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PDF FAN73402MX Data sheet ( Hoja de datos )
| Número de pieza | FAN73402MX | |
| Descripción | LED Backlight Driving Boost Switch | |
| Fabricantes | Fairchild Semiconductor | |
| Logotipo |  |
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July 2012
FAN73402
LED Backlight Driving Boost Switch
Features
Single-Channel Boost LED Switch
Internal Power MOSFET for PWM Dimming:
RDS(ON)=1.0Ω at VGS=10V, BVDSS=200V
Current-Mode PWM Control
Internal Programmable Slope Compensation
Wide Supply Voltage Range: 10V to 35V
LED Current Regulation: ±1%
Programmable Switching Frequency
Analog and PWM Dimming
Wide Dimming Ratio: On Time=10µs 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
Applications
LED Backlight for LCD TV
LED Backlight for LCD Monitor
LED Lighting
Description
The FAN73402 is a single-channel boost controller that
integrates an N-channel power MOSFET for PWM
dimming using Fairchild’s proprietary planar Double-
diffused MOSFET (DMOS) 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.
Ordering Information
Part Number
Operating
Temperature Range
Package
Packing Method
FAN73402MX
-40°C to +125°C
16-Lead, Small-Outline Integrated Circuit (SOIC)
Tape & Reel
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
www.fairchildsemi.com
1 page  
Electrical Characteristics
For typical values, TA = 25°C and VCC = 15V 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
Vth,hys
Ist
Start Threshold Voltage
Start Threshold Voltage Hysteresis
Standby Current
ON/OFF Section
VON
VOFF
On-State Input Voltage
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
Maximum Duty Cycle(4)
Reference Section
VREF
VREF,Line
VREF,Load
5V Regulation Voltage
5V Line Regulation
5V Load Regulation
PWM Dimming Section
VPDIM,L
VPDIM,H
RPDIM
PWM Dimming Input Low Voltage
PWM Dimming Input High Voltage
PWM Dimming Pull-Down Resistance
FET Section (for Dimming)
BVDSS Drain-Source Breakdown Voltage(4)
IDSS Zero-Gate-Voltage Drain Current(4)
RDS(ON) Drain-Source On-State Resistance
CISS
COSS
Input Capacitance(4)
Output Capacitance(4)
Condition
BDIM Connected to GND
VCC=Vth-0.2
VADIM=1V
VADIM=1V
VADIM=1V, VSENSE=2V
VADIM=1V, VSENSE=0V
Minimum
RT=100kΩ
Maximum
0<I5<3mA
Min. Typ. Max. Unit
10 35 V
2 4 mA
8.3 9.0 9.7
V
0.5 1.0 1.5
V
200 300 μA
2 5V
0.8 V
100 300 500 µmho
20 MΩ
60 dB
-10 10 mV
100 200 300 µA
100 200 300 µA
0 3V
0.7 4.0 V
50
190 200 210 kHz
300
86 90 94 %
4.9 5.0 5.1
V
25 mV
25 mV
0.8
25
100 160 220
V
V
kΩ
VCC=0V, ID=250μA
200
V
VDS=250V, TA=25°C
1 30 µA
VGS=10V, ID=1A
0.7 1.0
Ω
VDS=25V, VGS=0V, f=1MHz
VDS=25V,VGS=0V, f=1MHz
173 225
30 40
pF
pF
Continued on the following page…
© 2012 Fairchild Semiconductor Corporation
FAN73402 • 1.0.0
5
www.fairchildsemi.com
5 Page 
Functional Description
The FAN73402 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 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.
VCC Under-Voltage Lockout (UVLO)
An internal regulator provides the regulated 5V 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 1.22V (typical) to the ENA
pin enables the IC. Applying voltage lower than 1.15V
(typical) to the ENA pin disables the IC. If ENA pin
voltage is higher than 1.22V (typical) and VCC is higher
than 9.0V (typical), the IC starts to supply the 5V
reference 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 2V. The current through the RT pin
resistor determines the boost switching frequency
according to formula:
f.
kHz (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.
FAN73402 adapts the soft-start function in the boost
converter stage. During soft-start period, boost switch
turn-on duty is limited by the clamped CMP voltage. The
soft-start period is dependent on the boost switching
frequency, which is determined by the RT resistor
(Equation 1). Soft-start period is set to be cumulative
time when the BDIM (PWM dimming) signal is HIGH:
t 600 / f seconds
(2)
Figure 26. Soft-Start Waveforms
LED Current Setting
During the boost converter operating periods, the output
LED current can be set by equation:
I
ADIM V
R 60mΩ
(3)
where ADIM(V) is ADIM pin applied voltage and,
RSENSE is the sensing resistor value.
Note:
5. An additional 60mΩ comes from an internal wire
bonding resistor. To calculate LED current precisely,
consider the wire bonding resistor.
Analog Dimming and PWM Dimming
Analog dimming (ADIM) 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 0.3V to 3V is
recommended.
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
transconductance 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 op-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 using the backlight during an
extremely short period of time. FAN73402 can normally
drive the LED backlight under 0.1% dimming duty cycle
at 200Hz dimming frequency. Even operating at 5µs
dimming MOSFET turn-on time and extremely low
dimming duty, FAN73402 can operate LEDs with normal
peak current level.
© 2012 Fairchild Semiconductor Corporation
FAN73402 • 1.0.0
11
www.fairchildsemi.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet FAN73402MX.PDF ] | |
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