Evaluation Board for Step-Down DC-to-DC Converter Solution EVAL-ADP2105 FEATURES GENERAL DESCRIPTION Efficiency >95% Input voltage range: 2.7 V to 5.5 V Output voltage range: 0.8 V to VIN Maximum output current: 1.0 A Switching frequency: 1.2 MHz Quiescent current: 20 μA Shutdown current: 0.1 μA Enable/shutdown logic input Optimized for small ferrite core inductors Optimized for tiny ceramic input and output capacitors Programmable soft start with single capacitor Programmable compensation for optimizing transient performance The ADP2105 evaluation board is a complete step-down dc-to-dc converter solution using the ADP2105 step-down dc-to-dc converter. It provides a ±1% accurate (±3% over all conditions) regulated output voltage with load currents up to 1 A. It comes in two versions: the ADP2105-1.8-EVAL with fixed output voltage of 1.8 V and the ADP2105-EVAL with adjustable output voltage initially set to 2.5 V. The ADP2105 is a synchronous, step-down dc-to-dc converter that uses a current-mode pulse width modulation (PWM) control scheme at medium-to-heavy load currents for high efficiency and smoothly transitions to a pulse frequency modulation (PFM) mode at light loads to conserve power. The power switch and synchronous rectifier are integrated for minimal external part count and high efficiency. The ADP2105 is optimized for operation with small ferrite core inductors and tiny ceramic capacitors to deliver the maximum output power per square inch of the PCB board area. For more details, see the ADP2105 data sheet. FUNCTIONAL BLOCK DIAGRAM ADP2105 EVALUATION BOARD J1 R2 GND ENABLE V IN GND R3 C4 C7 C1 R4 ADP2105 L1 R5 V OUT R1 C6 C3 C2 VOUT: ANALOG DEVICES, POWER MANAGEMENT (STP) 06312-001 C5 Figure 1. Rev. 0 Evaluation boards are only intended for device evaluation and not for production purposes. Evaluation boards as supplied “as is” and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability or fitness for a particular purpose. No license is granted by implication or otherwise under any patents or other intellectual property by application or use of evaluation boards. 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. Analog Devices reserves the right to change devices or specifications at any time without notice. Trademarks and registered trademarks are the property of their respective owners. Evaluation boards are not authorized to be used in life support devices or systems. 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 ©2007 Analog Devices, Inc. All rights reserved. EVAL-ADP2105 TABLE OF CONTENTS Features .............................................................................................. 1 Modifying the Evaluation Board .....................................................4 General Description ......................................................................... 1 Measurement Setup...........................................................................5 Functional Block Diagram .............................................................. 1 Typical Performance Characteristics ..............................................6 Revision History ............................................................................... 2 Ordering Information.......................................................................7 Using the Evaluation Board............................................................. 3 Bill of Materials..............................................................................7 Powering Up the Evaluation Board............................................ 3 Ordering Guide .............................................................................9 Measuring Evaluation Board Performance .................................. 3 ESD Caution...................................................................................9 REVISION HISTORY 1/07—Revision 0: Initial Version Rev. 0 | Page 2 of 12 EVAL-ADP2105 USING THE EVALUATION BOARD POWERING UP THE EVALUATION BOARD Turning On the Evaluation Board The ADP2105 evaluation board is supplied fully assembled and tested. Before applying power to the evaluation board, follow the procedures outlined in this section. Once the power source and load are connected to the ADP2105 evaluation board, the board can be powered for operation. Slowly increase the input power source voltage until the input voltage exceeds the minimum input operating voltage of 2.7 V. Insert Jumper J1 and check to see if the output voltage rises to the regulated output voltage (1.8 V for the ADP2105-1.8-EVAL and 2.5 V for the ADP2105-EVAL). If the load is not already enabled, enable the load, and check that it is drawing the proper current and that the output voltage maintains voltage regulation. Jumper J1 Before turning on the ADP2105 evaluation board, make sure that all the components are present, but that Jumper J1 is removed. Input Power Source Before connecting the power source to the ADP2105 evaluation board, make sure it is turned off. If the input power source includes a current meter, use that meter to monitor the input current. Connect the positive terminal of the power source to the VIN terminal on the evaluation board, and the negative terminal of the power source to the GND terminal of the evaluation board. If the power source does not include a current meter, connect a current meter in series with the input source voltage. Connect the positive lead (+) of the power source to the ammeter positive (+) connection, the negative lead (−) of the power source to the GND terminal on the evaluation board, and the negative lead (−) of the ammeter to the VIN terminal on the board. MEASURING EVALUATION BOARD PERFORMANCE Measuring Output Voltage Ripple To observe the output voltage ripple, place an oscilloscope probe across the output capacitor (C3/C4) with the probe ground lead at the negative (−) capacitor terminal and the probe tip at the positive (+) capacitor terminal. Set the oscilloscope to ac, 20 mV/division, and 2 μs/division time base. In the PWM mode of operation, the output voltage ripple is small (<20 mV), but in PFM mode, the output voltage ripple can be as large as 50 mV. Output Load Measuring the Switching Waveform Although the ADP2105 evaluation board can sustain the sudden connection of the load, it is possible to damage the load if it is not properly connected. Make sure the board is turned off before connecting the load. If the load includes an ammeter, or if the current is not measured, connect the load directly to the evaluation board, with the positive (+) load connection to the VOUT terminal and the negative (−) load connection to the GND terminal. If an ammeter is used, connect it in series with the load: connect the positive (+) ammeter terminal to the evaluation board VOUT terminal, the negative (−) ammeter terminal to the positive (+) load terminal, and the negative (−) load terminal to the evaluation board GND terminal. To observe the switching waveform with an oscilloscope, place the oscilloscope probe tip at the end of the inductor that is connected to the LX pins with the probe ground at GND. Set the oscilloscope to dc, 2 V/division, and 2 μs/division time base. The switching waveform must alternate between 0 V and approximately the input voltage. Once the load is connected, make sure it is set to the proper current before powering the ADP2105 evaluation board. Measuring Line Regulation Measuring Load Regulation The load regulation must be tested by increasing the load at the output and looking at the change in output voltage. To minimize voltage drop, use short low-resistance wires, especially for heavy loads. Vary the input voltage and examine the change in the output voltage. Input and Output Voltmeters Measure the input and output voltages with voltmeters. Make sure that the voltmeters are connected to the appropriate evaluation board terminals and not to the load or power source themselves. If the voltmeters are not connected directly to the evaluation board, the measured voltages would be incorrect due to the voltage drop across the leads and/or connections between the evaluation board, the power source, and/or the load. Connect the input voltage measuring voltmeter positive terminal (+) to the evaluation board VIN terminal, and the negative (−) terminal to the evaluation board GND terminal. Connect the output voltage measuring voltmeter positive (+) terminal to the evaluation board VOUT terminal and the negative (−) terminal to the evaluation board GND terminal. Measuring Efficiency The efficiency, η, is measured by comparing the input power with the output power. η= VOUT × I OUT VIN × I IN Measure the input and output voltages as close as possible to the input and output capacitors to reduce the effect of IR drops. Measuring Inductor Current The inductor current can be measured by removing one end of the inductor from its pad and connecting a current loop in series with it. Then a current probe can be used to measure the current flowing through the current loop, as shown in Figure 2. Rev. 0 | Page 3 of 12 EVAL-ADP2105 MODIFYING THE EVALUATION BOARD The ADP2105 evaluation board is supplied fully assembled and tested for proper operation. It comes in two versions: the ADP2105-1.8-EVAL with fixed output voltage of 1.8 V and the ADP2105-EVAL with adjustable output voltage initially set to 2.5 V. ⎡ 2 V − 0.8 V ⎤ ⎡V − VFB ⎤ R4 = R5 × ⎢ OUT ⎥ = 60 kΩ ⎥ = 40 kΩ × ⎢ V ⎢⎣ 0.8 V ⎦⎥ FB ⎣ ⎦ The two most common modifications that can be done to the evaluation boards are changing the output voltage and changing the load transient response. Note that when the output voltage of ADP2105-EVAL is changed, the output capacitors (C3 and C4), inductor (L1), and compensation components (R1 and C6) are recalculated and changed according to the Application Information section in the ADP2105 data sheet to ensure stable operation. Changing the Output Voltage Changing the Load Transient Response The ADP2105-EVAL output regulation voltage can be changed by altering its external components. The ADP2105-1.8-EVAL output regulation voltage is fixed at 1.8 V and cannot be changed. The ADP2105 evaluation board load transient response can be altered by changing the output capacitors (C3 and C4) and compensation components (R1 and C6) as explained in the Output Capacitor Selection and Loop Compensation sections of the ADP2105 data sheet. By default, the load transient response of the ADP2105 evaluation board is set to 5% of the output voltage for a 1 A load transient. The ADP2105-EVAL output regulation voltage is set by a resistive voltage divider consisting of Resistors R4 and R5. Resistor R4 corresponds to the RTOP resistor in the ADP2105 data sheet, and Resistor R5 corresponds to the RBOT resistor in the ADP2105 data sheet. The output regulation voltage is determined by the equation ⎡R + RBOT ⎤ VOUT = 0.8 V × ⎢ TOP ⎥ R BOT ⎣ ⎦ where: RTOP is the value of the top resistor of the voltage divider (R4). RBOT is the value of the bottom resistor of the voltage divider (R5). VOUT is the output regulation voltage in volts. Consider an example where the load transient response of the ADP2105-1.8-EVAL is changed to 10% of the output voltage for a 1 A load transient. First, choose the output capacitors (C3 and C4) based on the load transient response requirements. The desired load transient response is 10% overshoot for a 1 A load transient. For this condition, the % Overshoot for a 1 A Load Transient Response vs. Output Capacitor × Output Voltage figure, in the ADP2105 data sheet, gives Output Capacitor × Output Voltage = 25 μC To set the output regulation voltage to the desired value, first determine the value of the bottom resistor, RBOT, by RBOT = ⇒ Output Capacitor = VFB I STRING where: VFB = 0.8 V, the internal reference. ISTRING is the resistor divider string current (20 μA nominally). Once RBOT is determined, calculate the value of the top resistor, RTOP, by I STRING = 0 .8 V 20 μA = 40 kΩ ≈ 14 μF Finally, calculate the compensation resistor and compensation capacitor as shown below: ⎛ ( 2 π ) FCROSS RCOMP = 0.8 ⎜⎜ ⎝ Gm GCS ⎞⎛ COUT VOUT ⎟⎜⎜ ⎟ ⎠⎝ VREF ⎞ ⎟⎟ ⎠ ⎛ ⎞⎛ 14 μF × 1.8 V ⎞ ( 2 π ) × 80 kHz ⎟⎟⎜⎜ ⎟⎟ = 135 kΩ = 0.8 ⎜⎜ 0 .8 V ⎝ 50 μA / V × 1.875 A / V ⎠⎝ ⎠ For example, to set the output regulation voltage of the ADP2105-EVAL to 2.0 V, calculate the value of Resistor R4 and Resistor R5 as shown below. VFB 1.8 V Next, taking into account the loss of capacitance due to dc bias as shown in the % Drop-In Capacitance vs. DC Bias for Ceramic Capacitors figure, in the ADP2105 data sheet, let C3 and C4 be two 10 μF X5R MLCC capacitors (GRM21BR61A106KE19L). ⎡V − VFB ⎤ RTOP = RBOT ⎢ OUT ⎥ ⎣ VFB ⎦ R5 = 25 μC CCOMP = 2 2 = = 60 pF πFCROSS RCOMP π × 80 kHz × 135 kΩ Therefore, the compensation resistor is 135 kΩ and the compensation capacitor is 68 pF. Rev. 0 | Page 4 of 12 EVAL-ADP2105 MEASUREMENT SETUP ELECTRONIC LOAD VOLTMETER 3A VOLTAGE SOURCE VIN IIN VOUT IOUT J1 R2 GND ENABLE VIN GND PROBE OUTPUT VOLTAGE ACROSS OUTPUT CAPACITOR R3 C4 C7 C1 R4 ADP2105 L1 R5 VOUT R1 C6 C5 C2 C3 CURRENT PROBE INDUCTOR OSCILLOSCOPE 1V SEP 1V SEP AT NORW OFF 0V H 0V V EVE OFF 0V H 0V V VD 1S DIV VD 1S DIV VPOS NVERT OUTPUT VOLTAGE WAVEFORM mV V mV DVA DVA ADD LX NODE WAVEFORM Figure 2. Typical Measurement Setup Rev. 0 | Page 5 of 12 CH INDUCTOR CURRENT WAVEFORM 06312-010 V EVAL-ADP2105 TYPICAL PERFORMANCE CHARACTERISTICS 100 100 95 95 VIN = 2.7V 90 EFFICIENCY (%) 80 75 VIN = 4.2V 70 VIN = 4.2V 80 VIN = 5.5V 75 70 65 65 60 INDUCTOR: SD3814, 3.3µH DCR: 93mΩ TA = 25°C 1 10 100 LOAD CURRENT (mA) INDUCTOR: SD3814, 3.3µH DCR: 93mΩ TA = 25°C 55 1000 50 06312-004 VIN = 5.5V 55 1 10 100 1000 LOAD CURRENT (mA) 06312-007 60 50 VIN = 3.6V 85 Figure 6. Efficiency—ADP2105-EVAL (2.5 V Output) Figure 3. Efficiency—ADP2105-1.8-EVAL (1.8 V Output) LX NODE (SWITCH NODE) LX NODE (SWITCH NODE) 3 3 1 1 OUTPUT VOLTAGE (AC-COUPLED) OUTPUT VOLTAGE (AC-COUPLED) INDUCTOR CURRENT CH4 200mAΩ M 2µs T 6% A CH3 3.88V 4 06312-005 CH1 50mV CH3 2V CH1 20mV CH3 2V CH4 1AΩ M 1µs T 17.4% A CH3 3.88V 06312-008 INDUCTOR CURRENT 4 Figure 7. PWM Mode of Operation at Medium/Heavy Load (1 A) Figure 4. PFM Mode of Operation at Light Load (10 mA) OUTPUT CURRENT T 3 OUTPUT CURRENT 3 CH2 LOW –112mV CH2 LOW –136mV 2 OUTPUT VOLTAGE (AC-COUPLED) 2 OUTPUT VOLTAGE (AC-COUPLED) 1 LX NODE (SWITCH NODE) CH2 100mV~ M 10µs CH3 1A 1 A CH3 LX NODE (SWITCH NODE) 0.5A OUTPUT CAPACITOR: 22µF + 22µF INDUCTOR: SD3814, 3.3µH COMPENSATION RESISTOR: 270kΩ COMPENSATION CAPACITOR: 39pF Figure 5. 1 A Load Transient Response for ADP2105-1.8-EVAL CH1 2V CH3 5V CH2 100mV~ M 10µs T 20.20% A CH3 2.60V 06312-009 CH1 2V 06312-006 EFFICIENCY (%) 90 VIN = 3.6V 85 VIN = 3.0V Figure 8. 1 A Load Transient Response for ADP2105-EVAL with VOUT Set to 2.5 V Rev. 0 | Page 6 of 12 EVAL-ADP2105 ORDERING INFORMATION BILL OF MATERIALS Table 1. Bill of Materials for ADP2105-1.8-EVAL Reference Designator C1, C2 Reference Name 1 CIN1, CIN2 Qty. 2 Manufacturer Murata Part Number GRM21BR61A475KA73L C3, C4 COUT 2 Murata GRM21BR60J226ME39L C5 CSS 1 Vishay Vitramon or equivalent VJ0603Y102KXJA Capacitor, MLCC, 39 pF, 50 V, 0603, NPO Capacitor, MLCC, 0.1 μF, 25 V, 0603, X7R, SMD Resistor, 274 kΩ, 1%, 0603, SMD C6 CCOMP 1 VJ0603Y390KXJA C7 IN (filter capacitor) RCOMP 1 Resistor, 100 kΩ, 1%, 0603, SMD R2 Resistor, 10 Ω, 1%, 0603, SMD R3 Resistor, 0 Ω, 1%, 0603, SMD R4 Vishay Vitramon or equivalent Vishay Vitramon or equivalent Vishay Dale or equivalent Vishay Dale or equivalent Vishay Dale or equivalent Vishay Dale or equivalent Bottom Resistor of Voltage Divider 2 Inductor 3.3 μH, 3.9 mm × 3.9 mm x 1.1 mm R5 1 Coilcraft®, Toko®, Cooper Bussmann 1.8 V, 1 A Step-Down DC-to-DC Converter U1 1 Analog Devices, Inc. LLPS4012-332MLB 1098ASDE2812C-3.3uH, SD3814-3.3uH ADP2105-1.8 Headers, 0.100, Single, Straight VOUT, VIN, GND, GND, J1, EN 12 Sullins Electronics or equivalent Description Capacitor, MLCC, 4.7 μF, 10 V, 0805, X5R, SMD Capacitor, MLCC, 22 μF, 6.3 V, 0805, X5R, SMD Capacitor, MLCC, 1 nF, 16 V, 0603, X7R, SMD 2 1 1 EN (pull down) IN (filter resistor) 1 1 L1 L CRCW06032743FRT1 CRCW06031003FRT1 CRCW060310R0FRT1 CRCW06030000ZSSF S1012-36-ND PTC36SAAN Refer to the Typical Applications Circuit for Fixed Output Voltage Options figure in the ADP2105 data sheet. Do not solder this component onto the board. V C7 R3 CC 0.1µF 10Ω VCC C1 4.7µF OUT J1 16 15 OUT_SENSE GND4 EN R2 100kΩ 14 13 IN1 PWIN1 3 GND2 U1 ADP2105-1.8 PGND 11 COMP SS AGND PADDLE NC 6 7 17 L1 3.3µH 1 LX1 10 PWIN2 9 4 GND1 5 GND LX2 12 1 EN 2 GND3 INPUT VOLTAGE: 2.7V TO 5.5V VIN VCC OUT C2 4.7µF 8 C5 1nF R4 0Ω OUTPUT VOLTAGE: 1.8V VOUT C3 C4 22µF 22µF GND R5 NS R1 274kΩ C6 39pF 2 NC = NO CONNECT Figure 9. Evaluation Board Schematic of ADP2105-1.8-EVAL with VOUT = 1.8 V Rev. 0 | Page 7 of 12 06312-002 1 R1 VJ0603Y104KXXA EVAL-ADP2105 Table 2. Bill of Materials for ADP2105-EVAL with VOUT Set to 2.5 V Reference Designator C1, C2 Reference Name1 CIN1, CIN2 Qty. 2 Manufacturer Murata Part Number GRM21BR61A475KA73L C3 COUT 1 Murata GRM21BR60J226ME39L C4 COUT 1 Murata GRM21BR61A106KE19L Capacitor, MLCC, 1 nF, 16 V, 0603, X7R, SMD Capacitor, MLCC, 39 pF, 50 V, 0603, NPO Capacitor, MLCC, 0.1 μF, 25 V, 0603, X7R, SMD Resistor, 274 kΩ, 1%, 0603, SMD Resistor, 100 kΩ, 1%, 0603, SMD C5 CSS 1 VJ0603Y102KXJA C6 CCOMP 1 C7 1 1 1 Resistor, 10 Ω, 1%, 0603, SMD R3 1 Vishay Dale or equivalent CRCW060310R0FRT1 Resistor, 87.6 kΩ, 0.5%, 0603, SMD Resistor, 41.2 kΩ, 0.1%, 0603, SMD Inductor 3.3 μH, 3.9 mm × 3.9 mm x 1.1 mm R4 IN (filter capacitor) RCOMP EN (pull down) IN (filter resistor) RTOP Vishay Vitramon or equivalent Vishay Vitramon or equivalent Vishay Vitramon or equivalent Vishay Dale or equivalent Vishay Dale or equivalent 1 Vishay Dale or equivalent TNPW060387K6DHTA R5 RBOT 1 Vishay Dale or equivalent TNPW060341K2BEEN L1 L 1 Coilcraft, Toko, Cooper Bussmann 1 A Step-Down DC-to-DC Converter with Adjustable Output Headers, 0.100, Single, Straight U1 1 Analog Devices LLPS4012-332MLB 1098ASDE2812C-3.3uH SD3814-3.3uH ADP2105-ADJ VOUT, VIN, GND, GND, J1, EN 6 Sullins Electronics or equivalent Description Capacitor, MLCC, 4.7 μF, 10 V, 0805, X5R, SMD Capacitor, MLCC, 22 μF, 6.3 V, 0805, X5R, SMD Capacitor, MLCC, 10 μF, 10 V, 0805, X5R, SMD VJ0603Y104KXXA CRCW06032743FRT1 CRCW06031003FRT1 S1012-36-ND PTC36SAAN Refer to the Typical Applications Circuit for Adjustable Output Voltage Options figure in the ADP2105 data sheet. VIN C7 R3 0.1µF 10Ω VCC J1 EN R2 100kΩ C1 4.7µF FB 16 15 14 FB GND4 IN1 GND 13 PWIN1 LX2 12 1 EN 2 GND3 INPUT VOLTAGE: 2.7V TO 5.5V VIN PGND U1 ADP2105-ADJ 11 L1 3.3µH OUTPUT VOLTAGE: 2.5V VOUT C3 C4 VCC 22µF 10µF FB GND 4 GND1 PWIN2 9 R4 C2 87.6kΩ COMP SS AGND PADDLE NC 4.7µF 3 GND2 5 LX1 10 6 7 17 1 8 R5 41.2kΩ R1 274kΩ C6 39pF C5 1nF 2 NC = NO CONNECT Figure 10. Evaluation Board Schematic for ADP2105-EVAL with Adjustable VOUT Initially Set to 2.5 V Rev. 0 | Page 8 of 12 06312-003 1 R1 R2 VJ0603Y390KXJA EVAL-ADP2105 ORDERING GUIDE Model ADP2105-1.8-EVAL ADP2105-EVAL Description Evaluation board with fixed output voltage Evaluation board with adjustable output voltage ESD CAUTION Rev. 0 | Page 9 of 12 EVAL-ADP2105 NOTES Rev. 0 | Page 10 of 12 EVAL-ADP2105 NOTES Rev. 0 | Page 11 of 12 EVAL-ADP2105 NOTES ©2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. EB06312-0-1/07(0) Rev. 0 | Page 12 of 12