FAIRCHILD FAN7340MX

FAN7340
LED Backlight Driving Boost Switch
Features
Description


The FAN7340 is a single-channel boost controller that
integrates an N-channel power MOSFET for PWM
dimming using Fairchild’s proprietary planar Doublediffused MOS (DMOS) technology.
Single-Channel Boost LED Switch
Internal Power MOSFET for PWM Dimming:
RDS(on) = 3.4Ω at VGS=10V, BVDSS=400V
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
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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
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
FAN7340M
FAN7340MX
Operating
Temperature
Range
-40°C to +125°C
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
Package
16-Lead, Small-Outline Integrated Circuit (SOIC)
Packaging
Method
Rail
Tape & Reel
www.fairchildsemi.com
FAN7340 — LED Backlight Driving Boost Switch
April 2012
FAN7340 — LED Backlight Driving Boost Switch
Block Diagram
Figure 1. Internal Block Diagram
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
www.fairchildsemi.com
2
FAN7340 — LED Backlight Driving Boost Switch
Pin Assignments
Figure 2. Package Diagram
Pin Definitions
Pin #
Name
Description
1
VCC
This pin is the supply voltage of the IC.
2
DRV
This pin is the gate drive signal of the boost switch.
3
GND
This pin is the ground of the IC.
This pin is for sensing the current flowing through an external MOSFET. It includes a built-in
300ns blanking time. The peak of the current flowing through the MOSFET is limited to this
pin voltage. Slope compensation of the boost controller can be programmed through the
series resistor of this pin.
4
CS
5
REF
6
FAULT
7
RT
8
SENSE
This pin is for sensing the current flowing through the LEDs. A sensing resistor is connected
from this pin to ground. This pin is connected to the negative input of the internal error
amplifier.
9, 10
DRAIN
Drain pin of PWM dimming power MOSFET.
12
ENA
Enable input pin. If voltage of this pin is higher than 1.22V, IC is starting to operate. If the
voltage of this pin is lower than 1.15V, the IC stops operating.
13
OVP
Over-voltage protection input pin. Output voltage of the boost circuit is connected to this pin
through a resistor divider circuit. If this pin voltage is higher than 3V, OVP is triggered.
14
CMP
This pin is the error amplifier output. Typically, a compensation capacitor and resistor are
connected to this pin from the ground.
15
ADIM
This pin is for setting the current flowing through the LEDs. This pin is connected to the
positive inputs of the internal error amplifier. Linear voltage range of ADIM is 0.3V~3.0V.
16
BDIM
This pin is for the burst dimming signal. If this pin voltage is HIGH, the internal dimming
MOSFET is turned on. If this pin voltage is LOW, the dimming MOSFET is turned off.
This pin is the 5V reference voltage pin. Maximum current capability is 3mA.
This pin is for indicating the fault signal. This pin is connected to the open drain. When OLP
protection is occurred, the FAULT pin is pulled HIGH.
Oscillator frequency set of the boost switch (50kHz ~ 300kHz).
Note:
1. Pin 11 is a “No Connect” pin (not shown in Figure 2).
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
www.fairchildsemi.com
3
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In
addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The
absolute maximum ratings are stress ratings only. TA=25C unless otherwise specified.
Symbol
Parameter
Min.
Max.
Unit
VCC
Supply Voltage
10
35
V
TA
Operating Temperature Range
-40
+125
C
TJ
Junction Temperature
+150
C
+150
C
120
C/W
0.9
W
TSTG
Storage Temperature Range
-65
ӨJA
Thermal Resistance Junction-to-Ambient
PD
Power Dissipation
(2, 3)
Notes:
2. Thermal resistance test board; size 76.2mm x 114.3mm x 1.6mm (1S0P); JEDEC standard: JESD51-2, JESD51-3.
3. Assume no ambient airflow.
Pin Breakdown Voltage
Pin #
Name
Value
Unit
Pin #
Name
Value
Unit
1
VCC
35
V
9
DRAIN
400
V
2
DRV
20
V
10
DRAIN
400
V
3
GND
V
11
N/A
4
CS
6
V
12
ENA
6
V
5
REF
6
V
13
OVP
6
V
6
FAULT
35
V
14
CMP
6
V
V
7
RT
6
V
15
ADIM
6
V
8
SENSE
6
V
16
BDIM
6
V
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
www.fairchildsemi.com
4
FAN7340 — LED Backlight Driving Boost Switch
Absolute Maximum Ratings
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
Condition
Min.
Typ.
Max.
Unit
35
V
2
4
mA
Supply Voltage Section
VCC
Input DC Supply Voltage Range(4)
ISD
Shutdown Mode Supply Current
10
BDIM Connected to GND
Under-Voltage Lockout Section
Vth
Vth,hys
Ist
Start Threshold Voltage
8.3
9.0
9.7
V
Start Threshold Voltage Hysteresis
0.5
1.0
1.5
V
200
300
μA
5
V
0.8
V
500
µmho
Standby Current
VCC=Vth-0.2
ON/OFF Section
Von
On-State Input Voltage
Voff
Off-State Input Voltage
2
Error Amplifier Section
Gm
Error Amplifier Transconductance(4)
VADIM=1V
100
(4)
300
AV_ro
Error Amplifier Output impedance
20
MΩ
AV
Error Amplifier Open-Loop Gain(4)
60
dB
Voffset
Input Offset Voltage
VADIM=1V
-10
Isin
CMP Sink Current
VADIM=1V, VSENSE=2V
100
Isur
CMP Source Current
VADIM=1V, VSENSE=0V
100
VIDR
VO
Input Differential Voltage Range
Output Voltage Range
10
mV
200
300
µA
200
300
µA
0
3
V
0.7
4.0
V
Oscillator Section
Min.
fosc
Boost Oscillator Frequency
RT=100kΩ
50
190
Max.
Dmax
(4)
Maximum Duty Cycle
200
kHz
210
300
kHz
kHz
86
90
94
%
4.9
5.0
5.1
V
Reference Section
VREF
5V Regulation Voltage
VREF,Line
5V Line Regulation
VREF,Load
5V Load Regulation
0<I5<3mA
25
mV
25
mV
PWM Dimming Section
VPDIM,L
PWM Dimming Input Low Voltage
VPDIM,H
PWM Dimming Input High Voltage
RPDIM
0.8
2
PWM Dimming Pull-Down Resistance
100
160
V
5
V
220
kΩ
FET Section (for Dimming)
BVDSS
Drain-Source Breakdown Voltage(4)
VCC=0V, ID=250μA
IDSS
Zero-Gate-Voltage Drain Current(4)
VDS=250V, TA=25°C
RDS(ON)
Drain-Source On-State Resistance
VGS=10V, ID=1A
3.4
(4)
400
V
1
30
µA
Ω
CISS
Input Capacitance
VDS=25V, VGS=0V, f=1MHz
173
225
pF
COSS
Output Capacitance(4)
VDS=25V,VGS=0V, f=1MHz
30
40
pF
Continued on the following page…
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
www.fairchildsemi.com
5
FAN7340 — LED Backlight Driving Boost Switch
Electrical Characteristics
For typical values, TA = 25°C and VCC = 15V, unless otherwise specified. Specifications to -25°C ~ 85°C are
guaranteed by design based on final characterization results.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
10.8
11.8
12.8
V
Output Section (Boost / Dimming)
VDRV
Gate Output Voltage
VCC=15V
Vuv
Gate Output Voltage Before Startup
-0.5
0.5
V
Idsur
Gate Output Drive Source Current(4)
80
180
280
mA
Idsin
Gate Output Drive Sink Current(4)
80
180
280
mA
trh
tfl
(4)
Gate Output Rising Time (Boost)
Gate Output Falling Time (Boost)
(4)
CL=2.0nF
200
ns
CL=2.0nF
120
ns
Current Sense Section
tblank
tdelay,cl
Voffset,clc
Leading-Edge Blanking(4)
150
300
Delay to Output of Current-Limit
Comparator(4)
Offset Voltage of Current-Limit
Comparator(4)
-20
450
ns
180
ns
20
mV
54
µA
Slope Compensation Section
Islope
Rslope
Ramp Generator Current
Slope Compensation Resistor
36
(4)
45
5
kΩ
3
ms
Soft-Start Section
tss
Soft-Start Period(4)
fosc=200kHz
Protection Section
td,ovp.tr
Delay for Triggering Over-Voltage
Protection(4)
15
20
25
µs
td,ovpr
Delay for Releasing Over-Voltage
Protection(4)
10
14
18
µs
td.ocp
Delay for Over-Current Protection(4)
tAR
Auto-Restart Time for Over-Current
Protection(4)
td,olpi
Delay for Triggering Open-LED Protection(4)
td,olp
Delay for Open-LED Protection
Vth,ovp
Over-Voltage Protection Threshold Voltage
Over-Voltage Protection Voltage Hysteresis
Vth.csocp
Boost Switch Current Limit Threshold
Voltage
Vth,ocp
LED Over-Current Protection Threshold
Voltage
Vth,olp
Open-LED Protection Threshold Voltage(4)
THYS
3
fosc=200kHz
Vhys,ovp
TSD
fosc=200kHz
µs
640
µs
5
7
40.96
2.85
3.00
Thermal Shutdown Temperature
(4)
µs
ms
3.15
0.1
(4)
Thermal Shutdown Hysteresis
1
V
V
0.45
0.50
0.55
V
1.4
(Min.
Clamp)
4.0xVADIM
4.0
(Max.
Clamp)
V
0.15
0.20
0.25
V
140
150
160
°C
20
°C
Notes:
4. These parameters, although guaranteed, are not tested in production.
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
www.fairchildsemi.com
6
FAN7340 — LED Backlight Driving Boost Switch
Electrical Characteristics (Continued)
9.9
1.7
9.7
1.5
9.5
1.3
Vth.hys, [V]
Vth, [V]
9.3
9.1
8.9
8.7
1.1
0.9
0.7
8.5
0.5
8.3
0.3
8.1
-50
-25
0
25
50
75
Temperature, [℃]
100
-50
125
Figure 3. Start Threshold Voltage vs. Temperature
-25
0
25
50
75
Temperature, [℃]
100
125
Figure 4. Start Threshold Voltage Hysteresis
vs. Temperature
350
4.5
4
300
3.5
ISD, [mA]
Ist, [uA]
250
200
150
3
2.5
2
1.5
100
1
50
0.5
-50
-25
0
25
50
75
Temperature, [℃]
100
-50
125
Figure 5. Standby Current vs. Temperature
0
25
50
75
Temperature, [℃]
100
125
Figure 6. Shutdown Mode Supply Current vs.
Temperature
1.4
1.3
1.35
1.25
1.3
1.2
1.25
Voff, [V]
Von, [V]
-25
1.2
1.15
1.1
1.15
1.1
1.05
1.05
1
-50
-25
0
25
50
75
Temperature, [℃]
100
-50
125
Figure 7. On-State Input Voltage vs. Temperature
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
-25
0
25
50
75
Temperature, [℃]
100
125
Figure 8. Off-State Input Voltage vs. Temperature
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7
FAN7340 — LED Backlight Driving Boost Switch
Typical Performance Characteristics
14
500
10
6
400
Voffset, [mV]
Gm, [umho]
600
300
200
100
-6
-14
-50
-25
0
25
50
75
Temperature, [℃]
100
125
-50
Figure 9. Error Amplifier Transconductance
vs. Temperature
350
350
300
300
250
250
200
150
100
100
50
50
-25
0
25
50
75
Temperature, [℃]
100
0
25
50
75
Temperature, [℃]
100
125
200
150
-50
-25
Figure 10. Input Offset Voltage vs. Temperature
Isur, [uA]
Isin, [uA]
-2
-10
0
-50
125
Figure 11. CMP Sink Current vs. Temperature
-25
0
25
50
75
Temperature, [℃]
100
125
Figure 12. CMP Source Current vs. Temperature
215
96
210
94
205
92
Dmax, [%]
fOSC, [KHz]
2
200
195
190
90
88
86
185
84
-50
-25
0
25
50
75
Temperature, [℃]
100
125
-50
Figure 13. Boost Oscillator Frequency vs. Temperature
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
-25
0
25
50
75
Temperature, [℃]
100
125
Figure 14. Maximum Duty Cycle vs. Temperature
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8
FAN7340 — LED Backlight Driving Boost Switch
Typical Performance Characteristics (Continued)
1.8
5.1
1.7
5.05
1.6
VPDIM,H, [V]
VREF, [V]
5.15
5
4.95
1.5
1.4
4.9
1.3
4.85
1.2
-50
Figure 15.
-25
0
25
50
75
Temperature, [℃]
100
-50
125
-25
0
25
50
75
100
125
Temperature, [℃]
5V Regulation Voltage vs. Temperature
Figure 16. PWM Dimming Input High Voltage
vs. Temperature
1.7
240
220
1.6
RPDIM, [Kohm]
VPDIM,L, [V]
200
1.5
1.4
1.3
180
160
140
120
1.2
100
80
1.1
-50
-25
0
25
50
75
Temperature, [℃]
100
-50
125
Figure 17. PWM Dimming Input Low Voltage
vs. Temperature
0
25
50
75
Temperature, [℃]
100
125
Figure 18. PWM Dimming Pull-Down Resistance
vs. Temperature
300
13.5
13
250
Idsin, [mA]
12.5
VDRV, [V]
-25
12
11.5
200
150
100
11
10.5
50
-50
-25
0
25
50
75
Temperature, [℃]
100
125
-50
Figure 19. Gate Output Voltage vs. Temperature
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
-25
0
25
50
75
Temperature, [℃]
100
125
Figure 20. Gate Output Drive Sink Current
vs. Temperature
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9
FAN7340 — LED Backlight Driving Boost Switch
Typical Performance Characteristics (Continued)
0.85
55
0.8
0.75
47
tAR,[mS]
Islope, [uA]
51
43
0.7
0.65
0.6
0.55
39
0.5
0.45
35
-50
-25
0
25
50
75
Temperature, [℃]
100
-50
125
-25
0
25
50
75
100
125
Temperature, [℃]
Figure 21. Ramp Generator Current vs. Temperature
Figure 22. Auto-Restart Time for OCP
vs. Temperature
3.2
0.2
3.15
0.16
3.05
Vhys,ovp,[V]
Vth,ovp,[V]
3.1
3
2.95
0.12
0.08
2.9
0.04
2.85
2.8
0
-50
-25
0
25
50
75
Temperature, [℃]
100
125
-50
Figure 23. OVP Threshold Voltage vs. Temperature
-25
0
25
50
75
Temperature, [℃]
100
125
Figure 24. OVP Hysteresis Voltage vs. Temperature
55
td,olp,[mS]
50
45
40
35
30
25
-50
Figure 25.
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
-25
0
25
50
75
Temperature, [℃]
100
125
Delay for Over-Current Protection vs. Temperature
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10
FAN7340 — LED Backlight Driving Boost Switch
Typical Performance Characteristics (Continued)
The FAN7340 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 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.
Figure 26.
Soft-Start Waveforms
VCC Under-Voltage Lockout (UVLO)
LED Current Setting
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.
During the boost converter operating periods, the output
LED current can be set by equation:
I
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 5V reference
voltage from VCC.
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 0.3V to 3V is
recommended.
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 boost switching frequency according
to formula:
.
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.
(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.
Dynamic Contrast Ratio
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:
T
600/f
sec
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
(3)
60mΩ
resistor value. An additional 60mΩ comes from an
internal wire bonding resistor. To calculate LED
current precisely, consider the wire bonding resistor.
Oscillator (Boost Switching Frequency)
kHz
R
where ADIM(V) is
ADIM pin applied voltage and, RSENSE is the sensing
Enable
f
ADIM V
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 200Hz dimming frequency.
Even operating at 5µs-dimming FET turn-on time and
extremely low dimming duty, FAN7340 can operate
LEDs with normal peak current level.
(2)
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11
FAN7340 — LED Backlight Driving Boost Switch
Functional Description
A dimming MOSFET (400V N-channel MOSFET; such
as FDD3N40) is incorporated in the FAN7340. The
power transistor is produced using Fairchild’s
proprietary, planar stripe, DMOS technology. This
advanced technology is tailored to minimize on-state
resistance (RDS(on)=3.4), to provide superior switching
performance. This device is suited for high-efficiency
SMPS and shows desirable thermal characteristic during
operation. To prevent initial LED current overshoot at low
VADIM levels, gate resistance of the internal dimming FET
is designed as 5kexperimentally.
Figure 27.
Slope Compensation Block Diagram
Feedback Loop Compensation
Cycle-by-Cycle Over-Current Protection
Stable closed-loop control can be accomplished by
connecting a compensation network between COMP and
GND. The compensation needed to stabilize the
converter can be either a Type-I circuit (a simple
integrator) or a Type-II circuit (and integrator with and
additional pole-zero pair). The type of the compensation
circuit required is dependent on the phase of the power
stage at the crossover frequency.
In boost topology, the switch can be damaged in
abnormal conditions (inductor short, diode short, output
short). It is always necessary to sense the switch current
to protect against over-current failures. Switch failures
due to excessive current can be prevented by limiting Id.
FAN7340 adopts a Type-II compensator circuit.
Programmed Current Control
FAN7340 uses a Current-Mode control method. CurrentMode control loops: an outer feedback loop that senses
output voltage (current) and delivers a DC control
voltage to an inner feedback loop, which senses the
peak current of the inductor and keeps it constant on a
pulse-by-pulse basis. One of the advantages of the
Current-Mode control is line/load regulation, which is
corrected instantaneously against line voltage changes
without the delay of an error amplifier.
Figure 28.
When the voltage drops at R1 and RS exceed a
threshold of approximately 0.5V, the power MOSFET
over-current function is triggered after minimum turn-on
time or LEB time (300ns).
Programmable Slope Compensation
The peak voltage level at CS terminal:
When the power converter operates in Continuous
Conduction Mode (CCM), the current programmed
controller is inherently unstable when duty is larger than
50%, regardless of the converter topology. The
FAN7340 uses a Peak-Current-Mode control scheme
with programmable slope compensation and includes an
internal transconductance amplifier to accurately control
the output current over all line and load conditions.
V
_
45μ
R
R
DT
i
R
(4)
Choose the boost switch current-sensing resistor (RCS):
0.25
R
(5)
i _
Open-LED Protection (OLP)
An internal Rslope resistor (5kΩ) connected to sensing
resistor RS and an external resistor R1 can control the
slope of VSC for the slope compensation. Although the
normal operating mode of the power converter is DCM,
the boost converter operates in CCM in the case of rapid
LED current increase. As a result, slope compensation
circuit is an important feature.
After the first PWM dimming-HIGH signal, the feedback
sensing resistor (RSENSE) starts sensing the LED
current. If the feedback voltage of the SENSE pin drops
below 0.2V, the OLP triggers to generate an error flag
signal. Because OLP can be detected only in PWM
dimming-HIGH; if OLP detecting time is over 5μs, PWM
dimming signal is pulled HIGH internally regardless of
external dimming signal. If OLP signal continues over
blanking time, an error flag signal is triggered.
The value of an external series resistor (R1) can be
programmed by the user. In normal DCM operation, 5kΩ
is recommended.
OLP blanking time is dependent on boost switch
frequency per Equation 6. FAULT OUT signal is made
through the FO pin, which needs to be connected 5V
reference voltage through a pull-up resistor. In normal
operation, FO pin voltage is pulled down to ground. In
OLP condition, FO pin voltage is pulled HIGH.
t
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
Cycle-by-Cycle OCP Circuit
.
8192 / f
sec
(6)
www.fairchildsemi.com
12
FAN7340 — LED Backlight Driving Boost Switch
Internal Dimming MOSFET
LED Over-Current Protection (OCP)
The primary purpose of the over-current protection
function is to protect the internal dimming MOSFET from
excessive current. The OCP is triggered when the
feedback voltage meets the clamping level (1.4V ~ 4V)
of the ADIM voltage x4. At 1μs delay after the OCP is
triggered, the IC turns off both the boost FET and
dimming FET and restarts the gate signal every tAR
automatically. tAR can be calculated as:
128 / f
sec
(7)
1.
When VADIM=0.3V (VADIMx4=1.2V).
2.
OCP threshold level is set to 1.4V.
3.
OCP is triggered at feedback voltage level = 1.4V.
VSENSE
VSENSE=1.4V
VADIM=0.3V
Figure 29. Open-LED Protection
GATE
In LED open load condition, OVP is triggered ahead of
OLP.
Over-Voltage Protection (OVP)
Figure 32. OCP Waveforms at VADIM=0.3V
Over-voltage protection is triggered when the voltage of
the external output voltage trip point meets 3V. After
triggering OVP, the dimming switch and boost switch are
turned off. The protection signal is recovered when the
output voltage divider is below 2.9V.
1.
When VADIM=0.8V (VADIMx4=3.2V).
2.
OCP threshold level is set to 3.2V.
3.
OCP is triggered at VSENSE = 3.2V.
Figure 33. OCP Waveforms at VADIM=0.8V
Figure 30. Over-Voltage Trip Point
Figure 31.
1.
When VADIM=1.2V (VADIMx4=4.8V).
2.
OCP threshold level is set to 4.0V.
3.
OCP is triggered at VSENSE = 4.0V.
OVP Trigger and Release
GATE
Figure 34.
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
OCP Waveforms at VADIM=1.2V
www.fairchildsemi.com
13
FAN7340 — LED Backlight Driving Boost Switch
In system operation, OLP is triggered in only direct-short
condition. Direct short means that some point of the LED
string is shorted to set ground. In direct-short condition,
the boost controller cannot control the LED current and a
large current flows into the LED string directly from input
power. To prevent this abnormal condition, the FO signal
is used to turn off input power or the total system. FO
signal is only triggered in OLP condition.
Application
Input Voltage Range
LED Backlight TV
120VDC 10%
Rated Output Power
Output current
(Rated Voltage)
LED
250mA (230V)
72-LEDs/1-String
Features



High Efficiency
Constant Current Boost Converters
High-Voltage, High-Current LED Driving
Typical Application Circuit
D1
CN1
Vin
Vin
Vin
GND
GND
GND
CN2
L1
200uH/PC44
1
2
3
4
5
6
C1
22uF/160V
FFD04H60S
DSP
C2
R1 10R
47uF/400V
CON6
R21
330k
Q1
FPDF7N50NF
D2 1SS355 R9 0R
VCC
1
D3
1N4148
5.1k
2
R8
0.2R/1W
R23
10k
3
On/Of f
VCC
GND
FO
BDIM
ADIM
On/Of f
C5
open
0
1
2
3
4
5
6
4
VCC
C3
FO
10uF/50V
C4
1u
5
C8
10n
CON6
R19
10k
6
FO
TP1
R12
100K
On/Of f
7
ADIM
R13 3.9K
TP
R14
20K
R15
220K
R20
100k
C10
1.2n
8
BDIM
VCC
FAN7340
C12
1.2n
CON6
R5
300k
IC1
ENA
R7
R2
300k
N.C
N.C
VLED
VLED
LED1
LED2
0
R4
100K
R22
330k
CN3
1
2
3
4
5
6
DRV
GND
CS
REF
FO
RT
SENSE
R16
2.7R/1W
ADIM
CMP
OVP
ENA
16
R6
300k
BDIM
OVP
15
ADIM
C13
1.2n
R10
11k
14
13
OVP
C6
6.8n
12
R11
15k
C7
100n
ENA
DRAIN
DRAIN
10
9
FAN7340
BDIM
R17 3.9K
R18
220K
Vin : 120V
Vout : 230V
Output current : 250mA
Switching frequency : 200kHz
C11
1.2n
0
Figure 35.
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
Typical Application Circuit
www.fairchildsemi.com
SLC1012C — LED Backlight Driving Boost Switch
Typical Application Circuit (Boost Topology for LED Backlight)
10.00
9.80
A
8.89
16
9
B
4.00
3.80
6.00
PIN ONE
INDICATOR
1.75
1
5.6
8
0.51
0.35
1.27
(0.30)
0.25
M
1.27
C B A
0.65
LAND PATTERN RECOMMENDATION
1.75 MAX
1.50
1.25
SEE DETAIL A
0.25
0.10
C
0.25
0.19
0.10 C
0.50
0.25 X 45°
(R0.10)
NOTES: UNLESS OTHERWISE SPECIFIED
GAGE PLANE
(R0.10)
0.36
8°
0°
A) THIS PACKAGE CONFORMS TO JEDEC
MS-012, VARIATION AC, ISSUE C.
B) ALL DIMENSIONS ARE IN MILLIMETERS.
C) DIMENSIONS ARE EXCLUSIVE OF BURRS, MOLD
FLASH AND TIE BAR PROTRUSIONS
D) CONFORMS TO ASME Y14.5M-1994
E) LANDPATTERN STANDARD: SOIC127P600X175-16AM
F) DRAWING FILE NAME: M16AREV12.
SEATING PLANE
0.90
0.50
(1.04)
DETAIL A
SCALE: 2:1
Figure 36. 16-Lead, Small Outline Integrated Circuit (SOIC)
Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner
without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or
obtain the most recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions,
specifically the warranty therein, which covers Fairchild products.
Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings:
http://www.fairchildsemi.com/packaging/.
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
www.fairchildsemi.com
15
FAN7340 — LED Backlight Driving Boost Switch
Physical Dimension
FAN7340 — LED Backlight Driving Boost Switch
© 2012 Fairchild Semiconductor Corporation
FAN7340 • 1.0.0
www.fairchildsemi.com
16