Holtek HT7939A Performance white led driver Datasheet

HT7939A
High Current and
Performance White LED Driver
Feature
General Description
• Input voltage range: 2.6V~5.5V
The HT7939A is a high efficiency boost converter
for driving multiple White LEDs using current mode
operation. The device is designed to drive up to 39
White LEDs from a 5V power supply. The White
LED current is setup using an external current setting
resistor, which has a low feedback voltage of 0.2V to
minimise resistor power losses and thus improving
efficiency.
• High efficiency - up to 90%
• Integrated N-ch MOSFET
• Can drive up to 39 WLEDs from a 5V input
• Low standby current: 0.1mA (typ.)
• Built-in OVP, OCP, OTP, UVLO protection
• EN pin dimming frequency up to 200kHz
The HT7939A has a dimming frequency of up to
200kHz, which has excellent linear performance
over this dimming frequency range. The over voltage
function prevents device damage by turning off the
converter should the LED load become open circuit.
The device also includes over current protection, over
temperature protection and under voltage protection
preventing damage to the device should the output be
overloaded.
• 1.2MHz fixed switching frequency
• SOT23-6 package
Applications
• Display backlighting
–– Automatic
–– DVD player
–– Digital photo frame
–– Handheld computer
Selection Guide
Part No.
Package
Marking
HT7939A
SOT23-6
39A-1 (OVP=17.6V)
39A-2 (OVP=32.0V)
Note: Both lead free and green compound devices are available.
Rev. 1.00
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April 19, 2012
HT7939A
Block Diagram
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Pin Assignment
Pin Descriptin
PIN No.
PIN Name
1
SW
2
GND
3
FB
Feedback pin. Reference voltage. The HT7939A feedback voltage is 0.2V.
4
EN
Shutdown & Dimming control input. Do not allow this pin to float.
5
OVP
Over voltage protection pin which is connected to the output.
6
VIN
The input supply pin for the IC. Connect VIN to a supply voltage between 2.6V~5.5V.
Rev. 1.00
Description
Switching pin. Connected to inductor and diode.
Ground.
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April 19, 2012
HT7939A
Absolute Maximum Ratings
Input Voltage, FB Voltage, EN . ........................... 6.0V
Operating Temperature Range ........... -40°C to +85°C
SW Voltage ........................................................... 36V
Storage Temperature Range ............. -55°C to +150°C
OVP Voltage ......................................................... 36V
Maximum Junction Temperature ...................... 150°C
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.
Electrical Characteristics
VIN= 5.0V, Ta= 25°C, unless otherwise specified (note 1)
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
Input Supply Voltage and Current
VIN
Input Voltage
―
2.6
―
5.5
V
UVLO
Under Voltage Lockout
―
1.8
2.1
2.4
V
IIN
Supply Current
Switching
―
1.0
5.0
mA
VEN= 0
―
0.1
1.0
μA
―
190
200
210
mV
VIN= 3.0V~4.3V, ILED= 20mA
―
1.0
―
%
0.8
1.2
1.6
MHz
85
90
―
%
Error Amplifier
VFB
Feedback Voltage
V
Line Regulation
Power Switch
fOSC
Switching Frequency
DC
Maximum Duty Cycle
RDS(ON)
SW ON Resistance
―
―
0.5
―
Ω
ISW(OFF)
Switch Leakage Current
―
―
0.1
1.0
μA
Measured at SW Pin
Enable
VIH
EN Voltage High
―
2.0
―
―
V
VIL
EN Voltage Low
―
―
―
0.8
V
fEN
Dimming Clock Rate
Duty= 5%~100%
100
―
200
kHz
No Load, for 39A-1 Marking
15.8
17.6
19.4
V
No Load, for 39A-2 Marking
28.8
32.0
35.2
V
―
―
1200
―
mA
Thermal Shutdown Threshold
―
―
150
―
°C
Thermal Shutdown Hysteresis
―
―
25
―
°C
OVP and OCP
VOVP
OVP Threshold
IOCP
N-channel MOSFET Current limit
Thermal Shutdown
tSHUT
Note 1. Specifications are production tested at Ta=25 degree. Specifications over -40°C to 85°C degree operating
temperature range are assured by design, characterization.
Rev. 1.00
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April 19, 2012
HT7939A
Functional Description
Application Information
VIN Under-Voltage Lockout -- UVLO
Inductor Selection
The HT7939A contains an Input Under Voltage
Lockout, UVLO, circuit. The purpose of the UVLO
circuit is to ensure that the input voltage is high
enough for reliable operation. When the Input Voltage
is below the UVLO threshold, the internal power
MOSFET will remain switched off .The UVLO
threshold is set below the minimum input voltage
of 2.6V to avoid any transient VIN drops under the
UVLO threshold and causing the converter to turn off.
There are three important electrical parameters that
need to be considered when choosing an inductor.
These are the inductor value, the DCR (parasitic serial
DC resistance) and the saturation current.
The inductor’s value determines the input ripple
current. Lower inductor values decrease the physical
size of the inductor, but increase the input ripple
current. However, larger inductor values decrease the
input ripple current, but have higher series resistances
and lower saturation currents. A good rule to choose
a sutiable inductor value is to allow the peak-topeak ripple current to be approximately 30~50% of
the maximum input current. Calculate the required
inductance value using the following equations:
Current Limit Protection
The HT7939A has a cycle-by-cycle current limit to
protect the internal power MOSFET. If the inductor
current reaches the current limit threshold, the
MOSFET will be turned off. It is important to note
that this current limit will not protect the output from
excessive current during an output short circuit. If
an output short circuit occurs, excessive current can
damage both the inductor and the diode.
Over-Voltage Protection -- OVP
The HT7939A provides an over-voltage function.
If the FB pin is shorted to ground or an LED is
disconnected from the circuit, the FB pin voltage
will be zero and the internal power MOSFET will
switch at its fully duty cycle. This may cause the
output voltage to exceed its maximum voltage
rating, possibly damaging the device and the external
components. Internal over voltage protection circuitry
turns off the power MOSFET and shuts down the
device as soon as the output voltage exceeds the threshold .As a result, the output voltage falls to the
level of the input supply voltage. The device remains
in this shutdown mode until it is enabled once again
to a reset condition by the EN pin or after the power
is restarted.
In the equations above, I OUT(MAX) is the maximum
load current, ∆IL is the peak-to-peak inductor ripple
current, η is the converter efficiency, F SW is the
switching frequency and IL(PEAK) is the peak inductor
current. To prevent inductor core saturation, ensure
that the inductor-saturation current is rated higher
than the peak inductor current. A 10µH inductor value
is recommended for most HT7939A applications.
Over-Temperature protection -- OTP
A thermal shutdown function is implemented to
prevent device damage due to excessive heat and
power dissipation. Typically the thermal shutdown
threshold is 150 °C . When the thermal shutdown
is triggered the device stops switching until the
temperature falls below a typical value of 125°C. After
this the device will once again resume switching.
Rev. 1.00
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April 19, 2012
HT7939A
Input and Output Capacitor Selection
LED Current Selection
The output capacitor determines the steady state
output voltage ripple. The voltage ripple is related
to the capacitor’s capacitance and its ESR which is
the Equivalent Series Resistance. Ceramic capacitors
with low ESR values will result in the lowest ripple
voltage values and are the recommended type. Due
to their low ESR values, the capacitance value can be
calculated using the following equation:
The LED current is controlled by the current sense
feedback resistor R fb, The current sense feedback
reference is 200mV. In order to ensure accurate LED
currents, precision resistors with a 1% tolerance are the
preferred types. The LED current can be calculated
using the following formula:
Where ILED is the output LED current, VFB=feedback
voltage, Rfb=current sense resistor.
In the equation above, Vripple= peak to peak output
ripple, FSW is the switching frequency.
Digital and Analog Dimming Control
The Digital dimming method uses a PWM signal
applied to the EN pin and the EN Pin dimming
frequency up to 200kHz. This is shown in fig.19. The
average LED current increases proportionally with the
PWM signal duty cycle. A 0% duty cycle corresponds
to zero LED current. A 100% duty cycle corresponds
to a full LED current.
The output capacitor is recommended to be in a range
of 1μF to 10μF. The input capacitor is required to be
in a range of 2.2μF to 10.0μF. The output capacitor
affects the loop stability of the boost regulator. If the
output capacitor is lower than this range, the boost
regulator could potentially become unstable.
There are two methods to control the LED brightness
for analog dimming. The first method uses a DC
voltage to control the feedback voltage. If the DC
voltage range is from 0V to 3.3V, the selection of
resistors provided in fig.20 controls the LED current
from 20mA to 0mA. Other applications a filtered
PWM signal, which is shown in fig.21. The filtered
PWM signal application acts the same way as the DC
voltage dimming control.
Schottky Diode Selection
The output rectifier diode supplies current to the
inductor when the internal MOSFET is off. The
average and peak current ratings of the diode must be
greater than the maximum output current and peak
inductor current. The reverse breakdown voltage
must be greater than the maximum output voltage. It
is recommended to use a schottky diode with a low
forward voltage to minimise power dissipation and
therefore to maximise the efficiency of the converter.
A 1N5819 diode type is recommended for HT7939A
applications.
Rev. 1.00
5
April 19, 2012
HT7939A
Typical Performance Characteristics
Fig.4 Efficiency V.S. Input Voltage
Fig.1 HT7939A-1 W-LED Current V.S. Dimming (3S13P)
Fig.5 Feedback Voltage V.S. Input Voltage
Fig.2 HT7939A-1 W-LED Current V.S. Dimming (3S10P)
Fig.6 HT7939A-1 3S10P Dimming=100Hz, D=50%,
Fig.3 HT7939A-2 W-LED Current V.S. Dimming (7S4P)
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
(CH1=VEN Signal, CH2=ILED Current)
Rev. 1.00
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April 19, 2012
HT7939A
Fig.7 HT7939A-1 3S10P Dimming=10kHz, D=50% ,
Fig.10 HT7939A-1 3S10P OVP Waveform VIN=5.0V
VIN = 5.0V, L=22mH, VIN=COUT=2.2mF
L=22mH, CIN=COUT=2.2mF
(CH1=VEN Signal, CH2=ILED Current)
(CH1=Switching Signal, CH2=VOUT)
Fig.8 HT7939A-1 3S10P Dimming=200kHz, D=50%,
Fig.11 HT7939A-1 3S10P Basic Waveform,
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
(CH1=VEN Signal CH2=ILED Current)
(CH1=Switching Signal, CH2=Inductor Current)
Fig.9 HT7939A-1 3S10P Start Up Waveform
Fig.12 HT7939A-2 7S4P Dimming=100Hz, D=50%
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
(CH1=CIN, CH2= VOUT)
Rev. 1.00
(CH1=VEN Signal, CH2=ILED Current)
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April 19, 2012
HT7939A
Fig.13 HT7939A-2 7S4P Dimming=10kHz, D=50%
Fig.16 HT7939A-2 7S4P OVP Waveform,
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
(CH1=VEN Signal, CH2=ILED Current)
(CH1= Switching Signal, CH2= VOUT)
Fig.14 HT7939A-2 7S4P Dimming=200kHz, D=50%,
Fig.17 HT7939A-2 7S4P basic waveform,
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
(CH1=VEN Signal, CH2=ILED Current)
Fig.15 HT7939A-2 7S4P Start Up Waveform,
VIN=5.0V, L=22mH, CIN=COUT=2.2mF
(CH1=CIN, CH2= VOUT)
Rev. 1.00
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April 19, 2012
HT7939A
Application Circuits
L
D1
10mH/22mH
1N5819
VIN
C1
2.2mF
VIN
SW
EN
OVP
GND
FB
VOUT
C2
2.2mF
3S13P
Rfb
1W
HT7939A
Fig.18 Application for Driving 3S13P WLEDs
L
D1
10mH/22mH
1N5819
VIN
C1
2.2mF
PWM Signal
VIN
SW
EN
OVP
GND
FB
VOUT
C2
2.2mF
3S13P
Rfb
1W
HT7939A
Fig.19 Application for Dimming Control Using A PWM Signal
L
D1
10mH/22mH
1N5819
VIN
C1
2.2mF
VIN
SW
EN
OVP
GND
FB
VOUT
C2
2.2mF
3S13P
10kW
Rfb
1W
150kW
HT7939A
0V~3.3V
Fig.20 Application for Dimming Control Using a DC Voltage
L
D1
10mH/22mH
1N5819
VIN
C1
2.2mF
VIN
SW
EN
OVP
GND
FB
VOUT
C2
2.2mF
3S13P
10kW
150kW
HT7939A
PWM Signal
Rfb
1W
0.1mF
Fig.21 Application for Dimming Control Using a Filtered PWM Signal
Rev. 1.00
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April 19, 2012
HT7939A
Package Information
Note that the package information provided here is for consultation purposes only. As this information may be
updated at regular intervals users are reminded to consult the Holtek website (http://www.holtek.com.tw/english/
literature/package.pdf) for the latest version of the package information.
6-pin SOT23–6 Outline Dimensions
Symbol
Dimensions in inch
Min.
Nom.
Max.
0.039
―
0.051
A1
―
―
0.004
A2
0.028
―
0.035
A
b
0.014
―
0.020
C
0.004
―
0.010
D
0.106
―
0.122
E
0.055
―
0.071
e
―
0.075
―
H
0.015
―
0.118
L
0.015
―
―
θ
0°
―
9°
Symbol
Rev. 1.00
Dimensions in mm
Min.
Nom.
A
1.00
―
Max.
1.30
A1
―
―
0.10
A2
0.70
―
0.90
b
0.35
―
0.50
C
0.10
―
0.25
D
2.70
―
3.10
E
1.40
―
1.80
e
―
1.90
―
H
2.60
―
3.00
L
0.37
―
―
θ
0°
―
9°
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April 19, 2012
HT7939A
Reel Dimensions
SOT23–6
Symbol
Rev. 1.00
Description
Dimensions in mm
A
Reel Outer Diameter
178.0+1.0
B
Reel Inner Diameter
62.0+1.0
C
Spindle Hole Diamete
13.0+0.2
D
Key Slit Width
2.50+0.25
T1
Space Between Flange
8.4 +1.5/-0.0
T2
Reel Thickness
11.4 +1.5/-0.0
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April 19, 2012
HT7939A
Carrier Tape Dimensions
SOT23–6
Symbol
Rev. 1.00
Description
Dimensions in mm
W
Carrier Tape Width
8.0+0.3
P
Cavity Pitch
4.0+0.1
E
Perforation Position
1.75+0.10
F
Cavity to Perforation (Width Direction)
0.50+0.05
D
Perforation Diameter
1.5 +0.1/-0.0
D1
Cavity Hole Diameter
1.5 +0.1/-0.0
P0
Perforation Pitch
P1
Cavity to Perforation (Length Direction)
2.00+0.05
A0
Cavity Length
3.15+0.10
B0
Cavity Width
3.2+0.1
K0
Cavity Depth
1.4+0.1
4.0+0.1
t
Carrier Tape Thickness
C
Cover Tape Width
0.20+0.03
5.3+0.1
12
April 19, 2012
HT7939A
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© 2012 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
13
April 19, 2012
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