HOLTEK HT7L4091

Universal Step-Down PWM Control
For High Brightness LED Lighting Control
HT7L4091
Revision: v1.00
Date: ��������������
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Table of Contents
Features.......................................................................................................................... 4
Applications.................................................................................................................... 4
General Description....................................................................................................... 4
Pin Assignment.............................................................................................................. 5
Pin Description............................................................................................................... 5
Absolute Maximum Ratings.......................................................................................... 5
Recommended Operating Ranges................................................................................ 6
Block Diagram................................................................................................................ 6
Electrical Characteristics.............................................................................................. 7
Functional Description.................................................................................................. 8
LED Current Control.................................................................................................................. 8
Programmable Off Time............................................................................................................ 8
Current Sense........................................................................................................................... 9
Leading-Edge Blanking............................................................................................................. 9
Frequency Jitter Function.......................................................................................................... 9
Input Supply Current................................................................................................................. 9
Start-up Current and Auxiliary Power Source......................................................................... 10
Linear Dimming....................................................................................................................... 10
PWM Dimming........................................................................................................................ 10
LED Open and Short Circuit Protection.................................................................................. 10
Enhanced Short Circuit Protection.......................................................................................... 11
Application Description............................................................................................... 12
Input Bulk Capacitor – C1....................................................................................................... 12
Switching Frequency and Duty Cycle..................................................................................... 13
Turn-off Time........................................................................................................................... 13
Off-time Resistor – RT ............................................................................................................ 14
Inductor Design....................................................................................................................... 14
Current Sense Resistor – RCS ................................................................................................ 14
Input Supply Current .............................................................................................................. 15
Input Limit Resistor (RIN)......................................................................................................... 15
Output Capacitor – CO ............................................................................................................ 15
Typical Performance Characteristics......................................................................... 16
Efficiency vs. Power Supply Circuit – Working Frequency..................................................... 16
Efficiency for Resistor Only Power and Single Input Voltage.................................................. 17
Efficiency Using Resistor Only Power and 85~265 VAC Input.................................................. 18
Typical Application Circuit.......................................................................................... 19
Other Application Circuit............................................................................................. 20
No Input Bulk Capacitor Circuit .............................................................................................. 20
High Efficiency Circuit............................................................................................................. 20
BJT Power Supply Application Circuit..................................................................................... 21
Rev. 1.00
2
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Package Information.................................................................................................... 23
8-pin SOP (150mil) Outline Dimensions................................................................................. 23
Reel Dimensions..................................................................................................................... 24
Carrier Tape Dimensions......................................................................................................... 25
Rev. 1.00
3
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Features
●● Input supply AC voltage range: 100V~240V
●● Ultra Low Power-on Start-up current < 30μA
●● Integrated 25V Zener diode internally connected to VIN pin
●● 5V LDO output voltage with 6mA driving current for external components
●● Frequency jitter function for enhanced EMI performance
●● Efficiency > 85%
●● Under Voltage Lockout Function - UVLO
●● Current mode operation with cycle-by-cycle current limiting
●● Over Temperature Protection Function
●● High-current FET Drive Output
●● Linear and PWM Dimming Function
●● Enhanced Short Circuit Protection Function
Applications
●● AC/DC and DC/DC Power control For High Power LED Lighting
●● RGB back lighting LED driver
●● Flat Panel Displays Back Lighting
●● General Purpose Constant Current Source
●● Signage and Decorative LED lighting
●● Battery Chargers
General Description
The HT7L4091 device provides a low-cost solution for active current mode PWM controls of High
Intensity LED drive systems supplied by either AC or DC line power lines. The device operates
in constant off-time mode which is suitable for buck LED drivers. The low start-up and operating
currents provides flexible power requirements for high efficiency or low cost applications. The
switch frequency off-time can be programmed using an external resistor. The peak current mode
control achieves good output current regulation without requiring loop compensations for a wide
range of input voltages.
Included in the device is a PWM dimming input which can accept an external control signal with a
duty ratio from 0 to 100%. The output current can be programmed from 0 to 250mA by applying an
external control voltage on the linear dimming control input.
The device includes a frequency jitter function which helps to reduce EMI power supply emissions.
from damage should the LEDs be short circuited. .
The device requires a minimum number of external standard components and is available in an 8-pin
NSOP package for small area PCB applications.
Rev. 1.00
4
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Pin Assignment
VIN
1
8
RT
CS
2
7
LD
GND
3
6
VDD
GDR
4
5
PDM
HT7L4091
8 SOP-A
Pin Description
Pin Name
I/O
Description
VIN
I
Input voltage pin
CS
I
LED string current sense input
GND
—
Power ground
GDR
O
Gate driver for the external MOSFET
PDM
I
PWM dimming pin
Also functions as enable input pin.
VDD
O
Positive Power supply
Used for the internal circuits except the gate driver circuit. A 0.1μF capacitor must be
connected between the VDD and the GND pins.
LD
I
Linear dimming pin
Set the current sense threshold as long as the voltage on this pin is less than 250mV
(typ.).
RT
I
Oscillator control pin
A resistor is connected between the RT and the GND pins to set the off-time.
Absolute Maximum Ratings
Output Current Peak ....................................................................................................................... 1A
Storage Temperature Range.......................................................................................-65°C ~ +150°C
Junction Temperature Range......................................................................................-40°C ~ +150°C
CS, PDM, LD ,RT, to GND..................................................................................-0.3V to (VDD +0.3V)
Power Dissipation at Ta<25 °C................................................................................................... 0.6W
Thermal Resistance, SOP-8 θJA..........................................................................................150°C/W
ESD Voltage Protection, Human Body Model............................................................................. 6KV
ESD Voltage Protection, Machine Model................................................................................... 400V
Note: These are stress ratings only. Stresses exceeding the range specified under “Absolute Maximum
Ratings” may cause substantial damage to the device. Functional operation of this device at other
conditions beyond those listed in the specification is not implied and prolonged exposure to extreme
conditions may affect device reliability.
Rev. 1.00
5
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Recommended Operating Ranges
Input Supply Voltage....................................................................................UVLO(H)+0.1V ~ VClamp
Operating Temperature Range......................................................................................-40°C ~ +85°C
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur.
Operating Ratings indicate conditions for which the device is intended to be functional, but do
not guarantee specific performance limits. The guaranteed specifications apply only for the test
conditions listed.
Note 2: The power supply pin should not be driven by a DC, low impedance power source greater than the
VCLAMP voltage specified in the Electrical Characteristics section.
Block Diagram
VIN
PDM
ON
UVLO
25V
VDD
LDO
PWMD
100k
GDR
OTP
Power
On Reset
0.5V
Q
CS
R
QB S
Blank
0.25V
Q
RT
OSC
(jitter)
R
QB S
LD
GND
Rev. 1.00
6
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Electrical Characteristics
Symbol
Description
(VIN=17V, Ta=25°C, unless otherwise specified)
Test Condition
Min.
Typ.
Max.
Unit
—
Input
VINDC
Input DC supply voltage
11
—
VClamp
V
—
0.6
1
mA
—
15
30
μA
25
27.6
V
IIN
Input Operation Current
VINDC ≥ 17V, RT = 410kΩ
GDR pin floating
IINST
Startup Input current
VINDC < 15V, RT = 410kΩ
VClamp
VIN Clamp Voltage
IIN=10mA
22.4
Internal Regulator
VDD
Internally regulated voltage
VINDC=12V~26V
4.5
5
5.5
V
ΔVDD, line
Line regulation of VDD
VINDC=12V~26V, IDD = 0mA
0
—
100
mV
ΔVDD, load
Load regulation of VDD
VINDC=17V, IDD = 0mA ~ 3mA
0
—
100
mV
VUVLO(H)
VINDC under voltage lockout high
VINDC rising
threshold
15
16
17
V
VUVLO(L)
VINDC under voltage lockout low
threshold
VINDC falling
9
10
11
V
VEN(L)
Input low voltage for PDM pin
VINDC=12V~26V
—
—
0.8
V
VEN(H)
Input high voltage for PDM pin
VINDC=12V~26V
2.0
—
—
V
REN
PDM pin Pull-low resistor
—
50
100
150
KΩ
VCS(TH)
Current sense trip threshold
voltage
—
0.24
0.248
0.255
V
Tdelay
Delay from CS trip to GDR
—
110
—
ns
VLD
Linear Dimming pin voltage
range
0
—
VCS_TH
V
Tblank
Blanking interval
Toff
Off time
RT=410kΩ
VOL
GATE Output Low Level
VOH
GATE Output High Level
Trise
Tfall
TOTP
Thermal shutdown temperature
∆TOTP
Thermal shutdown temperature
hysteresis
∆fJitter
Switch frequency jitter ratio
TJP
Jitter Period
VCS-short
Short circuit protection Voltage
VCS =VCS_TH + 50mV
—
—
200
300
400
ns
14.7
16.4
18.1
μs
VINDC = 17V, Io = -20mA
—
—
0.3
V
VINDC = 17V, Io = 20mA
12
—
—
V
Gate output rise time
CGATE = 500pF
—
120
—
ns
Gate output fall time
CGATE = 500pF
—
50
—
ns
—
—
140
—
—
—
—
25
—
—
—
—
±4
—
%
—
4
—
ms
0.45
0.5
0.55
V
fsw = 60kHz
—
Note 3: Specifications are production tested at TA=room temperature. Specifications over the -40°C to 85°C
operating temperature range are assured by design, characterization and correlation with Statistical Quality
Controls (SQC).
Rev. 1.00
7
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Functional Description
The HT7L4091 is a universal AC/DC constant current LED driver designed for peak current mode
control. The device provides both LED Linear and PWM dimming current functions. The high input
voltage from a rectified 85V to 260V AC power is clamped to under 25V by an external circuit and
an internal Zener diode. The device also contains an input Under-Voltage-Lockout (UVLO) circuit.
When the voltage supplied on the VIN pin exceeds the UVLO high threshold, the gate driver is
enabled. If the input voltage falls below the UVLO low threshold, the gate driver is turned off.
LED Current Control
The HT7L4091 device is a constant off-time peak current mode controller. With reference to the
Application Circuit, the LED peak current is programmed by an external current sense resistor (RCS)
connected between the CS and the ground pins. The CS pin is connected to a non-inverting terminal
of an internal comparator of which an internal 250mV reference is tied to the inverting terminal. The
LED peak current through the RCS resistor will generate a voltage which is applied on the comparator
non-inverting terminal and compare with the internal 250mV reference voltage. If the voltage on
the CS pin is less than the internal reference voltage 250mV, the LED gate driving circuitry will be
turned on. While the voltage on the CS pin is larger than the internal reference voltage, the LED
gate driving circuitry will be turned off for a constant Toff time. After the Toff time, the gate driving
circuitry will be turn on if the voltage on the CS pin is less than the internal reference voltage. Good
line regulation is a feature of constant off-time operation and the LED current is independent of the
input voltage. Since the inductor current ripple is dependent on the LED string voltage, the LED
string voltage variation will result in LED current variation. This is typically not a problem since the
LED voltage variation for a given load is fairly small.
RCS can be calculated using the following equation:
=
R CS
0.�5
=
I�eak
0.�5
1 + 1 × Ri���e ⋅ ILED
�
(
)
Where Ipeak is the Maximum LED Current, Ripple is the Peak to Peak LED Current, and ILED is the
Average LED Current. Ripple can be controlled by the inductor.
Toff × Vout
I LED × Ripple=I Ripple =
L
Refer to “Inductor Design” for the inductor calculation. Refer to “Programmable Off Time” for Toff
calculation.
Programmable Off Time
The device operates in a constant off-time mode. A resistor connected between the RT pin and the
ground pin generates a constant current source which is used to charge an internal capacitor and
determine the off-time. Increasing the resistance reduces the amplitude of the current source and
increases the off-time. The relationship between the resistor RT and the off-time is given by the
following formula:
Toff = CT × RT CT=36pF~44pF, CT_typ=40pF.
For a given Toff and duty cycle, the switching frequency (fs) can be decided. The duty cycle is
determined by the input and output voltages.
Rev. 1.00
8
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Current Sense
The current sense input is connected to the non-inverting inputs of two comparators. The inverting
terminal of one comparator is tied to an internal 250mV reference whereas the other comparator
inverting terminal is connected to the LD pin. The outputs of both these comparators are fed into an
OR gate and the output of the OR gate is fed into the reset pin of a flip-flop. If a flip-flop reset event
is triggered by the OR gate output a signal occurs where the external MOSFET gate driving circuitry
will be turned off. Therefore, the comparator which has the lower voltage at the inverting terminal
determines when the gate driving output is turned off.
Leading-Edge Blanking
Each time the power MOSFET is switched on, a turn-on transient spike will occur on the CS pin.
To avoid premature termination of the switching pulse, a TBlank leading-edge blank time is generated
during the MOSFET switch turn-on to prevent false triggering of the current sense comparator.
During this blanking period, the current-limit comparator is disabled and the gate driving circuitry
will not be switched off.
In certain rare situations, the internal blanking time might not be long enough to filter out the turnon spike. In such situations, it will be necessary to add an external RC filter between the external
sense resistor (RCS) and the CS pin.
Frequency Jitter Function
The device also includes a frequency jitter function. The frequency has a variation range of +4%
to -4% within four milliseconds. The frequency jitter function helps reduce power supply line EMI
emissions with minimum line filters.
Input Supply Current
The input supply current is determined by the input operating current and the current drawn by the
external MOSFET gate driver. This means that the input supply current depends upon the switching
frequency and the external MOSFET gate charge.
IINSP = IIN + Qgate × fS
, where IINSP is the input supply current taken from the VIN pin, fS is the switching frequency Qgate is
the gate charge of the external MOSFET and IIN is the input operation current.
The application circuit should provide enough IINSP to ensure the application can work properly
Rev. 1.00
9
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Start-up Current and Auxiliary Power Source
The power consumption of the HT7L4091 is one of the major efficiency losses if IINSP drops from
the rectified AC source whose voltage is much higher than the voltage used by the device. For
efficiency improvements, a small start-up current from the rectified AC source is used to start up
the HT7L4091 and IINSP can be provided from the auxiliary power source, for example: auxiliary
winding.
The start-up current should take into consideration the Cin (Vin Capacitor) charge current and the
current consumption of the HT7L4091 during start-up (Iinst). The Cin charge current shall consider
how fast (tstart-up) the application is required to start operation. The start-up current can be calculated
using the follow equation:
Istart −=
I inst +
up
Cin × VUVLO( H )
t start − up
The current from auxiliary power source should be:
=
I aux I INSP − Istart −up
The start-up current allows a start-up resistor with a high resistance and a low-power rating. The
start-up resistor (RINST) is used to supply the start-up power for the device from the rectified AC
source. RINST can be calculated using the following equation:
R INST =
2 ⋅ Vmin,AC − VUVLO(H)
Istart-up
Linear Dimming
The Linear Dimming pin is used to control the LED current. The VDD pin voltage can be connected
to the LD pin to obtain a voltage corresponding to the desired voltage across RCS. The LD pin can
adjust the current level to reduce the illumination intensity of the LEDs. To adjust the external LD
pin voltage from 0mV to 250mV can adjust the LED current during operation. To use the internal
250mV as the reference voltage, the LD pin can be connected to VDD.
PWM Dimming
An external enable input named PDM is provided and can be utilized for PWM dimming of the LED
string. When the external PWM signal is zero, the gate driving circuitry is turned off while the gate
driving circuits are turned on when the PWM signal is high.
LED Open and Short Circuit Protection
There will be no abnormal behavior if the LEDs are open circuit. While some LEDs are shorted, the
output voltage will be adjusted automatically for the condition.
Rev. 1.00
10
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Enhanced Short Circuit Protection
When most LEDs are shorted in the application circuit, the current regulation may lose control
resulting in the current increasing to an extremely high level. When the current is more than twice
of the set Ipeak, resulting from externally shorted LEDs, the device will shut down gate driving
operations.
The operation state is shown in the accompanying figure. When the circuit is operating normally,
VCS can be limited to VCS-TH, while some LEDs are shorted, the LED current is still limited and the
output voltage is adjusted to meet the current requirement. If the circuit encounters a serious short,
the voltage increase of (current) in TBlank would be larger than the decrease in TOFF, VCS will exceed
VCS-TH and reach VCS-Short. The HT7L4091 will then shut down the gate driver until UVLO resets the
HT7L4091.
Slight
Short
Normal
Serious
Short
Shut Down
VCS-Sho�t
VCS-TH
VCS
TB�ank TOff
Cin
Rlim
D1
L1
CVDD
VDD
Vin
LD
GDR
CS
PDM
RT
RCS
GND
Clim
Rev. 1.00
11
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Application Description
This section shows how to design a buck circuit LED application using a simple example. For other
application conditions, such as high efficiency solutions, refer to the HT7L4091 application notes
for more details.
For example:
AC Input voltage: VAC_typ =110Vrms; VAC_min =95Vrms; VAC_max =125Vrms; FAC=60Hz
Target working condition: FPWM > 40kHz
Output Voltage: LED string ×LED Voltage =8×(3~3.3)=24V~26.4V, typical 25.2
Average Output LED Current: ILED= 400mA
Expected efficiency: η=90%
Refer to the typical application circuit.
Input Bulk Capacitor – C1
The input Bulk Capacitor determines the ripple amplitude of input voltage after rectification. A
large capacitance generates a smaller input voltage ripple amplitude. The first design criterion to
meet is that the maximum LED string voltage should be less than 80% of the minimum AC input
voltage (Vmin,AC). Note that 80% is a rough estimate here. Here the large ripple amplitude has a wide
frequency variation which leads to increase in circuit power losses. Assume that the input voltage
DC ripple (ΔVDCripple%) is equal to 30% and then calculate the C1 value.
� ×VAC_min ×(1-ΔVDCripple%)×0.8= � ×95×(1-30%)×0.8=75.2V>26.4V(Maximum Output Voltage)
Above formula means 30% input voltage ripple is approved that exceed output voltage.
Finally, a useful rule can find the valley voltage of the input voltage. Using the figure below, it is
necessary to calculate the charge time and discharge time of the input bulk capacitor.
VIN
8.333ms =
1
120Hz
ΔV
Tcharge
Tdischarge
t
The waveform of input voltage in the C1
=
TCP
Charge period:
Tcha�ge =
Rev. 1.00
1
= 8.333ms
2 × FAC
∆V 

sin−1(1 −
)
TCP 
VIN 
× 1 −
 , where
� 
90



12
∆V
VIN
= ΔVDCripple%
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Tdischarge=TCP– Tcharge
TDischarge =8.333ms –
�.333ms  sin−1(1 − 30%) 
× 1 −
 = 6.2232ms
�
90


Then, the minimum capacitor value can be calculated as:
C1 ≥
(2 × n × VLEDmax × ILED ) × TDischa�ge
η× 

(
2 × V�Cmin
)
�
− ( VDCmin )
�


=
(2 × 16 × 3.3V × 200mA) × 6.2232ms
= 14.3uF
�
�
0.9 ×  � × �5 − � × �5 × 0.7 


(
) (
)
Choose C1=22uF
Considering ±20% capacitance variation, the worst case lower value of the capacitance is 17.6uF,
which is much larger than 14.3uF. It can be calculated that the input DC ripple is 24.5% when the
input Buck capacitor is 17.6uF.
Therefore, if the real capacitor value is less than the calculated value, the voltage ripple will exceed
the maximum range of 30% which is the specified assumption in the calculation.
Switching Frequency and Duty Cycle
Frequency interference should be taken into account to minimise interference with other electrical
appliances. Here set the minimum switching frequency to a value of 40kHz for safety. If EMI
suppression is good, the switching frequency can be decreased to 30kHz to obtain better efficiency.
Since the HT7L4091 operates in constant off time, the switching frequency would be changed by
the input and output voltage. The slowest switching frequency occurs when the duty cycle is at a
maximum value.
The maximum duty cycle can be calculated as,
=
Dmax
Vo_ max
=
VDC_ min
n ⋅ VLED_ max + VF�D1
2 ⋅ V�C_ min × (1 − V�i���e )
=
3.3 × � + 1.3
=0.2731
� × 95 × (1-�4.5%)
Turn-off Time
Toff =
Rev. 1.00
1 − Dmax
FPWM_ min
=
1 − 0.�731
=18.173us
40k
13
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Off-time Resistor – RT
A resistor connected to the RT pin determines the off-time which has a variation range from -10% to
+10%. Since the working frequency has a minimum target, the CT is considered to calculated the RT:
Toff = CT×RT → RT ≤
1�.173us
= 413.03kΩ
44�F
Choose 390KΩ and 13KΩ for RT are used
The off time is:
Toff_typ= CT_typ×RT = 40p x 403K = 16.1us
Toff_max= CT_max×RT = 44p x 403K = 17.7us
Toff_min= CT_max×RT = 36p x 403K = 14.5us
The actual minimum frequency can be calculated as:
F
=
PWM_ min
1 − Dmax 1 − 0.�731
=
= 41.17K
Toff_ max
17.7u
FPWM_TYP@Vac_min= 44.3KHz, FPWM_MAX@Vac_min =50.1 KHz
Inductor Design
The ripple current is selected to be 30% of the nominal LED current. If the LED average current
ILED is 400mA, the LED string Voltage = n × VLED, max = 8 × 3.3V where VLED, max is the LED
maximum forward voltage, then the inductor can be calculated by the following formula.
L=
Toff × n × VLED�max
17.7us  8  3.15
=
= 3.717mH
ILED × Ri���e
400mA  0.3
Choose L=3.8 mH
Current Sense Resistor – RCS
This current flows through the external sense resistor RCS and produces a ramp voltage on the CS
pin. The comparators are constantly comparing the CS pin voltage with both the voltage on the LD
pin and the internal 250mV reference voltage. Once the blanking time has elapsed, the output of
these comparators can then reset the flip flop. When one output of these two comparators switches
high, the flip flop is reset and the gate drive output switches low. The gate drive output stays low
until the SR flip flop is set by the oscillator. In assuming a 30% ripple in the inductor, the current
sense resistor RCS can be obtained using the following formula:
=
RCS
0.�5
=
I�eak
0.�5
0.�5
=
= 0.543Ω
(1
+
0.5
×
0.3)
× 400m�
1
1+
× Ri���e ⋅ ILEDavg
�
(
)
Choose RCS = 0.54Ω
Rev. 1.00
14
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Input Supply Current
Assume that the input current drawn by the internal circuit from the VIN pin is the sum of the
current with a value of 1.0mA and the current drawn by the gate driver of the external MOSFET
(which in turn depends upon the switching frequency and the gate charge of the external FET).
Assume that the gate charge Qgate is equal to 12nC.
IINSP =
IIN + Qgate ⋅ FPWM = 1mA + 12nC × 50kHz = 1.6mA
, where IINSP is the input current taken from the VIN pin, FPWM is the switching frequency, Qgate is the
gate charge of the external FET and IIN is the current taken by the internal circuit. FPWM is considered
about the minimum input voltage and CT has a minimum value.
Input Limit Resistor (RIN)
In this design, VAC_min = 95Vrms, VUVLO(H)_max = 17V
Rin =
2 ⋅ VAC_ min × (1 − ∆VDCripple% ) − VUVLO(H)_max
=
IINSP
� × 95 × (1 − 30%) − 17
=62.4kΩ
1.6m�
Choose Rin=60kΩ
The input limit resistor consider the high input voltage from the rectified clamp voltage of the
internal Zener diode and operating current. Two 30KΩ / 1W resistors are used for Rin.
Output Capacitor – CO
The capacitor, CO, filters the current through the LEDs thus limiting the peak current of the LED
string. Increasing the inductor ripple current corresponds to decreasing the inductor value and
inductor size. In order to reduce the inductor value and size and obtain a smaller LED current ripple,
the addition of a capacitor CO is a good way to do this. Usually, a several μF output capacitor is
added in practical application circuits.
Adding CO connected across the LED strings can reduce the LED current ripple and while increasing
the inductor current ripple variation can decrease the inductor value and size.
To assume inductor current ripple is 80%, a smaller inductor value could be calculated.
L=
Toff × n × VLED _ max 17.7us × � × 3.15
=
=1.393mH
ILED × Ri���e
400m� × 0.�
Choose L=1.4mH and CO=1uF
The actual values of CO and RCS may need to be adjusted to reduce the current ripple and obtain
the target average LED current. A 1uF capacitor and an RCS as shown in the above calculation are a
good start point to obtain an acceptable result. Since it takes some effort, it can reduce the inductor
size/cost significantly.
Rev. 1.00
15
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Typical Performance Characteristics
There are many different factors to influence efficiency of the application, such as the output power,
working frequency, power supply circuit of the HT7L4091 and so on. The following are some
measured results.
Efficiency vs. Power Supply Circuit – Working Frequency
There are several different power supply circuits for the device. Reference to the “Application
circuit” for some examples. The different circuits provide different advantages, such as high
efficiency or low cost.
Follow are some efficiency compare for different power supply circuits. The condition
i s VA C = 8 5 VA C ~ 2 6 0 VA C , F P W M > = 5 0 K H z ( H T 7 L 4 0 9 1 w o r k i n g f r e q u e n c y ) ,
output=52Vx0.2A=10.4W. Decreasing FPWM or increasing the output power can enhance the
efficiency.
efficiency compare in different application circuits
(freq,min=50kHz)
92
efficiency (%)
90
88
86
auxiliary circuit
84
82
BJT circuit
80
typical circuit
78
80
130
180
230
280
Vac (V)
The following is an example to enhance the efficiency by reducing the FPWM (HT7L4091 working
frequency) to >=30 KHz.
93
efficiency compare with different frequency in two application
circuits
efficiency (%)
91
89
auxiliary circuit 30kHz
87
BJT circuit 30kHz
auxiliary circuit 50kHz
85
83
BJT circuit 50kHz
81
80
130
180
230
280
Vac (V)
Rev. 1.00
16
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Efficiency for Resistor Only Power and Single Input Voltage
The results of these curves are that each voltage corresponds to each input limit resistor. Theseresults
show how good the application is designed for a narrow voltage range using a resistor to power the
device.
The “LED string” means how many LEDs are in one string. 16S means there are 16 LEDs in one
string.
The output (LED) power is kept at 10W.
Input Voltage vs. Efficiency
95
Efficiency(%)
90
16S LED
14S LED
12S LED
85
80
10S LED
75
8S LED
70
65
80
130
180
230
280
Vac(V)
LED String vs. Efficiency
95
85Vac
110Vac
170Vac
220Vac
260Vac
Efficiency(%)
90
85
80
75
70
65
6
8
10
12
14
16
18
LED String
Input voltage vs. LED Current
LED Current(mA)
450
8S LED
400
350
10S LED
300
12S LED
250
14S LED
16S LED
200
150
80
130
180
230
280
Vac(V)
Rev. 1.00
17
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
LED String vs. LED current
LED current(mA)
450
85Vac
110Vac
170Vac
220Vac
400
350
300
260Vac
250
200
150
6
8
10
12
14
16
18
LED String
Efficiency Using Resistor Only Power and 85~265 VAC Input
These result curves use the same input limit resistor with different voltages. These results show the
performance only using a resistor to power up the device for a full range voltage input. For improved
efficiency with a full range voltage input, refer to the following application circuit.
Input Voltage vs. Efficiency
95
Efficiency(%)
90
85
16S LED
14S LED
12S LED
10S LED
8S LED
80
75
70
65
60
80
130
180
230
280
Vac(V)
LED String vs. Efficiency
95
85Vac
110Vac
170Vac
220Vac
260Vac
Efficiency(%)
90
85
80
75
70
65
60
6
8
10
12
14
16
18
LED String
Rev. 1.00
18
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Input voltage vs. LED Current
LED Current(mA)
460
8S LED
410
360
10S LED
310
12S LED
260
14S LED
16S LED
210
160
80
130
180
230
280
Vac(V)
LED String vs. LED current
LED current(mA)
460
410
360
310
260Vac
220Vac
170Vac
110Va
85Vac
260
210
160
6
8
10
12
14
16
18
LED String
Typical Application Circuit
EMI
Lc
RIN
AC
Ca1
Ca2
C1
Cfilter
22uF
400V
0.1uF
400V
Zin
PDM
RT
CT
5pF
MOSFET
GDR
VDD
C7
CIN
1uF/50V
VIN
LD
0.1uF
VLED
L
Lc
Essential components
Used optional components
Unused optional components
Co
D1
CS
GND
Rc
CC
Rcs
RT
This typical application circuit uses a fundamental buck converter circuit. Adding a CO capacitor
can reduce the LED current ripple or reduce the inductor size while adding the RC and CC
components can reduce spikes on the CS pin.
If frequency jittering is considered to reduce EMI an optional 5pF CT may be used to stabilise the
effect.
Rev. 1.00
19
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Other Application Circuit
No Input Bulk Capacitor Circuit
EMI
Lc
RIN
Ra
AC
Ca1
Ca2
Co
D1
Cfilter
VLED
L
0.1uF
400V
Rb
CIN
Lc
1uF/50V
VIN
LD
Essential components
Used optional components
Unused optional components
0.1uF
C7
MOSFET
GDR
VDD
CS
PDM
RT
CT
5pF
Rc
GND
Rcs
CC
RT
The application circuit is a low cost implementation which can improve the PF used within the
signal input voltage range.
The auxiliary winding application circuit can be chosen when used for a universal input voltage. If
frequency jittering is considered to reduce EMI effects, an optional 5pF capacitor may be added for
stabilisation purposes. Refer to the application notes for more details.
For more details refer to the application note.
High Efficiency Circuit
EMI
Lc
RIN
AC
Ca1
Ca2
C1
Cfilter
22uF
400V
0.1uF
400V
D1
Zin
VLED
Tr
CIN
1uF/50V
Lc
Ra
LD
GDR
VDD
C7
Essential components
Used optional components
Unused optional components
PDM
RT
CT
5pF
Rsb
VIN
Dg
Rg
MOSFET
Rc
CS
GND
Da
Cc
Rs
RT
The application circuit uses the auxiliary inductor to supply the device power to obtain better
efficiency.
If frequency jittering is used to reduce EMI interference effects, an optional 5pF capacitor may be
used for stabilisation purposes. For more details, refer to the application note for auxiliary inductor
applications.
For more details refert to the application note.
Rev. 1.00
20
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
BJT Power Supply Application Circuit
The application circuit uses a BJT to supply the device power to obtain better efficiency.
EMI
Lc
RIN
BJT
AC
Ca1
Ca2
C1
Cfilter CIN
22uF
400V
0.1uF
400V
Co
D1
Zin
1uF
50V
VLED
L
Lc
VIN
LD
0.1uF
C7
PDM
RT
CT
5pF
MOSFET
GDR
VDD
CS
GND
Rc
CC
Rcs
RT
If frequency jittering is considered to reduce EMI an optional 5pF CT may be used to stabilise the
effect.
For more details refer to the application note.
Rev. 1.00
21
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Bill of Materials
AC Input voltage: VAC_typ =110Vrms; VAC_min =95Vrms; VAC_max =115Vrms, FPWM ≥ 40kHz
Output Voltage: LED string Voltage =24~26.4V
Average Output LED Current: ILED= 400mA
R+L+EMI circuit (8S20P)
Components
Value
Package
Part Number
RT
1
390kΩ+ 13kΩ
SMD 0805
—
RCS
1
R300(0.3Ω)+R240(0.24Ω)
SMD 1206
—
C1
1
22uF/ 200V
CapXon Radial
Cfilter
1
0.1uF/ 200V
Radial
—
RIN
1
30kΩ/1W x 2
AXIAL-0.6
—
CIN
1
1uF / 50V
SMD 0805
—
3~3.3V/30mA
Everlight P-LCC-2
L2����������
C���������
-B4556���
AC2CB2
P0260AD
LED
Rev. 1.00
Quantity
160
FK series
MOSFET
1
2A/600V
NIKO-SEM DPAK
C7
1
0.1uF
SMD 0805
DBridge
1
1A/400V
DF-S
DF04S-T
D1
1
2A/600V
SMB
STTH2R06U
U1
1
HT7L4091
NSOP8
HOLTEK
L
1
3.8mH
Coilcraft 335D
CM6676-AL
22
—
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Package Information
8-pin SOP (150mil) Outline Dimensions
●● MS-012
Symbol
Nom.
Max.
A
0.228
―
0.244
B
0.150
―
0.157
C
0.012
―
0.020
C’
0.188
―
0.197
D
―
―
0.069
E
―
0.050
―
F
0.004
―
0.010
G
0.016
―
0.050
H
0.007
―
0.010
α
0°
―
8°
Symbol
Rev. 1.00
Dimensions in inch
Min.
Dimensions in mm
Min.
Nom.
Max.
A
5.79
―
6.20
B
3.81
―
3.99
C
0.30
―
0.51
C’
4.78
―
5.00
D
―
―
1.75
E
―
1.27
―
F
0.10
―
0.25
G
0.41
―
1.27
H
0.18
―
0.25
α
0°
―
8°
23
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Reel Dimensions
●● SOP 8N
Symbol
Rev. 1.00
Description
Dimensions in mm
A
Reel Outer Diameter
330.0±1.0
B
Reel Inner Diameter
100.0±1.5
C
Spindle Hole Diameter
13.0+0.5/-0.2
D
Key Slit Width
T1
Space Between Flange
12.8+0.3/-0.2
T2
Reel Thickness
18.2±0.2
2.0±0.5
24
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Carrier Tape Dimensions
 ●● SOP 8N
Symbol
Rev. 1.00
Description
Dimensions in mm
W
Carrier Tape Width
P
Cavity Pitch
8.0±0.1
E
Perforation Position
1.75±0.1
F
Cavity to Perforation (Width Direction)
5.5±0.1
D
Perforation Diameter
1.55±0.1
D1
Cavity Hole Diameter
1.50+0.25/-0.00
P0
Perforation Pitch
4.0±0.1
P1
Cavity to Perforation (Length Direction)
2.0±0.1
A0
Cavity Length
6.4±0.1
B0
Cavity Width
5.2±0.1
K0
Cavity Depth
2.1±0.1
t
Carrier Tape Thickness
C
Cover Tape Width
12.0+0.3/-0.1
0.30±0.05
9.3±0.1
25
April 28, 2011
HT7L4091
Universal Step-Down PWM Control
For High Brightness LED Lighting Control
Holtek Semiconductor Inc. (Headquarters)
No.3, Creation Rd. II, Science Park, Hsinchu, Taiwan
Tel: 886-3-563-1999
Fax: 886-3-563-1189
http://www.holtek.com.tw
Holtek Semiconductor Inc. (Taipei Sales Office)
4F-2, No. 3-2, YuanQu St., Nankang Software Park, Taipei 115, Taiwan
Tel: 886-2-2655-7070
Fax: 886-2-2655-7373
Fax: 886-2-2655-7383 (International sales hotline)
Holtek Semiconductor Inc. (Shenzhen Sales Office)
5F, Unit A, Productivity Building, No.5 Gaoxin M 2nd Road, Nanshan District, Shenzhen, China 518057
Tel: 86-755-8616-9908, 86-755-8616-9308
Fax: 86-755-8616-9722
Holtek Semiconductor (USA), Inc. (North America Sales Office)
46729 Fremont Blvd., Fremont, CA 94538, USA
Tel: 1-510-252-9880
Fax: 1-510-252-9885
http://www.holtek.com
Copyright© 2011 by HOLTEK SEMICONDUCTOR INC.
The information appearing in this Data Sheet is believed to be accurate at the time of publication. However,
Holtek assumes no responsibility arising from the use of the specifications described. The applications
mentioned herein are used solely for the purpose of illustration and Holtek makes no warranty or
representation that such applications will be suitable without further modification, nor recommends the use
of its products for application that may present a risk to human life due to malfunction or otherwise. Holtek's
products are not authorized for use as critical components in life support devices or systems. Holtek reserves
the right to alter its products without prior notification. For the most up-to-date information, please visit our
web site at http://www.holtek.com.tw.
Rev. 1.00
26
April 28, 2011