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| Preliminary Technical Data FEATURES 95% peak efficiency Optimized for low output voltages Optimized for extremely small ceramic inductors Up to 600mA, load current 2.7 V to 5.5 V input voltage range Operates with a Single Li-Ion battery Fixed Output Voltage from 0.8V to 1.875V Adjustable Output Voltage from 0.8V to 1.875V Low 60A quiescent current Internal Synchronous rectifier 3 MHz Operating Frequency 0.1A Shutdown Supply Current Small 8-Lead 3 x3 LFCSP Package Enable /shutdown logic input Under Voltage Lockout Internal Soft Start Internal Compensation 600mA 3MHz Synchronous Step-Down DC-DC Converter ADP2102 GENERAL DESCRIPTION The ADP2102 is a low quiescent current step-down DC-DC converter optimized to regulate low output voltages in a compact 3mmx3mm LFCSP package. At high load currents, the ADP2102 uses a current mode, constant on time, pseudo fixed frequency, valley current control scheme for excellent stability and transient response with very few, small external components. To ensure the longest battery life in portable applications, the ADP2102 has a power saving mode that reduces the switching frequency under light load conditions to significantly reduce the quiescent current. The ADP2102 runs from input voltages from 2.7V to 5.5V allowing single Li+/Li- polymer cell, multiple Alkaline/Ni-MH cells and other standard power sources. ADP2102 output voltage is adjustable from 0.8V to 1.875V, while the suffix part numbers ADP2102-XX indicate pre-set voltage ranges of 1.875, 1.8, 1.5, 1.375, 1.25, 1.2, 1.0 & 0.8V. All versions include an internal power switch and a synchronous rectifier for high efficiency while internal compensation guarantees minimal number of external components. During logic-controlled shutdown, the input is disconnected from the output and it draws less than 0.1A from the input source. Other key features include under voltage lockout to prevent deep battery discharge and soft start to prevent input current overshoot at startup. APPLICATIONS Wireless Handsets Portable Media Players PDA's and Palmtop Computers Digital Cameras Smart Phones TYPICAL PERFORMANCE CHARACTERITICS TYPICAL APPLICATION CIRCUIT ADP2102_Efficiency Vout= 1.375V L =2.2uH Cin= Cout = 10uF 100 Efficiency( %) 90 80 70 60 0 100 200 300 400 500 600 Load Current ( mA) Vin= 2.7V Vin=3.0V Vin=3.6V Vin=4.2V Figure 1. Figure 2. Rev. PrA Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c)2007 Analog Devices, Inc. All rights reserved. Preliminary Technical Data SPECIFICATIONS VIN= 3.6V, Bold values indicate TJ = -40C to + 85C, unless otherwise noted. 1 Table 1. Parameters Input Voltage Range 2 Under voltage Lockout Threshold Under voltage Lockout Hysterisis Output Voltage Range Output Voltage Accuracy Load Regulation Line Regulation FB Regulation Voltage FB Bias current Operating Current Shutdown Current Output Current LX On Resistance LX Leakage Current LX Minimum -Off Time Forward Current Limit EN,MODE Input High Threshold EN,MODE Input Low Threshold EN,MODE Input Leakage Current Switching Frequency Soft Start Period Thermal Shutdown Threshold Thermal Shutdown Hysterisis 1 2 ADP2102 Conditions VIN rising ADP2102_Fixed Vout=0.8V -1.875V, Iload= 0-600mA Iout = 10mA Min 2.7 2.2 0.8 -1 Typ 2.4 200 Max 5.5 2.5 1.875 1 0.5 0.6 816 50 80 1 600 600 400 1 784 ADP2102, VFB= 0.9V EN=0V P-Channel Switch N-channel Synchronous Rectifier PVIN=5.5V, VLX= 0V,5.5V P-Channel Switch or N-Channel Synchronous Rectifier 1.3 EN=MODE= 0, 5.5V -1 250 0.3 0.3 800 1 60 0.1 300 250 100 1 0.1 3 500 150 15 0.4 1 800 Units V V mV V % % % mV nA A A mA m m A ns A V V A MHz s C C All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC). Typical values are at TA = +25C, VIN = 3.6 V. This is the VIN input voltage range over which the rest of the specifications are valid. The part operates as expected until VIN goes below the UVLO threshold. Rev. PrA | Page 2 of 7 Preliminary Technical Data ABSOLUTE MAXIMUM RATINGS Table 2. Parameter AVIN,EN,MODE,FB/OUT to AGND LX to PGND PVIN to PGND PGND to AGND AVIN to PVIN Operating Ambient Temperature Range Operating Junction Temperature Storage Temperature Range Soldering Conditions 1 ADP2102 THERMAL RESISTANCE Rating -0.3V to +6V -0.3V to +(VIN + 0.3 V) -0.3V to +6V -0.3V to 0.3V -0.3V to 0.3V -40C to +85C1 125C -65C to +150C JEDEC J-STD-020 Table 3. Thermal Resistance Package Type 8-Lead LFCSP Maximum Power Dissipation 1 JA1 54 1 Unit C/W W Junction-to-ambient thermal resistance (JA) of the package is based on modeling and calculation using a 4-layer board. The junction-to-ambient thermal resistance is application and board-layout dependent. In applications where high maximum power dissipation exists, attention to thermal board design is required. The value of JA can vary depending on PCB material, layout, and environmental conditions. For more information, please refer to Application Note AN-772: A Design and Manufacturing Guide for the Lead Frame Chip Scale Package (LFCSP). In applications where high power dissipation and poor thermal resistance are present, the maximum ambient temperature may have to be de-rated. Maximum ambient temperature (TA(MAX)) is dependent on the maximum operating junction temperature (TJ(MAXOP)) = 125C), the maximum power dissipation of the device (PD(MAX)), and the junction-to-ambient thermal resistance of the part/package in the application (JA), using the following equation: TA(MAX) = TJ(MAXOP) - (JA x PD(MAX)). BOUNDARY CONDITION Natural convection, 4-layer board, exposed pad soldered to the PCB. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Absolute maximum ratings apply individually only, not in combination. Unless otherwise specified all other voltages referenced to GND. ESD CAUTION Rev. PrA| Page 3 of 7 Preliminary Technical Data PIN CONFIGURATION AND FUNCTION DESCRIPTIONS ADP2102 Figure 3.Pin Configuration Table 4. Pin Function Descriptions Pin No. 1 2 3 Mnemonic MODE EN FB/OUT Description Mode Input. To set the ADP2102 to Forced Continuous Conduction Mode (CCM), drive MODE high. To set the ADP2102 to Power Saving Mode (PSM), drive MODE low. Enable Input. Drive EN high to turn on the ADP2102. Drive EN low to turn it off and reduce the input current to 0.1A. This pin cannot be left floating. Output Sense Input or Feedback Input. For fixed output versions, OUT is the top of the internal resistive voltage divider. Connect OUT to the Output Voltage. For adjustable (non-suffix) versions, FB is the input to the error amplifier. Drive FB through a resistive voltage divider to set the output voltage. The FB regulation threshold is 0.8V. Analog Ground. Connect AGND to PGND at a single point as close as to the ADP2102 as possible. Power Ground. Switch Output. LX is the drain of the p-channel MOSFET switch and n-channel Synchronous rectifier. Connect the output LC filter between LX and output voltage. Power Source Input. Drive PVIN with a 2.7V to 5.5V power source. Power Source Input. AVIN is the supply for the ADP2102 internal circuitry. For noise reduction, place an external RC filter between PVIN and AVIN. 4 5 6 7 8 AGND PGND LX PVIN AVIN Rev. PrA | Page 4 of 7 Preliminary Technical Data THEORY OF OPERATION The ADP2102 is a high frequency synchronous step down dcdc buck converter optimized for battery powered portable applications. It is based on a constant-ON time current mode control architecture with voltage feed forward to null frequency variation with line voltage thus creating a pseudo fixed frequency. This type of control allows generation of very low output voltages at higher switching frequency and offers a very fast load and line transient response with minimal external component count and size. The ADP2102 provides features like Under Voltage Lock Out, Thermal Shutdown and Short Circuit Protection. The ADP2102 uses valley current mode control, which helps to prevent minimum-ON time limitations at very low output voltages. This allows high frequency operation resulting in low filter inductor and capacitor values. ADP2102 load step occurs. When a load step occurs, the constant ONtime control loop responds by modulating the OFF time up or down to quickly get back to regulation. This momentary frequency variation results in a faster load transient response than a fixed frequency current mode control loop of similar bandwidth with similar external filter inductor and capacitor. This is an advantage of constant-ON time control scheme. As described above the frequency of the constant ON-time control loop remains constant to a first order with line and output voltage. There are some second order effects that cause this frequency to increase slightly with load current. Resistive voltage losses in the High and Low Side Power Switches, package parasitics, inductor DCR and board parasitic resistance cause the loop to compensate by reducing the OFFtime and there fore increasing the switching frequency with increasing load current. A minimum OFF-time constraint is introduced to allow the inductor valley current sensing on the synchronous switch. CONTROL SCHEME The ADP2102's High Side Power Switch ON-time is determined by a one shot timer whose pulse width is directly proportional to output voltage and inversely proportional to the input or line voltage. Another one-shot timer sets a minimum OFF time to allow for inductor valley current sensing, The constant ON-time one-shot timer is triggered at the rising edge of EN and subsequently when the Low Side Power Switch current is below the valley current limit threshold and the minimum OFF-time one-shot timer has timed out. While the constant ON-time is asserted, the high side power switch is turned on. This causes the inductor current to ramp positively. After the constant ON-time has completed the high side power switch turns off and the low side power switch turns on. This causes the inductor current to ramp negatively until the sensed current flowing in this switch has reached valley current limit. At this point, the low side power switch turns off and a new cycle begins again with the high side switch turning on provided the minimum OFF-time one shot has timed out. FORCED CONTINUOUS CONDUCTION MODE When the MODE pin is HIGH, the ADP2102 operates in Forced Continuous Conduction Mode. In this mode, irrespective of the load current, the inductor current stays continuous and is the preferred mode of operation for low noise applications. During this mode, the switching frequency stays close to 3MHz typically. In this mode, the efficiency is lower compared to the Power Save Mode during light loads but the output voltage ripple is minimized. POWER SAVE MODE When the MODE pin is LOW, the ADP2102 operates in Power Save Mode. In this mode, at light load currents, the part automatically goes into reduced frequency operation where some pulses are skipped to increase efficiency while still remaining in regulation. At light loads, a zero crossing comparator truncates the low side switch ON-time when the inductor current becomes negative. In this condition, the part works in Discontinuous Conduction Mode (DCM). The threshold between CCM and DCM is approximately Iload (skip) = (Vin- Vout) / (2 x L) x Ton For higher load currents, the inductor current does not cross zero threshold and the device switches to the Continuous Conduction Mode and the frequency is fixed to the nominal value. As a result of this auto -mode control technique, the losses are minimized at light loads, improving the system efficiency. CONSTANT ON-TIME TIMER The constant ON-time timer sets the High Side Switch on time. This fast, low jitter, adjustable one shot varies the ON-time in response to input voltage for a given output voltage. The High Side Switch ON -time is inversely proportional to the input voltage and directly proportional to the output voltage. Ton = K. (Vout /Vin) & Fsw = 1/K Where "K" is an internally set On-time scale factor constant resulting in a constant switching frequency. As can be seen in the above equation, the steady state switching frequency is theoretically independent of both the input and output voltages to a first order. Therefore, with line voltage feed forward the constant ON- time control scheme is pseudo fixed frequency. This means the loop switches at a constant frequency until a CURRENT LIMIT The ADP2102 has protection circuitry to limit the amount of current flowing through the High Side and the Low Side switches. When the current flowing in the forward direction becomes excessive due to a short on the OUT node to ground Rev. PrA | Page 5 of 7 ADP2102 or otherwise, the ADP2102 operates in frequency fold back by increasing the OFF time enough to keep the output current fixed. Therefore, during this fault condition the ADP2102 acts as a constant current source at the current limit of 1A typical. Preliminary Technical Data and the entire control circuitry is switched off. For proper operation, the EN pin must be terminated and must not be left floating. UNDER VOLTAGE LOCK OUT The under voltage lockout circuit prevents the device from operating incorrectly at low input voltages. It prevents the converter from turning on the main switch and the synchronous switch under undefined conditions and therefore preventing deep discharge of the battery supply SOFT START The ADP2102 has in internal soft start function that ramps the output voltage in a controlled manner upon startup by limiting the inrush current. This prevents possible input voltage drops when a battery or a high impedance power source is connected to the input of the converter. THERMAL SHUTDOWN When the Junction Temperature, Tj, exceeds typically 150 C, the device goes into Thermal Shutdown. In this mode, the High Side and Low Side Power Switches are turned off. The device continues its operation when the junction temperature when the junction temperature falls below typically 135 C again. ENABLE The device starts operation with soft start when the EN pin is brought high. Pulling the EN pin low forces the device into shutdown, with a typical shutdown current of 0.1a. In this mode both the High Side and Low Side Power Switches are turned off, the internal resistor feedback divider is disconnected Rev. PrA| Page 6 of 7 Preliminary Technical Data OUTLINE DIMENSIONS ADP2102 Figure 4. 8 -Lead Lead Frame Chip Scale Package [LFCSP] 3 mm x 3 mm Body, Dimensions shown in millimeters ORDERING GUIDE Model ADP2102 ADP2102-EVAL Temperature Range -40C to +85C Package Description 8-Lead Lead Frame Chip Scale Package [LFCSP] Evaluation Board Package Option Branding (c)2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. PR06631-0-2/07(PrA) Rev. PrA| Page 7 of 7 |
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