CCFL CONTROL IC PRESENTATION

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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 colin.wang_at_goldenroad.com.cn
jason.mai_at_goldenroad.com.cn
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
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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
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• 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 6.022V, 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.

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2 Schematic Diagram
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PIN Definition
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• Basic operation
• 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.

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3.2 BURST Oscillator
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.
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3.4 SRT pin 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.
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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.
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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.
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3.6 Soft Start 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 ICs
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 ICs standby
current is less than 10uA.
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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.
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Notes CBD
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CBD
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CBD
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CBD
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