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Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
KB4312
Very Low Cost
Tiny Package, High Performance, Constant Current 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 <1 A *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
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
APPLICATIONS
* LED Module * LED Backlight for LCD Display (1" ~6.5 " ) * Constant Current Source
SIMPLIFIED BLOC DIAGRAM
VIN
6 1
Soft-Start LX
EN
4
ON/OFF Control Logic / PWM Dimming Control CTL +
VREF 0.240V VBG 1.27V
N Control Logic
FB OVP
3 5
17V
-
KB4312B FB=240mV KB4312A FB=1.27V
VBG + Overvoltage Protection
Current Limit 0.25A + -
CTL
2
GND
REV: 3.2
1
Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
KB4312
SOT23-5
SOT23-5
PIN CONFIGURATION
SOT23-6
SOT23-6
LX 1 GND 2
6
5
VIN
LX 1 GND 2
5
VIN
OVP
EN
FB
3
4
FB
3
4
EN
KB4312B FB=240mV
KB4312A FB=1.27V
ORDER INFORMATION
Part number Package SOT23-5, Green Package SOT23-6, Green 5121x, ATxxxx, Marking xxxx: Date Code Marking x: Date Code
KB4312A- GRE
Part number
KB4312B- GRE
PIN DESCRIPTION
Pin N0. 1 2 3 4 5 6 Symbol LX GND FB EN OVP VIN I/O I P I I I P
5121m,Date Code with one bottom line
Description Step-up Regulator N-MOS Drain. Place output diode and inductor. Ground 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. Over-voltage protection input(ADJ) Power supply.
ABSOLUTE MAXIMUM RATINGS (Note 1)
Parameter VIN voltage LX , OVP voltage EN , FB to GND Switch Current (ILX) Continuous power dissipation (SOT23-6 Ta=+25 OC) Operating Junction Temperature Range Lead Temperature (Soldering 5 sec) Storage Temperature Package Thermal Resistance ( JA) ESD Susceptibility (HBM) ESD Susceptibility (MM) Rated Value -0.3 to +6.5 -0.3 to +28 -0.3 to +6.5 0.25 0.35 -35 to 85 260 -65 to 125 250 2 200 Unit V V V A W
/W KV 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
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KB4312
RECOMMENDED OPERATION CONDITIONS
Parameter Power supply voltage Operating temperature Symbol VIN Top Min. 2.5 -30 Values Typ. +25 Max. 6.5 +85 Unit V
ELECTRICAL CHARACTERISTICS
(VIN=2.5V, Ta=+25 , unless otherwise noted)
Parameter Operating V IN Range Under Voltage Thershold No Load Current Shutdown Current Feedback Reference (+/-5%) Feedback Reference (+/-2%) Over-voltage Threshold Over-voltage Hysteresis OVP Leakage Current Output Voltage Line Regulation Switching Frequency Maximum Duty Soft-Start charging time Switching Current Limit LX ON Resistance LX Leakage Current EN Input Current EN Input Level EN low Shutdown Delay EN Low Cycle Time EN High Cycle Time
Symbol Test Condition VIN input Voltage VIN UVLO I IN1 IIN3 V FB V FB VOVP IOVP fOSC DMAX tSS ILX RLX ILeakage IEN VIH VIL tCYCL tCYCH
Min. 2.5
Typ. Max. Units 6.5 V
VIN falling, 100mV hysteresis 1.4 1.5 1.6 V No Switching , FB>0.2V 1 3 mA EN=0V 1 uA KB4312B 0.225 0.240 0.255 V 1.245 1.270 1.295 V KB4312A 16 17 20 V KB4312B 2 V EN=0V 1 uA 2.5V< VIN <6.0V 0.1 % 0.5 0.05 1.5 0.05 0.05 0.8 90 0.2 0.15 0.40 4 1.0 1 1 0.4 4 4 MHz % ms A uA uA V V ms ms ms
VIN=3.0V,duty cycle=80% , VIN =2.5V, ILX =750mA VLX =16V, EN=0V EN=5V
Note(1) Note(1)
Note(1): tCYCL and tCYCH are included rising time and falling time of PWM signal.
Recommended PCB Layout
KB4312B
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Kingbor Technology Co.,Ltd
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KB4312
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current
2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 2 4 VIN (V) 6 8 25 C -50 C 100 C 400 350 300 250 200 150 100 50
SHDN Pin Bias Current
1.4 1.2 SHDN = 10V 1.0 0.8 0.6 SHDN = 3.6V SHDN = 3V 0.4 0.2 75 100
Switching Frequency
SHDN = 2.7V - 25 50 25 TEMPERATURE ( C) 0
0 - 50
0 -50
-25
50 25 0 TEMPERATURE ( C)
75
100
Feedback Bias Current
60 50 40 83 30 82 20 10 0 -50 81 85
Efficiency vs Temperature
VIN = 3.6V 3 LEDs 350 ILED = 20mA 300 250 ILED = 15mA 200 150 100 50 0 0 50 100 TEMPERATURE ( C)
Current Limit vs Duty Cycle
84
ILED = 10mA
-25
50 25 0 TEMPERATURE ( C)
75
100
80 -50
0
20
40 60 DUTY CYCLE (%)
80
100
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KB4312
VOUT=6~24V 1uF
APPLICATION CIRCUIT
Vin=2.7~6V 1uF 1 LX 6 VCC OVP 5 10uH 1N5819
KB4312B
PWM or ON/OFF 4 EN GND 2 FB 3 240mV 20MA Rset 12R~51R
Figure 1a.KB4312 For 2 to 6 LEDs Back Light Unit.(Step-Up)
BAT54s 1uF
1 3 2
2.2K
-10V 10uF VOUT +15V (15mA)
1uF Vin=2.7~6V 1uF 1 LX 5 VCC 10uH 1N5819 R1 510K 10uF
10V
KB4312A
ON/OFF 4 EN GND 2
FB 3
1.27V R2 47K
R1= ( VOUT 1.27V
-1 ) x R2
1uF
1 3 2
2.2K
-10V 10uF
BAT54s Vin=5~20V 1K 10uH 1uF
1 3 2
1uF
10V
VOUT +15V(15mA) 10uF R1 510K
1uF 5.1V 1 LX 5 VCC
1uF
KB4312A
ON/OFF 4 EN GND 2
FB 3 1.27V R2 47K
R1= ( VOUT -1 ) x R2 1.27V
5
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.
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.
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:
I LED
Where:
105mV TON PWM RSENSE TS PWM
TON-PWM : On time of PWM signal TS-PWM : A cycle time of PWM signal 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.
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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 VOVP is above 17V or LEDs are disconnected from the circuit, the FB pin is similar to pull down to 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 .
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 :
Pboost
where
[(
I O VO 2 ) Vin
1 Vin D 2 ( ) ] RDS (ON ) 12 f OSC L
D
IO : It is the load current. fOSC : It is a switching frequency.
7
Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
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 Lpeak I LAVG
where:
I LAVG IO 1D
IL 2
IL is the inductor peak-to-peak current ripple and is decided by:
IL
Vin L VO V in VO
D f OSC
D is the MOSFET turn on ratio and is decided by:
D
fOSC is the switching frequency. The inductor should be chosen to be able to handle this current and inductor saturation current rating should be greater than IPEAK.
Diode selection
The output diode has average current of IO, and peak current the same as the inductor's peak current 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.
Output Capacitor
The KB4312 is specially compensated to be stable with capacitors which have a worst- case minimum value of 1uF at the particular VOUT being set. Output ripple voltage requirements also determine the 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:
V RIPPLE
I LPEAK
ESR
VO Vin VO
IO C OUT f OSC
For low ESR ceramic capacitors, the output ripple is dominated by the charging or discharging of the output capacitor.
8
Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
KB4312
PAD LAYOUT DETAILS
PACAGE DESCRIPTION
PACKAGE OUTLINE
Small Outline SOT23-6
b e L
2
E
E1
e1 D A A2
a
DATUM A
C
A1
CONTROLLING DIMENSIONS IN MILLIMETRES APPROX CONVERSIONS INCHES.
PACKAGE DIMENSIONS
Millimetres DIM Min A A1 A2 b C D 0.90 0.00 0.90 0.35 0.09 2.80 Max 1.45 0.15 1.30 0.50 0.20 3.00 Min 0.35 0 0.035 0.014 0.0035 0.110 Max 0.057 0.006 0.051 0.019 0.008 0.118 E E1 L e e1 L Inches DIM Min 2.60 1.50 0.10 Max 3.00 1.75 0.60 Min 0.102 0.059 0.004 Max 0.118 0.069 0.002 Millimetres Inches
0.95 REF 1.90 REF 0 10
0.037 REF 0.074 REF 0 10
Small Outline SOT23-5
PACKAGE OUTLINE PACKAGE DIMENSIONS
Millimeters DIM MIN. A A1 A2 b C D E E1 e e1 L a 0.90 0.90 0.20 0.09 2.70 2.20 1.30 MAX. 1.45 0.15 1.30 0.50 0.26 3.10 3.20 1.80 MIN. 0.0354 0.0354 0.0078 0.0035 0.1062 0.0866 0.0511 MAX. 0.0570 0.0059 0.0511 0.0196 0.0102 0.1220 0.1181 0.0708 Inches
0.95 REF 1.90 REF 0.10 0 0.60 30
0.0374 REF 0.0748 REF 0.0039 0 0.0236 30
Kingbor Technology
TEL:(86)0755-26508846 FAX:(86)0755-26509052 www.kingbor.com
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