Datasheet KB4312A-GRE, KB4312B-GRE Datasheet (Kingbor) [ru]

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Tiny Package, High Performance, Constant Current

Very Low

Cost

KB4312

Switching Regulator for White LED

FEATURES

•Operating Voltage:2.5V~6.5V

•High Operating Frequency: 1.2MHz

•High Efficiency: Up to 92%

•High Output Voltage: Up to 28V(max)

•Shutdown Current <1PA

•18V Output Over-voltage protection (ADJ)

•Digital Dimming Control.

•Built-in Cycle-by Cycle Current-limiting.

•Built-in Soft-Start Function.

•0.24V Low Reference Voltage(+/-5%)

•Tiny SOT23 Package

APPLICATIONS

• LED Module

• LED Backlight for LCD Display (1 ~6.5 )

• Constant Current Source!

”

”

DESCRIPTION

The KB4312 step-up converter drives white LEDs
with a constant current to provide backlight in cell
phones, PDAs, and other hand-held devices. It
features allowing series connection of the white
LEDs so that the LED currents are identical for
uniform brightness. An enable input can be pulsed
repeatedly to adjust LED’s brightness. The fast 1.2
MHz current-mode PWM control allows for smaller
capacitor and inductor. Fault condition protection
uses cycle-by-cycle current limiting to sense
maximum inductor current, thermal protection and
over-voltage protection. Also included soft-start
eliminates inrush current during start-up. The 0.24V
low reference voltage minimized the power loss
across the current-setting resistor.

The KB4312 is available in SOT23 packages /

SIMPLIFIED BLOC DIAGRAM

VIN

6

VREF

0.240V

1.27V

EN

FB

OVP

4

3

KB4312B FB=240mV

17V

KB4312A FB=1.27V

5

VBG

ON/OFF

Control

Logic / PWM

Dimming

Control

CTL

+

-

Overvoltage

+

-

Protection

CTL

VBG

Control Logic

2

GND

Soft-Start

Current Limit

0.25A

LX

1

N

+

-

REV: 3.2

1

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PIN CONFIGURATION

KB4312

SOT23-6

-

6

3

2

T

O

S

LX

GND

FB

1

2

3

KB4312B

FB=240mV

6

5

4

V

IN

OVP

EN

S

-

5

3

2

T

O

LX

GND

FB

ORDER INFORMATION

Part number Package Marking

KB4312A-

Part number Package Marking

KB4312B-

PIN DESCRIPTION

Pin N0. Symbol I / O Description

1 LX I Step-up Regulator N-MOS Drain. Place output diode and inductor.
2 GND P Ground

3 FB I

4 EN I

5 OVP I Over-voltage protection input(ADJ)
6 VIN P Power supply.

GRE SOT23-5, Green

GRE SOT23-6, Green

Step-Up Regulator Feedback Input. Connect a sense resistor from FB to
ground. (KB4312B FB=240mV,KB4312A FB=1.27V)
Enable and Dimming Control Input. LED brightness and IC shutdown are
controlled by the voltage on EN. Driving low for longer than 4ms to
shutdown the IC.

ATxxxx, xxxx: Date Code

5121x, x: Date Code

5121m,Date Code with one bottom line

SOT23-5

1

2

3

KB4312A

FB=1.27V

5

V

IN

4

EN

ABSOLUTE MAXIMUM RATINGS

Parameter Rated Value Unit

VIN voltage -0.3 to +6.5 V
LX , OVP voltage -0.3 to +28 V
EN , FB to GND -0.3 to +6.5 V
Switch Current (ILX) 0.25 A
Continuous power dissipation (SOT23-6 Ta=+25OC) 0.35 W
Operating Junction Temperature Range -35 to 85

Lead Temperature (Soldering 5 sec) 260
Storage Temperature -65 to 125
Package Thermal Resistance (ӘJA)
ESD Susceptibility (HBM) 2 KV

ESD Susceptibility (MM) 200 V

Note1:Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability

(Note 1)

250

к
к
к

к/W

2

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RECOMMENDED OPERATION CONDITIONS

KB4312

Power supply voltage V

IN

Operating temperature Top

Va lu es Parameter Symbol

Min. Typ. Max.

2.5

ѧ

6.5 V

-30 +25 +85

Unit

к

ELECTRICAL CHARACTERISTICS

(VIN=2.5V, Ta=+25к, unless otherwise noted)

Parameter Symbol Test Condition Min. Typ. Max. Units

CYCL

IN

and t

Range

V

IN

IN1

IN3

VIN input Voltage

No Switching , FB>0.2V - 1 3 mA

EN=0V - - 1 uA

KB4312B

KB4312A

OVP

OVP

KB4312B

EN=0V - - 1 uA

2.5V< V

OSC

MAX

I

LX

LX

Leakage

0.5 0.8 1.0 MHz

- 90 - %

VIN=3.0V,duty cycle=80% , - 0.15 - A
VIN=2.5V, ILX =750mA

VLX =16V, EN=0V - - 1 uA

16 17 20 V

<6.0V

IN

VIH 1.5 - - V

- - 0.4 V

V

IL

Note(1) 0.05 4 ms

CYCL

Note(1) 0.05 4 ms

CYCH

are included rising time and falling time of PWM signal.

CYCH

2.5 - 6.5 V

- 0.1 - %

- 0.40 -

Ө

Operating V

Under Voltage Thershold UVLO VINfalling, 100mV hysteresis 1.4 1.5 1.6 V
No Load Current I
Shutdown Current I
Feedback Reference (+/-5%) VFB 0.225 0.240 0.255 V
Feedback Reference (+/-2%) VFB 1.245 1.270 1.295 V
Over-voltage Threshold V
Over-voltage Hysteresis 2 V
OVP Leakage Current I

Output Voltage Line Regulation

Switching Frequency f
Maximum Duty D
Soft-Start charging time tSS 0.05 0.2 ms

Switching Current Limit

LX ON Resistance R
LX Leakage Current I

EN Input Current IEN EN=5V - - 1 uA

EN Input Level

EN low Shutdown Delay 4 ms
EN Low Cycle Time t
EN High Cycle Time t

Note(1): t

Recommended PCB Layout

KB4312B

3

y

–

–

–

–

–

–

)

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TYPICAL PERFORMANCE CHARACTERISTICS

KB4312

Quiescent

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

02

Feedback Bias

60

50

40

30

20

10

Current

50qC

25qC

4

VIN(V)

100qC

Current

68

SHDN Pin Bias

400

350

300

250

200

150

100

50

0

25 0

50

Efficiencyvs

85

VIN=

3.6V

3

LEDs

84

83

82

81

Current

SHDN =

3.6V

SHDN =

2.7V

25

TEMPERATURE(q

Temperature

I

=

20mA

LED

I

=

15mA

LED

I

=

10mA

LED

SHDN =

10V

SHDN =

3V

50 75 100

C)

SwitchingFrequenc

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

50

25 0

TEMPERATURE(q

Current

LimitvsDutyCycle

350

300

250

200

150

100

50

50

25

C)

100

75

0

–50

25 0

TEMPERATURE

50

25

(q

C)

100

75

80

–50

050100

TEMPERATURE(q

C)

0

0

20 40

DUTY

CYCLE(%

60

80 100

4

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APPLICATION CIRCUIT

10uH

KB4312

VOUT=6~24VVin=2.7~6V

LX

1N5819

1

OVP

1uF

56

1uF

VCC

KB4312B

2

LX

FB

1uF

1N5819

1

34

FB

3

3

240mV

BAT54s

R1
510K

1.27V

1

2

1uF

10uF

R1= (

PWM or ON/OFF

EN

GND

Figure 1a.KB4312 For 2 to 6 LEDs Back Light Unit.(Step-Up)

Vin=2.7~6V

1uF

10uH

5

VCC

KB4312A

ON/OFF

4

EN

GND

2

R2
47K

2.2K

10V

VOUT

1.27V

10uF

VOUT +15V (15mA)

-1 ) x R2

20MA

Rset
12R~51R

-10V

1uF

Vin=5~20V

1K

1uF

5.1V

ON/OFF

10uH

5

VCC

KB4312A

4

EN

1uF

LX

GND

1uF

1

2

FB

3

BAT54s

3

3

1.27V

1uF

2.2K

10uF

R1= (

10V

VOUT

1.27V

1

2

1

2

R1

510K

R2
47K

-10V

10uF

VOUT +15V(15mA)

-1 ) x R2

5

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KB4312

Function Description

The KB4312 is a high efficiency and constant current DC-DC converter IC which is designed primarily

for use in LED module applications. The output voltage of the step-up converter can be set from Vin to

28V with external sense resistor. The device suits to drive series-connected LEDs and provides even

illumination by sourcing the same output current through each LED. KB4312 also consists of a logic

shutdown , cycle-by-cycle current-limited , soft-start functions.

Logic control input or PWM duty cycle control allows easy adjustment of LEDs brightness and on/off

control. The average LED current is proportionable the duty-cycle of the PWM signal. Typical PWM

frequency should be between 100Hz and 1kHz.

The boost converter operates in current-mode PWM and a constant frequency of 1.2 MHz. Depending

on duty cycle of each switching cycle can regulate output voltage. On the rising edge of the internal

clock , the control and driver logic block sets internal flip-flop when the output voltage is too low,

which turns on the N-MOS. The external inductor current ramps up linearly, storing energy in a

magnetic filed. Once peak current of inductor over trans-conductance output level , the N-MOS turns

off, the flip-flop resets, and external schottky diode turns on. This forces the current through the

inductor to ramp back down, transferring the energy stored in the magnetic field to the output capacitor

and LEDs. To reduce external component amount , the device will be built-in internal loop

compensation.

ʳ

Enable Control

Digital logic of EN provides an electrical ON/OFF control of the power supply. Connecting this pin to

ground or to any voltage less than 0.4V and sustain the level over 4ms will completely turn off the

regulator. In this state, current drain from the input supply is less than 1uA, the internal reference, error

amplifier, comparators, and biasing circuitry turn off . If holding time of low level is less than 3ms on

this pin, then the device only shutdown driver logic block.

ʳ

Dimming Control

Digital logic of EN also provides LEDs brightness control by applying a PWM signal on EN pin. With

this way, the LEDs operate with either zero or full current . The average LED current is proportional to

the duty-cycle of the PWM signal. Typical PWM frequency should be between 100Hz and 1kHz.

Output current is given by:

TmV

I

Where:

T

ON-PWM

T

S-PWM

If dimming control is not required , EN works as a simple on/off control. Drive EN high to enable the

device , or drive EN low for shutdown.

105

LED

: On time of PWM signal

: A cycle time of PWM signal

u

PWMON



TR

u



ʳ

PWMSSENSE

ʳ

6

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KB4312

Soft-Start

Soft-start allows a gradual increase of the internal current-limit level for the step-up converter during

power-up to reduce input surge currents. As the internal current source charges the internal soft-start

capacitor, the peak N-MOS current is limited by the voltage on the capacitor. In another story, when

toggle or a logic-level transition on EN pin from low to high, soft-start function must work to enable

constant current charging internal capacitor. When soft-start process has finished or appeared falling

edge of PWM signal on EN pin , soft-start capacitor must be discharged to ground level.

Cycle-by-Cycle Over-Current Protection

The KB4312 provides cycle-by-cycle over-current protection. Current limit is accomplished using a

separate dedicated comparator. The cycle-by-cycle current limit abbreviates the on-time of the N-MOS

in event that the current of flowing N-MOS is greater than the current limit value. The current-limit

feature protection against a hard short or over-current fault at the output.

Over-Voltage Protection

If V

ground with a sense resistor. This will cause N-MOS to switch with a maximum duty cycle and come

out output over-voltage. This may cause the LX pin voltage to exceed its maximum voltage rating to

damage built-in N-MOS. In the state, the OVLO protection circuitry stops the internal N-MOS .

is above 17V or LEDs are disconnected from the circuit, the FB pin is similar to pull down to

OVP

Power dissipation consideration

The KB4312 maximum power dissipation depends on the thermal resistance of the IC package and

circuit board, the temperature difference between the die junction and ambient air, and the rate of any

airflow. The power dissipation in the device depends on the operating conditions of the regulator.

The step-up converter dissipates power across the internal N-MOS as the controller ramps up the

inductor current. In continuous condition, the power dissipated internally can be approximated by :

VI

u

P

boost

w

here

I

: It is the load current.

O

f

: It is a switching frequency.

OSC

OO

)[(

V

in

1



12

in

OSC

DV

u

22

])(

Lf

u

DR

uu

ONDS

)(

7

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KB4312

Applications Information

External components of main boost converter can be designed by performing simple calculations. It

need to follow regulation by the output voltage and the maximum load current, as well as maximum

and minimum input voltages. Begin by selecting an inductor value. Once L is know, choose the diode

and capacitors.

Boost inductor

Inductor selection depends on input voltage, output voltage, maximum current , switching frequency

and availability of inductor values. The following boost circuit equations are useful in choosing the

inductor values based on the application. They allow the trading of peak current and inductor value

while allowing for consideration of component availability and cost.

The peak inductor current is given by:

'

I

L



II

I

LAVG

LAVGLpeak

I

O



1

D

2

where:

ϦI

is the inductor peak-to-peak current ripple and is decided by:

L

V

I u '

L

L

D is the MOSFET turn on ratio and is decided by:

V

is the switching frequency.

f

OSC

The inductor should be chosen to be able to handle this current and inductor saturation current rating

should be greater than I

D

in

f

OSC

VVD

inO

O

.

PEAK

Diode selection

The output diode has average current of I

and a voltage rating at least 1.5 times the output voltage. Schottky diode is recommended and it should

be able to handle those current.

, and peak current the same as the inductor’s peak current

O

Output Capacitor

The KB4312 is specially compensated to be stable with capacitors which have a worst- case minimum

value of 1uF at the particular V

minimum value and type of capacitors. Output ripple voltage consists of two components the voltage

drop caused by the switching current through the ESR of the output capacitor and the charging and

discharging of the output capacitor:

being set. Output ripple voltage requirements also determine the

OUT

VV



ESRIV

LPEAKRIPPLE

For low ESR ceramic capacitors, the output ripple is dominated by the charging or discharging of the

output capacitor.

u

inO

u

V

O

I

O

fC

u

OSCOUT

8

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PACAGE DESCRIPTION

PACKAGE OUTLINE

Small Outline SOT23-6

e

b

KB4312

PAD LAYOUT DETAILS

2

L

E

e1

D

AA2

CONTROLLING DIMENSIONS IN MILLIMETRES APPROX CONVERSIONS INCHES.

a

A1

E1

DA TUM A

C

PACKAGE DIMENSIONS

DIM

Millimetres Inches

Min Max Min Max Min Max Min Max

A 0.90 1.45 0.35 0.057 E 2.60 3.00 0.102 0.118
A1 0.00 0.15 0 0.006 E1 1.50 1.75 0.059 0.069
A2 0.90 1.30 0.035 0.051 L 0.10 0.60 0.004 0.002

b 0.35 0.50 0.014 0.019 e 0.95 REF 0.037 REF
C 0.09 0.20 0.0035 0.008 e1 1.90 REF 0.074 REF

D 2.80 3.00 0.110 0.118 L 0° 10° 0° 10°

DIM

Millimetres Inches

Small Outline SOT23-5

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PACKAGE DIMENSIONSPACKAGE OUTLINE

Millimeters Inches

DIM

MIN. MAX. MIN. MAX.

A 0.90 1.45 0.0354 0.0570

A1 - 0.15 - 0.0059

A2 0.90 1.30 0.0354 0.0511

b 0.20 0.50 0.0078 0.0196

C 0.09 0.26 0.0035 0.0102

D 2.70 3.10 0.1062 0.1220

E 2.20 3.20 0.0866 0.1181

E1 1.30 1.80 0.0511 0.0708

e 0.95 REF 0.037 4 REF

e1 1.90 REF 0.0748 REF

L 0.10 0.60 0.0039 0.0236

a 0° 30° 0° 30°

9