AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Description Feature ‧ 4.75V to 16V Supply Voltage Operating AT1314 is a voltage-mode PWM step-down DC-DC converter capable of driving up to 1A Range. over a wide input supply range with excellent ‧ 600KHz ±15% Fixed Switching Frequency. loads line and load regulation characteristics. High ‧ Voltage-Mode PWM Step-Down Regulator. efficiency is obtained through the use of a low ‧ Built-in Power MOSFET, Rds(on)≒100mΩ. Rds(on) P-channel power switch. ‧ 1A Output Current, Up to 91.9% Efficiency It uses a fixed switching frequency up to 600KHz ‧ 0.4V±1.5% Internal Reference thus allowing smaller sized components. The ‧ Shutdown Current less than 20uA. output voltage level is user-programmable via an ‧ Thermal-Shutdown and Built-in Soft-Start. external resistive voltage divider. The built-in ‧ Cycle-by-Cycle Current-Limit Protection. soft-start can reduce inrush current on the input ‧ Under-Voltage Lockout Protection. source at turn on. ‧ Output Voltage Adjustable From 0.4V to 16V. The device also has built-in cycle-by-cycle ‧ SOP-8 Package. current-limit, thermal shutdown, under-voltage lockout and an ON/OFF logic-control that can Application power down the regulator to a shutdown mode. In ‧ Backlight for LCD Panels shutdown mode the regulator draws less than 20uA of supply current. ‧ Battery-Powered Backlight Applications ‧ Cell Phones AT1314 is available in SOP-8 package. ‧ PDAs ‧ Other Handheld Devices with Dual Displays. Block Diagram EN Under-voltage lockout Regulator IN Current Sense Amplifier Current Sense + P-MOS Contol Logic OSC 600KHz SW PWM Comparator Error Amplifier SoftStart + GND 0.4V FB COMP Aimtron reserves the right without notice to change this circuitry and specifications. 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Pin Configuration Ordering Information Part number AT1314S_GRE Package SOP-8,Green Marking AT1314S,Date Code with one bottom line *For more marking information, contact out sales representative directly Pin Descriptions Pin N0. Symbol I/O Description 1 IN P 2 EN I 3 COMP O 4 FB I 5,6 GND P Ground. 7,8 SW O Power Switching Output. Power Input. IN supplies power to the IC and Step-down converter switch. IN must be bypassed with a low-ESR capacitor. Enable input. EN is a digital input that turns the regulator on/off. Driver EN high to turn on the regulator, drive it low to turn it off. EN pin is also a dimming control input. Error Amplifier Output. A series RC network connected to this pin compensates AT1314. Feedback Input. Connect a resistive divider from switching output to FB to ground. 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Absolute Maximum Ratings Parameter Rated Value unit IN , EN voltage -0.3 to 18 V SW voltage -1 to IN+1 V FB, COMP voltage -0.3 to 6 V Quiescent current 5 mA Junction Temperature 150 ℃ Lead Temperature (For Green product) 260 ℃ Storage Temperature -65~150 ℃ HBM 2 KV MM 200 ESD Susceptibility*2 V 1. Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2. Device are ESD sensitive. Handling precaution recommended. The Human Body model is a 100pF capacitor discharged through a 1.5KΩ resistor into each pin. Recommended Operation Conditions Parameter Symbol Min. Values Typ. Max. Unit Power supply voltage IN 4.75 12 16 V Operating temperature Top -20 +25 +85 ℃ 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Electrical Characteristics (IN=12V, EN=5V, Ta=+25℃, unless otherwise noted) Parameter Symbol Test Condition Min. Typ. Max. Units 4.75 12 16 V 3.8 4.2 4.6 V - 500 - mV Input operating voltage IN Input under-voltage lockout threshold UVLO hysteresis VUVLO Quiescent Current Iin VFB=0.5V - 3.5 - mA Shutdown Current ISHDN EN =GND - 20 50 uA Oscillator Frequency FSW Ta=+25℃ - 600 - KHz Feedback Regulation voltage VFB Ta=+25℃ - 0.4 - V FB Input Bias Current IFB VFB=0.4V -50 - 50 nA - 1 - A IN Rising Current limit Maximum Duty Cycle DMAX FB=0.3V - - 100 % Minimum Duty Cycle DMIIN FB=0.5V 0 - - % SW Switch On-Resistance RSW-DS(ON) ISW=1A - 100 130 mΩ SW Leakage Current ISW IN=13.5V,VSW=GND , EN=0V - 0.1 20 µA - 70 - dB 500 800 - 0.8 - ms - 1 - µA VIH 2.0 - - V VIL - - 0.5 V - 160 - ℃ Error Amplifier Voltage Gain Error Amplifier Trans-conductance Soft-Start Time EN Pull Up Current EN Trip Level Thermal Shutdown EN=0V 1000 µA/V 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Typical characteristics (See the Typical Applications Circuit, L=8.2uH ~ 47uH,unless otherwise noted) LED Current = 180mA LED Current = 1A 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Typical Application Circuit Direct – PWM Dimming VFB VEN IIN 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs General Description The AT1314 features a PWM step-down converter operating with a fixed switching frequency of 600 KHz and uses internal power MOSFET to provide maximum efficiency. The output voltage of the converter can be set as low as 0.4V with external resistive divider. When trans-conductance signal is higher than saw-tooth wave, then PWM comparator will produce ON-time signal to set internal flip-flop, which turns on the switching power MOSFET. The external inductor current ramps up linearly, storing energy in a magnetic field. Once peak current of flowing through switching power MOSFET over current-limited threshold or trans-conductance signal level is lower than saw-tooth wave, the switching power MOSFET will 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 add higher flexibility to the selection of external component values, the device uses external loop compensation. Soft-Start AT1314 is built-in soft-start function. When power up, after input voltage is above the under-voltage lockout threshold, then soft-start allows a gradual increase of COMP voltage to get to a steady state operating point. Therefore, reducing input surge currents. During this time, the COMP voltage increases and the output duty cycle is allowed to increase from zero to the value required for regulation. The maximum load current is available after the soft-start cycle is completed. When EN pin is taken low, the soft-start capacitor is discharge to ground. Cycle-by-Cycle Over-Current Protection The AT1314 provides cycle-by-cycle over-current protection. Current limit is accomplished using a separate dedicated comparator. If the current sense amplifier output voltage is larger than current-limited threshold level, it will be immediately turned off power MOS. The current-limit feature protects against a hard short or over current fault at the output. Thermal-Overload Protection Thermal-overload protection limits total power dissipation in the AT1314. When the junction temperature exceeds Tj=160 ℃, a thermal sensor activates the thermal protection, which shuts down the IC, allowing the IC to cool. Once the device cools down by 15 ℃, IC will automatically recover normal operation. For continuous operation , do not exceed the absolute maximum junction-temperature rating of Tj=150 ℃. 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Applications Information External components of step-down converter can be designed by performing simple calculations. It must be 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. PWM Dimming Control EN is also used as a digital input, allowing LED brightness control with a logic-level PWM signal applied directly to EN. The frequency range is from 100Hz to 1kHz, while 0% duty cycle corresponds to zero current and 100% duty cycle corresponds to full current. The error amplifier and compensation Capacitor form a lowpass filter, so PWM dimming results in DC current to the LEDs without any additional RC filters required Inductor Inductor selection depends on input voltage, output voltage, maximum current, switching frequency and availability of inductor values. The following buck circuit equations are useful in choosing the inductor values based on the application. Choose an inductor that does not saturate under the maximum rating load conditions. The magnitude of inductance is selected to maintain a peak to peak ripple current of 30% of the maximum load current. The peak inductor current is given by: I Lpeak = I LAVG + I LAVG = D= ∆I L 2 I in D VO Vin D is the MOSFET turn on ratio where: △IL is the inductor peak-to-peak current ripple and is decided by: V − VO (V − VO ) × D D ∆I L = in × ⇒ L = in L f OSC ∆I L × f OSC 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. 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Diode selection When the power switch turns off, the current through the inductor continues to flow. The path for this current is through the diode connected between the switch output and ground. This forward biased diode must has a minimum voltage drop and recovery times. Schottky diode is recommended and it should be able to handle those current. As usual, the reverse voltage rating of the diode should be at least 1.3 times greater than the maximum input voltage, and current rating is greater than the maximum load current. Setting the Maximum LED Current Resistor REF sets the maximum current in the primary chains of LEDs: I LEDMAX = 400mV RFB Where ILEDMAX is the maximum LED current. Input capacitor An input capacitor helps to provide additional current to the power supply as well as smooth input voltage variations in high current switching regulators. When selecting an input capacitor, a low ESR capacitor is required to keep the noise at the IC to a minimum. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice. Choose an input capacitor who’s maximum voltage rating is 1.3 times greater than the maximum input voltage, and who’s RMS current rating is equal to one-half of the maximum dc load current. It may be necessary in some designs to add a small valued ceramic type capacitor in parallel with the input capacitor to prevent any ring. Output Capacitor The output capacitor acts to smooth the dc output voltage and also provides energy storage. Selection of an output capacitor, with an associated equivalent series resistance (ESR), impacts both the amount of output ripple voltage and stability of the control loop. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple is estimated to be: (1 − D) × VO ∆Vripple = 2 8 × L × COUT × f OSC 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs For low ESR ceramic capacitors, the output ripple is dominated by the charging or discharging of the output capacitor. In the case of low-ESR electrolytic capacitors, Output ripple voltage drop caused by the switching current through the ESR of the output capacitor. The output ripple is estimated as: VRIPPLE ≅ ∆I L × R ESR Impacting frequency stability of the overall control loop, the output capacitance, in conjunction with the inductor, creates a double pole inside the feedback loop. In addition the capacitance and the ESR value create a zero. These frequency response effects together with the internal frequency compensation circuitry of AT1314 modify the gain and phase shift of the closed loop system. Compensation The step-down loop can be compensated by adjusting the external components connected to the COMP pin. The COMP pin is connected to the output of the internal trans-conductance error amplifier. The compensation capacitor adjusts the low frequency gain , and the series resistor value adjusts the high frequency gain. A series capacitor-resistor combination sets a pole-zero combination to control the characteristics of the control system. The system has 2 poles and one zero of importance, 2 poles consist of compensation capacitor and output capacitor. One zero is produced by the compensation capacitor and the compensation resistor. If electrolytic capacitor with relatively high ESR is used, the zero due to the capacitance and ESR of the output capacitor can be compensated by a third pole set by the compensation resistor and another compensation capacitor connected form COMP pin to ground. 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 buck converter diode and inductor close to the SW pin and no via. ‧ Please ceramic bypass capacitors near the input pin. ‧ Locate all feedback resistive dividers as close to their respective feedback pins as possible. ‧ Use wide traces and trace length is short as possible. 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Outline 8-pin SOP SYMBOL A B C D E F H J K M e1 α INCHES MIN MAX 0.188 0.197 0.149 0.158 0.228 0.244 0.050 BSC 0.013 0.020 0.004 0.010 0.053 0.069 0.011 0.019 0.007 0.010 0.016 0.050 45O 80 00 MILLIMETERS MIN MAX 4.80 5.00 3.80 4.00 5.80 6.20 1.27 BSC 0.33 0.51 0.10 0.25 1.35 1.75 0.28 0.48 0.19 0.25 0.40 1.27 45O 0 0 80 NOTES - - 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected] AT1314 Preliminary Product Information High-Efficiency Step-Down Current Regulator For LEDs Reflow Profiles Profile Feature Average ramp-up rate (TL to TP) Preheat -Temperature Min(Tsmin) -Temperature Max (Tsmax) -Time (min to max)(ts) Tsmax to TL -Ramp-up Rate Time maintained above: -Temperature (TL) -Time (tL) Peak Temperature(TP) Time within 5°C of actual Peak Temperature (tP) Ramp-down Rate Time 25°C to Peak Temperature Sn-Pb Eutectic Assembly Pb-Free Assembly Large Body Small Body Large Body Small Body Pkg. thickness Pkg. thickness Pkg. thickness Pkg. thickness ≥2.5mm or Pkg. <2.5mm or Pkg. ≥2.5mm or Pkg. ≥2.5mm or Pkg. volume volume volume volume ≥350mm3 3 3 <350mm ≥350mm ≥350mm3 3°C/second max. 3°C/second max. 100°C 150°C 60-120 seconds 150°C 200°C 60-180 seconds 3°C/second max. 183°C 60-150 seconds 217°C 60-150 seconds 225+0/-5°C 10-30 seconds 240+0/-5°C 10-30 seconds 6°C/second max. 6 minutes max. 245+0/-5°C 10-30 seconds 250+0/-5°C 20-40 seconds 3°C/second max. 8 minutes max. *All temperatures refer to topside of the package, measured on the package body surface. 7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 3/24/2006 REV:2.0 Email: [email protected]