AT1308 Preliminary Product Information Micro-Power Step up DC-DC Converter Feature Description •Operating Voltage:2.5V~6.0V 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 0.3Ω 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. •High Operating Frequency: 1MHz •Built-in N-MOS, Rds(on)≒ 0.3Ω (TYP) •High Output Voltage: Up to 28V •Shutdown Current <1µA •Built-in Cycle-by-Cycle Current-limited. •Built-in Soft-Start Function. •1.5% 1.23V Reference. •Tiny SOT-25 Package Application • STN/OLED Bias • Personal Digital Assistants (PDAs) • DSC Block Diagram VIN LX ON/OFF Control Logic EN 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: [email protected] 1 Rev A ; 01/18/05 AT1308 Preliminary Product Information Micro-Power Step up DC-DC Converter Pin Configuration SOT-25 (TOP VIEW) LX 1 GND 2 FB 3 5 VIN 4 EN 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 I/O I P 3 FB I 4 EN I 5 VIN 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 (ΘJA) 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: [email protected] 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 Values Typ. ― +25 Symbol VIN Top Min. 2.5 -20 Unit Max. 6.0 +85 V ℃ Electrical Characteristics (VIN=2.5V, Ta=+25℃, unless otherwise noted) Parameter Operating V IN Range Symbol Test Condition VIN input Voltage VIN Min. Under Voltage Thershold Switch- Off Input Current Shutdown Current Feedback Reference FB Input Bais Current UVLO IIN1 IIN3 VFB IFB 2.2 100 120 1 1.212 1.23 1.248 1 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 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 VIN=3.0V,duty cycle=80% ILX =350mA VLX =29V, EN=0V EN=5V 0.1V hysteresis 2.5 Typ. Max. Units - 6.0 V V uA uA V uA - 0.1 - % - 1 90 0.5 400 0.3 120 - MHz % ms mA Ω uA uA V V ℃ 2.0 - 1 8 0.8 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: [email protected] 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 MBR140WS 1uF 3.3V/ 50mA L1 4u7F/ 6V3 VIN LX 10uH L2 10pF 500K AT1308 EN 10uF/ 6V3 R1 FB R2 297K ※L1, L2 : SR0302 (0.25Ohm/0.8A) GND ※VOUT=VREFX (1+R1/R2) Fig1. 1-Cell Li-Ion to 3.3V SEPIC Converter 10uH VIN 3.0V to 6.0V MBR140WS 1uF 5V/ 40mA L1 4u7F/ 6V3 VIN LX 10uH 10pF L2 10uF/ 6V3 AT1308 R1 500K FB EN R2 GND 163K ※L1, L2 :SR0302 (0.25Ohm/0.8A) ※VOUT=VREFX (1+R1/R2) 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: [email protected] 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 4.7uF/ 16V BAT54S -15V/ 4mA 0.1uF 15V/ 4mA L1 4u7F/ 6V3 VIN BAT54S LX 10pF AT1308 4.7uF/ 16V 500K FB EN 44K GND ※L1 :SR0302 (0.25Ohm/0.8A) Fig3. ±15V Dual Output Converter with Output Disconnect 10uH VIN 2.5V to 5.0V 15V/ 20mA L1 4.7uF/ 6V3 VIN MBR140WS LX 10uF/ 16V 10pF AT1308 500K R1 FB EN 44K R2 GND ※L1 :SR0302 (0.25Ohm/0.8A) ※VOUT=VREFX (1+R1/R2) 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: [email protected] 5 Rev A ; 01/18/05 AT1308 Preliminary Product Information Micro-Power Step up DC-DC Converter VOUT3 -13V_TFT 510 VOUT2 17V_TFT 10K BAT54S 1uF/25V 0.1uF BAT54S 0.1uF 1uF/25V Zener 13V 10uF/25V Zener 17V open open 1uF 0.1uF BAT54S 0.1uF 1uF BAT54S 4.7uH VOUT1 7.5V_TFT VIN 5V MBR140S 10uF/10V VIN LX 10pF SW 1uF AT1308 500K FB EN 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: [email protected] 6 Rev A ; 01/18/05 AT1308 Preliminary Product Information Micro-Power Step up DC-DC Converter Efficiency-% Typical Characteristics 90 85 80 75 70 65 60 55 50 45 40 EFFICIENCY vs OUTPUT CURRENT Vo=15V L=10uH 2.5V 3.6V 5.0V Efficiency-% 1 90 85 80 3 5 8 10 13 15 18 20 Io-Output Current-mA EFFICIENCY vs LOAD CURRENT Vo=15V Vin=3.3V 75 70 65 60 55 50 6.8uH 10uH 22uH 1 3 5 7 10 13 15 18 20 Io-Load Current-mA 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: [email protected] 7 Rev A ; 01/18/05 AT1308 Preliminary Product Information Micro-Power Step up DC-DC Converter 90 EFFICIENCY vs INPUT VOLTAGE Vo=15V L=10uH Efficiency-% 85 80 75 5mA 10mA 20mA 70 2.5 3 3.3 3.6 3.9 4.2 4.5 5 5.5 Vin-Input Voltage-V CURRENT LIM IT vs SUPPLY VO LTAG E 700 CURRENT LIMIT (mA) 650 Vo=15V 600 550 500 450 400 L=10uH 350 L=22uH 300 2.5 3 3.5 4 4.5 5 5.5 6 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: [email protected] 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 QUIESCENT CURRENT (uA) 500 450 400 Vo=15V L=10uH 350 300 TA=25OC 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 ) SWITCHING FREQUENCY (KHz) SW ITC H IN G FR EQ U EN C Y v s TEM PER A TU R E 975 970 VIN=2.5V Vo=15V L=10uH 965 960 955 950 945 940 -20 -1 0 0 10 25 40 55 85 TE M PER A TU R E ( o C ) 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: [email protected] 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: [email protected] 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: [email protected] 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: [email protected] 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 = [( I O × VO 2 1 Vin × D 2 ) ] × RDS ( ON ) × D ) + ( Vin 12 f OSC × L where 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 = ∆I L 2 IO 1− D where: △IL is the inductor peak-to-peak current ripple and is decided by: ∆I L = Vin D × 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: [email protected] 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 × ESR + VO − Vin IO × VO C OUT × 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: [email protected] 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: [email protected] 15 Rev A ; 01/18/05