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OB3350 の電気的特性と機能

OB3350のメーカーはOn-Brightです、この部品の機能は「Cost Effective LED Controller」です。


製品の詳細 ( Datasheet PDF )

部品番号 OB3350
部品説明 Cost Effective LED Controller
メーカ On-Bright
ロゴ On-Bright ロゴ 




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OB3350 Datasheet, OB3350 PDF,ピン配置, 機能
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/

1 Page





OB3350 pdf, ピン配列
OB3350
Cost Effective LED Controller
Pin Configuration
VIN
GATE
GND
CS
18
27
OB3350
36
45
PWM
OVP
COMP
FB
No. Name
1 VIN
2 GATE
3 GND
4 CS
5 FB
6 COMP
7 OVP
8 PWM
I/O
Power
I/O
GND
I/O
I/O
I/O
I/O
I/O
Pin Function
Power Supply Input
Gate Driver Output Pin
Ground
Current Sense Input
LED Current Feedback Input
Boost Converter Loop Compensation Pin
Over Voltage Protection Sense Input
External PWM Dimming Control
©On-Bright Electronics
Confidential
-3-
Preliminary datasheet
OB_DOC_DS_335000
Free Datasheet http://www.datasheetlist.com/


3Pages


OB3350 電子部品, 半導体
OB3350
Cost Effective LED Controller
Function Description
General Operation
The OB3350 is a LED driver designed for boost
DC-DC converters in a constant frequency mode.
The controller implements a peak current mode
control scheme and an internal transconductance
amplifier to accurately control the output current
over a wide input and load conditions.
Low frequency PWM dimming input that can
accept an external control signal with a duty ratio
of 1%-100%. OB3350 offers comprehensive
protection features to protect the system in various
fault conditions such as output over voltage
protection, boost diode disconnection protection
and output short circuit protection. The
cycle-by-cycle current limit function limits the
maximum current flowing through the external
MOSFET. The over temperature protection
ensures that the system will not run into condition
of thermal runaway and blow up.
Startup
OB3350 is enabled by applying a voltage of
greater than approximately 2.5V to PWM pin. An
on-chip internal 150k ohm pull down resistor is
inserted between PWM pin and ground. When the
first rising edge is applied to PWM input, also the
pin of PWM is logic high, the OB3350 will power up
immediately, and remains power up until the PWM
input has been hold low for at least 50ms(typ), at
this time the chip will enter sleep mode. At sleep
mode, the power of theOB3350 will be lower than
400uA (typ).
Once OB3350 is enabled the internal 5V regulator
will be activated to source a current less than 4mA
to the whole chip.
When PWM is active high, the OB3350 checks the
topology connection first. The chip monitors the
OVP pin to see if the Schottky diode (boost diode)
is connected or the boost output is short to GND, if
the voltage at OVP pin is lower than 100mV, the
output will be disabled. The OB3350 will also
check other faults (UVLO, OCP and OTP), if there
is no fault, then the boost converter will boost up
the output with the internal soft start.
switching operation when the voltage at pin VIN
increases to a voltage above 7.5V.
LED Current Regulation
The LED current is sensed by current sense
resistors connected between pin FB and GND.
The sensed error signal is amplified and compared
to the CS pin sensing current signal plus the slope
compensation to determine the on-time of the
switching MOSFET. The error amplifier sources or
sinks the current to the COMP pin to adjust the
required inductor current as the load changes. The
slope-compensation signal is added to the
current-sense signal to improve the stability at high
duty cycles.
The average LED current is approximated by the
following equation
300[mV ]
I LED [mA] RFB [ ]
At light loading, the OB3350 automatically skips
some pulses to improve efficiency and prevent
overcharging the output capacitor. In this
pulse-skipping mode, the inductor current ramps
up for a minimum on-time (typical 300ns), then
deliver the stored energy to the output. The switch
remains off until another pulse is needed to boost
the output voltage.
Slope Compensation
The OB3350 uses a current mode control scheme.
The main advantages of current mode control are
inherent cycle-by-cycle current limit for the switch
and simpler control loop characteristics. However,
current mode control has an inherent instability for
duty cycles greater than 50%, which is also called
sub-harmonic oscillation. The OB3350 has a
build-in slope compensation to avoid sub-harmonic
oscillation.
UVLO
An under-voltage lockout protection feature with a
hysteresis of about 300mv is provided for VDDH.
When the voltage at this pin exceeds a threshold
of approximately 7.5V (typ), the IC starts the
normal operation. If the voltage at this pin drops
below a threshold of approximately 7(typ) V, the IC
stops switching operation. The IC resumes
Figure4 Sub-harmonic oscillation at duty>50%
and compensation slope to avoid sub-harmonic
oscillation
If the control signal (which applied to the negative
input of the PWM comparator) has no slope and
©On-Bright Electronics
Confidential
-6-
Preliminary datasheet
OB_DOC_DS_335000
FreeDatasheethttp://www.datasheetlist.com/

6 Page



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部品番号部品説明メーカ
OB3350

Cost Effective LED Controller

On-Bright
On-Bright


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