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PDF FAN7340 Data sheet ( Hoja de datos )
| Número de pieza | FAN7340 | |
| Descripción | LED Backlight Driving Boost Switch | |
| Fabricantes | Fairchild Semiconductor | |
| Logotipo |  |
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July 2013
FAN7340
LED Backlight Driving Boost Switch
Features
Single-Channel Boost LED Switch
Internal Power MOSFET for PWM Dimming:
RDS(on) = 3.4 Ω at VGS=10 V, BVDSS=400 V
Current Mode PWM Control
Internal Programmable Slope Compensation
Wide Supply Voltage Range: 10 V to 35 V
LED Current Regulation: ±1%
Programmable Switching Frequency
Analog and PWM Dimming
Wide Dimming Ratio: On Time=10 µs to DC
Cycle-by-Cycle Current Limiting
Thermal Shutdown: 150°C
Open-LED Protection (OLP)
Over-Voltage Protection (OVP)
Over-Current Protection (OCP)
Error Flag Generation (for External Load Switch)
Internal Soft-Start
16-Lead SOIC Package
Description
The FAN7340 is a single-channel boost controller that
integrates an N-channel power MOSFET for PWM
dimming using Fairchild’s proprietary planar Double-
diffused MOS (D MOS) technology.
The IC operates as a constant-current source for driving
high-current LEDs.
It uses Current Mode control with programmable slope
compensation to prevent subharmonic oscillation. The IC
provides protections including: open-LED protection,
over-voltage protection, and direct-short protection for
high system reliability.
The IC internally generates a FAULT signal with delay if
an abnormal LED string condition occurs. PWM dimming
and analog dimming functions can be implemented
independently. Internal soft-start prevents inrush current
flowing into output capacitor at startup.
Applications
LED Backlight for LCD TV
LED Backlight for LCD Monitor
LED Lighting
Ordering Information
Part Number
FAN7340MX
Operating
Temperature
Range
-40°C to +125°C
Package
16-Lead, Small-Outline Integrated Circuit (SOIC)
Packaging
Method
Tape & Reel
© 2013 Fairchild Semiconductor Corporation
FAN7340 • 1.0.1
www.f airchildsemi.com
1 page  
Electrical Characteristics
For typical values, TA = 25°C and VCC = 15 V unless otherwise specified. Specifications to -40°C ~ 125°C are
guaranteed by design based on final characterization results .
Symbol
Parameter
Supply Voltage Section
VCC Input DC Supply Voltage Range(4)
ISD Shutdown Mode Supply Current
Under-Voltage Lockout Section
Vth Start Threshold Voltage
Vth,hys Start Threshold Voltage Hysteresis
Ist Standby Current
ON/OFF Section
Von On-State Input Voltage
Voff Off-State Input Voltage
Error Amplifier Section
Gm
AV _ro
AV
Error Amplifier Transconductance(4)
Error Amplifier Output impedance(4)
Error Amplifier Open-Loop Gain(4)
Voffset Input Offset Voltage
Isin CMP Sink Current
Isur CMP Source Current
VIDR Input Differential Voltage Range
VO Output Voltage Range
Oscillator Section
fosc Boost Oscillator Frequency
Dmax
Ma ximum Duty Cycle(4)
Reference Section
VREF
5V Regulation Voltage
VREF,Line 5V Line Regulation
VREF,Load 5V Load Regulation
PWM Dimming Section
VPDIM,L PWM Dimming Input Low Voltage
VPDIM,H PWM Dimming Input High Voltage
RPDIM PWM Dimming Pull-Down Resistance
FET Section (for Dimming)
BVDSS Drain-Source Breakdown Voltage(4)
IDSS Zero-Gate-Voltage Drain Current(4)
RDS(ON)
CISS
COSS
Drain-Source On-State Resistance
Input Capacitance(4)
Output Capacitance(4)
Condition
Min. Typ. Max. Unit
BDIM Connected to GND
VCC= Vth-0.2
VADIM=1 V
VADIM=1 V
VADIM=1 V, VSEN SE=2 V
VADIM=1 V, VSEN SE=0 V
Min.
RT=100 kΩ
Ma x.
0<I5<3 mA
10
2
35 V
4 mA
8.3 9.0 9.7 V
0.5 1.0 1.5 V
200 300 μA
2 5V
0.8 V
100 300
20
60
-10
100 200
100 200
0
0.7
500 µmho
MΩ
dB
10 mV
300 µA
300 µA
3V
4.0 V
50 kHz
190 200 210 kHz
300 kHz
86 90 94 %
4.9 5.0 5.1 V
25 mV
25 mV
0.8 V
2 5V
100 160 220 kΩ
VCC=0 V, ID=250 μA
400
V
VDS=250 V, TA=25°C
1 30 µA
VGS=10 V, ID=1 A
3.4 Ω
VDS=25 V, VGS=0 V, f=1 MHz
173 225 pF
VDS=25 V,VGS=0V, f=1 MH z
30 40 pF
Continued on the following page…
© 2013 Fairchild Semiconductor Corporation
FAN7340 • 1.0.1
5
www.f airchildsemi.com
5 Page 
Functional Description
The FAN7340 operates as a constant-current source for
driving high-current LEDs. It uses Current-Mode control
with programmable slope compensation to prevent sub-
harmonic oscillation.
The IC provides protections such as open-LED
protection, over-voltage protection, and over-current
protection for improved system reliability. The IC
internally generates a FAULT OUT signal with a delay in
case an abnormal LED string condition occurs. PWM
dimming and analog dimming functions can be
implemented independently. Internal soft-start prevents
inrush current flowing into output capacitor at startup.
Circuit operation is explained in the following sections.
VCC Under-Voltage Lockout (UVLO)
An internal regulator provides the regulated 5 V used to
power the IC. The Under-Voltage Lockout (UVLO) turns
off the IC in the event of the voltage dropping below the
specific threshold level. The UVLO circuit inhibits
powering the IC until a voltage reference is established,
up to predetermined threshold level.
Enable
Applying voltage higher than 1.22 V (typical) to the ENA
pin enables the IC. Applying voltage lower than 1.15 V
(typical) to the ENA pin disables the IC. If ENA pin
voltage is higher than 1.22 V (typical) and VCC is higher
than 9.0 V (typical.), the IC starts to supply 5 V re ference
voltage from VCC.
Oscillator (Boost Switching Frequency)
Boost switching frequency is programmed by the value
of the resistor connected from the RT pin to ground. RT
pin voltage is set to 2 V. The current through the RT pin
resistor determines boost switching frequency according
to formula:
(1)
Soft-Start Function at Startup
During initial startup, the switching device can be
damaged due to the over-current coming from the input
line by the negative control. This can result in the initial
overshoot of the LED current. Therefore, during initial
startup, the soft-start control gradually increases the duty
cycle so that the output voltage can rise smoothly to
control inrush current and overshoot.
FAN7340 adapts the soft-start function in the boost
converter stage. During soft-start period, boost switch
turn-on duty is limited by clamped CMP voltage. The
soft-start period is dependent on boost switching
frequency, which is decided by the RT resistor (Equation
(1)). Soft-start period is set to be cumulative time when
the BDIM (PWM dimming) signal is HIGH:
(2)
V
GATE
VLED
VCMP
Soft-Start Period
ILED
Figure 26. Soft-Start Waveforms
t
LED Current Setting
During the boost converter operating periods, the output
LED current can be set by equation:
(3)
Ω
where ADIM(V) is
ADIM pin applied voltage and, RSENSE is the sensing
resistor value. An additional 60 mΩ comes from an
internal wire bonding resistor. To calculate LED
current precisely, consider the wire bonding resistor.
Analog Dimming and PWM Dimming
Analog dimming is achieved by varying the voltage level
at the ADIM pin. This can be implemented either with a
potentiometer from the VREF pin or from an external
voltage source and a resistor divider circuit. The ADIM
voltage level is adjusted to be the same as the feedback
level (VSENSE). A VADIM range from 0.3 V to 3 V is
recomm ended.
PWM dimming (BDIM) helps achieve a fast PWM
dimming response in spite of the shortcomings of the
boost converter. The PWM dimming signal controls three
nodes in the IC; gate signal to the switching FET, gate
signal to the dimming FET, and output connection of the
trans-conductance amplifier. When the PWM dimming
signal is HIGH, the gates of the switching FET and
dimming FET are enabled. At the same time, the output
of the transconductance ap-amp is connected to the
compensation network. This allows the boost converter
to operate normally.
Dynamic Contrast Ratio
The Dynamic Contrast Ratio (DCR) means the maximum
contrast ratio achievable by adjusting the amount of light
(dimming) of the screen instantaneously using the
backlight during the extremely short period of time.
FAN7340 can normally drive the LED backlight under
0.1% dimming duty cycle at 200 Hz dimming frequency.
Even operating at 5 µs-dimming FET turn-on time and
extremely low dimming duty, FAN7340 can operate
LEDs with normal peak current level.
© 2013 Fairchild Semiconductor Corporation
FAN7340 • 1.0.1
11
www.f airchildsemi.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet FAN7340.PDF ] | |
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