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July 2013

FAN73402 • 1.0.1

FAN73402 — LED Backlight Driving Boost Switch

FAN73402

LED Backlight Driving Boost Switch

Features

 Single-Channel Boost LED Switch

 Internal Power MOSFET for PWM Dimming:

RDS(ON)=1.0 Ω at VGS=10 V, BVDSS=200 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

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

FAN73402 • 1.0.1 2

FAN73402 — LED Backlight Driving Boost Switch

Block Diagram

Figure 1. Internal Block Diagram

+

-

+

-R

SQGate

Driver

CMP

ADIM DRV

GND

CS

BDIM

TSD

16 Steps

Internal Soft-Start

1/4

gm

OCP

+

-

VCC

5V, max. 3mA

UVLO 9V

Voltage Reference

& Internal Bias

Hys. 1.0V

-

+

Current

Sense

Drain

SEN

PWM

Current

Sense

3V OVP

+

-

OVP 100mV

20μs Delay

ADIM*4

1.4~4V

1μs

Delay

BDIM

OLPi

+

-

0.2V

PWM

5μs Delay

PWM

REF

0.3~3V

Slope

Compensation

CLK+LEB

45µA

-

+

0.5V

5k

Switch Off

-

+Burst

Operation

100mV

0.5V

4V

3ms at 200kHz

POR

640µs at 200kHz

Auto-Restart

S

R

Q

Dim off

RT

Oscillator

OLPi

ENA -

+

1.22V

40.96ms

at 200kHz

Debounce

Time

OLP

FAULT

Hys. 70mV

End of Soft-Start

FAN73402 • 1.0.1 3

FAN73402 — LED Backlight Driving Boost Switch

Pin Assignments

F PXYTT

FAN73402

1

2

3

4

5

6

7

8

16

15

14

13

12

10

9

OVP

DRAIN

VCC

FAULT

ENA

CS

RT

DRAIN

DRV ADIM

CMP

SENSE

GND

REF

BDIM

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.

4

CS

This pin is for sensing the current flowing through an external MOSFET. It includes a built-in

300 ns 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.

5

REF

This pin is the 5 V reference voltage pin. Maximum current capability is 3 mA.

6

FAULT

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.

7

RT

Oscillator frequency set of the boost switch (50 kHz ~ 300 kHz).

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 1.22 V, the IC starts to operate. If the

voltage of this pin is lower than 1.15 V, 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 3 V, 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 0.3 V~3.0 V.

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.

Note:

1. Pin 11 is a “No Connect” pin (not shown in Figure 2).

FAN73402 • 1.0.1 4

FAN73402 — LED Backlight Driving Boost Switch

Absolute Maximum Ratings

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

TSTG

Storage Temperature Range

-65

+150

C

ӨJA

Thermal Resistance Junction-to-Ambient(2,3)

120

C/W

PD

Power Dissipation

0.9

W

Notes:

2. Thermal resistance test board; size 76.2 mm x 114.3 mm x 1.6 mm (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

200

V

2

DRV

20

V

10

DRAIN

200

V

3

GND

V

4

CS

6

V

12

ENA

6

V

5

REF

6

V

13

OVP

6

V

6

FAULT

35

V

14

CMP

6

V

7

RT

6

V

15

ADIM

6

V

8

SENSE

6

V

16

BDIM

6

V

FAN73402 • 1.0.1 5

FAN73402 — LED Backlight Driving Boost Switch

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

Condition

Min.

Typ.

Max.

Unit

Supply Voltage Section

VCC

Input DC Supply Voltage Range(4)

10

35

V

ISD

Shutdown Mode Supply Current

BDIM Connected to GND

2

4

mA

Under-Voltage Lockout Section

Vth

Start Threshold Voltage

8.3

9.0

9.7

V

Vth,hys

Start Threshold Voltage Hysteresis

0.5

1.0

1.5

V

Ist

Standby Current

VCC=Vth-0.2

200

300

μA

ON/OFF Section

VON

On-State Input Voltage

2

5

V

VOFF

Off-State Input Voltage

0.8

V

Error Amplifier Section

Gm

Error Amplifier Transconductance(4)

VADIM=1 V

100

300

500

µmho

AV_ro

Error Amplifier Output impedance(4)

20

MΩ

AV

Error Amplifier Open-Loop Gain(4)

60

dB

Voffset

Input Offset Voltage

VADIM=1 V

-10

10

mV

Isin

CMP Sink Current

VADIM=1 V, VSENSE=2 V

100

200

300

µA

Isur

CMP Source Current

VADIM=1 V, VSENSE=0 V

100

200

300

µA

VIDR

Input Differential Voltage Range

0

3

V

VO

Output Voltage Range

0.7

4.0

V

Oscillator Section

fosc

Boost Oscillator Frequency

Minimum

50

kHz

RT=100 kΩ

190

200

210

Maximum

300

Dmax

Maximum Duty Cycle(4)

86

90

94

%

Reference Section

VREF

5 V Regulation Voltage

4.9

5.0

5.1

V

VREF,Line

5 V Line Regulation

25

mV

VREF,Load

5 V Load Regulation

0<I5<3 mA

25

mV

PWM Dimming Section

VPDIM,L

PWM Dimming Input Low Voltage

0.8

V

VPDIM,H

PWM Dimming Input High Voltage

2

5

V

RPDIM

PWM Dimming Pull-Down Resistance

100

160

220

kΩ

FET Section (for Dimming)

BVDSS

Drain-Source Breakdown Voltage(4)

VCC=0 V, ID=250 μA

200

V

IDSS

Zero-Gate-Voltage Drain Current(4)

VDS=250 V, TA=25°C

1

30

µA

RDS(ON)

Drain-Source On-State Resistance

VGS=10 V, ID=1A

0.7

1.0

Ω

CISS

Input Capacitance(4)

VDS=25 V, VGS=0 V, f=1 MHz

173

225

pF

COSS

Output Capacitance(4)

VDS=25 V,VGS=0 V, f=1 MHz

30

40

pF

Continued on the following page…

FAN73402 • 1.0.1 6

FAN73402 — LED Backlight Driving Boost Switch

Electrical Characteristics (Continued)

For typical values, TA = 25°C and VCC = 15 V, 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

Output Section (Boost / Dimming)

VDRV

Gate Output Voltage

VCC=15 V

10.8

11.8

12.8

V

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

Gate Output Rising Time (Boost)(4)

CL=2.0 nF

200

ns

tfl

Gate Output Falling Time (Boost) (4)

CL=2.0 nF

120

ns

Current Sense Section

tblank

Leading-Edge Blanking(4)

150

300

450

ns

tdelay,cl

Delay to Output of Current-Limit

Comparator(4)

180

ns

Voffset,clc

Offset Voltage of Current-Limit

Comparator(4)

-20

20

mV

Slope Compensation Section

Islope

Ramp Generator Current

36

45

54

µA

Rslope

Slope Compensation Resistor (4)

5

kΩ

Soft-Start Section

tss

Soft-Start Period(4)

fosc=200 kHz

3

ms

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)

1

µs

tAR

Auto-Restart Time for Over-Current

Protection(4)

fosc=200 kHz

640

µs

td,olpi

Delay for Triggering Open-LED Protection(4)

3

5

7

µs

td,olp

Delay for Open-LED Protection

fosc=200 kHz

40.96

ms

Vth,ovp

Over-Voltage Protection Threshold Voltage

2.85

3.00

3.15

V

Vhys,ovp

Over-Voltage Protection Voltage Hysteresis

0.1

V

Vth.csocp

Boost Switch Current-Limit Threshold

Voltage

0.45

0.50

0.55

V

Vth,ocp

LED Over-Current Protection Threshold

Voltage

1.4

(Min.

Clamp)

4.0xVADIM

4.0

(Max.

Clamp)

V

Vth,olp

Open-LED Protection Threshold Voltage(4)

0.15

0.20

0.25

V

TSD

Thermal Shutdown Temperature(4)

140

150

160

°C

THYS

Thermal Shutdown Hysteresis(4)

20

°C

Note:

4. These parameters, although guaranteed, are not tested in production.

FAN73402 • 1.0.1 7

FAN73402 — LED Backlight Driving Boost Switch

Typical Performance Characteristics

Figure 3. Start Threshold Voltage vs. Temperature

Figure 4. Start Threshold Voltage Hysteresis

vs. Temperature

Figure 5. Standby Current vs. Temperature

Figure 6. Shutdown Mode Supply Current vs.

Temperature

Figure 7. On-State Input Voltage vs. Temperature

Figure 8. Off-State Input Voltage vs. Temperature

8.1

8.3

8.5

8.7

8.9

9.1

9.3

9.5

9.7

9.9

-50 -25 0 25 50 75 100 125

Vth, [V]

Temperature, [℃]

0.3

0.5

0.7

0.9

1.1

1.3

1.5

1.7

-50 -25 0 25 50 75 100 125

Vth.hys, [V]

Temperature, [℃]

50

100

150

200

250

300

350

-50 -25 0 25 50 75 100 125

Ist, [µA]

Temperature, [℃]

0.5

1

1.5

2

2.5

3

3.5

4

4.5

-50 -25 0 25 50 75 100 125

ISD, [mA]

Temperature, [℃]

1.05

1.1

1.15

1.2

1.25

1.3

1.35

1.4

-50 -25 0 25 50 75 100 125

VON, [V]

Temperature, [℃]

1

1.05

1.1

1.15

1.2

1.25

1.3

-50 -25 0 25 50 75 100 125

VOFF, [V]

Temperature, [℃]

FAN73402 • 1.0.1 8

FAN73402 — LED Backlight Driving Boost Switch

Typical Performance Characteristics (Continued)

Figure 9. Error Amplifier Transconductance

vs. Temperature

Figure 10. Input Offset Voltage vs. Temperature

Figure 11. CMP Sink Current vs. Temperature

Figure 12. CMP Source Current vs. Temperature

Figure 13. Boost Oscillator Frequency vs. Temperature

Figure 14. Maximum Duty Cycle vs. Temperature

0

100

200

300

400

500

600

-50 -25 0 25 50 75 100 125

Gm, [umho]

Temperature, [℃]

-14

-10

-6

-2

2

6

10

14

-50 -25 0 25 50 75 100 125

Voffset, [mV]

Temperature, [℃]

50

100

150

200

250

300

350

-50 -25 0 25 50 75 100 125

Isin, [µA]

Temperature, [℃]

50

100

150

200

250

300

350

-50 -25 0 25 50 75 100 125

Isur, [µA]

Temperature, [℃]

185

190

195

200

205

210

215

-50 -25 0 25 50 75 100 125

fOSC, [KHz]

Temperature, [℃]

84

86

88

90

92

94

96

-50 -25 0 25 50 75 100 125

Dmax, [%]

Temperature, [℃]

FAN73402 • 1.0.1 9

FAN73402 — LED Backlight Driving Boost Switch

Typical Performance Characteristics (Continued)

Figure 15. 5 V Regulation Voltage vs. Temperature

Figure 16. PWM Dimming Input High Voltage

vs. Temperature

Figure 17. PWM Dimming Input Low Voltage

vs. Temperature

Figure 18. PWM Dimming Pull-Down Resistance

vs. Temperature

Figure 19. Gate Output Voltage vs. Temperature

Figure 20. Gate Output Drive Sink Current

vs. Temperature

4.85

4.9

4.95

5

5.05

5.1

5.15

-50 -25 0 25 50 75 100 125

VREF, [V]

Temperature, [℃]

1.2

1.3

1.4

1.5

1.6

1.7

1.8

-50 -25 0 25 50 75 100 125

VPDIM,H, [V]

Temperature, [℃]

1.1

1.2

1.3

1.4

1.5

1.6

1.7

-50 -25 0 25 50 75 100 125

VPDIM,L, [V]

Temperature, [℃]

80

100

120

140

160

180

200

220

240

-50 -25 0 25 50 75 100 125

RPDIM, [Kohm]

Temperature, [℃]

10.5

11

11.5

12

12.5

13

13.5

-50 -25 0 25 50 75 100 125

VDRV, [V]

Temperature, [℃]

50

100

150

200

250

300

-50 -25 0 25 50 75 100 125

Idsin, [mA]

Temperature, [℃]

FAN73402 • 1.0.1 10

FAN73402 — LED Backlight Driving Boost Switch

Typical Performance Characteristics (Continued)

Figure 21. Ramp Generator Current vs. Temperature

Figure 22. Auto-Restart Time for OC vs. Temperature

Figure 23. OVP Threshold Voltage vs. Temperature

Figure 24. OVP Hysteresis Voltage vs. Temperature

Figure 25. Delay for Over-Current Protection vs. Temperature

35

39

43

47

51

55

-50 -25 0 25 50 75 100 125

Islope, [µA]

Temperature, [℃]

0.45

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

-50 -25 0 25 50 75 100 125

tAR,[mS]

Temperature, [℃]

2.8

2.85

2.9

2.95

3

3.05

3.1

3.15

3.2

-50 -25 0 25 50 75 100 125

Vth,ovp,[V]

Temperature, [℃]

0

0.04

0.08

0.12

0.16

0.2

-50 -25 0 25 50 75 100 125

Vhys,ovp,[V]

Temperature, [℃]

25

30

35

40

45

50

55

-50 -25 0 25 50 75 100 125

td,olp,[mS]

Temperature, [℃]

FAN73402 • 1.0.1 11

FAN73402 — LED Backlight Driving Boost Switch

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 1.22 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 the 5 V

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:

 

󰇛󰇟󰇠󰇜 󰇟󰇠

(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:

 󰇟󰇠

(2)

VCMP

ILED

VLED

GATE

Soft-Start Period

t

V

Figure 26. Soft-Start Waveforms

LED Current Setting

During the boost converter operating periods, the output

LED current can be set by equation:

 󰇛󰇜

 

(3)

where ADIM(V) is ADIM pin applied voltage and, RSENSE

is the sensing resistor value.

Note:

5. 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 (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 0.3 V to 3 V

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 200 Hz dimming frequency. Even operating at 5 µs

dimming MOSFET turn-on time and extremely low

dimming duty, FAN73402 can operate LEDs with normal

peak current level.

FAN73402 • 1.0.1 12

FAN73402 — LED Backlight Driving Boost Switch

Internal Dimming MOSFET

A dimming MOSFET (200 V N-channel MOSFET) is

incorporated in the FAN73402. 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)=1.0 ) 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

5 k.

Feedback Loop Compensation

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 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.

FAN73402 adopts a Type-II compensator circuit.

Programmed Current Control

FAN73402 uses Current-Mode control. Current-Mode

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.

Programmable Slope Compensation

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 FAN73402

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.

An internal Rslope resistor (5 kΩ) 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 is

an important feature.

The value of an external series resistor (R1) can be

programmed. In normal DCM operation, 5 k is

recommended.

5k R1

RS

Ipeak=45µA

Iramp

VCS

VS

VSC

VCMP

Iinductor

m1 m2

m

Ts

Figure 27. Slope Compensation

Cycle-by-Cycle Over-Current Protection

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.

DRV

CS

CLK+LEB

-

+

0.5V

5k

Switch Off

R1RS

Id

vcs

Figure 28. Cycle-by-Cycle OCP Circuit

When the voltage drops at R1 and RS exceed a threshold

of approximately 0.5 V, the power MOSFET over-current

function is triggered after minimum turn-on time or LEB

time (300 ns).

The peak voltage level at CS terminal:

   󰇛 󰇜   

(4)

Choose the boost switch current-sensing resistor (RCS):

 



(5)

Open-LED Protection (OLP)

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 0.2 V,

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 5 μs, 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.

OLP blanking time is dependent on the boost switch

frequency, per Equation 6. FAULT OUT signal is made

through the FAULT pin, which needs to be connected 5 V

reference voltage through a pull-up resistor. In normal

operation, the FAULT pin voltage is pulled down to

ground. In OLP condition, the FAULT pin voltage is

pulled HIGH.

FAN73402 • 1.0.1 13

FAN73402 — LED Backlight Driving Boost Switch

 󰇟󰇠

(6)

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 FAULT

signal is used to turn off input power or the total system.

FAULT signal is only triggered in OLP condition.

V

0.2V

Time

OLPi

Triggered

VSENSE<0.2V

over 5µs

Dimming

off

If OLPi is triggerd,

Dimming is pulled

to 100% full duty

Dimming

VSENSE

FO

Dimming

off

OLP Released

VSENSE>0.2V

8192/f

seconds

Figure 29. Open-LED Protection

Note:

6. In LED-open load condition, OVP is triggered ahead

of OLP.

Over-Voltage Protection (OVP)

Over-voltage protection is triggered when the voltage of

the external output voltage reaches 3 V. After triggering

OVP, the dimming switch and boost switch are turned off.

The protection signal is recovered when the output

voltage divider is below 2.9 V.

OVP 3V

ROVP1

ROVP2

VLED

(Open)

Figure 30. Over-Voltage Trip Point

VOVP

3.0V

Time

2.9V

Boost

Gate

Figure 31. OVP Trigger and Release

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 (1.4 V ~ 4 V)

of the ADIM voltage x4. At 1 μs 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:

 󰇟󰇠

(7)

When VADIM=0.3 V (VADIMx4=1.2 V).

1. OCP threshold level is set to 1.4 V.

2. OCP is triggered at feedback voltage level =

1.4 V.

VSENSE

VADIM=0.3V

VSENSE=1.4V

GATE

Figure 32. OCP Waveforms at VADIM=0.3 V

When VADIM=0.8 V (VADIMx4=3.2 V).

1. OCP threshold level is set to 3.2 V.

2. OCP is triggered at VSENSE = 3.2 V.

VSENSE

VADIM=0.8V

VSENSE=3.2V

GATE

Figure 33. OCP Waveforms at VADIM=0.8 V

When VADIM=1.2 V (VADIMx4=4.8 V).

1. OCP threshold level is set to 4.0 V.

2. OCP is triggered at VSENSE = 4.0 V.

VSENSE

VADIM=1.2V

VSENSE=4.0V

GATE

Figure 34. OCP Waveforms at VADIM=1.2 V

FAN73402 • 1.0.1 14

FAN73402 — LED Backlight Driving Boost Switch

Typical Application Circuit (Boost Topology for LED Backlight)

Application

Input Voltage Range

Rated Output Power

Output Current

(Rated Voltage)

LED

LED Backlight TV

90 VDC 10%

250 mA (160 V)

48-LEDs/1-String

Features

 High Efficiency

 Constant Current Boost Converters

 High-Voltage, High-Current LED Driving

Typical Application Circuit

Figure 35. Typical Application Circuit

OVP

C13

1.2n

CN1

CON6

Vin 1

Vin 2

Vin 3

GND 4

GND 5

GND 6

R9 0R

C2

47uF/400V

D2 1SS355

C8

10n

C1

22uF/160V

IC1

FAN7340

FO

6

REF

5

SENSE

8DRAIN 9

RT

7

GND

3

CS

4

DRV

2

DRAIN 10

CMP 14

ENA 12

1VCC

OVP 13

BDIM 16

ADIM 15

R15

220K

C11

1.2n

R11

15k

C4

1u

R20

100k

Q1

FDPF7N50F

D3

1SS355

R4

100K

L1

200uH/PC44

C5

open

C10

1.2n

R8

0.2R/1W

R14

20K/open

R23

10k

R7 5.1k

R21

300k

R5

270k

R1 10R

R19

10k

C7

100n

R17 3.9K

TP1

TP

C6

6.8n

D1

FFD04H60S

C3

10uF/50V

CN2

CON6

N.C

1

N.C

2

VLED

3

VLED

4

LED1

5

LED2

6

R18

220K

R16

2.7R/1W

R10

16k

C12

1.2n

R22

300k

R13 3.9K

R6

300k

CN3

CON6

GND 2

On/Of f 6

ADIM 5

BDIM 4

VCC 1

FO 3

R12

100K/open

R2

270k

BDIM

FO

BDIM

ADIM

VCC

On/Of f

ENA

0

FAN73402

Vin : 90V

Vout : 160V

Output current : 250mA

Switching frequency : 200kHz

0

FAN73402 • 1.0.1 15

FAN73402 — LED Backlight Driving Boost Switch

Physical Dimension

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/.

X 45°

DETAIL A

SCALE: 2:1

8°

0°

NOTES: UNLESS OTHERWISE SPECIFIED

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

GAGE PLANE

C

C0.10

SEE DETAIL A

LAND PATTERN RECOMMENDATION

PIN ONE

INDICATOR

1

16

8

M

0.25

9

C B A

B

A

5.6

1.27 0.65

1.75

10.00

9.80

8.89

6.00

1.27

(0.30)

0.51

0.35

1.75 MAX

1.50

1.25

0.25

0.10 0.25

0.19

(1.04)

0.90

0.50

0.36

(R0.10)

0.50

0.25

4.00

3.80

FAN73402 • 1.0.1 16

FAN73402 — LED Backlight Driving Boost Switch

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