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Highly Integrated U Type CCFL Backlight Controller
OB3309
Product Specification
GENERAL DESCRIPTION
OB3309 is a highly integrated and high performance U-type Cold Cathode Fluorescent Lamp (CCFL) controller optimized for LCD display backlight application. Comprehensive protection functions are integrated, thus it provides a cost effective yet high reliability LCD backlight solution. Operating in push pull configuration, OB3309 converts DC input voltage to the pure sinusoidal voltage and current waveforms, to ignite and operate CCFL lamps. It provides a high degree of design flexibility by offering great programmability for key parameters which include operating frequency, striking frequency, striking time, dimming polarity, burst dimming frequency, soft-start time, and soft on/off time for burst dimming. Various dimming modes control and dimming polarity programmability are offered. Both internal burst and external low frequency PWM (LPWM) dimming methods are available for a wide range of dimming control. Analog dimming is also provided through external DC input control to achieve wide dimming range. The highly integrated OB3309 provides complete protection features covering output over voltage, over output current protection, lamp fail safe function, and IC under voltage lockout.
FEATURES
High performance push pull topology Optimized for U type CCFL solution Adjustable dimming polarity
Analog dimming control
Internal burst dimming control
Adjustable minimum duty for internal burst dimming
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The OB3309 is available in SOP-16 Packages.
VIN
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TYPICAL APPLICATION
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LCD Monitor LCD TV
PRT
0-2V DC voltage direct dimming control without external circuits Output over voltage protection (OVP) Output over current protection (OCP) Open lamp protection and short lamp protection Arcing protection
Comprehensive Protection Coverage:
APPLICATIONS
Flat panel display
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Adjustable minimum reference voltage for analog dimming
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External burst (LPWM) dimming control
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DIM
1 2 3 4 5 6 7 8
ENA RI RT DRC BF/DMOD POL VDD GATE1
DIM STIME CMP CS PRT VS GND GATE2
16 15 14 13 12 11 10 9
ENA
On -
PRT VS
+5V
OB3309
GND
Figure1. OB3309 Typical Application Schematic ŠOn-Bright Electronics Confidential -1Preliminary Datasheet OB_DOC_DS_330900
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VS VS
Flexible Dimming mode Control:
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Adjustable striking frequency & time
Highly Integrated U Type CCFL Backlight Control
OB3309
Absolute Maximum Ratings
Parameter VDD Input Voltage to GND CS to GND I/O to GND Operating Ambient Temp. TA Operating Junction Temp. TJ Min/Max Storage Temp. Tstg Lead Temp. (10 Sec) Value 7V -1.5V to VDD+0.3V -0.3V to VDD + 0.3V -20 oC ~ 85oC 150oC -55 oC ~150oC 260 oC
may affect device reliability.
Recommended Operating Range
Parameter VDD Voltage Operating Frequency Value 4.5V to 5.5V 30K to 150KHz
Ordering Information
Part Number OB3309QP OB3309QPA
ratings" may cause permanent damage to the device. These are stress ratings only, functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not implied. Exposure to absolute maximum-rated conditions for extended periods
Package Marking Information
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Preliminary Datasheet OB_DOC_DS_330900
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Note: Stresses beyond those listed under "absolute maximum
Description SOP16, pb-free in tube SOP16, pb-free in T&R
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Parameter Thermal resistance JA (SOP)
Value 85 oC /W
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Package Thermal Characteristics
Highly Integrated U Type CCFL Backlight Control
OB3309
Pin Configuration
Terminal Assignment
Number
1 2 3
ENA RI RT
Input I/O I/O
Enable control input, active high
Connected an external resistor to ground to set striking frequency (No Floating) Connected an external resistor to ground to set operation frequency Dimming range setting. ˇ Connect 0.2V to 2V DC voltage can set minimum burst duty from 100% to 0% for bust dimming; ˇ Connect 0V to 1.25V DC voltage can set minimum Vref_ea from 0V to 1.25V for analog dimming;
5
BF/DMOD
I/O
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6 7 8 9
POL
Input
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VDD
Power Output Output Ground Input Input Input I/O I/O Input
GATE 1 GATE 2
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10 11 12 13 14 15 16
GND VS PRT CS CMP STIME DIM
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DRC
Input
Connected to VDD to set analog dimming mode Connected to GND to set external LPWM dimming mode Connect an external capacitor to GND to set internal burst dimming mode. The burst mode frequency is determined by the external capacitor PWM Dimming polarity selection : ˇ POL<2V: Negative analog / burst mode , positive LPWM dimming ˇ POL>2V: Positive burst mode , negative analog / LPWM dimming +5V Power supply Output drive Output drive
Power ground Lamp voltage feedback Lamp fault detection Lamp current feedback Loop compensation and soft start time setting Connect an external capacitor to GND to set striking time Dimming signal input
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Pin Name
I/O
Pin Function
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Highly Integrated U Type CCFL Backlight Control
OB3309
Functional Block Diagram
Figure2. OB3309 Functional Block Diagram
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Highly Integrated U Type CCFL Backlight Control
OB3309
Electrical Characteristics
VDD=5V, ENA=5V, RT=36Kohm, RI=120Kohm, TA=25, if not otherwise noted. Parameter Current Consumption
Standby current Operating supply current Operating supply current Istandby IVDD IVDD ENA=0V No loading, CMP=5V Cload=2nF, CMP=5V 4.5 5.5 8 6 8
Symbol
Conditions
Min
Typ
Max Units
VDD UVLO
UVLO on UVLO off
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3.6 ON
Enable / Disable
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2.0 0.8 100
ENA (Enable) threshold voltage
High Frequency Oscillator
Operating frequency Striking frequency Max. (overlap) duty cycle FOP FSTK
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OFF RENA
Pull down resistor
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50 65 45
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Low Frequency Oscillator for Burst Mode Dimming
Max. burst duty Min. burst duty 1 (set by DRC)
1
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Burst frequency
CBF/DMOD=22nF CBF/DMOD=22nF, DIM<0.2V POL=0V, CBF/DMOD=22nF, VDRC=VRT, DIM>2V POL=0V, CBF/DMOD=22nF, VDRC=92%VRT , VDRC
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200 100 0 9 0 9
DMAX
Min. burst duty 2 (set by DRC) 1 Min. burst duty 3 (set by DRC) 1 Min. burst duty 4 (set by DRC) 1
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DMIN1 DMIN2 DMIN1 DMIN2
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Analog Dimming Control
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Min. Lamp Current Reference Voltage 1 (set by DRC) 1 Min. Lamp Current Reference Voltage 2 1 (set by DRC) Max. Lamp Current Reference Voltage
Vref_EA_MIN1 Vref_EA_MIN2 Vref_EA_MAX
BF/DMOD=VDD, VDRC=0V , DIM>2V BF/DMOD=VDD, VDRC=25%VRT , DIM>1.28V BF/DMOD=VDD, DIM<0.2V
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0 0.5 1.25
On -
External LPWM Dimming Control
External LPWM duty External LPWM Logic input level high low BF/DMOD=0V BF/DMOD=0V BF/DMOD=0V 0 2.0 0.8 100 % V V
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Preliminary Datasheet OB_DOC_DS_330900
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V 4.4 V V % Hz % % % % % V V V
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uA mA mA Kohm KHz KHz
Highly Integrated U Type CCFL Backlight Control
OB3309
Parameter Error Amplifier
Reference voltage Open loop voltage gain Unity gain bandwidth Soft on current Soft off current
Symbol
Conditions
Min
Typ
Max
Units
Vref_EA
CBF/DMOD=22nF or BF/DMOD=0V CMP=15nF
1.2
1.25 60 350 60 120
1.3
V dB Hz uA uA
Soft start
Soft start current ISST 1.3
Striking time
Striking timer current Striking timer threshold ISTIME1 Vth_STIME1
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1.3 3
Control and Protection Threshold / Debounce time
Ignition completion threshold VS regulate voltage at Striking Threshold voltage for PRT Fault timer currnet Fault timer threshold CS threshold voltage for OLP (open lamp protection) OLP debounce time VS threshold voltage for OVP (over voltage protection) OVP debounce time Normal protection blanking time Dimming_on time for OLP disable Vth_CS Vth_PRT Vth_REG Vth_PRT ISTIME2 Vth_STIME2 Vth_OLP TOLP
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2.05 -
nf
Striking Normal Normal Normal Normal, BF/DMOD=0V or CBF/DMOD=22nF Normal, BF/DMOD=VDD Normal Normal
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0.85 1.25 2.0 1.25 14 3 0.8
60%*Vref_EA 160 2.0 160 0.48 480 ms V ms Sec uS
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Vth_OVP
TOVP T_nom
T_dim_on
Dimming Polarity Control
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Normal Normal Normal, BF/DMOD=0V or CBF/DMOD=22nF
Dimming Polarity Selection
Vth_POL
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RPOL
Negative internal burst mode or positive external PWM dimming Positive internal burst mode or negative external PWM dimming Pull down resistor
45K
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Gate Driver Output
Gate1 Gate2 RON RON Isink/Isource=70mA Isink/Isource=70mA 8 8 12 12 ohm ohm
Note: 1 Detail description to see Figure4 of page 8; For analog dimming mode, Vth_OLP tracks with Vref_EA. Vref_EA can be calculated by the following equation:
2
Vref _ EA =
25 × (2 - VDIM ) for 0.2V VDIM 2V 36
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uA uA V V V V uA V V 2.0 V ohm
ISOFT_ON ISOFT_OFF
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Highly Integrated U Type CCFL Backlight Control
OB3309
Function Description
General Operation OB3309 CCFL controller is designed for U-type CCFL's LCD backlight system applications configured in push pull topology; it converts the DC input voltage to pure sinusoidal waveforms for CCFL operating with high efficiency and low EMI emission. The resonant frequency of the tank is set by the transformer leakage inductance and secondary parallel capacitor. The lamp fault protection functions are integrated to provide a high reliability & simplifier solution with low system cost. Dimming polarity selection can be achieved by setting the voltage level at POL Pin. A typical application scheme is shown in figure 8 on page 10. Enable the Controller OB3309 is activated by applying logic high to the ENA input. It is TTL logic compatible. The controller is enabled when the voltage at ENA pin is higher than 2.0V. Toggling the ENA signal resets the state machine hence restarts the inverter system.
Vstime
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1.5s Striking frequency
3V
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0
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64ms
After the striking time out, the striking frequency will be switched to normal frequency and last for 64ms, if any one of the lamps still can not be lit, OB3309 will enters the shutdown mode as show in Figure 3.
Normal frequency
Figure 3 Striking mode control Soft Start and Soft On/off External capacitor connected to CMP pin provides soft start and soft on/off control. At start up, an internal current source starts to charge the capacitor. Consequently, voltage at CMP pin increases gradually and so as to the pulse width of the PWM Gate signals. This soft start control helps to reduce the MOSFET inrush current and voltage stresses, thus expand the lamp life time. The slope of the soft start V / T can be approximated as:
The normal operation frequency, FOP, is set by the resistor connected to RT pin. It is given by
FSTRIKING (KHz) =
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1800 RT(Kohm) The striking frequency, Fstriking, is set by the resistors connected to both RI and RT pins. It can be calculated by the following equation: FOP (KHz) =
1800 RT//RI(Koh m)
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Normal Operation and Striking Frequency
Lamp Ignition and Striking Voltage Regulation To ignite CCFL, a much higher voltage than that in normal operation is required, especially for aged lamp or in low ambiance temperature. The output voltage is divided by the capacitive voltage divider. A voltage signal is fed into VS pins with diodes and their peaks are compared with internal 2.0V threshold voltage. Consequently, the maximum output voltage is regulated and limited. During ignition, OB3309 monitors the peak voltage levels at CS & PRT pins, it is recognized that all lamps are lit If the peak voltage of CS pin is higher than 0.85V and the voltage level at PRT pin is ŠOn-Bright Electronics
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217 V[V] = T[mS] C CMP [nF] × RT//RI[kohm]
Once lamps are ignited, the capacitor connected to CMP pin performs the loop compensation function. In internal burst mode dimming or external burst (PWM) mode dimming conditions, the voltage ramping up and down at this pin performs a soft on/off control function in each burst cycle. Lamp Current Regulation Lamp current is regulated by the currents feedback loop with an internal transconductance error amplifier. Preliminary Datasheet OB_DOC_DS_330900
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T(sec) = 2.31 × C[uF]
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lower than 1.25V, then the system enters normal operating mode. Otherwise, the duty cycle of the gate drive signal will increase further to deliver more power to ignite the lamp. Once the duty cycle of gate drive signal reaches maxima of 45%, the internal striking timer will be triggered. If the lamps are lit before the time out, OB3309 enters the normal operation mode. Otherwise, it enters the shutdown mode. The striking time is given by:
Highly Integrated U Type CCFL Backlight Control
OB3309
Ilamp ( A) = N *
Where N is the coupling inductance turns ratio, N=NLV/NHV, the inductance T2 ,as shown in figure8. Dimming Control Three commonly used dimming modes, analog mode dimming, internal burst mode dimming and external burst (PWM) dimming functions, are supported without any additional components. Different dimming modes are selected by BF/DMOD pin. The lamp brightness is determined by the control signal at DIM pin. Both in internal burst mode dimming and external PWM mode dimming, the polarity can be set by the voltage level at POL pin as shown in the following table:
Function Analog dimming Internal Burst External LPWM Polarity POL< 2V POL >2V
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Duty =
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Figure. 4 Vref of EA vs DIM voltage Internal burst mode dimming is obtained by connecting a capacitor to BF/DMOD pin. A low frequency triangular waveform generator is formed by the capacitor and internal circuit of IC. The triangular voltage waveform with peak of 2V and valley of 0.2V at this pin is used for the internal low frequency burst PWM generation. Duty cycle so as to lamp brightness is controlled by the analog signal at DIM pin. The burst mode dimming frequency Fburst is set by the following equation:
Negative Negative Positive
Negative Positive
Fburst ( Hz) =
On -
External LPWM burst dimming mode is selected by shorting BF/DMOD pin to ground. OB3309 accepts an external LPWM signal to DIM pin with a swing voltage of 0V to a level greater than 2V. The lamp brightness is controlled by the duty cycle of the LPWM signal. The burst frequency is equal to LPWM frequency.
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Negative
A DC voltage ranging from 0.2V to 2V at DIM pin corresponds to a lamp brightness of approximately 100% to (2 - VDRC ) × 100% , as shown in Figure 5. 1.8
Connecting BF/DMOD pin to VDD selects analog mode dimming. A DC voltage ranging from 0.2V to 2V at DIM pin performs analog mode dimming control. The voltage at DIM pin modulates internal error amplifier reference voltage Vref_EA from 1.25V to VDRC, which corresponds to a lamp current of approximately 100% to (VDRC/1.25)×100%. Vref_EA can be calculated by the following equation:
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(2 - VDIM ) × 100% for 0.2V VDIM VDRC 1.8
Figure. 5 Duty of burst vs DIM voltage (Negative internal burst mode dimming)
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158400 C BF [nF ] × RT[ Kohm]
Preliminary Datasheet OB_DOC_DS_330900
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1.33 2 × Rsense
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The AC lamp currents are sensed by the sense resistors (refer to R24 in figure 8) connected in series with high voltage coupling inductance. The AC voltage across the sense resistors are fed into the CS pins. The peak of the sensed AC voltage is detected. The peak value is compared with an internal reference voltage. The error is amplified that controls the on time of the push pull switches, as a result, the lamp current is regulated. The lamp current can be calculated by the following equation:
Vref _ EA(V ) =
25 × (2 -VDIM ) for 36
0.2V V DIM 2 -
36 × V DRC 25
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The minimum voltage of Vref_EA is determined by the voltage at DRC which should be set in the range from 0V to 1.25V for analog dimming mode.
Highly Integrated U Type CCFL Backlight Control
OB3309
If the voltage of POL is higher than 2.05V, the dimming polarity is changed, and DC voltage from 0.2V to 2V at DIM pin corresponds to the lamp's brightness of approximately minimum duty cycle of burst dimming to 100%, as shown in Figure 6. The minimum duty cycle of burst dimming can be calculated by the following equation:
(VDRC - 0.2) × 100% 1.8
for V DRC > 0.2V for V DRC 0.2V
Figure. 7 Use DRC PIN to set Dimming Range
0%
VDRC (V ) = 2 × RT = R1 + R 2
Lamp Fail Safe Functions
Duty =
(V DIM - V DRC ) ×100% for 0.2V < VDRC < VDIM 2 - V DRC
(Positive internal burst mode dimming)
Function Analog dimming Internal Burst Pin Connection BF/DMOD DIM >4.5V
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0.2V-2V
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Capacitor <0.2V
0.2V-2V PWM
External LPWM
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Figure. 6 Duty of burst vs DIM voltage
Set by customer Set by customer Set by customer
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A DC voltage at DRC pin determines the minimum dimming thus it is used to adjust dimming range for analog mode dimming or internal burst mode dimming. Because the voltage of RT pin is fixed 2V when OB3309 is in operation, the voltage of DRC can be set by RT divided resistors, as shown in Figure 7. (Patent pending)
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The OB3309 provides complete protection features that cover all common lamp fault conditions including: Lamp open or broken Two terminals of lamp are short together High voltage terminal of lamp is short to ground The sensed lamp voltage and current signals, CS, VS and PRT are used to monitor and detect the faults.
During normal operation, if the peak voltage level at CS pin is less than Vth_OLP, the lamp open or lamp broken is recognized and the system will shutdown after 160ms. If the peak voltage level at PRT pin is higher than Vth_PRT, an internal source current (14uA) charges the capacitor which connected STIME pin to ground. Once the voltage at STIME pin reaches 3V, the IC will shut down. But in internal burst mode dimming or external PWM mode dimming, if the dimming_on time is less than 480uS, these two protections are disabled. During normal operation, if VS peak voltage is more than 2.0V, it enters latched shutdown mode.
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R2 R1 + R 2
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Figure8.OB3309 Reference Application Schematic
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Reference Application Circuit for 2U Lamps
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Highly Integrated U Type CCFL Backlight Control
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Preliminary Datasheet OB_DOC_DS_330900
VIN: 10.8-13.2V ADIM: 0V, Max. Brightness; 5V, Min. Brightness (for analog mode dimming) PWM: 0V, Max. Brightness; 5V, Min. Brightness (for internal burst mode dimming) 100%, Max. Brightness; 30%Min. Brightness (for external burst mode dimming) ENA: Disable, 0-0.8V; Enable, 2-5V
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OB3309
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Highly Integrated U Type CCFL Backlight Control
OB3309
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Symbol A A1 A2 b c D E E1 e L
Dimensions In Millimeters Min Max 1.350 1.750 0.100 0.300 1.350 1.550 0.330 0.510 0.170 0.250 9.800 10.400 3.800 4.040 5.800 6.240 1.270 (BSC) 0.400 1.270 0ē 8ē
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Dimensions In Inches Min Max 0.053 0.069 0.004 0.012 0.053 0.061 0.013 0.020 0.007 0.010 0.386 0.409 0.150 0.159 0.228 0.246 0.050 (BSC) 0.016 0.050 0ē 8ē Preliminary Datasheet OB_DOC_DS_330900
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Highly Integrated U Type CCFL Backlight Control
OB3309
Important Notice
Right to make changes On-Bright Electronics Corp. reserves the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. Warranty information On-Bright Electronics Corp. warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with its standard warranty. Testing and other quality control techniques are used to the extent it deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. On-Bright Electronics Corp. assumes no liability for applications assistance or customer product design. Customers are responsible for their products and applications using On-Bright's components, data sheet and application notes. To minimize the risks associated with customer products and applications, customers should provide adequate design and operating safeguards. Life support On-Bright Electronics Corp.'s products are not designed to be used as components in devices intended to support or sustain human life. On-bright Electronics Corp. will not be held liable for any damages or claims resulting from the use of its products in medical applications. Military On-Bright Electronics Corp.'s products are not designed for use in military applications. On-Bright Electronics Corp. will not be held liable for any damages or claims resulting from the use of its products in military applications.
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