL = 330pF
10% to 90%
50
ns
Fall time (Note 2)
tF
TA = 25°C, CL = 330pF
90% to 10%
30
ns
200
kHz
Maximum switching frequency
(Note 3)
fSW(MAX)
VCC SECTION (Pin 8)
Maximum operating voltage
VCC(MAX)
Start-up threshold
VCC(ST)
VCC rising
11
Undervoltage lockout threshold
VCC(UVL)
VCC falling
7
Operating current
Zener diode clamp voltage
ICCQ
VZ(CLAMP)
CL = 330 pF,
VSENSE = 1.5V
TA= 25°C, IZ = 5mA
Rev. 0.7
iW3614
Preliminary
18.5
16
V
12
13
V
7.5
8
V
4.1
4.7
mA
19
20.5
V
Page 4
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
6.0 Electrical Characteristics (cont.)
VCC = 12V, -40°C ≤ TA ≤ 85°C, unless otherwise specified (Note 1)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
1.83
1.89
1.95
V
ISENSE SECTION (Pin 6)
Over-current limit threshold
VOCP
Isense short protection reference
VRSNS
0.16
V
VREG-TH
1.8
V
Power limit high threshold (Note 4)
VP-LIM(HI)
0.56
V
Power limit low threshold (Note 4)
VP-LIM(LO)
0.44
V
Shutdown threshold (Note 4)
VSH-TH
0.22
V
Input leakage current
IIN(VT)
Pull up current source
IVT
CC regulation threshold limit (Note 4)
VT SECTION (Pin 4)
VT = 1.0V
90
100
1
µA
110
µA
OUTPUT(TR) SECTION (Pin 1)
Output low level ON-resistance
RDS-TR(ON)LO
ISINK = 5mA
100
Ω
Output high level ON-resistance
RDS-TR(ON)HI
ISOURCE = 5mA
200
Ω
Notes:
Note 1. Adjust VCC above the start-up threshold before setting at 12V.
Note 2. These parameters are not 100% tested, guaranteed by design and characterization.
Note 3. Operating frequency varies based on the line and load conditions, see Theory of Operation for more details.
Note 4. These parameters refer to digital preset values, and are not 100% tested.
Rev. 0.7
iW3614
Preliminary
Page 5
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
VCC Start-up Threshold (V)
VCC Supply Start-up Current (µA)
7.0 Typical Performance Characteristics
9.0
6.0
3.0
0.0
0.0
2.0
4.0
8.0
6.0
VCC (V)
10.0
12.0
14.0
12.2
12.0
11.8
11.6
-50
Internal Reference Voltage (V)
% Deviation of Switching Frequency from Ideal
-0.3 %
-0.9 %
-1.5 %
-50
-25
0
25
50
75
Ambient Temperature (°C)
100
125
Figure 7.3 : % Deviation of Switching Frequency to
Ideal Switching Frequency vs. Temperature
Rev. 0.7
iW3614
Preliminary
0
25
50
75
Ambient Temperature (°C)
100
125
Figure 7.2 : Start-Up Threshold vs. Temperature
Figure 7.1 : VCC vs. VCC Supply Start-up Current
0.3 %
-25
2.01
2.00
1.99
1.98
-50
-25
0
25
50
75
Ambient Temperature (°C)
100
125
Figure 7.4 : Internal Reference vs. Temperature
Page 6
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
8.0 Functional Block Diagram
iW3614 combines two functions: 1) wall dimmer type
detection and dimmer phase measurement; and 2) output
LED light dimming. It uses iWatt’s proprietary digital control
technology, which consists of: 1) chopping circuit, which
helps to increase the power factor and serves as a dynamic
impedance to load the dimmer; 2) primary side controlled
isolated flyback converter. The iW3614 provides a low cost
dimming solution which enables LED bulb to be used with
most of the common wall dimmers. This allows LED bulbs to
directly replace conventional incandescent bulbs with ease.
The iW3614 can detect and operate with leading-edge, and
trailing-edge dimmers as well as no-dimmer. The controller
operates in critical discontinuous conduction mode (CDCM)
to achieve high power efficiency and minimum EMI. It
VIN
incorporates proprietary primary-feedback constant current
control technology to achieve tight LED current regulation.
Figure 3.1 shows a typical iW3614 application schematic.
Figure 8.1 shows the functional block diagram. The advanced
digital control mechanism reduces system design time and
improves reliability. The start-up algorithm makes sure the
VCC supply voltage is ready before powering up the IC.
The iW3614 provides multiple protection features for
current limit, over-voltage protection, and over temperature
protection. The VT function can provide overtemperature
compensation for the LED. The external NTC senses the
LED temperature. If the VT pin voltage is below VP-LIM(HI), the
controller reduces the LED current. If the VT pin voltage is
below VSH-TH then the controller turns off.
3
VCC
1
OUTPUT(TR)
7
OUTPUT
6
ISENSE
Start-up
Enable
VIN_A
0.0V ~ 1.8V
Enable
8
ZIN
100µA
VT
ADC
MUX
Dimmer
Detection
and
Dimmer Phase
Measurement
ADC
4
VVMS
VSENSE
2
Signal
Conditioning
VOVP
65kΩ
Gate
Driver
Constant
Current
Control
VFB
Gate
Driver
65kΩ
+
DAC
GND
IPEAK
–
VOCP
1.89V
+
–
5
VIPK 0V ~ 1.8V
Figure 8.1 : iW3614 Functional Block Diagram
Rev. 0.7
iW3614
Preliminary
Page 7
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
9.0 Theory of Operation
The iW3614 is a high performance AC/DC off-line power
supply controller for dimmable LED luminaires, which uses
advanced digital control technology to detect the dimmer
type and dimmer phase to control the LED brightness. A
PWM-dimming scheme is used to modulate the LED current
at the PWM dimming frequency at low dimming levels.
iW3614 can work with all types of wall dimmers including
leading-edge dimmer, trailing-edge dimmer, as well as
dimmer configurations such as R-type, R-C type or R-L type
without visible flicker. The controller can also work when no
dimmer is connected.
iW3614 operates in quasi-resonant mode to provide high
efficiency and simplify EMI design. In addition, the iW3614
includes a number of key built-in protection features. Using
iWatt’s state-of-the-art primary-feedback technology, the
iW3614 removes the need for secondary feedback circuitry
while achieving excellent line and load regulation. iW3614
also eliminates the need for loop compensation components
while maintaining stability over all operating conditions.
Pulse-by-pulse waveform analysis allows for accurate
LED current regulation. Hence, the iW3614 can provide
high performance dimming solutions, with minimal external
component count and low bill of materials cost.
9.1 Pin Detail
Pin 6 – ISENSE
Primary current sense. Used for cycle by cycle peak current
control.
Pin 7 – OUTPUT
Gate drive for the external MOSFET switch.
Pin 8 – VCC
Power supply for the controller during normal operation. The
controller will start-up when VCC reaches 12V (typical) and
will shut down when the VCC voltage is below 7.5V (typical).
High-frequency transients and ripples can be easily generated
on the VCC pin due to power supply switching transitions,
and line and load disturbances. Excess ripples and noises
on VCC may cause the iW3614 to function undesirably, hence
a decoupling capacitor should be connected between the
VCC pin and GND. A ceramic capacitor of minimum 0.1 uF
connected as close as possible to the VCC pin is suggested.
9.2 Wall Dimmer Detections
There are two types of wall dimmers: leading-edge dimmer
and trailing-edge dimmer.
Pin 1 – OUTPUT(TR)
Gate drive for the chopping circuit MOSFET switch.
AC line before Walldimmer
Pin 2 – VSENSE
Sense signal input from auxiliary winding. This provides the
secondary voltage feedback used for output regulation.
Pin 3 – VIN
Sense signal input from the rectified line voltage. VIN is
used for dimmer phase detection. The input line voltage is
scaled down using a resistor network. It is used for input
under-voltage and over-voltage protection. This pin also
provides the supply current to the IC during start-up.
AC line after
Wall-dimmer
Figure 9.1 : Leading-Edge Wall Dimmer Waveforms
Pin 4 – VT
External power limit and shutdown control. If the shutdown
control is not used, this pin should be connected to GND via
a resistor.
Pin 5 – GND
Ground.
Rev. 0.7
iW3614
Preliminary
Page 8
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
period measurement. The VIN period is measured during
the second cycle of the dimmer detection process and is
latched for use thereafter. Using the measured VIN period
in subsequent calculations rather than a constant allows
for automatic 50-/60-Hz operation and allows for a 10%
frequency variation.
AC line before Walldimmer
The phase measurement starts when VIN exceeds the rising
threshold until VIN falls below the falling threshold.
AC line after
Wall-dimmer
0.14 V
t0
Figure 9.2 : Trailing-Edge Wall Dimmer Waveforms
Dimmer detection, or discovery, takes place during the third
cycle after start-up. The controller determines whether no
dimmer exists, or there is a leading edge dimmer or a trailing
edge dimmer.
VCROSS is internally generated by comparing the digitalized
VIN signal to the threshold of 0.25V during dimming or
0.14V without a dimmer. The VIN period (tPERIOD) is measured
between two consecutive rising edge zero-crossings. tCROSS
is generated by the internal digital block (refer to Figure 9.3);
when VIN_A is higher than 0.14V tCROSS is set to high and
when VIN_A falls below 0.14V tCROSS is reset to zero. If tCROSS is
much shorter than the VIN period then a dimmer is detected.
The controller uses the filtered derivatives to decide which
type of dimmer is present. A large positive derivative value
indicates a leading edge dimmer. Then the controller enters
leading edge dimmer mode; otherwise it enters trailing edge
dimmer mode.
During the dimmer detection stage, the OUTPUT(TR) keeps
high to turn on the switch FET in the chopping circuit. This
creates a resistive load for the wall dimmer.
tCROSS
tPERIOD
Figure 9.4 : Dimmer Phase Measurement
The dimmer phase is calculated as:
Dimmer Phase =
tCROSS
t PERIOD
OUTPUT(TR)
tCROSS
tperiod
LED(EN)
(9.1)
The calculated dimmer phase is used to generate the signal
DRATIO, which determines LED current. If the dimmer phase
is less than 0.14 then the DRATIO is clamped at 0.14; if the
dimmer phase is greater than 0.7 then DRATIO is clamped at
1.0; otherwise DRATIO is calculated by equation 9.2.
=
DRATIO Dimmer Phase × K1 − K 2
(9.2)
Where, K1 is set to 1.768 and K2 is set to 0.238.
Using VIsense(NOM) to represent the nominal 100% LED current,
the VIsense, which modulates the output LED current, is
controlled by:
=
VIsense VIsense ( NOM ) × DRATIO
0.14 V
VIN_A
VCROSS
VCROSS
(9.3)
When DRATIO is 1, the converter outputs 100% of nominal
power to the LED. If DRATIO is 0.01, the converter outputs 1%
of nominal power to the LED.
VLED
Figure 9.3 : Dimmer Detection
9.3 Dimmer Tracking and Phase
Measurements
The dimmer detection algorithm and the dimmer tracking
algorithm both depend on an accurate input voltage
Rev. 0.7
iW3614
Preliminary
Page 9
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
9.4 Chopping Operation
D1
AC
BR
Wall
Dimmer
D2
LC
R1
OUTPUT(TR)
*R
VIN_A
*R
2
2
VCB
RC
QC
+
VIN pin signal
3
500 mV/div
CB
OUTPUT(TR)
2
10.0 V/div
RS
is internal ZIN of IC
ILC
100 mA/div 4
Figure 9.5 : Chopping Schematic
Chopping circuit provides the dynamic impedance for the
dimmer and builds the energy to the LED power converter. It
consists of LC, QC, RC, RS, and D2. LC is the chopping inductor.
During the chopping period, LC is used to store the energy
when the QC is on, and then release the energy to CB when
QC is off. The on-time of QC during the chopping period when
no dimmer exists is calculated by the following equation:
TON (Qc ) = 8µs − 4.4
µs
V
× VIN _ A
(9.4)
If dimmer exists, the on-time of QC is half the on-time specified
by equation 9.4. The period of QC is calculated by:
TPERIOD (Qc=
12.2µs + 8.8 µs V × VIN _ A
)
(9.5)
VIN_A is the scale voltage of VIN. VCB is the voltage across CB.
When tCROSS is low, QC is always on. When tCROSS is high, QC
operates according to equation 9.4 and 9.5.
During the chopping period, the average current of LC
is in phase with the input AC line voltage, so it inherently
generates high power factor. D1 in the chopping circuit is
used to charge CB when the voltage of CB is lower than the
input line voltage. This helps to reduce the inrush current
when the TRIAC is fired.
tCROSS
1
5.0 V/div
Time (2.0 ms/div)
Figure 9.6 : Signals of Chopping Circuit
9.5 Start-up
Prior to start-up the VIN pin charges up the VCC capacitor
through a diode between VIN and VCC. When VCC is fully
charged to a voltage higher than the start-up threshold
VCC(ST), the ENABLE signal becomes active and enables the
control logic, shown by Figure 9.7. When the control logic
is enabled, the controller enters normal operation mode.
During the first 3 half AC cycles, OUTPUT(TR) keeps high.
After the dimmer type and AC line period are measured, the
constant current stage is enabled and the output voltage
starts to ramp up. When the output voltage is above the
forward voltage of the LED, the controller begins to operate
in constant current mode.
An adaptive soft-start control algorithm is applied during
start-up state, where the initial output pulses are short and
gradually get wider until the full pulse width is achieved.
The peak current is limited cycle by cycle by the IPEAK
comparator.
Start-up
Sequencing
VIN
VIN pin signal
3
500 mV/div
VCC(ST)
OUTPUT(TR)
2
10.0 V/div
VCC
ILC
4
100 mA/div
tCROSS
1
5.0 V/div
Time (2.0 ms/div)
ENABLE
Figure 9.7 : Start-up Sequencing Diagram
Rev. 0.7
iW3614
Preliminary
Page 10
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
9.6 Understanding Primary Feedback
Figure 9.8 illustrates a simplified flyback converter. When the
switch Q1 conducts during tON(t), the current ig(t) is directly
drawn from rectified sinusoid vg(t). The energy Eg(t) is stored
in the magnetizing inductance LM. The rectifying diode D1
is reverse biased and the load current IO is supplied by the
secondary capacitor CO. When Q1 turns off, D1 conducts and
the stored energy Eg(t) is delivered to the output.
iin(t)
+
ig(t)
id(t)
N:1
vg(t)
vin(t)
VAUX = VO x
VAUX
CO
IO
VAUX = -VIN x
VAUX
–
Figure 9.8 : Simplified Flyback Converter
In order to tightly regulate the output voltage, the information
about the output voltage and load current needs to be
accurately sensed. In the DCM flyback converter, this
information can be read via the auxiliary winding or the
primary magnetizing inductance (LM). During the Q1 on-time,
the load current is supplied from the output filter capacitor CO.
The voltage across LM is vg(t), assuming the voltage dropped
across Q1 is zero. The current in Q1 ramps up linearly at a
rate of:
dt
=
vg (t )
(9.6)
LM
At the end of on-time, the current has ramped up to:
ig _ peak (t ) =
vg (t ) × tON
LM
(9.7)
LM
× ig _ peak (t ) 2
2
(9.8)
When Q1 turns off, ig(t) in LM forces a reversal of polarities on
all windings. Ignoring the communication-time caused by the
leakage inductance LK at the instant of turn-off, the primary
current transfers to the secondary at a peak amplitude of:
id =
(t )
NP
× ig _ peak (t )
NS
NP
N AUX
(VO + ∆V )
NS
(9.10)
and reflects the output voltage as shown in Figure 9.9.
The voltage at the load differs from the secondary voltage by
a diode drop and IR losses. The diode drop is a function of
current, as are IR losses. Thus, if the secondary voltage is
always read at a constant secondary current, the difference
between the output voltage and the secondary voltage will
be a fixed ΔV. Furthermore, if the voltage can be read when
the secondary current is small; for example, at the knee of
the auxiliary waveform (see Figure 9.9), then ΔV will also be
small. With the iW3614, ΔV can be ignored.
The real-time waveform analyzer in the iW3614 reads the
auxiliary waveform information cycle by cycle. The part then
generates a feedback voltage VFB. The VFB signal precisely
represents the output voltage and is used to regulate the
output voltage.
9.7 Valley Mode Switching
This current represents a stored energy of:
E
=
g
NAUX
The auxiliary voltage is given by:
Q1
VAUX
=
dig (t )
NS
Figure 9.9 : Auxiliary Voltage Waveforms
VAUX
TS(t)
NAUX
0V
VO
+
D1
Assuming the secondary winding is master and the auxiliary
winding is slave.
In order to reduce switching losses in the MOSFET and EMI,
the iW3614 employs valley mode switching during constant
output current operation. In valley mode switching, the
MOSFET switch is turned on at the point where the resonant
voltage across the drain and source of the MOSFET is at its
lowest point (see Figure 9.10). By switching at the lowest
VDS, the switching loss will be minimized.
(9.9)
Rev. 0.7
iW3614
Preliminary
Page 11
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
V
t
1
I OUT = × N PS × REG −TH × R
2
RSENSE tS
Gate
(9.11)
where NPS is the turns ratio of the primary and secondary
windings and RSENSE is the ISENSE resistor.
9.9 VIN Resistors
VDS
Figure 9.10 : Valley Mode Switching
Turning on at the lowest VDS generates lowest dV/dt, thus
valley mode switching can also reduce EMI. To limit the
switching frequency range, the iW3614 can skip valleys
(seen in the first cycle in Figure 9.10) when the switching
frequency is greater than fSW(MAX).
VIN resistors are chosen primarily to scale down the input
voltage for the IC. The scale factor for the input voltage in the
IC is 0.0043 for 230VAC, and 0.0086 for 115VAC or, 0.0099 for
100VAC if the internal impedance of this pin is selected to be
2.5kΩ. Then for high line, the VIN resistors should equate to:
R=
Vin
2.5k W
− 2.5k=
W 579k W
0.0043
(9.12)
At each of the switching cycles, the falling edge of VSENSE
is checked. If the falling edge of VSENSE is not detected, the
off-time will be extended until the falling edge of VSENSE is
detected.
The VIN resistors are shown in Figure 11.1 as R3, R4, and
R22.
9.8 LED Current Regulation
The iW3614 includes a function that protects against an
input over-voltage (VIN OVP) and output over-voltage (OVP).
iW3614 incorporates a patented primary-side only constant
current regulation technology. The iW3614 regulates the
output current at a constant level regardless of the output
voltage, while avoiding continuous conduction mode. To
achieve this regulation the iW3614 senses the load current
indirectly through the primary current. The primary current
is detected by the ISENSE pin through a resistor from the
MOSFET source to ground.
tOFF
tON
tS
IP
9.10 Voltage Protection Functions
The input voltage is monitored by VIN_A, as shown in Figure
8.1. If this voltage exceeds 1.73 V for 15 continuous half AC
cycles the iW3614 considers VIN to be over-voltage. Output
voltage is monitored by the VSENSE pin. If the voltage at this
pin exceeds VSENSE(MAX) for 2 continuous switching cycles the
iW3614 considers the output voltage to be over-voltage.
In both input over-voltage and output over-voltage cases,
the IC shuts off immediately but remains biased to discharge
the VCC supply. In order to prevent overcharging the output
voltage or overcharging the bulk voltage, the iW3614
employs an extended discharge time before restart. Initially
if VCC drops below the UVLO threshold, the controller resets
itself and then initiates a new soft-start cycle.
Figure 9.11 : Constant LED Current Regulation
Under the fault condition, the controller tries to start-up for
three consecutive times. If all three start-up attempts fail, the
controller enters the inactive mode, during which the controller
does not respond to VCC power-on requests. The controller
will be activated again after it sees 29 start-up attempts. The
controller can also be reset to the initial condition if VCC is
discharged. Typically, this extended discharge time is around
3 to 5 seconds.
The ISENSE resistor determines the maximum current output
of the power supply. The output current of the power supply
is determined by:
This extended discharge time allows the iW3614 to support
hot-plug LED modules without causing dangerously high
output voltages while maintaining a quick recovery.
IS
IO
tR
Rev. 0.7
iW3614
Preliminary
Page 12
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
100
80
60
40
20
0.4
0.6
PLI
M
V
V
0.8
1.0
(H
I)
(L
O)
0.2
PLI
M
0
0.0
SH
-T
H
Peak-current limit (PCL), over-current protection (OCP) and
sense-resistor short protection (SRSP) are features builtin to the iW3614. With the ISENSE pin the iW3614 is able to
monitor the primary peak current. This allows for cycle by
cycle peak current control and limit. When the primary peak
current multiplied by the ISENSE sense resistor is greater than
VOCP over-current protection engages and the IC immediately
turns off the gate drive until the next cycle. The output driver
continues to send out switching pulses, but the IC will
immediately turn off the gate drive if the OCP threshold is
reached again.
V
Percentage of Nominal Output Current (%)
9.11 PCL, OC and SRS Protection
VT Pin Voltage
If the ISENSE sense resistor is shorted there is a potential
danger of the over-current condition not being detected.
Thus the IC is designed to detect this sense-resistor-short
fault after the start-up, and shutdown immediately. The VCC
will be discharged since the IC remains biased. In order
to prevent overcharging the output voltage, the iW3614
employs an extended discharge time before restart, similar
to the discharge time described in section 9.10.
When the VT pin voltage reaches VP-LIM(HI) the output current
begins to reduce as shown in Figure 9.12. At VP-LIM(LO) the
output current reduces to 1%. The device can be placed
in shutdown mode by pulling the VT pin to ground or below
VSH-TH.
9.12 Over Temperature Protection
9.13 Thermal Design
If an NTC thermistor is connected from the VT pin to GND
then, the iW3614 is able to detect and protect against an
over temperature event (OTP).
The iW3614 is typically installed inside a small enclosure,
where space and air volumes are constrained. Under these
circumstances θJA (thermal resistance, junction to ambient)
measurements do not provide useful information for this
type of application. Instead we have provided ψJB which
estimates the increase in die junction temperature relative to
the PCB surface temperature. Figure 9.14 shows the PCB
surface temperature is measured at the IC’s GND pin pad.
80
GND pin
Printed Circuit Board
PCB Bottom Copper Trace
Figure 9.14 : Ways to Improve Thermal Resistance
20
1.0
Using ψJB the junction temperature (TJ) of the IC can be
found using the equation below.
(H
I)
0.8
PL
IM
IM
PL
V
SH
V
0.6
(L
O)
0.4
V
0.2
a) VT from 1.0 V to 0.0 V
Figure 9.12 : VT Pin Voltage vs. % of Nominal Output Current
VT from 1.0V to 0.0V
100
IC Die
Thermal Vias
Connect top thermal pad
to bottom copper
40
0
0.0
PCB Top Copper Trace
Printed Circuit Board
60
ψJB
B
Exposed
Die Pad
100
VT Pin Voltage
of Nominal Output Current (%)
J
Thermal Epoxy
Artic Silver
Copper Thermal Pad
Under Package
-T
H
Percentage of Nominal Output Current (%)
The iW3614 provides a current (IVT) to the VT pin and detects
the voltage on the pin. Based on this voltage the iW3614
can monitor the temperature on the NTC thermistor. As the
VT pin voltage reduces, the iW3614 reduces the amount of
chopping and the output current according to Figure 9.12.
There is a hysteresis of 84 mV on VT pin voltage for each
power limiting step.
Figure 9.13 : VT Pin Voltage vs. % of Nominal Output Current
VT from 0.0V to 1.0V
T=
TB + PH ⋅ ψ JB
J
(9.13)
where, TB is the PCB surface temperature and PH is the
power applied to the chip or the product of VCC and ICCQ.
80
Rev. 0.760
iW3614
Preliminary
40
Page 13
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
The iW3614 uses an exposed pad package to reduce the
thermal resistance of the package. The exposed pad can
be electrically connected to the GND pin of the IC. Although
by having an exposed package can provide some thermal
resistance improvement, more significant improvements can
be obtained with simple PCB layout and design. Figure 9.14
demonstrates some recommended techniques to improve
thermal resistance, which are also highlighted below.
Effect of Thermal Resistance Improvements
85
ΨJB (˚C/Watt)
75
Ways to Improve Thermal Resistance
●● Increase PCB area and associated amount of copper
interconnect.
No adhesive
70 °C/W
Use thermal adhesive to pad
63 °C/W
Use thermal adhesive to pad with thermal vias
49 °C/W
Table 9.1 : Improvements in ψJB Based on Limited
Experimentation
55
B
45
25
5
10
15
20
25
30
PCB Area (cm2)
●● Connect PCB thermal pad to additional copper on PCB
using thermal vias.
ψJB
65
35
●● Use thermal adhesive to attach the package to a thermal
pad on PCB.
Environment
A
~ 30%
A: without thermal adhesive and thermal vias
B: with thermal adhesive and thermal vias
Figure 9.15 : Effect of Thermal Resistance Improvements
Figure 9.15 shows improvement of approximately 30% in
thermal resistance across different PCB sizes when the
exposed pad is attached to PCB using a thermal adhesive
and thermal vias connect the pad to a larger plate on the
opposing side of the PCB.
Rev. 0.7
iW3614
Preliminary
Page 14
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
10.0 Performance Characteristics
Trailing Edge Dimmer
Trailing Edge Dimmer
VIN pin signal
4
1.0 V/div
VIN pin signal
4
1.0 V/div
AC line
current 1
500 mA/div
AC line
current 1
500 mA/div
AC line
3
200 V/div
AC line
3
200 V/div
Ch1
Ch3
500mA
200V
Ch4
Ch1
Ch3
Time (2.0 ms/div)
1.0V
Figure 10.1 : Trailing Edge Dimmer
500mA
200V
Leading Edge Dimmer
VIN pin signal
4
1.0 V/div
VIN pin signal
4
1.0 V/div
AC line
current 1
500 mA/div
AC line
current 1
500 mA/div
AC line 3
200 V/div
AC line
3
200 V/div
500mA
Ch3
200V
Ch4
Time (2.0 ms/div)
1.0V
Figure 10.3 : Leading Edge Dimmer
Time (2.0 ms/div)
1.0V
Figure 10.2 : Trailing Edge Dimmer 2
Leading Edge Dimmer
Ch1
Ch4
Ch1
500mA
Ch3
200V
Ch4
Time (2.0 ms/div)
1.0V
Figure 10.4 : Leading Edge Dimmer 2
No Dimmer
VIN pin signal
1.0 V/div 4
AC line
current 1
100 mA/div
AC line
3
200 V/div
Time (2.0 ms/div)
Figure 10.5 : No Dimmer
Rev. 0.7
iW3614
Preliminary
Page 15
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
11.0 Typical Application Schematic
L1
3.7 mH
F1
1A 250 V
AC Input
From Dimmer
L4
450 µH
R1
4.7 kΩ
L2
3.7 mH
D1
RSIM
L5
0.65 mH
R24
4.7 kΩ
CX1
10 nF
275 V
D2
RSIM
R26
R25
100 kΩ 100 kΩ
CX2
22 nF
275 V
BR1
DB107
L3
EE10
4.0mH
R5
390 Ω
2W
R3
300 kΩ
R4
300 kΩ
R2
4.7 kΩ
D3
ESIJ
C1
10 nF
500 V
R7
100 kΩ
D7
HER306G
VOUT
+
C2
C11
22 nF/500 V 10 µF
450 V
Q2
02N6
R22
24 kΩ
C3
1 nF
250 V
R10
220 kΩ
R8
120 kΩ
+
D4
RSIM
R9
120 kΩ
C9
47 µF
50 V
R6
47 Ω
+ R20
100 kΩ
Q3
DMZ6005
U1
iW3614
R18
24 kΩ
R19
2.7 kΩ
C5
22 pF
C6
4.7 nF
C12
100 pF
D5
1N4148
VCC 8
1
OUTPUT(TR)
2
VSENSE
3
VIN
ISENSE 6
4
VT
GND 5
OUTPUT 7
R11
10 Ω
D6
1N4148
R17
10 Ω
Q1
04N6
R13
1 kΩ
Z1
C4
100 pF 15 V
C7
2.2 µF
25 V
+ C8
R12
47 µF 100
kΩ
25 V
R15
3.3 Ω
R14
3.3 Ω
RTN
NTC
22 kΩ
Figure 11.1 : Schematic of a 40-V, 350-mA Dimmable LED Driver for 230-VAC Application
Rev. 0.7
iW3614
Preliminary
Page 16
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
12.0 Physical Dimensions
8-Lead Small Outline (SOIC) Package
E
M
8
5
1
4
8
5
N
H
4
e
TOP VIEW
1
EXPOSED
PAD
BOTTOM VIEW
Inches
Symbol
D
MIN
MAX
MIN
A
0.051
0.067
1.30
1.70
A1
0.0020
0.0060
0.05
0.150
B
0.014
0.019
0.36
0.48
C
0.007
0.010
0.18
0.25
D
0.189
0.197
4.80
5.00
E
0.150
0.157
3.81
3.99
e
A1
A
COPLANARITY
0.10 (0.004)
B
α
SEATING
PLANE
C
SIDE VIEWS
L
Millimeters
0.050 BSC
MAX
1.27 BSC
H
0.228
0.244
5.79
6.20
N
0.086
0.118
2.18
3.00
2.39
M
0.094
0.126
L
0.016
0.050
0.41
1.27
α
0°
8°
3.20
Figure 12.1 : Physical dimensions, 8-lead SOIC package
Compliant to JEDEC Standard MS12F
Controlling dimensions are in inches; millimeter dimensions are for reference only
This product is RoHS compliant and Halide free.
Soldering Temperature Resistance:
[a] Package is IPC/JEDEC Std 020D Moisture Sensitivity Level 3
[b] Package exceeds JEDEC Std No. 22-A111 for Solder Immersion Resistance; package can withstand
10 s immersion < 270˚C
Dimension D does not include mold flash, protrusions or gate burrs. Mold flash, protrusions or gate burrs shall
not exceed 0.15 mm per end. Dimension E does not include interlead flash or protrusion. Interlead flash or
protrusion shall not exceed 0.25 mm per side.
The package top may be smaller than the package bottom. Dimensions D and E are determined at the
outermost extremes of the plastic bocy exclusive of mold flash, tie bar burrs, gate burrs and interlead flash, but
including any mismatch between the top and bottom of the plastic body.
13.0 Ordering Information
Part Number
Options
Package
Description
iW3614-00
1% to 100% Dimming Range, PWM Dimming Frequency = 900Hz
SOIC-8
(exposed pad)
Tape & Reel1
iW3614-02
3% to 100% Dimming Range, PWM Dimming Frequency = 630Hz
SOIC-8
(exposed pad)
Tape & Reel1
Note 1: Tape & Reel packing quantity is 2,500/reel.
Rev. 0.7
iW3614
Preliminary
Page 17
iW3614
AC/DC Digital Power Controller for
High Power Factor Dimmable LED Drivers
Trademark Information
© 2013 iWatt Inc. All rights reserved. iWatt, the iWatt logo, BroadLED, EZ-EMI, Flickerless, and PrimAccurate are registered
trademarks and AccuSwitch and Power Management Simplified Digitally are trademarks of iWatt Inc. All other trademarks
are the property of their respective owners.
Contact Information
Web: https://www.iwatt.com
E-mail: [email protected]
Phone: +1 (408) 374-4200
Fax: +1 (408) 341-0455
iWatt Inc.
675 Campbell Technology Parkway, Suite 150
Campbell, CA 95008
Disclaimer and Legal Notices
iWatt reserves the right to make changes to its products and to discontinue products without notice. The applications
information, schematic diagrams, and other reference information included herein is provided as a design aid only and are
therefore provided as-is. iWatt makes no warranties with respect to this information and disclaims any implied warranties of
merchantability or non-infringement of third-party intellectual property rights.
This product is covered by the following patents: 6,385,059; 6,730,039; 6,862,198; 6,900,995; 6,956,750; 6,990,000; 7,443,700; 7,505,287;
7,589,983; 6,972,969; 7,724,547; 7,876,582; 7,880,447; 7,974,109; 8,018,743; 8,049,481; 7,936,132; 7,433,211; 6,944,034. A full list of
iWatt patents can be found at www.iwatt.com.
Certain applications using semiconductor products may involve potential risks of death, personal injury, or severe property
or environmental damage (“Critical Applications”).
iWATT SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED, OR WARRANTED TO BE
SUITABLE FOR USE IN LIFE‑SUPPORT APPLICATIONS, DEVICES OR SYSTEMS, OR OTHER CRITICAL APPLICATIONS.
Inclusion of iWatt products in critical applications is understood to be fully at the risk of the customer. Questions concerning
potential risk applications should be directed to iWatt Inc.
iWatt semiconductors are typically used in power supplies in which high voltages are present during operation. High-voltage
safety precautions should be observed in design and operation to minimize the chance of injury.
Rev. 0.7
iW3614
Preliminary
Page 18