AT1308 ETC1 | Alldatasheet

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Technical content

Preliminary Product Information Micro-Power Step up DC-DC Converter 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

-FB ON/OFF Control Logic GND Control Logic EN N VBG 1.23V VIN Current Limit 400mA Soft-Start Thermal Protection Feature

  • Operating V oltage:2.5V~6.0V
  • High Operating Frequency: 1MHz
  • Built-in N-MOS, Rds(on)≒ 0.3Ω (TYP)
  • High Output V oltage: 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

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 0.3Ω N-MOS that allows for smaller capacitor and inductor. Fault condition protection uses cycle-by- cycle current limiting to sense maximum inductor current and thermal protection. Also included soft-start circuitry eliminates inrush current during start-up. The AT1308 is av ailable in 5-pin SOT-25 packages. Block Diagram Aimtron reserves the right without notice to change this circuitry and specifications.

Preliminary Product Information Micro-Power Step up DC-DC Converter 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

(TOP VIEW) FB VINLX EN GND

Ordering Information

Absolute Maximum Ratings[note1] 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 Part number Package Marking AT1308X SOT-25 Date Code AT1308X_GRE SOT-25,Green ,Date Code with one bottom line Pin N0. Symbol I / O Description 1 LX I Step-up Regulator N-MOS Drai n. Place output diode and inductor.

2 GND P Ground

3 FB I Step-Up Regulator Feedback Input. Connect a resistive divider from output to FB to analog ground. 4 EN I Enable Control Input. Pull EN low to force the controller into shutdown. If unused , connect EN to Vin for normal operation. 5 VIN P Power supply. Parameter Rated Value Unit VIN voltage -0.3 to +6.5 V LX voltage -0.3 to +30 V EN , FB to GND -0.3 to +6.5 V Switch Current (ILX) 0.8 A Continuous power dissipation (SOT-25 Ta=+25OC) 0.25 W Operating Junction Temperature Range -30 to 85 ℃ Lead Temperature (Soldering 5 sec) 260 ℃ Storage Temperature -65 to 125 ℃ Package Thermal Resistance (ΘJA) 250 ℃/W ESD Susceptibility (HBM) 2 KV ESD Susceptibility (MM) 200 V

Preliminary Product Information Micro-Power Step up DC-DC Converter 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

Recommended Operation Conditions

Electrical Characteristics

(VIN=2.5V , Ta=+25℃, unless otherwise noted) Values Parameter Symbol Min. Typ. Max. Unit Power supply voltage V IN 2.5 ― 6.0 V Operating temperature Top -20 +25 +85 ℃ Parameter Symbol Test Condition Min. Typ. Max. Units Operating V IN Range VIN VIN input V oltage 2.5 - 6.0 V Under V oltage Thershold UVLO V IN falling, 100mV hysteresis - 2.2 - V Switch- Off Input Current I IN1 No Switching - 100 120 uA Shutdown Current I IN3 EN=0V - - 1 uA Feedback Reference V FB 1.212 1.23 1.248 V FB Input Bais Current I FB V FB =1.23V - - 1 uA Output V oltage Line Regulation 2.5V< VIN <6.0V - 0.1 - % Switching Frequency f OSC - 1 - MHz Maximum Duty D MAX - 90 - % Soft-Start charging time t SS 0.5 ms Switching Current Limit ILX VIN=3.0V ,duty cycle=80% - 400 - mA LX ON Resistance R LX ILX =350mA - 0.3 - Ω LX Leakage Current I Leakage V LX =29V , EN=0V - - 1 uA EN Input Current I EN EN=5V - - 8 uA VIH 0.1V hysteresis 2.0 - - V EN Input Level VIL - - 0.8 V Thermal Shutdown 120 ℃

Preliminary Product Information Micro-Power Step up DC-DC Converter 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

2.5V to 4.2V AT1308 EN 500K 297K 10uF/ 6V3 3.3V/ 50mA 10uH 1uF L1, L2 : SR0302 (0.25Ohm/0.8A)※ V※ OUT=VREFX (1+R1/R2) Fig1. 1-Cell Li-Ion to 3.3V SEPIC Converter LX GND FB 10pF VIN MBR140WS10uH 4u7F/ 6V3 VIN 3.0V to 6.0V AT1308 EN 500K 163K 10uF/ 6V3 5V/ 40mA 10uH 1uF L1, L2 :SR0302 (0.25Ohm/0.8A)※ V※ OUT=VREFX (1+R1/R2) Fig2. 4-Cell to 5V SEPIC Converter

Preliminary Product Information Micro-Power Step up DC-DC Converter 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

2.5V to 5.0V AT1308 EN 500K 44K 4.7uF/ 16V 15V/ 4mA L1 :SR0302 (0.25Ohm/0.8A)※ BAT54S 4.7uF/ 16V -15V/ 4mA 0.1uF 0.1uF Fig3. ±15V Dual Output Converter with Output Disconnect LX GND FB VIN MBR140WS 10uH 4.7uF/ 6V3 VIN 2.5V to 5.0V AT1308 EN 500K 44K 10uF/ 16V 15V/ 20mA 10pF L1 :SR0302 (0.25Ohm/0.8A)※ V※ OUT=VREFX (1+R1/R2) Fig4. 15V Boost Converter

Preliminary Product Information Micro-Power Step up DC-DC Converter 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

4.7uH 10uF/10V VIN AT1308 EN 500K 98K 1uF VOUT1 7.5V_TFT BAT54S 1uF0.1uF SW open BAT54S 1uF/25V VOUT2 17V_TFT 0.1uF 10K 10uF/25V Zener 17V BAT54S1uF 0.1uF open BAT54S 1uF/25V VOUT3 -13V_TFT 0.1uF 510 Zener 13V Fig5. TFT_ Power solution

Preliminary Product Information Micro-Power Step up DC-DC Converter 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

EFFICIENCY vs OUTPUT CURRENT 1 3 5 8 10 13 15 18 20 Io-Output Current-mA Efficiency-% 2.5V 3.6V 5.0V EFFICIENCY vs LOAD CURRENT 1 3 5 7 1 01 31 51 82 0 Io-Load Current-mA Efficiency-% 6.8uH 10uH 22uH V o=15V L=10uH V o=15V Vin=3.3V

Preliminary Product Information Micro-Power Step up DC-DC Converter 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

EFFICIENCY vs INPUT VOLTAGE Vin-Input Voltage-V Efficiency-% 5mA 10mA 20mA CURRENT LIMIT vs SUPPLY VOLTAGE 300 350 400 450 500 550 600 650 700 2.5 3 3.5 4 4.5 5 5.5 6 VIN-SUPPLY VOLTAGE (V) CURRENT LIMIT (mA) L=10uH L=22uH V o=15V L=10uH V o=15V

Preliminary Product Information Micro-Power Step up DC-DC Converter 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

QUIESCENT CURRENT vs INPUT VOLTAGE 100 150 200 250 300 350 400 450 500 VIN-INPUT VOLTAGE (V) QUIESCENT CURRENT (uA) SWITCHING FREQUENCY vs TEMPERATURE 940 945 950 955 960 965 970 975 - 2 0 - 1 00 1 02 54 05 58 5 TEMPERATURE ( oC) SWITCHING FREQUENCY (KHz) V o=15V L=10uH TA=25OC VIN=2.5V V o=15V L=1 0uH

Preliminary Product Information Micro-Power Step up DC-DC Converter Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 1 0 Rev A ; 01/18/05 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

Preliminary Product Information Micro-Power Step up DC-DC Converter Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 1 1 Rev A ; 01/18/05 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

Preliminary Product Information Micro-Power Step up DC-DC Converter Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 1 2 Rev A ; 01/18/05 Function Description The AT1308 is designed primarily for use in STN/OL ED 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 regul ate 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 lin early, 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 th e 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 inte rnal reference, error amp lifier, 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 cycl e-by-cycle current limit abbrevia tes 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 ℃.

Preliminary Product Information Micro-Power Step up DC-DC Converter Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 1 3 Rev A ; 01/18/05 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 : DRLf DV V VIP ONDS OSC in in OO boost ××× ×+×= )( 22 ])(12 1)[( 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 a llow the trading of peak current and inductor value while allowing for consideration of component availability and cost. The peak inductor current is given by: D II III O LAVG L LAVGLpeak ∆+= where: △IL is the inductor peak-to-peak current ripple and is decided by: OSC in L f D L VI ×=∆ D is the MOSFET turn on ratio and is decided by: O inO V VVD −= 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.

Preliminary Product Information Micro-Power Step up DC-DC Converter Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 1 4 Rev A ; 01/18/05 Diode selection The output diode has average current of I O, 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 V OUT 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: OSCOUT O O inO LPEAKRIPPLE fC I V VVESRIV ××−+×= 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 contro l loop, Ceramic capacitors are preferred on the output capacitance, but tantalum capacitor may also su ffice., If it use tantalum capacitor on the output terminal, that in addition the capacitance parallel w ith 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 importa nt 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 V IN and VOUT should be as close together as possible.

Preliminary Product Information Micro-Power Step up DC-DC Converter Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw Fax: 886-3-563-0879 Email: service@aimtron.com.tw 1 5 Rev A ; 01/18/05 Small Outline SOT-25