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CCFL Backlighting Inverter
Solution
Golden Road Electronic Technology Co., Ltd.
E1, 24F Zhao Feng Universe Building NO. 1800 Shanghai PRC
WEB: www.goldenroad.com.cn
TEL: 021-64401740 64401741 64401742 64401743
FAX: 021-64401629 64403212
Designed By: Colin (FAE)
E-mail: [email protected]
[email protected]
Golden Road Electronic Co., Ltd.
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Rohm CCFL Control IC presentation
High Performance PWM Controller
Half Bridge Topologies for 1 lamp BD9883FV
Half Bridge Topologies for 4 lamp or above BD9884FV
Golden Road Electronic Co., Ltd.
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1 Lamp Solution
LCD BACKLIGHT INVERTER DRIVE IC BD9883FV
Features:
High Efficiency Single Stage Power Conversion
Half Bridge Topology And Reduce External Component
Wide Input Voltage Rang From 6V To 30V
Lamp Current and Voltage Feedback Control
Soft Start Control & Dead Time Control
Short Circuit Protection With Timer Latch
Under Voltage Lock Out
Analog And Burst Dimming Control
PWM Control at Fixed Frequency
ON / OFF Control
SSOP-20 Package
Golden Road Electronic Co., Ltd.
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1 Descriptions
Designs for a CCFL inverter used in notebook or portable DVD player
applications include small size, high efficiency and low cost. The BD9883FV
provide the necessary function blocks to implement a highly efficient CCFL
backlight inverter in a small footprint 20 SSOP package. It typically consumes
less than 9mA of operating current, improving overall system efficiency.
External components count is minimized and system cost is reduced by
integration such features as a feedback controlled PWM driver stage, the soft
start, the lamp voltage and current feedback, the UVLO, The short circuit
protection. It includes a shunt regulator, allowing it to operate with wide input
voltage from 6.0~22V, supporting analog and burst dimming modes of
operation. Standby function also reduces power dissipation.
The BD9883FV also provide lamp current and voltage sense feedback
control circuit which it can protect the transformer from over voltage during
start up or when an open lamp occurs. The transformer voltage is regulated
with reducing duty circle when an over voltage is detected. The latter can be
used to shut IC down when an open lamp condition continue more than a
specific time.
Golden Road Electronic Co., Ltd.
2 Schematic Diagram:
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Golden Road Electronic Co., Ltd.
PIN Definition
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PIN NO.
PIN NAME
FUNCTION
1
DUTY
Control PWM and BURST Mode
2
BCT
External capacitor from BCT to GND for adjusting the
BURST Triangle Oscillator
3
BRT
External resistor from BRT to GND for adjusting the
BURST Triangle Oscillator
4
CT
External capacitor from CT to GND for adjusting the
Triangle Oscillator
5
RT
External resistor from RT to GND for adjusting the
Triangle Oscillator
6
SRT
External resistor from SRT to RT for adjusting the
Triangle Oscillator
7
GND
GROUND
8
FB
Feed Back Output
Golden Road Electronic Co., Ltd.
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PIN NO.
PIN NAME
FUNCTION
9
IS
I sense Detect
10
VS
V sense Detect
11
STB
Stand-by Switch
12
SCP
Timer latch setting
13
SS
Soft Start Control
14
PGND
Ground for MOS-FET Drivers
15
LN
N MOS-FET Driver
16
HN
N MOS-FET Driver
17
SW
Low Voltage for HN Output
18
BST
Boost-Strap Input for HN Output
19
REG
Voltage Reference Output
20
VCC
Power Supply
Golden Road Electronic Co., Ltd.
3 Basic operation
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3.1 DUTY
Lamp intensity is controlled with the signal DUTY. There would
be two kinds of dimming modes as below:
Analog dimming
Lamp intensity decrease from 100% to 0% when the DC voltage
between 2.0V and 0.5V on DUTY pin. When voltage more than 2V
on DUTY commands full brightness.
BURST dimming
Lamp intensity is controlled with signal DUTY. 2V on DUTY
commands full brightness. The duty cycle of the burst dimming
comparator determines the lamp brightness as a percent of rated
lamp current.
Golden Road Electronic Co., Ltd.
3.2 BURST Oscillator
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Timing capacitor BCT is charged by the reference current source, and
formed by the timing resistor BRT whose voltage is regulated at 1.25V. The
saw-tooth waveform charges up to 2.0V, once reached, capacitors begin
discharging down to 0.5V. Next timing capacitors start charging again and a
new switching cycle begins.
BRT would be recommended between 10 and 500k Ohm and BCT is
from 0.001uF to 0.2uF.
3.3 Main Oscillator
Timing capacitor CT is charged by the reference current source, formed
by the timing resistor RT whose voltage is regulated at 1.25V. The saw-tooth
waveform charges up to 2.0V, once reached, capacitors begin discharging
down to 0.5V. Next timing capacitors start charging again and a new
switching cycle begins.
RT would be recommended between 10 and 150k Ohm and BCT is from
100pF to 1000pF.
Golden Road Electronic Co., Ltd.
3.4 SRT pin
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Operating Frequency setting pin use an External resistor from SRT
to RT for which adjusting the triangle oscillator. If you want to change
the operating frequency when an open lamp occurs, please keep it
unconnected. Otherwise, please connect a resistor between 80k to 500k
Ohm to RT.
3.5 Control loop feedback
This block includes lamp voltage loop and lamp current loop. The
lamp voltage loop is consist of voltage detect pin Vs and the error
output, The lamp current sense loop has little difference from the
voltage one, both the lamp voltage and the current lamp are the most
important feedback circuit of the IC. PWM output cycle is determined by
FB, both Is and Vs are compared with the VREF, the output (FB) will
compared with CT, then determine PWM output.
Golden Road Electronic Co., Ltd.
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The lamp current loop:
Current feedback input pin detect the lamp current through a half
rectifier circuit and a resistor, output compared with VREF (1.25V)which it
is using an internal error amplifier to adjusting the PWM duty. In this loop,
please must keep Is more than 0.4V, or the SRT will turn to LOW, SCP
start to work, IC power off. FB will turn low when Is is high which is
forced by an external signal.
The lamp current loop gain will be determined by the reactive
circuit which it is using a capacitor, connect to the error output for
limiting loop gain and increase the frequency action. The capacitor
between Is and FB range is from 1500pF to 10000pF.
Golden Road Electronic Co., Ltd.
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The lamp voltage loop:
Lamp current feedback input pin detect the lamp current through a
half rectifier circuit and a resistor, output compared with VREF
(1.25V)which it is using an internal error amplifier to adjusting the PWM
duty. In this loop, more than 1.25V on Vs will make the overall system into
protect stage. So please keep the voltage on Vs between 0.5v and 1V.
The lamp voltage loop gain will be determined by the reactive
circuit which it is using a capacitor, connect to the error output for
limiting loop gain and increase the frequency action. The capacitor
between Vs and FB range is from 1000pF to 4700pF.
Golden Road Electronic Co., Ltd.
3.6 Soft Start
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The soft start function is provided that SS pin is connected
through a capacitor to GND, a soft start circuit ensures a
gradual increase in the input and output power. The
capacitor connected to SS pin determines the rate of rise the
duty ratio. It is charged by a current source of 1uA.
3.7 UVLO Under voltage lockout
The under voltage lockout circuit guarantees stable
operation of the IC’s control circuit by stopping and starting
it as a function of the VIN value. The UVLO circuit turns on
the control circuit when VIN exceeds 5.4V. When it is lower
than 5.4V, the IC’s standby current is less than 10uA.
Golden Road Electronic Co., Ltd.
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3.8 STB
Applying the higher voltage than 2V to STB pin enables
the operation of the IC. Applying to the voltage than 0.7V to
STB pin will disable the operation of the inverter.
3.9 SCP
The short circuit protection function is to protect the overall
system it is shorted. The capacitor connected to SCP pin
determines the rate of the timer from system beginning to
end when there is a short in output occurs. It is charged by a
current source of 0.5uA.
Golden Road Electronic Co., Ltd.
Notes:
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CBD
Golden Road Electronic Co., Ltd.
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CBD
Golden Road Electronic Co., Ltd.
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CBD
Golden Road Electronic Co., Ltd.
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CBD
Golden Road Electronic Co., Ltd.