BD9408FV_技术文档

Datasheet

LED Drivers for LCD Backlights

1ch Boost Up Type

White LED Driver for Large LCD

BD9408FV

General Description

Key Specifications

BD9408FV is a high efficiency driver for white LEDs and

it is designed for large LCDs. BD9408FV has a boost

DC/DC converter that can supply appropriate voltage to

the light source of LEDs series array.

BD9408FV has some protect functions against fault

conditions, such as over voltage protection(OVP), over

current limit protection of DC/DC(OCP), LED OCP

protection, and over boost protection(FBMAX). Therefore,

it is available for a wide range output voltage and a wide

range load current.



Operating Power Supply Voltage Range:

9.0V to 35.0V



Oscillator Frequency of DC/DC:

150kHz(R_RT=100kΩ)

3mA(Typ)



Operating Current:

Operating Temperature Range: -40°C to +105°C

Package

SSOP-B14

W(Typ) x D(Typ) x H(Max)

5.00mm x 6.40mm x 1.35mm

Features



DC/DC Converter with Current Mode

LED Protection Circuit(Over Boost Protection, LED

OCP Protection)



Over Voltage Protection(OVP) for the Output Voltage

Adjustable Soft Start

Adjustable Oscillation Frequency of DC/DC

Wide Range of Analog Dimming 0.2V to 3.0V

LED Dimming PWM Over Duty Protection(ODP)

Applications



TV, Computer Display

Other LCD Backlighting

SSOP-B14

Typical Application Circuit

部品の記号を記入すること

〇Product structure: Silicon monolithic integrated circuit 〇This product has no designed protection against radioactive rays

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Contents

General Description........................................................................................................................................................................1

Features..........................................................................................................................................................................................1

Applications ....................................................................................................................................................................................1

Key Specifications ..........................................................................................................................................................................1

Package..........................................................................................................................................................................................1

Typical Application Circuit ...............................................................................................................................................................1

Contents .........................................................................................................................................................................................2

Pin Configuration ............................................................................................................................................................................3

Pin Descriptions..............................................................................................................................................................................3

Block Diagram ................................................................................................................................................................................4

Description of Pin Function.............................................................................................................................................................5

Absolute Maximum Ratings ............................................................................................................................................................8

Thermal Resistance........................................................................................................................................................................8

Recommended Operating Conditions.............................................................................................................................................8

Electrical Characteristics.................................................................................................................................................................9

Typical Performance Curves.........................................................................................................................................................11

List of Protection Detection Condition...........................................................................................................................................12

List of Protection Function Operation............................................................................................................................................12

Timing Chart .................................................................................................................................................................................13

Application Examples ...................................................................................................................................................................19

Selection of Components Externally Connected...........................................................................................................................20

I/O Equivalent Circuits ..................................................................................................................................................................28

Operational Notes.........................................................................................................................................................................29

Ordering Information.....................................................................................................................................................................31

Marking Diagram ..........................................................................................................................................................................31

Physical Dimension and Packing Information...............................................................................................................................32

Revision History............................................................................................................................................................................33

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Pin Configuration

(TOP VIEW)

1

2

3

4

5

6

7

14

13

12

11

10

9

VCC

OVP

REG90

CS

SFTON

ADIM

GATE

GND

RT

ISENSE

SSFB

DUTYP

DUTYON

PWM

8

Pin Descriptions

Pin No.

Pin Name

VCC

Function

1

2

Power supply voltage input

OVP

Over voltage protection detection

PWM dimming soft start setting

Analog dimming signal input

3

4

SFTON

ADIM

5

RT

DC/DC switching frequency setting

Over duty protection ON/OFF

External PWM dimming signal input

Over duty protection setting

6

DUTYON

PWM

7

8

DUTYP

SSFB

ISENSE

GND

9

Soft start setting, error amplifier output

LED current sensing

GND

10

11

12

13

14

GATE

CS

MOSFET GATE signal

Inductor current sensing

9.0V output voltage

REG90

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Block Diagram

V_CC

V_IN

VCC

OVP

REG90

VCC

UVLO

VREG

TSD

OVP

REG90

UVLO

REG90

PWM

COMP

RT

GATE

CS

+

-

OSC

CONTROL

LOGIC

-

LEB

Current

sense

SFTON

PWM

SFTON

LEDOCP

-

ISENSE

SSFB

+

1.515V

+

DUTYP

R_S

ERROR

amp

Over Duty

Protection

OSC

REG90

OverBoost

Auto-

Restart

Control

Fail

detect

DUTYON

ADIM

1/2

GND

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Description of Pin Function

If there is no description, the mentioned values are typical value.

Pin 1: VCC

This is the power supply pin of the IC. Input range is from 9V to 35V.

The operation starts at 7.5V or more and shuts down at less than 7.2V.

Pin 2: OVP

The OVP pin is the input for over voltage protection. If V_OVP≥ 3.0V, the over voltage protection will work. At the moment

of these detections, it sets GATE=L and starts to count up the abnormal interval. If OVP detection continues to count 4

GATE clks, IC reaches latch off. (Refer to “Timing Chart OVP Detection”) The OVP pin is high impedance, because the

internal resistance is not connected to a certain bias.

Even if OVP function is not used, input appropriate voltage because the open connection of this pin is not a fixed

voltage.

The setting example is separately described in the section ”OVP Setting”.

Pin 3: SFTON

The SFTON pin sets the soft start time for LED electric current at PWM=L to PWM=H. It performs the constant current

charge of 30.0μA to external capacitance C_SFTON(external capacitance of SFTON). The switching duty of GATE output

will be limited during 0V to SSFB voltage of the SFTON voltage. So the soft on interval t_SFTONcan be expressed as

follows.

퐶

×푉

ꢀꢁꢂꢃꢄ

ꢀꢀꢁ퐵

−6

푡_{푆퐹푇푂푁}

=

[s]

30×10

where:

푡_{푆퐹푇푂푁}is the operation period of soft on.

ꢅ_{푆퐹푇푂푁}is the external capacitance of the SFTON pin.

ꢆ

푆푆퐹ꢇ

is the SSFB pin voltage.

Pin 4: ADIM

This is the input pin for analog dimming signal. The ISENSE feedback voltage is set as 1/2 of this pin voltage. If V_ADIM

≥

3.03V, ISENSE feedback voltage is clamped to limit to flow LED large current. In this condition, the input current is

caused. Refer to ”ISENSE pin explanation”.

Pin 5: RT

This is the DC/DC switching frequency setting pin. DC/DC switching frequency is decided by connected resistor.

○Relation between Drive Frequency and RT resistance(ideal).

15000

푅_ꢈ푇

=

[kΩ]

−ꢉ

푓

×10

ꢀ푊

where:

푅_ꢈ푇is the external resistance of RT.

is DC/DC switching frequency.

ꢊ

푆ꢋ

Oscillation setting ranges 50kHz to 2000kHz.

Setting example is separately described in the section ”DC/DC Oscillation Frequency Setting”.

Pin 6: DUTYON

This is the ON/OFF setting pin of the LED PWM Over Duty Protection(ODP).

By adjusting DUTYON input voltage, ON/OFF of the ODP is adjusted.

State

DUTYON Input Voltage

V_{DUTYON_L}=-0.3V to +0.8V

V_{DUTYON_H}=1.5V to 18.0V

ODP=ON

ODP=OFF

And this is FAIL signal output(OPEN DRAIN) pin. At normal operation, PMOS will be OPEN state. During abnormality

detection PMOS will be in ON state and this pin is pulled up to the REG90 pin by 3.4kΩ.

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Description of Pin Function - continued

Pin 7: PWM

This is the PWM dimming signal input pin. High/Low level of PWM are the following.

State

PWM Input Voltage

V_{PWM_H}=1.5V to 18.0V

V_{PWM_L}=-0.3V to +0.8V

PWM=H

PWM=L

Do not input the pulse with Low section less than following values into the PWM pin at ODP function ON.

−ꢉ

푅_{퐷푈ꢌ푌ꢍ}×10

푡_{푃ꢋ푀퐿_푀퐼푁}

=

< 푡_푃ꢋ푀퐿[μs]

15

where:

푡_{푃ꢋ푀퐿_푀퐼푁}is the narrowest width of available PWM=L.

푅_{ꢎꢏ푇ꢐ푃}is the external resistance of DUTYP.

푡_푃ꢋ푀퐿is Low section of PWM.

Pin 8: DUTYP

This is the ODP setting pin. ODP(Over Duty Protection) is the function to limit duty of LED PWM by ODP detection

duty(ODP_DUTY) set by resistance(R_DUTYP) connected to DUTYP.

○Relation between LED PWM frequency f_PWM, ODP Detection Duty and DUTYP resistance(ideal)

1172×푂ꢎ푃

ꢑꢒꢂꢓ

푅_{ꢎꢏ푇ꢐ푃}

=

[kΩ]

푓

ꢔ푊ꢕ

where:

푅_{ꢎꢏ푇ꢐ푃}is the external resistance of DUTYP.

ꢖ퐷ꢍ_ꢎꢏ푇ꢐis ODP detection duty.

ꢊ

푃ꢋ푀

is PWM frequency.

R_DUTYPsetting ranges 15kΩ to 600kΩ.

Setting example is separately described in the section ”ODP Setting”.

Pin 9: SSFB

This is the pin which sets the soft start interval of DC/DC converter and the output pin of error amplifier. It performs the

constant current charge of 10.0μA to external capacitance C_SSFB, works as a soft start of DC/DC. When C_SSFB≤ 1nF,

be careful if the in-rush current during startup is too large, or if over boost detection(FBMAX) mask timing is too short.

It makes the following action after soft start completion(V_SSFB≥ 3.7V). When PWM=H, it compares ISENSE voltage to

analog dimming voltage(ADIM) and outputs error signal. When PWM=L, it holds V_SSFBat the edge of PWM=H to L,

and operates to hold the adjacent voltage. It detects over boost(FBMAX). If V_SSFB≥ 4.0V and PWM=H continue to

count 4 GATE clks, the CP counter starts. After that, only V_SSFB≥ 4.0V is monitored, When CP counter reaches 2048

clk(2¹¹clk), IC will be latched off.

(Refer to section “Timing Chart FBMAX Detection ”.)

The loop compensation setting is described in section "Loop Compensation".

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Description of Pin Function - continued

Pin 10: ISENSE

This is the input pin for the current sensing. Error amplifier compares the lower one among 1/2 of V_ADIMand 1.515V.

And it detects abnormal LED over current at V_ISENSE≥ 3.0V. If the GATE pin continues to count 4 GATE clks, it

becomes latch-off. (Refer to section “Timing Chart LED OCP Detection”.)

V_OUT

1.515

1.5

Error AMP

ISENSE

-

+

Gain=1/2

1.515V

ADIM

1/2

R_S

0.1

0

SSFB

0.2

3.0

V_ADIM[V]

Figure 1. Relation of the Feedback Voltage and V_ADIM

Figure 2. The ISENSE Pin Circuit Example

Pin 11: GND

This is the GND pin of the IC.

Pin 12: GATE

This is the output pin for driving the gate of the boost MOSFET. The high level is REG90. Frequency can be set by

resistor connected to the RT pin. Refer to ”DC/DC Oscillation Frequency Setting”, for pin description for the frequency

setting.

Pin 13: CS

The CS pin has two functions.

V_IN

(1) DC/DC Current Mode Feedback Pin

The inductor current is converted to the CS pin voltage by the sense resistor

R_CS.This voltage compared to the voltage set by error amplifier controls the

output pulse.

(2) Inductor Current Limit(OCP) Pin

The CS pin also has an over current protection(OCP). If V_CS≥ 0.4V, the

switching operation will be stopped compulsorily. And the next boost pulse

will be restarted to normal frequency.

I_D

GATE

CS

In addition, if V_CS≥ 1.0V continues to count 4 GATE clks, IC will be latch off.

As above OCP operation, if the current continues to flow nevertheless

GATE=L because of the destruction of the boost MOS, IC will stop the

operation completely.

C_CS

R_CS

GND

Figure 3. The CS Pin Circuit Example

Both of the above functions are enabled after 300ns when the GATE pin asserts high, because the Leading Edge

Blanking function(LEB) is included into this IC to prevent the effect of noise.

Refer to section “OCP Setting/Calculation Method for the Current Rating of DC/DC Parts”, for detailed explanation.

If C_CSis micro order, be careful that the limited value of NMOS drain current I_Dis more than the simple calculation.

Because the current I_Dflows not only through R_CSbut also through C_CS, as the CS pin voltage moves according to I_D.

Pin 14: REG90

This is the 9.0V output pin. Max source current is 15mA(Min).

VCC must be used in 10.5V or more for stable 9V output.

Place the ceramic capacitor connected to REG90 pin(1.0μF to 10μF) closest to REG90-GND pin.

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Absolute Maximum Ratings (Ta=25°C)

Parameter

Symbol

V_CC

Rating

Unit

V

Power Supply Voltage

-0.3 to +36

SFTON, RT, DUTYP, SSFB,

ISENSE, CS Pin Voltage

REG90 Pin Voltage

V_SFTON, V_RT, V_DUTYP

V_SSFB, V_ISENSE, V_CS

V_REG90

,

-0.3 to +7

V

-0.3 to +13

-0.3 to +15

V

GATE Pin Voltage

V_GATE

OVP, ADIM, DUTYON, PWM Pin

Voltage

V_OVP, V_ADIM, V_DUTYON,

-0.3 ~ +20

V

V_PWM

Tjmax

Maximum Junction Temperature

150

°C

Tstg

Storage Temperature Range

- 55 to + 150

Caution 1: Operating the IC over the absolute maximum ratings may damage the IC. The damage can either be a short circuit between pins or an open circuit

between pins and the internal circuitry. Therefore, it is important to consider circuit protection measures, such as adding a fuse, in case the IC is

operated over the absolute maximum ratings.

Caution 2: Should by any chance the maximum junction temperature rating be exceeded the rise in temperature of the chip may result in deterioration of the

properties of the chip. In case of exceeding this absolute maximum rating, design a PCB boards with thermal resistance taken into consideration by

increasing board size and copper area so as not to exceed the maximum junction temperature rating.

Thermal Resistance^{(Note 1)}

Thermal Resistance (Typ)

Parameter

Symbol

Unit

1s^{(Note 3)}

2s2p^{(Note 4)}

SSOP-B14

Junction to Ambient

Junction to Top Characterization Parameter^{(Note 2)}

θ_JA

159.6

13

92.8

9

°C/W

Ψ_JT

(Note 1) Based on JESD51-2A(Still-Air).

(Note 2) The thermal characterization parameter to report the difference between junction temperature and the temperature at the top center of the outside

surface of the component package.

(Note 3) Using a PCB board based on JESD51-3.

(Note 4) Using a PCB board based on JESD51-7.

Layer Number of

Measurement Board

Material

Board Size

Single

FR-4

114.3mm x 76.2mm x 1.57mmt

Top

Copper Pattern

Thickness

70μm

Footprints and Traces

Layer Number of

Measurement Board

Material

Board Size

114.3mm x 76.2mm x 1.6mmt

2 Internal Layers

4 Layers

FR-4

Top

Copper Pattern

Bottom

Copper Pattern

74.2mm x 74.2mm

Thickness

70μm

Copper Pattern

Thickness

35μm

Thickness

70μm

Footprints and Traces

74.2mm x 74.2mm

Recommended Operating Conditions

Parameter

Symbol

Topr

Min

Typ

+25

24.0

150

2.0

Max

+105

35.0

2000

3.0

Unit

°C

V

Operating Temperature

-40

9.0

50

Power Supply Voltage

V_CC

DC/DC Oscillation Frequency

Effective Range of ADIM Signal

PWM Input Frequency

f_SW

kHz

V

V_ADIM

f_PWM

C_REG90

C_SFTON

0.2

90

2000

10.0

1000

120

2.2

Hz

μF

pF

REG90 Pin External Capacitance^{(Note 5)}

1.0

SFTON Pin External Capacitance

100

470

(Note 5) There are the characteristic parts that effective capacitance value largely becomes small when the DC voltage is applied, and be careful because output

voltage may oscillate.

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Electrical Characteristics (Unless otherwise specified V_CC=24V Ta=25°C)

Parameter

Symbol

Min

Typ

Max

Unit

Conditions

Total Current Consumption

Circuit Current

I_CC

-

3

6

mA

V_PWM=3.0V

UVLO

Operation Voltage(VCC)

Hysteresis Voltage(VCC)

DC/DC

V_{UVLO_VCC}

V_{UHYS_VCC}

6.5

7.5

8.5

V

V_CC=Sweep Up

150

300

600

mV

V_CC=Sweep Down

ISENSE Threshold Voltage 1

ISENSE Threshold Voltage 2

ISENSE Threshold Voltage 3

V_LED1

V_LED2

V_LED3

0.346

0.992

1.489

0.350

1.000

1.500

0.354

1.008

1.511

V

V_ADIM=0.7V

V_ADIM=2.0V

V_ADIM=3.0V

V_ADIM=3.3V

(as Masking Analog Dimming)

ISENSE Clamp Voltage

Oscillation Frequency

V_LED4

f_SW

1.497

142.5

-0.3

1.515

150

-

1.533

157.5

V

kHz

V

R_RT=100kΩ

V_{RT_1}

x 90%

RT Short Protection Range

V_{RT_DET}

V_RT=Sweep Down

RT Pin Voltage

V_{RT_1}

-

2.0

95

-

V

R_RT=100kΩ

GATE Pin MAX Duty Output

D_{MAX_DUTY}

90

99

%

GATE Pin ON Resistance

(as source)

R_{ON_GSO}

R_{ON_GSI}

2.5

2.0

5.0

4.0

10.0

8.0

Ω

GATE Pin ON Resistance

(as sink)

SFTON Pin Source Current

I_SFTSO

R_SFTDIS

I_SSSO

-37.5

-

-30.0

1.5

-22.5

2.5

μA

kΩ

μA

V_PWM=3.0V

V_SSFB=2.0V

SFTON Pin Discharge Resistance

SSFB Source Current(at Soft Start)

-13.0

-10.0

-7.0

V_ISENSE=0.2V, V_ADIM=3.0V,

V_SSFB=1.0V

V_ISENSE=2.0V, V_ADIM=3.0V,

V_SSFB=1.0V

SSFB Source Current

SSFB Sink Current

I_SSFBSO

I_SSFBSI

-115

85

-100

100

-85

μA

115

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Electrical Characteristics - continued (Unless otherwise specified V_CC=24V Ta=25°C)

Parameter

DC/DC Protection

Symbol

Min

Typ

Max

Unit

Conditions

OCP Detect Voltage

OCP Latch Off Detect Voltage

OVP Detect Voltage

OVP Detect Hysteresis

OVP Pin Leak Current

LED Protection Block

LED OCP Detect Voltage

Over Boost Detection Voltage

Dimming

V_OCP

360

0.85

2.88

150

-2

400

1.00

3.00

200

0

440

1.15

3.12

250

+2

mV

V

V_CS=Sweep Up

V_OCPOFF

V_{OVP_DET}

V_{OVP_HYS}

I_{OVP_LK}

V_CS=Sweep Up

V_OVP=Sweep Up

V_OVP=Sweep Down

V_OVP=4.0V

V

mV

μA

V_LEDOCP

V_FBMAX

2.88

3.84

3.00

4.00

3.12

4.16

V

V_ISENSE=Sweep Up

V_SSFB=Sweep Up

ADIM Pin Leak Current

ISENSE Pin Leak Current

REG90

I_{ADIM_LK}

-2

0

+2

μA

V_ADIM=2.0V

I_{ISENSE_LK}

V_ISENSE=4.0V

REG90 Output Voltage 1

REG90 Output Voltage 2

V_{REG90_1}

V_{REG90_2}

8.955

8.910

9.000

9.045

9.090

V

I_REG90=0mA

I_REG90=-15mA

I_{REG90_SOM}

REG90 Max Source Current

REG90_UVLO Detect Voltage

15

-

mA

V

AX

V_{REG90_UVD}

ET

5.22

6.00

6.78

V_REG90=Sweep Down

PWM

PWM Pin H Voltage

V_{PWM_H}

V_{PWM_L}

R_PWM

1.5

-0.3

600

-

18

V

PWM Pin L Voltage

+0.8

1400

PWM Pin Pull Down Resistance

DUTYON

1000

kΩ

V_PWM=3.0V

DUTYON Pin H Voltage

DUTYON Pin L Voltage

DUTYON Pin Pull Down Resistance

Over Duty Protection

PWM ODP Protection Detect Duty

V_{DTYON_H}

V_{DTYON_L}

R_DTYON

1.5

-0.3

600

-

18

V

+0.8

1400

1000

kΩ

V_DUTYON=3.0V

D_ODP

-

-0.3

-

35

-

%

V

f_PWM=120Hz,R_DUTYP=341kΩ

V_DUTYP=Sweep Down

R_DUTYP=100kΩ

V_{DUTYP_1}

x 90%

DUTYP Short Protection Range

V_{DUTYP_DET}

V_{DUTYP_1}

DUTYP Pin Voltage

Timer

2.0

-

V

Abnormal Detection Time

Auto-Restart Time

t_LATCH

-

2.5

-

ms

f_SW=800kHz

t_AUTO

163

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Typical Performance Curves

(Reference Characteristic)

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

10

8

6

4

PWM=3.0V

Ta=25°C

2

0

10

15

20

25

30

35

10

15

20

25

30

35

Power Supply Voltage:V_CC[V]

Figure 4. Circuit Current vs Power Supply Voltage

Figure 5. REG90 Voltage vs Power Supply Voltage

1.6

1.4

1.2

1.0

0.8

100

80

60

40

0.6

V_CC=24V

Ta=25°C

V_CC=24V

Ta=25°C

0.4

0.2

0.0

20

0

1

2

3

4

0

1

2

3

4

SSFB Voltage:V_SSFB[V]

ADIM Voltage:V_ADIM[V]

Figure 6. ISENSE Feedback Voltage vs ADIM Voltage

Figure 7. Duty Cycle vs SSFB Voltage

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List of Protection Detection Condition

If there is no description, the mentioned values are typical value.

Detect Condition

Protect

Function

Detection

Timer

Operation

Release Condition

Protection Type

Detection Condition

PWM

Auto-Restart

(Judge Periodically

whether Normal or Not)

Auto-Restart

(Judge Periodically

whether Normal or Not)

FBMAX

SSFB

V_SSFB≥ 4.0V

H(4clk)

V_SSFB< 4.0V

2¹¹clk

4clk

LED OCP

ISENSE

V_ISENSE≥ 3.0V

-

V_ISENSE< 3.0V

RT GND Short

RT High Short

RT

V_RT< V_{RT_1}×90%

V_RT≥ 5.0V

-

Release RT=GND

Release RT=H

NO

Restart by Release

REG90 UVLO

VCC UVLO

REG90

VCC

V_REG90< 6.0V

V_CC< 7.2V

-

V_REG90≥ 6.5V

VCC ≥ 7.5V

NO

Restart by Release

Auto-Restart

OVP

OCP

OVP

CS

V_OVP≥ 3.0V

V_CS≥ 0.4V

V_CS≥ 1.0V

-

V_OVP< 2.8V

-

4clk

NO

(Judge Periodically

whether Normal or Not)

Pulse by Pulse

Auto-Restart

(Judge Periodically

whether Normal or Not)

OCP LATCH

CS

V_CS< 1.0V

4clk

DUTYP GND

Short

V_DUTYP< V_{DUTYP_1}

x 90%

Release

DUTYP=GND

DUTYP

-

NO

Restart by Release

DUTYP High

Short

V_DUTYP≥ 5.0V

Release DUTYP=H

-

DUTYON=H

and

PWM On Duty >

Setting Duty by

DUTYP Resistor

ODP^{(Note 1)}

PWM

H

NO

Cycle by Cycle

The clk number of the list corresponds to the oscillation frequency of DC/DC.

(Note 1) When PWM=L → H is input, PWM duty count start. When PWM=H → L is input, the count is reset. The GATE output maintain Low until PWM=H → L is

inputted again in PWM = 100% when ODP works once.

List of Protection Function Operation

Operation of the Protect Function

Protect Function

DC/DC Gate Output

SSFB Pin

SFTON Pin

PMOS of DUTYON Pin

Stop after timer

operation

Discharge after timer

operation

Discharge after timer

operation

ON after timer

operation

FBMAX

Discharge after timer

operation

Discharge after timer

operation

ON after timer

operation

LED OCP

Stop Immediately

RT GND Short

RT High Short

REG90 UVLO

VCC UVLO

Stop Immediately

Not Discharge

OPEN

Discharge Immediately Discharge Immediately

Discharge after timer

operation

Discharge after timer

operation

ON after timer

operation

OVP

OCP

Stop Immediately

Not Discharge

OPEN

Stop after timer

operation

Discharge after timer

operation

Discharge after timer

operation

ON after timer

operation

OCP LATCH

DUTYP GND Short

DUTYP High Short

ODP

Stop Immediately

Immediately Low

Not Discharge

OPEN

Refer to section “Timing Chart” for details.

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Timing Chart

If there is no description, the mentioned values are typical value.

1

PWM Start-up

VCC

7.5V

PWM

6.5V

REG90

SSFB

0.4V

SFTON

ADIM

0.4V

V_ＡＤＩＭ

2

ISENSE

GATE

STATE

NORMAL

STANDBY

SS

OFF

(*1)(*2)

(*3)

(*4)

Figure 8. PWM Start Up

(*1) REG90 starts up when VCC reaches 7.5V. In the state where the PWM signal is not inputted, the SSFB pin is not

charged and DC/DC does not start to boost, either.

(*2) When REG90 is 6.5V or more, the reset signal is released.

(*3) The charge of the SS pin starts at the positive edge of PWM=L to H, and the soft start starts. And while V_SSFBor

V_SFTONis less than 0.4V, the GATE pulse does not output. The SSFB pin continues charging regardless of PWM

and OVP level.

(*4) The soft start interval will end if V_ISENSEreaches V_ADIM/2. At this time, V_OUT(LED anode voltage) reaches the

voltage which the setting LED electric current flows in.

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Timing Chart - continued

2

Turn Off

10V

VCC

7.2V

PWM

9.0V

REG90

SSFB

SFTON

0.4V

GATE

V_OUT

STATE

ON

OFF

(*1)(*2)

Figure 9. Turn Off

(*1)When V_CC< 10.0V, IC cannot keep V_REG90=9V.

(*2)When V_CC< 7.2V, boost operation stops and IC becomes OFF.

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Timing Chart - continued

3

Soft Start Function

7.2V

7.5V

VCC

PWM

6.0V

REG90

OVP

6.5V

3.0V

2.8V

4clk

DUTYON

SSFB

SFTON

(*1)

(*2)

(*3)

(*4)

Figure 10. Soft Start Function

(*1) The SSFB and SFTON pin charge do not start by just V_CC=7.5V. PWM=H is required to start the soft start. In the

low SSFB or SFTON voltage, the GATE pin duty depends on the SSFB or SFTON voltage. And while the SSFB or

SFTON is less than 0.4V, the pulse does not output.

(*2) When V_CC< 7.2V, the SSFB and SFTON pin are discharged.

(*3) When V_REG90< 6.0V, the SSFB and SFTON pin are discharged.

(*4) The SSFB and SFTON pin are not discharged by the abnormal detection of the latch off type such as OVP until

the latch off.

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Timing Chart - continued

4

OVP Detection

VCC

PWM

REG90

OVP

3.0V

2.8V

3.0V

Abnormal

COUNTER

Less than

Gate 4count

Less than

Gate 4count

AUTO COUNTER

SSFB

131072 count

0.4V

SFTON

GATE

DUTYON

STATE

Latch off and

AUTO COUNTER

NORMAL

OVP

NORMAL

OVP

SS

NORMAL

(*6) (*7)

OVP

NORMAL

abnormal

(*1)

(*2)

(*3)

(*4) (*5)

Figure 11. OVP Detection

(*1) As OVP is detected, the output GATE=L and the abnormal counter starts.

(*2) If OVP is released less than 4 GATE clks, the boost operation restarts.

(*3) As the OVP is detected again, the boost operation is stopped.

(*4) As the OVP detection continues to count 4 GATE clks, IC will be latched off. After latched off, auto counter starts

counting.

(*5) Once IC is latched off, the boost operation does not restart even if OVP is released.

(*6) When auto counter reaches 131072clk(2¹⁷clk), IC will be auto-restarted. The auto-restart interval can be

calculated by the external resistor of the RT pin. (Refer to the section “Abnormal Detection Time and Auto-Restart

Time Setting”.)

(*7) The operation of the OVP detection is not related to the logic of PWM.

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Timing Chart - continued

5

FBMAX Detection

VCC

PWM

REG90

4.0V

SSFB

GATE

0.4V

・・・・・

①

②

③

④

CP COUNTER

2048 count

AUTO COUNTER

SFTON

131072 count

DUTYON

Latch off and

AUTO COUNTER

STANDBY

SS

NORMAL

(*1)

CP COUNTER

SS

STATE

(*3)

(*4)

(*2)

Figure 12. FBMAX Detection

(*1) When the PWM=H and SSFB=H(V_SSFB≥ 4.0V), the abnormal counter does not start immediately.

(*2) The CP counter will start if the PWM=H and the SSFB=H detection continues up to 4 clks of the GATE frequency.

Once the count starts, only SSFB level is monitored.

(*3) When the FBMAX detection continues till the CP counter reaches 2048 clks(2¹¹clks), IC will be latched off. The

latch off interval can be calculated by the external resistor of the RT pin. (Refer to the section “Abnormal Detection

Time and Auto-Restart Time Setting”.)

(*4) When auto counter reaches 131072 clks(2¹⁷clks), IC will be auto-restarted. The auto-restart interval can be

calculated by the external resistor of the RT pin. (Refer to the section “Abnormal Detection Time and Auto-Restart

Time Setting”.)

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Timing Chart - continued

6

LED OCP Detection

VCC

REG90

PWM

3.0V

ISENSE

Abnormal

COUNTER

4count

Less than

4count

Less than

4count

AUTO COUNTER

131072 count

SSFB

GATE

0.4V

SFTON

DUTYON

Latch off and

AUTO COUNTER

STATE NORMAL LEDOCP NORMAL

abnormal

LEDOCP

abnormal

SS

LEDOCP NORMAL

abnormal

NORMAL

(*6) (*7)

(*1)

(*2)

(*3)

(*4) (*5)

Figure 13. LED OCP Detection

(*1) If V_ISENSE≥ 3.0V and LED OCP is detected, GATE becomes Low.

(*2) If LED OCP is released within 4 GATE clks, the boost operation restarts.

(*3) As the LED OCP is detected again, the boost operation is stopped.

(*4) If the LED OCP detection continues to count 4 GATE clks. IC will be latched off. After latched off, auto counter

starts counting.

(*5) Once IC is latched off, the boost operation does not restart even if the LED OCP releases.

(*6) When auto counter reaches 131072 clks(2¹⁷clks), IC will be auto-restarted. The auto-restart interval can be

calculated by the external resistor of the RT pin. (Refer to the section “Abnormal Detection Time and Auto-Restart

Time Setting Timer Latch Time Setting”.)

(*7) The operation of the LED OCP detection is not related to the logic of the PWM.

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Application Examples

Introduce an example application using the BD9408FV.

1

Basic Application Example

V_OUT

V_CC

V_IN

VCC

OVP

REG90

RT

GATE

CS

SFTON

PWM

ADIM

ISENSE

SSFB

DUTYP

R_S

DUTYON

GND

Figure 14. Basic Application Example

2

Analog Dimming or PWM Dimming Examples

V_OUT

V_CC

V_IN

V_CC

V_IN

VCC

OVP

REG90

RT

REG90

RT

GATE

CS

GATE

CS

SFTON

REG90

PWM

ADIM

PWM

ADIM

ISENSE

SSFB

ISENSE

SSFB

DUTYP

R_S

DUTYON

GND

Figure 15. Example Circuit for Analog Dimming

Figure 16. Example Circuit for PWM Dimming

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Selection of Components Externally Connected

If there is no description, the mentioned values are typical value.

1

Start Up Operation and Soft Start External Capacitance Setting

The below explanation is the startup sequence of this IC.

1

5V

V_OUT

VCC

SSFB

COMP

SFTON

VSSFB

OSC

GATE

CS

DRIVER

OSC

PWM

GATE

V_OUT

2

SSFB

ISENSE

PWM

3

I_LED

4

LED_OK

5

Figure 17. Start Up Waveform

(1)Explanation of start up sequence

Figure 18. Circuit Behavior at Startup

1. Reference voltage REG90 starts by V_CC=7.5V.

2. SSFB starts to charge at the time of first PWM=H.

3. When SSFB reaches the lower point of internal sawtooth waveform, the GATE pin outputs pulse and starts to

boost V_OUT

.

4. It boosts V_OUTand V_OUTreaches the voltage to be able to flow LED current.

5. If LED current flows the decided level or more, start up behavior completes.

(2)Method of setting SSFB external capacitance

According to the sequence described above, start time t_SSFBis the time that LED current flows the decided level or

more. The equality on t_SSFBis as follows.

퐶

×푉

ꢀꢀꢁ퐵

푡_푆푆퐹ꢇ

=

[s]

퐼

ꢀꢀꢁ퐵

where:

푡_푆푆퐹ꢇis start time.

ꢅ_푆푆퐹ꢇis the external capacitance of the SSFB pin.

is the SSFB pin voltage.

ꢆ

푆푆퐹ꢇ

ꢗ_푆푆퐹ꢇis SSFB source current.

If C_SSFBis set to very small value, rush current flows into the inductor at startup. On the contrary, if C_SSFBis enlarged

too much, LED will light up gradually. Since C_SSFBdiffers in the constant set up with the characteristic searched for

and differs also by factors, such as a voltage rise ratio, an output capacitance, DC/DC frequency and LED current,

confirm with the actual device.

[Setting Example]

When C_SSFB=0.1μF, V_SSFB=3.7V, I_SSFB=10μA, t_SSFBis as follows.

−6

0.1×10

푡_푆푆퐹ꢇ

=

^×3.7= ꢘ.ꢘꢙꢚ

[s]

−6

10×10

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Selection of Components Externally Connected - continued

2

SFTON External Capacitance Setting

t_SFTON

It sets the soft start time for LED electric current at PWM=L to PWM=H.

It performs the constant current charge of 30.0μA to external

capacitance C_SFTON. The switching duty of GATE output will be limited

during 0V to SSFB voltage of SFTON voltage. So the soft on interval

t_SFTONcan be expressed as follows.

PWM

SFTON

SSFB

퐶

×푉

ꢀꢁꢂꢃꢄ

ꢀꢀꢁ퐵

−6

푡_{푆퐹푇푂푁}

=

[s]

30×10

where:

I_LED

푡_{푆퐹푇푂푁}is the operation period of soft on.

ꢅ_{푆퐹푇푂푁}is the external capacitance of the SFTON pin.

ꢆ

.

is the SSFB pin voltage.

푆푆퐹ꢇ

GATE

Figure 19. Soft ON Function

[Setting Example]

When C_SFTON=1000pF, V_SSFB=3V, soft on time is as follows.

−ꢛꢜ

1000×10

30×10

×3

푡_{푆퐹푇푂푁}

=

= ꢝꢘꢘ × ꢝꢘ^ꢞꢟ

[s]

−6

3

VCC Series Resistance Setting

Here are the following effects of inserting series resistor R_VCCinto VCC line.

(1) In order to drop the voltage VCC, it is possible to suppress the

heat generation of the IC.

V_CC

(2) It can limit the inflow current to VCC line. However, if

resistance R_VCCis set bigger, VCC voltage becomes under

minimum operation voltage(V_CC< 9V). R_VCCmust be set to an

appropriate series resistance.

R_VCC

ΔV

VCC

I_IN

IC’s inflow current line I_INhas the following inflow lines.

●IC’s circuit current…I_CC

I_CC

●Current to DC/DC DRIVER…I_DCDC

●Current of R_REGconnected to REG90…I_REG

Internal

-

REG90

I_REG

+

These decide the voltage ΔV at R_VCC

.

BLOCK

R_REG

VCC pin voltage at that time can be expressed as follows.

I_DCDC

ꢆ_퐶퐶= ꢆ ꢠ (ꢗ_퐶퐶+ ꢗ_ꢎ퐶ꢎ퐶+ ꢗ_ꢈ퐸퐺) × 푅_푉퐶퐶≥ 9

[V]

퐼푁

I_GATE

GATE

DC/DC

Here, judgment is the 9V minimum operation voltage.

DRIVER

Consider a sufficient margin when setting the series resistor of

VCC.

Figure 20. VCC Series Resistance Circuit Example

[Setting Example]

Above equation is translated as follows.

ꢆ ꢠ 9

퐼푁

푅_푉퐶퐶

=

ꢗ_퐶퐶+ ꢗ_ꢎ퐶ꢎ퐶+ ꢗ_ꢈ퐸퐺

When V_IN=24V, I_CC=3.0mA, I_DCDC=2.0mA, I_REG=0.9mA(R_REG=10kΩ), R_VCCvalue is calculated as follows.

24ꢞꢡ

푅_푉퐶퐶

=

= ꢣ.ꢤꢥ

[kΩ]

(

)

0.003ꢢ0.002ꢢ0.000ꢡ ×1000

Set each values with tolerance and margin.

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Selection of Components Externally Connected – continued

4

LED Current Setting

LED current can be adjusted by setting the resistance R_S[Ω] which connects to the ISENSE pin and ADIM[V].

With DC dimming(V_ADIM< 3.03V)

1

푅_푆= × ^푉

[Ω]

퐴ꢑꢦꢕ

퐼

ꢧꢨꢑ

2

푅_푆is the external resistance of ISENSE.

is the ADIM pin voltage.

ꢆ

ꢩꢎ퐼푀

ꢗ_퐿퐸ꢎis LED current.

Without DC dimming(V_ADIM≥ 3.03V)

1

3.03

푅_푆= × _퐼

[Ω]

2

ꢧꢨꢑ

[Setting Example]

When I_LED=200mA, V_ADIM=2.0V, R_Sis as below.

1

2.0

푅_푆= × ^푉

= × = ꢤ

[Ω]

퐴ꢑꢦꢕ

2

퐼

2

0.2

ꢧꢨꢑ

5

DC/DC Oscillation Frequency Setting

R_RTwhich connects to the RT pin sets DC/DC oscillation frequency f_SW

Frequency (fsw)

.

15000

푅_ꢈ푇

=

[kΩ]

−ꢉ

푓

×10

ꢀ푊

GATE

CS

푅_ꢈ푇is the external resistance of RT.

is DC/DC oscillation frequency.

ꢊ

푆ꢋ

RT

R_CS

R_RT

[Setting Example]

When f_SW=200kHz, R_RTis as follows.

GND

15000

푅_ꢈ푇

=

= ꢚꢤ

−ꢉ

[kΩ]

Figure 21. The RT Pin Setting Example

−ꢉ

ꢉ

푓

×10

200×10 ×10

ꢀ푊

6

ODP Setting

R_DUTYPwhich connects to the DUTYP pin sets the ODP detection duty.

1172×푂ꢎ푃

GATE

ꢑꢒꢂꢓ

푅_{ꢎꢏ푇ꢐ푃}

=

[kΩ]

푓

ꢔ푊ꢕ

CS

DUTYP

R_CS

R_DUTYP

푅_{ꢎꢏ푇ꢐ푃}is the external resistance of DUTYP.

ꢖ퐷ꢍ_ꢎꢏ푇ꢐis ODP detection duty [%]

ꢊ

푃ꢋ푀

is PWM frequency.

ISENSE

GND

R_S

PWM

Figure 22. The ODP Pin Setting Example

[Setting Example]

When f_PWM=120Hz, ODP_DUTY=35%, R_DUTYPis as follows.

f_PWM

PWM

GATE

LED current

1172×35

푅_{ꢎꢏ푇ꢐ푃}

=

= ꢙꢥꢝ.8

[kΩ]

120

ODP_DUTY

Figure 23. PWM Dimming Wave Form at ODP

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7

OVP Setting

The OVP pin is the input for over-voltage protection of output voltage.

Even if OVP function is not used, input appropriate voltage because the open connection of this pin is not a fixed

voltage.

(1)OVP Detection Equation

If V_OUTis boosted abnormally, V_OVPDET(the detect voltage of OVP),

R₁, R₂can be expressed by the following formula.

V_OUT

R₁

ꢞ3.0)

푅₁= 푅₂× ^(푉

[Ω]

ꢃꢪꢔꢃꢒꢂ

OVP

+

-

3.0

2.8V/3.0V

R₂

where:

C_OVP

ꢆ_{푂푉푃푂ꢏ푇}is OVP detection voltage in V_OUT

푅₁is resistance between the OVP pin and V_OUT

푅₂is resistance between the OVP pin and GND.

.

Figure 24. OVP Setting Example

(2)OVP Release Equation

By using R₁and R₂in the above equation, the release voltage of OVP, V_OVPCANcan be expressed as follows.

ꢆ_{푂푉푃퐶ꢩ푁}= ꢣ.8ꢆ × ^{(ꢈ ꢢꢈ )}

[V]

ꢛ

ꢜ

ꢈ

ꢜ

where:

ꢆ_{푂푉푃퐶ꢩ푁}is OVP release voltage.

[Setting Example]

When V_OUT=40V, V_OVPOUT=48V, R₂=10kΩ, R₁is as follows.

ꢞ3.0)

푅₁= 푅₂× ^(푉

= ꢝꢘ × ꢝꢘ³× ^(4ꢫꢞ3)= ꢝꢤꢘ × ꢝꢘ³

[Ω]

ꢃꢪꢔꢃꢒꢂ

3.0

3

By using these R₁and R₂, the release voltage of OVP, V_OVPCANis as follows.

ꢉ

ꢆ_{푂푉푃퐶ꢩ푁}= ꢣ.8 × ^{(ꢈ ꢢꢈ )}= ꢣ.8 × ^{(150×10 ꢢ10×10 )}= ꢥꢥ.8

[V]

ꢛ

ꢜ

ꢉ

ꢈ

10×10

ꢜ

8

Abnormal Detection Time and Auto-Restart Time Setting

About over boost protection(FBMAX), abnormal detection counter(CP Counter) is set by counting GATE clk frequency

which is set at the RT pin. About the behavior from abnormal detection to latch-off and auto-restart, refer to the section

“Timing Chart”.

The condition V_SSFB≥ 4.0V and PWM=H continues to count 4 GATE clks, counting starts from the timing. After that,

only the SSFB voltage is monitored and latch off occurs after below time has passed.

ꢈ

ꢬꢂ

푡_{퐿ꢩ푇퐶퐻}= ꢣ¹¹× _1.5×10= ꢣꢘꢥ8 ×

[s]

ꢛꢭ

1.5×10

ꢈ

ꢬꢂ

푡_ꢩꢏ푇푂= ꢣ¹⁷× _1.5×10= ꢝꢙꢝꢘꢚꢣ ×

ꢛꢭ

1.5×10

where:

푡_{퐿ꢩ푇퐶퐻}is the time until latch condition occurs.

푡_ꢩꢏ푇푂is the auto restart time.

푅_ꢈ푇is the resistor value connected to the RT pin.

[Setting Example]

When R_RTis 100kΩ, t_LATCHand t_AUTOare as follows.

ꢉ

100×10

푡_{퐿ꢩ푇퐶퐻}= ꢣꢘꢥ8 × _1.5×10= ꢝꢙ.ꢚ

[ms]

ꢛꢭ

ꢉ

푡_ꢩꢏ푇푂= ꢝꢙꢝꢘꢚꢣ × ^100×10= 8ꢚꢙ.8

1.5×10

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Selection of Components Externally Connected – continued

9

OCP Setting/Calculation Method for the Current Rating of DC/DC Parts

OCP detection stops the switching when the CS pin voltage is 0.4V or more. The resistor value of the CS pin, R_CS

needs to be considered by the inductor current. And the current rating of DC/DC external parts is required more than

the peak current of the inductor.

Shown below are the calculation method of the inductor peak current, the selection method of R_CS(the resistor value

of the CS pin) and the current rating of the external DC/DC parts at Continuous Current Mode.

(The calculation method of the inductor peak current, I_PEAKat continuous current mode)

At first, since the ripple voltage at the CS pin depends on

the application condition of DC/DC. And then, the average input

current of the inductor is calculated as follows.

V_OUT

L

V_IN

I_L

푉

×퐼

ꢃꢒꢂ ꢃꢒꢂ

ꢗ_퐼푁=

[A]

−ꢜ

푉

ꢦꢄ

×휂×10

fsw

ꢗ_퐼푁is the average input current of the inductor.

ꢆ_푂ꢏ푇is DC/DC output voltage.

ꢗ_푂ꢏ푇is LED total current.

GATE

ꢆ

is DC/DC input voltage.

퐼푁

CS

ꢮ is Efficiency of DC/DC [%].

R_cs

GND

And the ripple current of the inductor caused by DC/DC operation

can be calculated as follows.

(푉

ꢞ푉 )×푉

ꢃꢒꢂ

ꢦꢄ

∆ꢗ_퐿=

[A]

Figure 25. Calculation Method of I_PEAK

퐿×푉

×푓

ꢃꢒꢂ

ꢀ푊

∆ꢗ_퐿is the ripple current of the inductor.

ꢯ is the inductor value.

ꢊ

푆ꢋ

is DC/DC oscillation frequency.

(V)

On the other hand, the peak current of the inductor I_PEAKis

as follows.

ꢗ_푃퐸ꢩ퐾= ꢗ_퐼푁+ ^∆퐼

[A]

(1)

ꢧ

2

ꢗ_푃퐸ꢩ퐾is the peak current of the inductor.

（A)

(t)

Therefore, the bottom current of the inductor is as follows.

I_PEAK

I_IN

ΔI_L

ꢗ_푀퐼푁= ꢗ_퐼푁ꢠ ^∆퐼표푟 ꢘ

[A]

ꢧ

2

I_MIN

ꢗ_푀퐼푁is the bottom current of the inductor.

(t)

（V)

0.4V

If I_MIN> 0, the operation mode is CCM(Continuous Current Mode),

otherwise the mode is DCM(Discontinuous Current Mode).

(The selection method of R_CSat Continuous Current Mode)

I_PEAKflows into R_CSand that causes the voltage signal to the CS pin.

(Refer to the timing chart at the right)

V_CSPEAK

The peak voltage of the CS pin is as follows.

(t)

ꢆ_{퐶푆푃퐸ꢩ퐾}= 푅_퐶푆× ꢗ_푃퐸ꢩ퐾[V]

Figure 26. Inductor Current Waveform

ꢆ

is the peak voltage of the CS pin.

퐶푆푃퐸ꢩ퐾

As this V_CSPEAKreaches 0.4V, the DC/DC output stops the switching.

Therefore, R_CSvalue is necessary to meet the condition below.

푅_퐶푆× ꢗ_푃퐸ꢩ퐾≪ ꢘ.ꢥ [V]

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Selection of Components Externally Connected – continued

(The current rating of the external DC/DC parts)

The peak current as the CS voltage reaches OCP level(0.4V) is defined as I_{PEAK_DET}

.

0.4

ꢗ_{푃퐸ꢩ퐾_ꢎ퐸푇}

=

[A]

(2)

ꢈ

ꢰꢀ

ꢗ_{푃퐸ꢩ퐾_ꢎ퐸푇}is the inductor peak current when V_CSis 0.4V.

The relationship among I_PEAK(equation(1)), I_{PEAK_DET}(equation(2)) and the current rating of parts is required to meet the

following.

ꢗ_푃퐸ꢩ퐾≪ ꢗ_{푃퐸ꢩ퐾_ꢎ퐸푇}≪ ꢌℎ푒 푐푢푟푟푒푛푡 푟푎푡ꢱ푛푔 표ꢊ 푝푎푟푡푠

Make the selection of the external parts such as FET, Inductor, diode meet the above condition.

[Setting Example]

When V_OUT=40V, I_OUT=0.48A, V_IN=24V, η=90%, I_INis as follows.

푉

×퐼

40×0.4ꢫ

ꢃꢒꢂ ꢃꢒꢂ

ꢗ_퐼푁=

=

= ꢘ.89

−ꢜ

[A]

−ꢜ

푉

ꢦꢄ

×휂×10

24×ꢡ0×10

If f_SW=200kHz, L=100μH, ΔI_Lcan be calculated as follows.

(푉

ꢞ푉 )×푉

ꢦꢄ

(40ꢞ24)×24

ꢃꢒꢂ

ꢦꢄ

∆ꢗ_퐿=

=

= ꢘ.ꢥ8

ꢉ

[A]

−6

퐿×푉

×푓

100×10 ×40×200×10

ꢃꢒꢂ

ꢀ푊

Therefore the inductor peak current I_PEAKis as follows.

0.4ꢫ

2

ꢗ_푃퐸ꢩ퐾= ꢗ_퐼푁+ ^∆퐼= ꢘ.89 +

= ꢝ.ꢝꢙ

[A]

ꢧ

2

If R_CSis assumed to be 0.3Ω, V_CSPEAKis as follows.

ꢆ_{퐶푆푃퐸ꢩ퐾}= 푅_퐶푆× ꢗ_푃퐸ꢩ퐾= ꢘ.ꢙ × ꢝ.ꢝꢙ = ꢘ.ꢙꢙ9 ≪ ꢘ.ꢥ [V]

That meets the above condition.

And I_{PEAK_DET}that is the current OCP works is as follows.

0.4

0.3

ꢗ_{푃퐸ꢩ퐾_ꢎ퐸푇}

=

= ꢝ.ꢙꢙ

[A]

ꢈ

ꢰꢀ

If the current rating of the used parts is 2A,

ꢗ_푃퐸ꢩ퐾≪ ꢗ_{푃퐸ꢩ퐾_ꢎ퐸푇}≪ ꢌℎ푒 푐푢푟푟푒푛푡 푟푎푡ꢱ푛푔 = ꢝ.ꢝꢙ ≪ ꢝ.ꢙꢙ ≪ ꢣ.ꢘ

[A]

This inequality meets the above relationship. The parts selection is proper.

And I_MINthat is the bottom of the I_Lripple current can be calculated as follows.

ꢗ_푀퐼푁= ꢗ_퐼푁ꢠ ^∆퐼= ꢘ.89 ꢠ ꢘ.ꢣꢥ = ꢘ.ꢲꢤ ≫ ꢘ

[A]

ꢧ

2

This inequality implies that the operation is continuous current mode.

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Selection of Components Externally Connected – continued

10

Inductor Selection

The inductor value affects the input ripple current, as shown the previous section “OCP Setting/Calculation Method for

the Current Rating of DC/DC Parts”.

(푉

ꢞ푉 )×푉

ꢃꢒꢂ

ꢦꢄ

∆ꢗ_퐿=

ꢗ_퐼푁=

[A]

ΔI_L

퐿×푉

×푓

ꢃꢒꢂ

ꢀ푊

푉

×퐼

ꢃꢒꢂ ꢃꢒꢂ

−ꢜ

[A]

V_IN

푉

ꢦꢄ

×휂×10

ꢗ_푃퐸ꢩ퐾= ꢗ_퐼푁+ ^∆퐼

I_L

L

ꢧ

2

V_OUT

where:

ꢯ is the inductor inductance.

ꢆ_푂ꢏ푇is the DC/DC output voltage.

is the input voltage.

ꢆ

퐼푁

ꢗ_푂ꢏ푇is the output load current(the summation of LED current).

ꢗ_퐼푁is the input current.

C_OUT

R_CS

ꢊ

푆ꢋ

is the oscillation frequency.

Figure 27. Inductor Current Waveform and Diagram

In continuous current mode, ΔI_Lis set to 30% to 50% of the output load current in many cases.

In using smaller inductor, the operation mode is the discontinuous current mode in which the inductor current returns

to zero at every period. The current exceeding the rated current value of inductor flown through the inductor causes

magnetic saturation, results in decreasing in efficiency. Inductor needs to be selected to have such adequate margin

that peak current does not exceed the rated current value of the inductor. To reduce inductor loss and improve

efficiency, inductor with low resistance components(DCR, ACR) needs to be selected

11

Output Capacitance C_OUTSelection

Output capacitor needs to be selected in consideration of the capacitance value

C_OUTand the equivalent series resistance R_ESR. R_ESRof it needs to be small

V_IN

enough to smooth ripple voltage.

Output ripple voltage ΔV_OUTis determined as follows.

L

I_L

∆ꢆ_푂ꢏ푇= ∆ꢗ_퐿× 푅_퐸푆ꢈ

[V]

V_OUT

where:

∆ꢆ_푂ꢏ푇is V_OUTripple voltage.

∆ꢗ_퐿is LED ripple current.

R_ESR

푅_퐸푆ꢈis the equivalent series resistance of output capacitance.

R_CS

C_OUT

When the inductor current is charged to the output capacitor as MOS turns off,

much output ripple is caused. If output ripple voltage is big, that causes the LED

current ripple is big.

Figure 28. Output Capacitor Diagram

Rating of capacitor needs to be selected to have adequate margin for output voltage.

To use an electrolytic capacitor, adequate margin for allowable current is also necessary. Be aware that the LED

current is more than the set value transitionally in case that LED is provided with PWM dimming especially.

12

13

MOSFET Selection

There is no problem if the absolute maximum rating is more than the sum of V_OVPOUT(OVP detection voltage in V_OUT

)

and V_F(the forward voltage of the rectifying diode). Recommended rated current is more than over current protection

setting. The product with small gate capacitance(injected charge) needs to be selected to achieve high-speed

switching. The selection of one with small on resistance results in high efficiency.

Rectifying Diode Selection

A schottky barrier diode with rated current of L or more, reverse voltage more than V_OVPOUT, and low forward voltage V_F

especially needs to be selected.

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Selection of Components Externally Connected – continued

14

Loop Compensation

A current mode DC/DC converter has each one pole (phase lag) f_Pdue to CR filter composed of the output capacitor

and the output resistance(=LED current) and zero (phase lead) f_Zby the output capacitor and the ESR of the capacitor.

Moreover, a step up DC/DC converter has RHP zero(right-half plane zero point) f_ZRHPwhich is unique with the boost

converter. This zero may cause the unstable feedback. To avoid this by RHP zero, the loop compensation band

frequency f_C,set as follows, is suggested.

푓

푍ꢬꢳꢔ

ꢊ =

퐶

[Hz]

5

where:

ꢊ is loop compensation band frequency.

퐶

ꢊ

ꢴꢈ퐻푃

is RHP zero frequency.

Considering the response speed, the calculated constant below is not always optimized completely. It needs to be

adequately verified with an actual device.

V_IN

V_OUT

I_LED

L

V_OUT

-

SSFB

gm

R_ESR

R_SSFB1

+

C_SSFB2

R_CS

C_OUT

C_SSFB1

Figure 29. Output Stage and Error Amplifier Diagram

(1)Calculate the pole frequency f_Pand the RHP zero frequency f_ZRHPof DC/DC converter.

퐼

ꢧꢨꢑ

ꢊ =

푃

[Hz]

2휋×푉

×퐶

ꢃꢒꢂ

ꢜ

푉

ꢃꢒꢂ

×(1ꢞꢎ)

ꢊ

ꢴꢈ퐻푃

=

[Hz]

2휋×퐿×퐼

ꢧꢨꢑ

where:

ꢊ

is DC/DC pole frequency.

is RHP zero frequency.

P

ꢊ

ꢴꢈ퐻푃

푉_ꢃꢒꢂꢞ푉

ꢦꢄ

D is switching duty. (퐷 =

)

푉_ꢃꢒꢂ

(2)Calculate the phase compensation of the error amp output(f_C=f_ZRHP/5).

푓

×ꢈ ×퐼

ꢰꢀ ꢧꢨꢑ

ꢬꢳ푍ꢔ

푅_{푆푆퐹ꢇ1}

ꢅ_{푆푆퐹ꢇ1}

=

[Ω]

5×푓ꢵ×ꢶ푚×푉

×(1ꢞꢎ)

ꢃꢒꢂ

1

5

=

[F]

2휋×ꢈ

×푓

2휋×ꢈ

×푓

ꢀꢀꢁ퐵ꢛ 푍ꢬꢳꢔ

ꢀꢀꢁ퐵ꢛ

ꢰ

푔ꢷ = ꢥ.ꢘ × ꢝꢘ^ꢞ4

[S]

Above equation is described for lighting LED without the oscillation. The value may cause much error if the quick response

for the abrupt change of dimming signal is required.

To improve the transient response, R_SSFB1needs to be increased, and C_SSFB1needs to be decreased. It needs to be

adequately verified with an actual device in consideration of variation from parts to parts since phase margin is decreased.

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I/O Equivalent Circuits

Pin2: OVP

Pin3: SFTON

Pin6: DUTYON

Pin9: SSFB

Pin4: ADIM

ADIM

OVP

SFTON

Pin5: RT

Pin7: PWM

REG90

PWM

RT

DUTYON

Pin8: DUTYP

Pin10: ISENSE

ISENSE

DUTYP

SSFB

Pin12: GATE, Pin13: CS,

Pin14: REG90

REG90

GATE

GND

CS

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Operational Notes

1.

2.

Reverse Connection of Power Supply

Connecting the power supply in reverse polarity can damage the IC. Take precautions against reverse polarity when

connecting the power supply, such as mounting an external diode between the power supply and the IC’s power

supply pins.

Power Supply Lines

Design the PCB layout pattern to provide low impedance supply lines. Furthermore, connect a capacitor to ground at

all power supply pins. Consider the effect of temperature and aging on the capacitance value when using electrolytic

capacitors.

3.

4.

Ground Voltage

Ensure that no pins are at a voltage below that of the ground pin at any time, even during transient condition.

Ground Wiring Pattern

When using both small-signal and large-current ground traces, the two ground traces should be routed separately but

connected to a single ground at the reference point of the application board to avoid fluctuations in the small-signal

ground caused by large currents. Also ensure that the ground traces of external components do not cause variations

on the ground voltage. The ground lines must be as short and thick as possible to reduce line impedance.

5.

6.

Recommended Operating Conditions

The function and operation of the IC are guaranteed within the range specified by the recommended operating

conditions. The characteristic values are guaranteed only under the conditions of each item specified by the electrical

characteristics.

Inrush Current

When power is first supplied to the IC, it is possible that the internal logic may be unstable and inrush current may flow

instantaneously due to the internal powering sequence and delays, especially if the IC has more than one power

supply. Therefore, give special consideration to power coupling capacitance, power wiring, width of ground wiring, and

routing of connections.

7.

8.

Operation Under Strong Electromagnetic Field

Operating the IC in the presence of a strong electromagnetic field may cause the IC to malfunction.

Testing on Application Boards

When testing the IC on an application board, connecting a capacitor directly to a low-impedance output pin may

subject the IC to stress. Always discharge capacitors completely after each process or step. The IC’s power supply

should always be turned off completely before connecting or removing it from the test setup during the inspection

process. To prevent damage from static discharge, ground the IC during assembly and use similar precautions during

transport and storage.

9.

Inter-pin Short and Mounting Errors

Ensure that the direction and position are correct when mounting the IC on the PCB. Incorrect mounting may result in

damaging the IC. Avoid nearby pins being shorted to each other especially to ground, power supply and output pin.

Inter-pin shorts could be due to many reasons such as metal particles, water droplets (in very humid environment) and

unintentional solder bridge deposited in between pins during assembly to name a few.

10. Unused Input Pins

Input pins of an IC are often connected to the gate of a MOS transistor. The gate has extremely high impedance and

extremely low capacitance. If left unconnected, the electric field from the outside can easily charge it. The small

charge acquired in this way is enough to produce a significant effect on the conduction through the transistor and

cause unexpected operation of the IC. So unless otherwise specified, unused input pins should be connected to the

power supply or ground line.

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Operational Notes – continued

11. Regarding the Input Pin of the IC

This monolithic IC contains P+ isolation and P substrate layers between adjacent elements in order to keep them

isolated. P-N junctions are formed at the intersection of the P layers with the N layers of other elements, creating a

parasitic diode or transistor. For example (refer to figure below):

When GND > Pin A and GND > Pin B, the P-N junction operates as a parasitic diode.

When GND > Pin B, the P-N junction operates as a parasitic transistor.

Parasitic diodes inevitably occur in the structure of the IC. The operation of parasitic diodes can result in mutual

interference among circuits, operational faults, or physical damage. Therefore, conditions that cause these diodes to

operate, such as applying a voltage lower than the GND voltage to an input pin (and thus to the P substrate) should be

avoided.

Resistor

Transistor (NPN)

Pin A

Pin B

B

E

C

Pin A

B

C

E

P

P⁺

N

P⁺

P

P⁺

N

Parasitic

Elements

Parasitic

Elements

P Substrate

GND GND

P Substrate

GND

Parasitic

Elements

Parasitic

Elements

N Region

close-by

Figure 30. Example of monolithic IC structure

12. Ceramic Capacitor

When using a ceramic capacitor, determine a capacitance value considering the change of capacitance with

temperature and the decrease in nominal capacitance due to DC bias and others.

13. Area of Safe Operation (ASO)

Operate the IC such that the output voltage, output current, and the maximum junction temperature rating are all within

the Area of Safe Operation (ASO).

14. Thermal Shutdown Circuit (TSD)

This IC has a built-in thermal shutdown circuit that prevents heat damage to the IC. Normal operation should always

be within the IC’s maximum junction temperature rating. If however the rating is exceeded for a continued period, the

junction temperature (Tj) will rise which will activate the TSD circuit that will turn OFF power output pins. When the Tj

falls below the TSD threshold, the circuits are automatically restored to normal operation.

Note that the TSD circuit operates in a situation that exceeds the absolute maximum ratings and therefore, under no

circumstances, should the TSD circuit be used in a set design or for any purpose other than protecting the IC from

heat damage.

15. Over Current Protection Circuit (OCP)

This IC incorporates an integrated overcurrent protection circuit that is activated when the load is shorted. This

protection circuit is effective in preventing damage due to sudden and unexpected incidents. However, the IC should

not be used in applications characterized by continuous operation or transitioning of the protection circuit.

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Ordering Information

B D 9

4

0

8

F

V -

E 2

Part Number

Package

FV: SSOP-B14

Packaging and forming specification

E2: Embossed tape and reel

(SSOP-B14)

Marking Diagram

SSOP-B14(TOP VIEW)

Part Number Marking

D9408

LOT Number

Pin 1 Mark

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Physical Dimension and Packing Information

Package Name

SSOP-B14

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Revision History

Date

Revision

001

Changes

16.May.2018

New Release

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Notice

Precaution on using ROHM Products

1. Our Products are designed and manufactured for application in ordinary electronic equipment (such as AV equipment,

OA equipment, telecommunication equipment, home electronic appliances, amusement equipment, etc.). If you

intend to use our Products in devices requiring extremely high reliability (such as medical equipment ^{(Note 1)}, transport

equipment, traffic equipment, aircraft/spacecraft, nuclear power controllers, fuel controllers, car equipment including car

accessories, safety devices, etc.) and whose malfunction or failure may cause loss of human life, bodily injury or

serious damage to property (“Specific Applications”), please consult with the ROHM sales representative in advance.

Unless otherwise agreed in writing by ROHM in advance, ROHM shall not be in any way responsible or liable for any

damages, expenses or losses incurred by you or third parties arising from the use of any ROHM’s Products for Specific

Applications.

(Note1) Medical Equipment Classification of the Specific Applications

JAPAN

USA

EU

CHINA

CLASSⅢ

CLASSⅣ

CLASSⅡb

CLASSⅢ

2. ROHM designs and manufactures its Products subject to strict quality control system. However, semiconductor

products can fail or malfunction at a certain rate. Please be sure to implement, at your own responsibilities, adequate

safety measures including but not limited to fail-safe design against the physical injury, damage to any property, which

a failure or malfunction of our Products may cause. The following are examples of safety measures:

[a] Installation of protection circuits or other protective devices to improve system safety

[b] Installation of redundant circuits to reduce the impact of single or multiple circuit failure

3. Our Products are designed and manufactured for use under standard conditions and not under any special or

extraordinary environments or conditions, as exemplified below. Accordingly, ROHM shall not be in any way

responsible or liable for any damages, expenses or losses arising from the use of any ROHM’s Products under any

special or extraordinary environments or conditions. If you intend to use our Products under any special or

extraordinary environments or conditions (as exemplified below), your independent verification and confirmation of

product performance, reliability, etc, prior to use, must be necessary:

[a] Use of our Products in any types of liquid, including water, oils, chemicals, and organic solvents

[b] Use of our Products outdoors or in places where the Products are exposed to direct sunlight or dust

[c] Use of our Products in places where the Products are exposed to sea wind or corrosive gases, including Cl2,

H2S, NH3, SO2, and NO2

[d] Use of our Products in places where the Products are exposed to static electricity or electromagnetic waves

[e] Use of our Products in proximity to heat-producing components, plastic cords, or other flammable items

[f] Sealing or coating our Products with resin or other coating materials

[g] Use of our Products without cleaning residue of flux (even if you use no-clean type fluxes, cleaning residue of

flux is recommended); or Washing our Products by using water or water-soluble cleaning agents for cleaning

residue after soldering

[h] Use of the Products in places subject to dew condensation

4. The Products are not subject to radiation-proof design.

5. Please verify and confirm characteristics of the final or mounted products in using the Products.

6. In particular, if a transient load (a large amount of load applied in a short period of time, such as pulse. is applied,

confirmation of performance characteristics after on-board mounting is strongly recommended. Avoid applying power

exceeding normal rated power; exceeding the power rating under steady-state loading condition may negatively affect

product performance and reliability.

7. De-rate Power Dissipation depending on ambient temperature. When used in sealed area, confirm that it is the use in

the range that does not exceed the maximum junction temperature.

8. Confirm that operation temperature is within the specified range described in the product specification.

9. ROHM shall not be in any way responsible or liable for failure induced under deviant condition from what is defined in

this document.

Precaution for Mounting / Circuit board design

1. When a highly active halogenous (chlorine, bromine, etc.) flux is used, the residue of flux may negatively affect product

performance and reliability.

2. In principle, the reflow soldering method must be used on a surface-mount products, the flow soldering method must

be used on a through hole mount products. If the flow soldering method is preferred on a surface-mount products,

please consult with the ROHM representative in advance.

For details, please refer to ROHM Mounting specification

Notice-PGA-E

Rev.003

Precautions Regarding Application Examples and External Circuits

1. If change is made to the constant of an external circuit, please allow a sufficient margin considering variations of the

characteristics of the Products and external components, including transient characteristics, as well as static

characteristics.

2. You agree that application notes, reference designs, and associated data and information contained in this document

are presented only as guidance for Products use. Therefore, in case you use such information, you are solely

responsible for it and you must exercise your own independent verification and judgment in the use of such information

contained in this document. ROHM shall not be in any way responsible or liable for any damages, expenses or losses

incurred by you or third parties arising from the use of such information.

Precaution for Electrostatic

This Product is electrostatic sensitive product, which may be damaged due to electrostatic discharge. Please take proper

caution in your manufacturing process and storage so that voltage exceeding the Products maximum rating will not be

applied to Products. Please take special care under dry condition (e.g. Grounding of human body / equipment / solder iron,

isolation from charged objects, setting of Ionizer, friction prevention and temperature / humidity control).

Precaution for Storage / Transportation

1. Product performance and soldered connections may deteriorate if the Products are stored in the places where:

[a] the Products are exposed to sea winds or corrosive gases, including Cl2, H2S, NH3, SO2, and NO2

[b] the temperature or humidity exceeds those recommended by ROHM

[c] the Products are exposed to direct sunshine or condensation

[d] the Products are exposed to high Electrostatic

2. Even under ROHM recommended storage condition, solderability of products out of recommended storage time period

may be degraded. It is strongly recommended to confirm solderability before using Products of which storage time is

exceeding the recommended storage time period.

3. Store / transport cartons in the correct direction, which is indicated on a carton with a symbol. Otherwise bent leads

may occur due to excessive stress applied when dropping of a carton.

4. Use Products within the specified time after opening a humidity barrier bag. Baking is required before using Products of

which storage time is exceeding the recommended storage time period.

Precaution for Product Label

A two-dimensional barcode printed on ROHM Products label is for ROHM’s internal use only.

Precaution for Disposition

When disposing Products please dispose them properly using an authorized industry waste company.

Precaution for Foreign Exchange and Foreign Trade act

Since concerned goods might be fallen under listed items of export control prescribed by Foreign exchange and Foreign

trade act, please consult with ROHM in case of export.

Precaution Regarding Intellectual Property Rights

1. All information and data including but not limited to application example contained in this document is for reference

only. ROHM does not warrant that foregoing information or data will not infringe any intellectual property rights or any

other rights of any third party regarding such information or data.

2. ROHM shall not have any obligations where the claims, actions or demands arising from the combination of the

Products with other articles such as components, circuits, systems or external equipment (including software).

3. No license, expressly or implied, is granted hereby under any intellectual property rights or other rights of ROHM or any

third parties with respect to the Products or the information contained in this document. Provided, however, that ROHM

will not assert its intellectual property rights or other rights against you or your customers to the extent necessary to

manufacture or sell products containing the Products, subject to the terms and conditions herein.

Other Precaution

1. This document may not be reprinted or reproduced, in whole or in part, without prior written consent of ROHM.

2. The Products may not be disassembled, converted, modified, reproduced or otherwise changed without prior written

consent of ROHM.

3. In no event shall you use in any way whatsoever the Products and the related technical information contained in the

Products or this document for any military purposes, including but not limited to, the development of mass-destruction

weapons.

4. The proper names of companies or products described in this document are trademarks or registered trademarks of

ROHM, its affiliated companies or third parties.

Notice-PGA-E

Rev.003


型号：	BD9408FV
厂家：	ROHM
描述：	BD9408FV是白色LED用高效率驱动器，适用于大屏幕液晶驱动器。BD9408FV内置了可向光源(LED串联连接的阵列)提供适当电压的DC/DC转换器。BD9408FV中内置了应对异常状态的几种保护功能。过电压保护(OVP: over voltage protection)、过电流检测(OCP: over current limit protection of DC/DC)、LED过流保护(LED OCP: LED Over Current Protection)、过升压保护(FBMAX)等。因此，可在更宽的电压条件及负载条件下使用。驱动驱动器转换器
文件：	总36页 (文件大小：2001K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

BD9408FV [ROHM]

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