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AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter Feature
*Operating Voltage:2.5V~6.0V *High Operating Frequency: 1MHz *Built-in N-MOS, Rds(on) 0.3 (TYP) *High Output Voltage: Up to 28V *Shutdown Current <1A *Built-in Cycle-by-Cycle Current-limited. *Built-in Soft-Start Function. *1.5% 1.23V Reference. *Tiny SOT-25 Package
Description
The AT1308 step-up converter is designed for small or medium size LCD panel of high bias voltage with a constant current to provide PDAs, and other hand-held devices. It features a fast 1.0 MHz current-mode PWM control with a built-in 0.3 N-MOS that allows for smaller capacitor and inductor. Fault condition protection uses cycle-bycycle current limiting to sense maximum inductor current and thermal protection. Also included soft-start circuitry eliminates inrush current during start-up. The AT1308 is available in 5-pin SOT-25 packages.
Application
* STN/OLED Bias * Personal Digital Assistants (PDAs) * DSC
Block Diagram
VIN
LX
EN
ON/OFF Control Logic
VBG 1.23V
Soft-Start
Thermal Protection
VBG N + Control Logic FB -
Current Limit 400mA
+ -
GND
Aimtron reserves the right without notice to change this circuitry and specifications.
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 1 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter Pin Configuration
SOT-25 (TOP VIEW) LX GND FB 1 2 3 4 EN 5 VIN
Ordering Information
Part number AT1308X AT1308X_GRE Package SOT-25 SOT-25,Green Marking Date Code ,Date Code with one bottom line
Pin Description
Pin N0. Symbol 1 LX 2 GND 3 4 5 FB EN VIN I/O I P I I P Description Step-up Regulator N-MOS Drain. Place output diode and inductor. Ground Step-Up Regulator Feedback Input. Connect a resistive divider from output to FB to analog ground. Enable Control Input. Pull EN low to force the controller into shutdown. If unused , connect EN to Vin for normal operation. Power supply.
Absolute Maximum Ratings[note1]
Parameter VIN voltage LX voltage EN , FB to GND Switch Current (ILX) Continuous power dissipation (SOT-25 Ta=+25OC) 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 +30 -0.3 to +6.5 0.8 0.25 -30 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
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 2 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
Recommended Operation Conditions
Parameter Power supply voltage Operating temperature Symbol VIN Top Min. 2.5 -20 Values Typ. +25 Max. 6.0 +85 Unit V
Electrical Characteristics
(VIN=2.5V, Ta=+25, unless otherwise noted)
Parameter Operating V IN Range Under Voltage Thershold Switch- Off Input Current Shutdown Current Feedback Reference FB Input Bais 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 Thermal Shutdown
Symbol Test Condition VIN input Voltage VIN UVLO IIN1 IIN3 VFB IFB fOSC DMAX tSS ILX RLX ILeakage IEN VIH VIL VIN falling, 100mV hysteresis No Switching EN=0V VFB =1.23V 2.5V< VIN <6.0V
Min. 2.5
Typ. Max. Units 6.0 V V uA uA V uA % MHz % ms mA uA uA V V
2.2 100 120 1 1.212 1.23 1.248 1 0.1 1 90 0.5 400 0.3 120 1 8 0.8
VIN=3.0V,duty cycle=80% ILX =350mA VLX =29V, EN=0V EN=5V 0.1V hysteresis
2.0 -
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 3 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter Application Circuit
10uH VIN 2.5V to 4.2V 4u7F/ 6V3 L1 1uF MBR140WS 3.3V/ 50mA
VIN
LX
10uH L2 10pF 500K R1 10uF/ 6V3
AT1308
EN FB
R2
297K
GND
L1, L2 : SR0302 (0.25Ohm/0.8A) VOUT=VREF (1+R1/R2) X
Fig1. 1-Cell Li-Ion to 3.3V SEPIC Converter
10uH VIN 3.0V to 6.0V 4u7F/ 6V3 L1
1uF
MBR140WS 5V/ 40mA
VIN
LX
10uH L2 10pF 10uF/ 6V3 R1 500K
AT1308
EN FB
R2
163K
GND
L1, L2 :SR0302 (0.25Ohm/0.8A) VOUT=VREF (1+R1/R2) X
Fig2. 4-Cell to 5V SEPIC Converter
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 4 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
0.1uF 10uH VIN 2.5V to 5.0V 4u7F/ 6V3 L1 0.1uF
BAT54S
4.7uF/ 16V
-15V/ 4mA
15V/ 4mA BAT54S
VIN
LX
10pF
4.7uF/ 16V
AT1308
EN FB
500K
44K
GND
L1 :SR0302 (0.25Ohm/0.8A)
Fig3. 15V Dual Output Converter with Output Disconnect
10uH VIN 2.5V to 5.0V 4.7uF/ 6V3 L1 15V/ 20mA MBR140WS
VIN
LX
10uF/ 16V 500K R1
10pF
AT1308
EN FB
44K R2
GND
L1 :SR0302 (0.25Ohm/0.8A) VOUT=VREF (1+R1/R2) X
Fig4. 15V Boost Converter
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 5 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
VOUT3 -13V_TFT 510 10K VOUT2 17V_TFT
1uF/25V Zener 13V
BAT54S
0.1uF
0.1uF
BAT54S
1uF/25V Zener 17V
10uF/25V
open
open
1uF
BAT54S
0.1uF 4.7uH
0.1uF
BAT54S
1uF
VIN 5V MBR140S 10uF/10V
VOUT1 7.5V_TFT
VIN
LX
10pF 1uF
SW
AT1308
EN FB
500K
98K
GND
Fig5. TFT_ Power solution
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 6 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter Typical Characteristics
90 85 80 75 70 65 60 55 50 45 40
EFFICIENCY vs OUTPUT CURRENT
Vo=15V L=10uH
Efficiency-%
2.5V 3.6V 5.0V 1 3
Io-Output Current-mA
5
8 10 13 15 18 20
Efficiency-%
90 85 80 75 70 65 60 55 50
EFFICIENCY vs LOAD CURRENT
Vo=15V Vin=3.3V
6.8uH 10uH 22uH 1 3
Io-Load Current-mA
5
7
10 13 15 18 20
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 7 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
90 85 Efficiency-% 80 75 70
EFFICIENCY vs INPUT VOLTAGE
Vo=15V L=10uH
5mA 10mA 20mA 2.5 3 3.3 3.6 3.9 4.2 4.5 Vin-Input Voltage-V 5 5.5
CURRENT LIM IT vs SUPPLY VO LTAG E 700 650 CURRENT LIMIT (mA) 600 550 500 450 400 350 300 2.5 3 3.5 4 4.5 5 L=10uH L=22uH 5.5 6
Vo=15V
VIN-SUPPLY VO LTAG E (V)
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 8 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
Q U IESC EN T C U R R EN T vs IN PU T V O LTA G E 500 QUIESCENT CURRENT (uA) 450 400 350 300 250 200 150 100 50 0 2.5 2.8 3 3.3 3.6 4 4.2 4.5 5 5.5 6 V IN -IN PU T V O LTA G E (V )
Vo=15V L=10uH
TA=25OC
SW ITC H IN G FR EQ U EN C Y v s TEM PER A TU R E SWITCHING FREQUENCY (KHz) 975 970 965 960 955 950 945 940 -20 -1 0 0 10 25 40 55 85 TE M PER A TU R E ( o C )
VIN=2.5V Vo=15V L=10uH
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 9 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
Load Transient Response VIN=2.5V, Vout=15V, L=10uH, Iout=5mA to 25mA
Ch1:Vout (AC mode), Ch4:Iout, Time:0.5ms/div Line Transient Response VIN=2.5V to 6.0V, Vout=15V, L=10uH, Iout=20mA
Ch1:VIN, Ch2:Vout (AC mode), Ch4:IIN, Time:0.5s/div 2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 10 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
Start up Waveform with Load VIN=2.5V, Vout=15V, L=10uH, Iout=20mA
Ch1:Vout, Ch2:EN, Ch4:IIN, Time:1.0ms/div LX Switching Waveform VIN=3.3V, Vout=20V, L=10uH
Ch1:LX, Ch4:ILX, Time:0.5us/div 2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 11 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter Function Description
The AT1308 is designed primarily for use in STN/OLED bias applications. The output voltage of the step-up converter can be set from Vin to 26V with external resistive voltage divider. The boost converter operates in current-mode PWM and a constant frequency of 1.0 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 load. 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 0.7V 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 . EN works as a simple on/off control. Drive EN high to enable the device, or drive EN low for shutdown. 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. Cycle-by-Cycle Over-Current Protection The AT1308 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. Thermal-Overload Protection Thermal-overload protection limits total power dissipation in the AT1308. When the junction temperature exceeds Tj=130 , a thermal sensor activates the thermal protection, which shuts down the IC, allowing the IC to cool. Once the device cools down by 10 , IC will automatically recover normal operation. For continuous operation , do not exceed the absolute maximum junction-temperature rating of Tj=120 .
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 12 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
Power dissipation consideration The AT1308 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 x VO 2 1 Vin x D 2 ) ] x RDS ( ON ) x D )+ ( Vin 12 f OSC x L
IO : It is the load current. fOSC : It is a switching frequency.
Applications Information
External components of 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 + I LAVG =
where:
I L 2
IO 1- D
IL is the inductor peak-to-peak current ripple and is decided by:
I L =
Vin D x L f OSC
D is the MOSFET turn on ratio and is decided by:
D=
VO -V in VO
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. 2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 13 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
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 AT1308 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 x ESR +
VO - Vin IO x VO C OUT x f OSC
For low ESR ceramic capacitors, the output ripple is dominated by the charging or discharging of the output capacitor. Impacting frequency stability of the overall control loop, Ceramic capacitors are preferred on the output capacitance, but tantalum capacitor may also suffice., If it use tantalum capacitor on the output terminal, that in addition the capacitance parallel with feedback resistor network is necessary. These frequency response effects together with the internal frequency compensation circuitry of AT308 modify the gain and phase shift of the closed loop system. PCB layout guidelines Careful printed circuit layout is extremely important to avoid causing parasitical capacitance and line inductance. The following layout guidelines are recommended to achieve optimum performance. * Please the boost converter diode and inductor close to the LX pin and no via. Keep traces short, direct, and wide. * Please ceramic bypass capacitors near the input/output pin. * Locate all feedback sense resistor as close to the feedback pins as possible. * The ground connections of VIN and VOUT should be as close together as possible.
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 14 Rev A ; 01/18/05
AT1308
Preliminary Product Information Micro-Power Step up DC-DC Converter
Small Outline SOT-25
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 15 Rev A ; 01/18/05

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