Page 1
Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
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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Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
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
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y
–
–
–
–
–
–
)
Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
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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Kingbor Technology Co.,Ltd
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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
Page 6
Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
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
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Kingbor Technology Co.,Ltd
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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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Kingbor Technology Co.,Ltd
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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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Kingbor Technology Co.,Ltd
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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
Kingbor Technology
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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°
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