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OB3350 PDF 데이터시트 ( Data , Function )

부품번호 OB3350 기능
기능 Cost Effective LED Controller
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OB3350 데이터시트, 핀배열, 회로
OB3350
Cost Effective LED Controller
GENERAL DESCRIPTION
OB3350 is a highly integrated and cost effective
Light Emitting Diode (LED) driver optimized for
LCD monitor and LCD TV backlighting application.
It provides a high performance LED backlight
solution with minimized BOM count.
The OB3350 contains a PWM boost driver which
uses current mode control and fixed frequency
operation to regulate the LED current. The LED
current is sensed through an external current
sense resistor. The voltage across the sensing
resistor is compared with reference level of 300mV,
the error is amplified to control the pulse width of
the power switch thus to regulate the current
flowing the LED.
The OB3350 offers external low frequency PWM
(LPWM) dimming method for a wide range of
dimming control.
The OB3350 offers comprehensive protection
such as power MOSFET over current protection
(OCP), output over voltage protection (OVP), IC
power supply under voltage lockout (UVLO), and
LED open protection.
FEATURES
Current Mode PWM Controller With Good
Dynamic Response
8V to 35V Input Voltage Range
External PWM Dimming Mode
Over Voltage Protection
Over Current Protection
Under Voltage Lockout (UVLO)
Thermal Shutdown
APPLICATIONS
LCD Monitor
LCD TV
Flat panel display
The OB3350 is offered in SOP-8 Packages.
TYPICAL APPLICATION
Figure1. OB3350 Typical Application Schematic
©On-Bright Electronics
Confidential
-1-
Preliminary datasheet
OB_DOC_DS_335000
Free Datasheet http://www.datasheetlist.com/




OB3350 pdf, 반도체, 판매, 대치품
Functional Block Diagram
OB3350
Cost Effective LED Controller
COMP
FB
CS
DIM
OSC
UVLO
Ramp
Adjust
Thermal
Shutdown
5V Reference
Soft-start
EA
Sense
Amplifer
S PW
M
PWM
Comparator
Vth_ovp
Control
Logic
Gate
Drive
DIM
Control
OVP
Figure2. OB3350 Functional Block Diagram
VIN
GATE
PWM
GND
©On-Bright Electronics
Confidential
-4-
Preliminary datasheet
OB_DOC_DS_335000
Free Datasheet http://www.datasheetlist.com/

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OB3350 전자부품, 판매, 대치품
OB3350
Cost Effective LED Controller
the slope which representing inductor current ramp
up until the comp signal is reached, then ramp
down. If the duty > 50%, any distribution won’t be
converged from duty to duty and thus
sub-harmonic oscillation happens. For the
equation below:
I (n 1)
Sf
Sn
Se
Se
I (n)
To avoid sub-harmonic oscillation happening, just
make sure (Sf-Se) / (Sn+Se) smaller than 1.
For boost applications, the slopes Se, Sf and Sn
can be calculated with the formulas below and a
typical value of VSL is 50mV.
Se VSL f s
S f Rsen Vout Vin / L
S n Rsen Vin / L
When Se increases then the factor which can
determine whether the sub-harmonic oscillation
will occur decreases. When the duty cycle is
greater than 50% and the inductance becomes
less, the factor increases. And for more flexibility
slope compensation amplitude can be increased
by adding one external resistor, RSL, in the CS
path. Figure 4 shows the setup. The externally
generated slope compensation is then added to
the internal slope compensation of the OB3350.
When using external slope compensation, the
formula for Se becomes:
Se (VSL I s RSL ) f s
A typical value of Is is 40uA.
Dimming Control
The LED brightness is controlled by the PWM
signal at PWM pin which has different duty cycle.
OB3350 can accept an external PWM signal to
PWM pin in the range of 100Hz to 1 KHz with a
swing voltage of 0V to a level greater than 2.5V.
OVP Protection
OB3350 shuts down the output if the output
voltage is higher than the predetermined threshold
level. In case of LED failing, the current of LED
and the resulted voltage drop on sensing resistor
is nearly zero; the converter will run at maximum
duty cycle that boosts the output voltage to a very
high level. To prevent this happen, the output
voltage is monitored through Pin OVP and
converter is shut down if the output voltage
exceeds the predetermined level. This protection
is latched and OB3350 can be reset from VIN or
PWM.
VOUT SHORT Protection
VOUT short condition is monitored by the voltage
at pins OVP. During normal operation, when the
voltage at OVP pin drops below a threshold of
approximately 0.2V, the VOUT-short protection
function is activated and the GATE is turned off.
This state is latched and can be reset from VIN or
PWM.
Thermal Shutdown
The OB3350 includes a thermal protection circuit.
When the junction temperature exceeds 160°C
(typical), the controller and current sources shut
down and do not restart until the junction
temperature drops below 140°C (typical).
Figure5 Adding external slope compensation to OB3350
It’s good design practice to only add as much
slope compensation as needed to avoid
sub-harmonic oscillation. Additional slope
compensation minimized the influence of the
sensed current in the control loop. With very large
slope compensation the control loop
characteristics are similar to a voltage mode
regulator which compares the error voltage to a
saw tooth waveform rather than the inductor
current.
©On-Bright Electronics
Confidential
-7-
Preliminary datasheet
OB_DOC_DS_335000
Free Datasheet http://www.datasheetlist.com/

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OB3350

Cost Effective LED Controller

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