HT7963 LED Backlight Driver

HT7963
LED Backlight Driver
Features
General Description
• Integrated high power boost DC-DC controller
The HT7963 is a high efficiency boost converter with
a fixed oscillator frequency for LED backlighting and
LED lighting application. The white LED current is
setup using an external current setting resistor, which
has a low feed-back voltage of only 0.3V. The DIM
input allows a wide range of dimming control for LED
backlighting or LED lighting. The device offers a full
range of protection functions such as power MOSFET
over current protection (OCP), IC power supply under
voltage lockout (UVLO), over-voltage protection
(OVP), output voltage short circuit protection (OSP)
and over temperature protection (OTP).
• Wide input voltage range from 9V to 30V
• High Voltage Gate-Drive provides lower RDS(ON)
and higher efficiencies
• Dimming frequency from 100Hz to 1kHz
• 0.3V LED feedback current sensing voltage with
±3% tolerance
• Device protection features include:
Soft-start, OCP, UVLO, OVP, OTP and output
short protection – OSP
• LED protection: LED Open/Short Protection
• Package type: 8-pin SOP
Applications
• LED Backlighting for LCD TV/Monitor
• LED lighting
Typical Application Circuit
D1
L
VIN = 12V~24V
VOUT
47uH
CIN
220uF
COUT
51Ω
47uF
R1
10kΩ
PWM
RC
47KΩ
1
VIN
8
DIM
6
COMP
3
GND
HT7963
DRV
2
CS
4
OVP
7
FB
5
0.1uF
RCS
10pF
R2
optional
100Ω
ILED=
0.3V
RFB
optional
100Ω
RFB
CC
33nF
CFB
470pF
Note: The VOUT/VIN ratio is suggested to be lower than 5 to gain better dimming linearity.
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HT7963
Block Diagram
VIN
OTP
UVLO
6V/8.5V
VIN
VREF
Pre-Driver
OSC
1.938V
DRV
PWM
Comparator
OVP
clamped
to 13V
Control
Logic
OVP
GND
OSP
OCP
OVP
IDIM
OSP
0.1V
UVLO
LED Short
Slope
Compensation
Dimming
Control
DIM
LEB
OCP
IDIM
CS
0.5V
FB
GND
EA
COMP
1.2V
0.3V
Soft-start
GND
LED Short
Pin Assignment
VIN
1
8
DIM
DRV
GND
2
7
OVP
3
6
CS
4
5
COMP
FB
HT7963
8 SOP-A
Pin Description
Pin Order
Name
Type
1
VIN
P
Power Supply
Pin Discription
2
DRV
O
Boost Converter Gate Drive Output
3
GND
G
Ground Terminal
4
CS
I
Boost Converter Current Sense Input
5
FB
I
LED Current Feedback Input
6
COMP
I/O
7
OVP
I
Over Voltage Protection Input – setup using resistor divider
8
DIM
I
External PWM Dimming Control / Enable Control
Boost Converter Loop Compensation
Absolute Maximum Ratings
Parameter
VIN, DRV, CS, FB and OVP
GND
Value
Unit
-0.3 to 33
V
+/-0.3
V
DIM and COMP
-0.3 to +7.0
V
Operating Temperature Range
-40 to +85
°C
+160
°C
Maximum Junction Temperature
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HT7963
Recommended Operating Range
Parameter
Value
Unit
VIN
9~30
V
CS, OVP and FB
≤30
V
DRV (Internal Voltage Clamped)
13
V
DIM and COMP
0~5.5
V
Dimming Frequency
DC to 1000
Hz
Dimming Duty Cycle
1 to 100
%
≤125
°C
Operating Junction Temperature
Note that Absolute Maximum Ratings indicate limitations beyond which damage to the device may occur.
Recommended Operating Ratings indicate conditions for which the device is intended to be functional, but do not
guarantee specified performance limits.
Electrical Characteristics
Symbol
VIN=12V and Ta=25˚C, unless otherwise specified
Parameter
Test Condition
Min.
Typ.
Max.
Unit
Supply Voltage
VIN
Input Voltage
VIN
9
—
30
V
ICC1
Operating Current
DIM=5V
—
2.5
3
mA
ICC2
Standby Current
DIM=0V
—
500
650
μA
ISHD
Shutdown Current
DIM=0V, over 50ms
—
35
50
μA
VDIM_LH
DIM High Threshold
VIN=9V to 30V
—
—
2.4
V
VDIM_HL
DIM Low Threshold
VIN=9V to 30V
0.6
—
—
V
RPD_DIM
DIM Internal Pull Down Resistance
—
—
500
—
kΩ
fDIM
Dimming Frequency
DIM pin
100
—
1000
Hz
fDUTY
Dimming Duty Cycle
DIM pin
0
—
100
%
TSHD
Shutdown Mode Entry Period
DIM=0V (Figure1)
—
50
—
ms
TRT
Recovery Time from Shutdown Mode
DIM from "L" to "H" (Figure1)
—
30
—
ms
Dimming
Boost Converter
fSW
Switching Frequency
—
175
200
225
kHz
DMAX
Maximum Duty Cycle
—
—
95
97.5
%
VDRV(CLAMP) DRV Clamp Voltage
VIN=24V
—
13
14.5
V
tr_DRV
DRV Rise Time
C=0.5nF
—
40
—
ns
tf_DRV
DRV Falling Time
C=0.5nF
—
20
—
ns
tLEB
LEB Time of Current Sense
Lead-Edge Blanking
—
200
—
ns
—
200
—
mV/ms
Protections
SRSS
Soft Start Slope
SS
VOVP
Output Over Voltage Detect Threshold
VOVP
ERROVP
Tolerance of VOVP
VUVLO+
Input Supply Turn ON Level
VUVLO–
Input Supply Turn OFF Level
VOSP
Output Short Circuit Threshold
OSP
VOCP
Over Current Protection Threshold
VSHORT
LED Short Protection Threshold
—
1.938
—
V
-5.0
—
+5.0
%
UVLO (on)
—
—
8.5
V
UVLO (off)
6
—
—
V
0.05
0.1
—
V
OCP, V(CS)
—
0.5
0.65
V
LED Short, V(FB)
—
1.2
1.56
V
—
70
—
mV
—
150
—
°C
—
VSHORT_HYS LED Short Protection Hysteresis
THSHD
Rev. 1.00
Thermal Shutdown
—
OTP
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HT7963
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
—
—
30
—
°C
—
0.3
—
V
—
-3.0
—
+3.0
%
THSHD_HYS Hysteretic Temperature
LED Output Current
VFB
Current Feedback Sensing Voltage
ERRFB
Tolerance of VFB
DIM
VFB
50ms, TSHD
Shutdowm mode
30ms
TRT
IOUT
Figure1
Functional Description
Current Limiting
The device has a cycle-by-cycle current limit to protect
the external power MOSFET. If the inductor current
reaches the current limit threshold, which is when
the CS pin voltage is greater than 0.5V, the external
MOSFET will be switched off. The Rcs value can be
calculated from the following formula:
General Operation
The device is an LED driver operating as a DCDC boost converter in a constant frequency mode.
It implements a peak current mode control and has
an internal amplifier to accurately control the output
current over conditions of wide input voltage and
varying load.
ILIMIT =
Soft Start – SS
Dimming Control
The device has dedicated protection circuitry running
during normal operation. The Soft Start function is
set to have an internal time of around 5ms and is used
to prevent a large inrush current during the power-on
period.
The LED brightness control is implemented using a
PWM signal on the DIM pin. The PWM duty cycle
is proportional to the dimming value. The device
can apply an external PWM signal on the DIM pin
with a frequency range from 100Hz to 1kHz with the
required high/low ratio.
Output Gate Drive Stage
Output Over Voltage Protection – OVP
A CMOS buffer output stage is included to drive
a power MOSFET directly. The output voltage is
clamped at 13V to protect the MOSFET gate even
when the VCC voltage is higher than 13V.
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over-voltage protection function. In abnormal conditions, the output voltage may
exceed its maximum voltage rating, possibly damaging external components and the LEDs. Protection
circuitry turns off the power MOSFET and shuts
down the device as soon as the output voltage exceeds
the VOVP threshold. As a result, the output voltage falls
to the level of the input supply voltage. The device
remains in ����������������������������������������
the ������������������������������������
shutdown mode until the power is recycled. The VOUT_OVP value can be calculated from the
following formula:
Input Under Voltage Lockout – UVLO
The device contains an input under-voltage lockout
circuit. The purpose of the UVLO circuit is to ensure
that the input voltage is high enough for reliable operation. When the input voltage falls below the under
voltage threshold, the external FET switch is switched
off. If the input voltage rises ����������������������
beyond����������������
the under voltage lockout hysteresis value, the device will restart.
The UVLO threshold is set below the minimum input
voltage of 6V to avoid any transient VIN drops under
the UVLO threshold which may cause the converter
to switch off.
Rev. 1.00
0.5V
RCS
VOUT_OVP = 1.938V ×
R1+R2
R2
Output Short Protection – OSP
An output short condition is detected by the voltage
on pin OVP. In the period during the fault, if the
voltage on the OVP pin drops by less than a threshold
of around 0.1V, then the output short protection will
be activated and the power MOSFET will be switched
off.
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HT7963
Thermal Shutdown
MOSFET
A thermal shutdown function is implemented to
prevent 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 temperature of 125°C, after which the
device will again begin operation.
Component Selection Guide
It is recommended to use a MOSFET with small on
resistance to minimi�����������������������������������
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e the power�����������������������
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dissipation and therefore to maximise the converter efficiency. MOSFETs
with small gate capacitance values need to be selected
to have high-speed switching. The maximum voltage
rating of the MOSFET should be higher than the sum
of VOUT and the rectifying diode VF. The maximum
current rating must be greater than the over current
protection setting and peak inductor current to ensure
the best reliability in most applications.
Inductor
Input Capacitor
The selected inductor should have a saturation
current that meets the maximum peak current of the
converter. Another important inductor parameter is
the dc resistance. Lower dc resistance values results in
higher converter efficiencies. For most applications,
the inductor value can be obtained as below.
A low ESR ceramic capacitor is required to be
connected between the VIN and GND pins. Use
ceramic capacitors with X5R or X7R dielectrics for
their low ESRs and small temperature coefficients.
This capacitor must be connected very close to the
VIN pin and the inductor with short traces for good
noise performance.
L=
VIN × (VOUT - VIN)
∆IL × fSW × VOUT
Output Capacitor
A higher value of ripple current reduces the inductance value, but increases the conductance loss, core
loss and current stress for the inductor and switching
devices. A suggested choice is for the inductor ripple
current to be 30% of the maximum load current. This
requires that the inductor saturation current be above
IL(PEAK) .
IIN(MAX) =
A low ESR ceramic capacitor is suggested for use
here as it will result in lower output ripple voltages.
The selection of output capacitor is driven by the
maximum allowable output voltage ripple. A ceramic
capacitor with a low ESR value will provide the
lowest voltage ripple and is therefore recommended. A
capacitance in the range of 33μF to 47μF is sufficient.
Capacitor voltage ratings needs to be selected to have
an adequate margin against the highest output voltage.
VOUT × IOUT(MAX)
VIN × η
∆IL = 30% × IIN(MAX)
LED Current Selection
1
IL(PEAK) = IIN(MAX) + ∆IL
2
The LED current is controlled by the current sense
feedback resistor RFB, The current sense feedback reference voltage (VFB)����������������������������������
is ������������������������������
0.3���������������������������
V. In order to ������������
obtain������
accurate LED currents, precision resistors are the preferred
type with a 1% tolerance. The LED current (ILED) can
be calculated from the following formula.
IOUT(MAX) is the maximum load current, ΔIL is the peakto-peak inductor ripple current, η is the converter efficiency, fSW is the switching frequency and IL(PEAK) is
the peak inductor current.
Schottky Diode
ILED =
It is recommended to use a Schottky diode with low
forward voltage to minimise the power dissipation
and therefore to maximise the converter efficiency.
The breakdown voltage rating of the diode should be
higher than the maximum output voltage. The average
and peak current rating must be greater than the
maximum output current and peak inductor current to
ensure the best reliability in most applications.
Rev. 1.00
VFB 0.3V
=
RFB RFB
CS Pin and FB Pin RC Filter
Whether an RC low pass filer is employed or
not depends upon the design layout and must be
considered on a case-by-case basis.
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HT7963
Layout Considerations
Circuit board layout is a very important consideration for switching regulators if they are to function properly.
Poor circuit layout may result in related noise problems. In order to minimise EMI and switching noise, the
following guidelines should be adhered to:
• All tracks should be as wide as possible
• The input and output capacitors, CIN and COUT, should be placed close to the VIN, VOUT and GND pins
• The Schottky diode, D1, and inductor, L, must be placed close to the power MOSFET drain
• Feedback resistor, RFB, must be placed close to the FB and GND pins
• A full ground plane is always helpful for better EMI performance
A recommended PCB layout with component locations is shown below.
57mm
35mm
Top Layer
Rev. 1.00
Bottom Layer
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HT7963
Typical Performance Characteristics
Fig.2 Feedback Voltage VS Temperature
Fig.5 Frequency VS Temperature
Fig.3 CS Protection Voltage VS Temperature
Fig.6 Operating Current VS Temperature
Fig.4 FB Protection Voltage VS Temperature
Fig.7 OVP Protection Voltage VS Temperature
Rev. 1.00
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HT7963
Dimming Linearity
Fig.8 VIN=12V, LED=16S5P, VOUT=44.5V, IOUT=453mA,
Fig.9 VIN=12V, LED=16S5P, VOUT=45.8V, IOUT=719mA,
COUT=47μF, POUT=20W (Ta=25°C)
COUT=47μF, POUT=33W (Ta=25°C)
Fig.10 VIN=24V, LED=30S5P, VOUT=81.5V, IOUT=245mA,
Fig.11 VIN=24V, LED=30S5P, VOUT=84.3V, IOUT=602mA,
COUT=47μF, POUT=20W (Ta=25°C)
COUT=47μF, POUT=50W (Ta=25°C)
Fig.12 VIN=30V, LED=40S5P, VOUT=106.8V,
Fig.13 VIN=30V, LED=40S5P, VOUT=110.5V,
IOUT=188mA, COUT=47μF, POUT=20W (Ta=25°C)
IOUT=451mA, COUT=47μF, POUT=50W (Ta=25°C)
Rev. 1.00
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August 14, 2015
HT7963
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 for the latest version of the package
information.
Additional supplementary information with regard to packaging is listed below. Click on the relevant section to be
transferred to the relevant website page.
• Further Package Information (include Outline Dimensions, Product Tape and Reel Specifications)
• Packing Meterials Information
• Carton information
Rev. 1.00
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HT7963
8-pin SOP (150mil) Outline Dimensions
Symbol
A
Dimensions in inch
Min.
Nom.
Max.
—
0.236 BSC
—
B
—
0.154 BSC
—
C
0.012
—
0.020
C'
—
0.193 BSC
—
D
—
—
0.069
E
—
0.050 BSC
—
F
0.004
—
0.010
G
0.016
—
0.050
H
0.004
—
0.010
α
0°
—
8°
Symbol
Rev. 1.00
Dimensions in mm
Min.
Nom.
Max.
A
—
6.00 BSC
—
B
—
3.90 BSC
—
C
0.31
—
0.51
C'
—
4.90 BSC
—
D
—
—
1.75
E
—
1.27 BSC
—
F
0.10
—
0.25
G
0.40
—
1.27
H
0.10
—
0.25
α
0°
—
8°
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August 14, 2015
HT7963
Copyright© 2015 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
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