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Compact, 600 mA, 3 MHz, Step-Down DC-to-DC Converter
ADP2108
FEATURES
Peak efficiency: 95% 3 MHz fixed frequency operation Typical quiescent current: 18 A Maximum load current: 600 mA Input voltage: 2.3 V to 5.5 V Uses tiny multilayer inductors and capacitors Current mode architecture for fast load and line transient response 100% duty cycle low dropout mode Internal synchronous rectifier Internal compensation Internal soft start Current overload protection Thermal shutdown protection Shutdown supply current: 0.2 A 5-ball WLCSP
GENERAL DESCRIPTION
The ADP2108 is a high efficiency, low quiescent current stepdown dc-to-dc converter in an ultrasmall 5-ball WLCSP package. The total solution requires only three tiny external components. It uses a proprietary, high speed current mode, constant frequency PWM control scheme for excellent stability and transient response. To ensure the longest battery life in portable applications, the ADP2108 has a power save mode that reduces the switching frequency under light load conditions. The ADP2108 runs on input voltages of 2.3 V to 5.5 V, which allows for single lithium or lithium polymer cell, multiple alkaline or NiMH cell, PCMCIA, USB, and other standard power sources. The maximum load current of 600 mA is achievable across the input voltage range. The ADP2108 is available in fixed output voltages of 3.3 V, 3.0 V, 2.5 V, 2.3 V, 1.82 V, 1.8 V, 1.5 V, 1.3 V, 1.2 V, 1.1 V, and 1.0 V. All versions include an internal power switch and synchronous rectifier for minimal external part count and high efficiency. The ADP2108 has an internal soft start and is internally compensated. During logic controlled shutdown, the input is disconnected from the output and the ADP2108 draws less than 1 A from the input source. Other key features include undervoltage lockout to prevent deep battery discharge and soft start to prevent input current overshoot at startup. The ADP2108 is available in a 5-ball WLCSP.
APPLICATIONS
PDAs and palmtop computers Wireless handsets Digital audio, portable media players Digital cameras, GPS navigation units
TYPICAL APPLICATIONS CIRCUIT
ADP2108
2.3V TO 5.5V VIN 4.7F OFF ON EN FB
07375-003
1H
SW
1.0V TO 3.3V 10F
GND
Figure 1.
Rev. A
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)2008 Analog Devices, Inc. All rights reserved.
ADP2108 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications ....................................................................................... 1 General Description ......................................................................... 1 Typical Applications Circuit............................................................ 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 4 Thermal Resistance ...................................................................... 4 ESD Caution .................................................................................. 4 Pin Configuration and Function Descriptions ............................. 5 Typical Performance Characteristics ............................................. 6 Theory of Operation ...................................................................... 11 Control Scheme .......................................................................... 11 PWM Mode ................................................................................. 11 Power Save Mode........................................................................ 11 Enable/Shutdown ....................................................................... 11 Short-Circuit Protection............................................................ 12 Undervoltage Lockout ............................................................... 12 Thermal Protection .................................................................... 12 Soft Start ...................................................................................... 12 Current Limit .............................................................................. 12 100% Duty Operation ................................................................ 12 Applications Information .............................................................. 13 External Component Selection ................................................ 13 Thermal Considerations............................................................ 14 PCB Layout Guidelines.............................................................. 14 Evaluation Board ............................................................................ 15 Outline Dimensions ....................................................................... 16 Ordering Guide .......................................................................... 16
REVISION HISTORY
12/08--Rev. 0 to Rev. A Changes to Figure 4 .......................................................................... 6 Updated Outline Dimensions ....................................................... 16 9/08--Revision 0: Initial Version
Rev. A | Page 2 of 16
ADP2108 SPECIFICATIONS
VIN = 3.6 V, VOUT = 1.8 V, TJ = -40C to +125C for minimum/maximum specifications, and TA = 25C for typical specifications, unless otherwise noted. 1 Table 1.
Parameter INPUT CHARACTERISTICS Input Voltage Range Undervoltage Lockout Threshold OUTPUT CHARACTERISTICS Output Voltage Accuracy POWER SAVE MODE TO PWM CURRENT THRESHOLD PWM TO POWER SAVE MODE CURRENT THRESHOLD INPUT CURRENT CHARACTERISTICS DC Operating Current Shutdown Current SW CHARACTERISTICS SW On Resistance Current Limit ENABLE CHARACTERISTICS EN Input High Threshold EN Input Low Threshold EN Input Leakage Current OSCILLATOR FREQUENCY START-UP TIME THERMAL CHARACTERISTICS Thermal Shutdown Threshold Thermal Shutdown Hysteresis
1
Test Conditions/Comments
Min 2.3
Typ
Max 5.5 2.3 2.25 +2 +2.5
Unit V V V % % mA mA
VIN rising VIN falling PWM mode VIN = 2.3 V to 5.5 V, PWM mode
2.05 -2 -2.5
2.15
85 80 ILOAD = 0 mA, device not switching EN = 0 V, TA = TJ = -40C to +85C PFET NFET PFET switch peak current limit 18 0.2 320 300 1300 30 1.0
A A m m mA V V A MHz s C C
1100 1.2
1500
EN = 0 V, 3.6 V ILOAD = 200 mA
-1 2.5
0 3.0
0.4 +1 3.5 550
150 20
All limits at temperature extremes are guaranteed via correlation using standard statistical quality control (SQC).
Rev. A | Page 3 of 16
ADP2108 ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter VIN, EN FB, SW to GND Operating Ambient Temperature Range Operating Junction Temperature Range Storage Temperature Range Lead Temperature Range Soldering (10 sec) Vapor Phase (60 sec) Infrared (15 sec) ESD Human Body Model ESD Charged Device Model ESD Machine Model Rating -0.4 V to +6.5 V -1.0 V to (VIN + 0.2 V) -40C to +85C -40C to +125C -65C to +150C -65C to +150C 300C 215C 220C 1500 V 500 V 100 V
THERMAL RESISTANCE
JA is specified for a device mounted on a JEDEC 2S2P PCB. Table 3. Thermal Resistance
Package Type 5-Ball WLCSP JA 105 Unit C/W
ESD CAUTION
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.
Rev. A | Page 4 of 16
ADP2108 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
BALL A1 INDICATOR 1 VIN A SW B EN C FB 2 GND
Figure 2. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. A1 A2 B C1 C2 Mnemonic VIN GND SW EN FB Description Power Source Input. VIN is the source of the PFET high-side switch. Bypass VIN to GND with a 2.2 F or greater capacitor as close to the ADP2108 as possible. Ground. Connect all the input and output capacitors to GND. Switch Node Output. SW is the drain of the PFET switch and NFET synchronous rectifier. Enable Input. Drive EN high to turn on the ADP2108. Drive EN low to turn it off and reduce the input current to 0.2 A. Feedback Input of the Error Amplifier. Connect FB to the output of the switching regulator.
Rev. A | Page 5 of 16
07375-002
TOP VIEW (BALL SIDE DOWN) Not to Scale
ADP2108 TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 3.6 V, TA = 25C, VEN = VIN, unless otherwise noted.
24 +85C 22 1400 1300 1200 20
QUIESCENT CURRENT (A)
CURRENT LIMIT (mA)
+25C
1100 1000 900 800
18 -40C 16
14
700 600 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 INPUT VOLTAGE (V)
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
Figure 3. Quiescent Supply Current vs. Input Voltage
3500 3400 3300
07375-014
Figure 6. PMOS Current Limit vs. Input Voltage
0.15 0.14 0.13
OUTPUT CURRENT (A)
FREQUENCY (kHz)
3200 3100 3000 2900 2800 2700 2600 2.8 3.3 3.8 4.3 4.8 5.3
07375-015
0.12 0.11 0.10 0.09 0.08 0.07 0.06 0.05 0.04 2.5 +85C -40C PWM TO PSM PSM TO PWM
-40C
+25C +85C
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Figure 4. Switching Frequency vs. Input Voltage
1.840 IOUT = 10mA 1.835 1.830
Figure 7. Mode Transition Across Temperature
0.15 0.14 0.13
OUTPUT VOLTAGE (V)
1.825 1.820 1.815 1.810 1.805 1.800 -25 -5 15
IOUT = 150mA
OUTPUT CURRENT (A)
0.12 0.11 0.10 0.09 0.08 0.07 PSM TO PWM PWM TO PSM
IOUT = 500mA
35
55
75
TEMPERATURE (C)
INPUT VOLTAGE (V)
Figure 5. Output Voltage vs. Temperature
Figure 8. Mode Transition
Rev. A | Page 6 of 16
07375-019
07375-016
1.795 -45
0.06
2.5
3.0
3.5
4.0
4.5
5.0
5.5
07375-018
2500 2.3
07375-017
12 2.5
ADP2108
1.825 100 90 1.815 80 VIN = 2.7V VIN = 3.6V VIN = 4.5V VIN = 5.5V 70
EFFICIENCY (%)
OUTPUT VOLTAGE (V)
1.805
60 50 40 30
VIN = 2.7V VIN = 3.6V VIN = 4.5V VIN = 5.5V
1.795
1.785
20 10 0 0.1 0.2 0.3 0.4 0.5 0.6
07375-020
0.01
0.1
1
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Figure 9. Load Regulation, VOUT = 1.8 V
1.025 1.020 1.015 VIN = 2.7V VIN = 3.6V VIN = 4.5V VIN = 5.5V
Figure 12. Efficiency, VOUT = 1.8 V
100 90 80 70
OUTPUT VOLTAGE (V)
1.010 1.005 1.000 0.995
EFFICIENCY (%)
60 50 40 30 20
VIN = 2.7V VIN = 3.6V VIN = 4.5V VIN = 5.5V
0.990 0.985
10
0 0.1 0.2 0.3 0.4 0.5 0.6
07375-021
0.01
0.1
1
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Figure 10. Load Regulation, VOUT = 1.0 V
100 90
3.3575
Figure 13. Efficiency, VOUT = 1.0 V
3.3775
80
OUTPUT VOLTAGE (V)
3.3375 3.3175 3.2975 3.2775 3.2575 3.2375 3.2175
70
EFFICIENCY (%)
VIN = 3.6V VIN = 4.5V VIN = 5.5V
VIN = 3.6V VIN = 4.5V VIN = 5.5V
60 50 40 30 20 10
07375-022
0
0.1
0.2
0.3
0.4
0.5
0.6
0.01
0.1
1
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Figure 11. Load Regulation, VOUT = 3.3 V
Figure 14. Efficiency, VOUT = 3.3 V
Rev. A | Page 7 of 16
07375-025
0 0.001
07375-024
0 0.001
07375-023
1.775
0 0.001
ADP2108
VIN
3
3
VIN
SW
SW
4
4
VOUT
1
07375-026
1
VOUT
07375-029
CH1 50mV CH3 1V
CH4 2V
M 40s T 10.80%
A CH3
3.26V
CH1 50mV CH3 1V
CH4 2V
M 40s T 10.80%
A CH3
4.4V
Figure 15. Line Transient, VOUT = 1.8 V, Power Save Mode, 20 mA
Figure 18. Line Transient, VOUT = 3.3 V, PWM, 200 mA
SW VIN
4
SW
1
3 4
VOUT
VOUT
07375-027
2
IOUT
07375-030
1
CH1 20mV CH3 1V
CH4 2V
M 40s T 10.80%
A CH3
3.26V
CH1 50mV
CH2 200mA CH4 2V
M 40s T 19.80%
A CH2
36mA
Figure 16. Line Transient, VOUT = 1.8 V, PWM, 200 mA
Figure 19. Load Transient, VOUT = 1.8 V, 300 mA to 600 mA
VIN
4
SW
SW
1
3 4
VOUT IOUT VOUT
1
07375-028
2
07375-031
CH1 50mV CH3 1V
CH4 2V
M 40s T 10.80%
A CH3
3.26V
CH1 50mV
CH2 250mA CH4 2V
M 40s T 25.4%
A CH2
5mA
Figure 17. Line Transient, VOUT = 1.0 V, PWM, 200 mA
Figure 20. Load Transient, VOUT = 1.8 V, 50 mA to 300 mA
Rev. A | Page 8 of 16
ADP2108
SW
4
SW
4
VOUT
1
IL
2
IOUT
2
1 3
VOUT EN
07375-035
CH1 50mV
CH2 50mA CH4 2V
M 40s T 25.4%
A CH2
12mA
07375-032
CH1 500mV CH2 500mA CH3 5V CH4 5V
M 40s T 19.80%
A CH3
2.1V
Figure 21. Load Transient, VOUT = 1.8 V, 5 mA to 50 mA
Figure 24. Start-Up, VOUT = 1.0 V, 600 mA
SW
4
SW
4
IL
2
2
IL
VOUT
1 3
EN
VOUT
1 3
EN
07375-033
CH1 1V CH3 5V
CH2 250mA CH4 5V
M 40s T 10.80%
A CH3
2V
CH1 2V CH3 5V
CH2 250mA CH4 5V
M 40s T 10.80%
A CH3
2V
Figure 22. Start-Up, VOUT = 1.8 V, 400 mA
Figure 25. Start-Up, VOUT = 3.3 V, 150 mA
SW
4
SW
4
2
IL IL VOUT
2
1 3
EN
1
VOUT
07375-034 07375-037
CH1 1V CH3 5V
CH2 250mA CH4 5V
M 40s T 10.80%
A CH3
2V
CH1 50mV
CH2 500mA CH4 2V
M 2s T 20%
A CH4
2.64mA
Figure 23. Start-Up, VOUT = 1.8 V, 5 mA
Figure 26. Typical Power Save Mode Waveform, 50 mA
Rev. A | Page 9 of 16
07375-036
ADP2108
SW
4
IL
2 1
VOUT
07375-038
CH1 20mV
CH2 200mA CH4 2V
M 200ns T 20%
A CH4
2.64V
Figure 27. Typical PWM Waveform, 200 mA
Rev. A | Page 10 of 16
ADP2108 THEORY OF OPERATION
GM ERROR AMP PWM COMP
VIN SOFT START ILIMIT FB PSM COMP PWM/ LOW PSM CONTROL CURRENT SW
OSCILLATOR UNDERVOLTAGE LOCKOUT
DRIVER AND ANTISHOOTTHROUGH
GND
EN
Figure 28. Functional Block Diagram
The ADP2108 is a step-down dc-to-dc converter that uses a fixed frequency and high speed current mode architecture. The high switching frequency and tiny 5-ball WLCSP package allow for a small step-down dc-to-dc converter solution. The ADP2108 operates with an input voltage of 2.3 V to 5.5 V and regulates an output voltage down to 1.0 V.
POWER SAVE MODE
The ADP2108 smoothly transitions to the power save mode of operation when the load current decreases below the power save mode current threshold. When the ADP2108 enters power save mode, an offset is induced in the PWM regulation level, which makes the output voltage rise. When the output voltage reaches a level approximately 1.5% above the PWM regulation level, PWM operation is turned off. At this point, both power switches are off, and the ADP2108 enters an idle mode. COUT discharges until VOUT falls to the PWM regulation voltage, at which point the device drives the inductor to make VOUT rise again to the upper threshold. This process is repeated while the load current is below the power save mode current threshold.
CONTROL SCHEME
The ADP2108 operates with a fixed frequency, current mode PWM control architecture at medium to high loads for high efficiency, but shifts to a power save mode control scheme at light loads to lower the regulation power losses. When operating in fixed frequency PWM mode, the duty cycle of the integrated switches is adjusted and regulates the output voltage. When operating in power save mode at light loads, the output voltage is controlled in a hysteretic manner, with higher VOUT ripple. During part of this time, the converter is able to stop switching and enters an idle mode, which improves conversion efficiency.
Power Save Mode Current Threshold
The power save mode current threshold is set to 80 mA. The ADP2108 employs a scheme that enables this current to remain accurately controlled, independent of VIN and VOUT levels. This scheme also ensures that there is very little hysteresis between the power save mode current threshold for entry to and exit from the power save mode. The power save mode current threshold is optimized for excellent efficiency over all load currents.
PWM MODE
In PWM mode, the ADP2108 operates at a fixed frequency of 3 MHz, set by an internal oscillator. At the start of each oscillator cycle, the PFET switch is turned on, sending a positive voltage across the inductor. Current in the inductor increases until the current sense signal crosses the peak inductor current threshold that turns off the PFET switch and turns on the NFET synchronous rectifier. This sends a negative voltage across the inductor, causing the inductor current to decrease. The synchronous rectifier stays on for the rest of the cycle. The ADP2108 regulates the output voltage by adjusting the peak inductor current threshold.
ENABLE/SHUTDOWN
The ADP2108 starts operation with soft start when the EN pin is toggled from logic low to logic high. Pulling the EN pin low forces the device into shutdown mode, reducing the shutdown current below 1 A.
Rev. A | Page 11 of 16
07375-001
ADP2108
THERMAL SHUTDOWN
ADP2108
SHORT-CIRCUIT PROTECTION
The ADP2108 includes frequency foldback to prevent output current runaway on a hard short. When the voltage at the feedback pin falls below half the target output voltage, indicating the possibility of a hard short at the output, the switching frequency is reduced to half the internal oscillator frequency. The reduction in the switching frequency allows more time for the inductor to discharge, preventing a runaway of output current. After the EN pin is driven high, internal circuits start to power up. The time required to settle after the EN pin is driven high is called the power-up time. After the internal circuits are powered up, the soft start ramp is initiated and the output capacitor is charged linearly until the output voltage is in regulation. The time required for the output voltage to ramp is called the soft start time. Start-up time in the ADP2108 is the measure of when the output is in regulation after the EN pin is driven high. Start-up time consists of the power-up time and the soft start time.
UNDERVOLTAGE LOCKOUT
To protect against battery discharge, undervoltage lockout (UVLO) circuitry is integrated on the ADP2108. If the input voltage drops below the 2.15 V UVLO threshold, the ADP2108 shuts down, and both the power switch and the synchronous rectifier turn off. When the voltage rises above the UVLO threshold, the soft start period is initiated, and the part is enabled.
CURRENT LIMIT
The ADP2108 has protection circuitry to limit the amount of positive current flowing through the PFET switch and the synchronous rectifier. The positive current limit on the power switch limits the amount of current that can flow from the input to the output. The negative current limit prevents the inductor current from reversing direction and flowing out of the load.
THERMAL PROTECTION
In the event that the ADP2108 junction temperature rises above 150C, the thermal shutdown circuit turns off the converter. Extreme junction temperatures can be the result of high current operation, poor circuit board design, or high ambient temperature. A 20C hysteresis is included so that when thermal shutdown occurs, the ADP2108 does not return to operation until the on-chip temperature drops below 130C. When coming out of thermal shutdown, soft start is initiated.
100% DUTY OPERATION
With a drop in VIN or with an increase in ILOAD, the ADP2108 reaches a limit where, even with the PFET switch on 100% of the time, VOUT drops below the desired output voltage. At this limit, the ADP2108 smoothly transitions to a mode where the PFET switch stays on 100% of the time. When the input conditions change again and the required duty cycle falls, the ADP2108 immediately restarts PWM regulation without allowing overshoot on VOUT.
SOFT START
The ADP2108 has an internal soft start function that ramps the output voltage in a controlled manner upon startup, thereby 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.
Rev. A | Page 12 of 16
ADP2108 APPLICATIONS INFORMATION
EXTERNAL COMPONENT SELECTION
Trade-offs between performance parameters such as efficiency and transient response can be made by varying the choice of external components in the applications circuit, as shown in Figure 1.
Y5V and Z5U dielectrics are not recommended for use with any dc-to-dc converter because of their poor temperature and dc bias characteristics. The worst-case capacitance accounting for capacitor variation over temperature, component tolerance, and voltage is calculated using the following equation: CEFF = COUT x (1 - TEMPCO) x (1 - TOL) where: CEFF is the effective capacitance at the operating voltage. TEMPCO is the worst-case capacitor temperature coefficient. TOL is the worst-case component tolerance. In this example, the worst-case temperature coefficient (TEMPCO) over -40C to +85C is assumed to be 15% for an X5R dielectric. The tolerance of the capacitor (TOL) is assumed to be 10%, and COUT is 9.2481 F at 1.8 V, as shown in Figure 29. Substituting these values in the equation yields CEFF = 9.2481 F x (1 - 0.15) x (1 - 0.1) = 7.0747 F To guarantee the performance of the ADP2108, it is imperative that the effects of dc bias, temperature, and tolerances on the behavior of the capacitors be evaluated for each application.
12
Inductor
The high switching frequency of the ADP2108 allows for the selection of small chip inductors. For best performance, use inductor values between 0.7 H and 3 H. Recommended inductors are shown in Table 5. The peak-to-peak inductor current ripple is calculated using the following equation:
I RIPPLE =
VOUT x (VIN - VOUT ) VIN x f SW x L
where: fSW is the switching frequency. L is the inductor value. The minimum dc current rating of the inductor must be greater than the inductor peak current. The inductor peak current is calculated using the following equation:
I PEAK
I = I LOAD( MAX ) + RIPPLE 2
CAPACITANCE (F)
10
Inductor conduction losses are caused by the flow of current through the inductor, which has an associated internal DCR. Larger sized inductors have smaller DCR, which may decrease inductor conduction losses. Inductor core losses are related to the magnetic permeability of the core material. Because the ADP2108 is a high switching frequency dc-to-dc converter, shielded ferrite core material is recommended for its low core losses and low EMI.
Table 5. Suggested 1.0 H Inductors
Vendor Murata Murata Coilcraft Toko TDK Model LQM21PN1R0M LQM31PN1R0M LPS3010-102 MDT2520-CN CPL2512T Dimensions 2.0 x 1.25 x 0.5 3.2 x 1.6 x 0.85 3.0 x 3.0 x 0.9 2.5 x 2.0 x 1.2 2.5 x 1.5 x 1.2 ISAT (mA) 800 1200 1700 1800 1500 DCR (m) 190 120 85 100 100
8
6
4
2
0
1
2
3
4
5
6
DC BIAS VOLTAGE (V)
Figure 29. Typical Capacitor Performance
The peak-to-peak output voltage ripple for the selected output capacitor and inductor values is calculated using the following equation:
Output Capacitor
Higher output capacitor values reduce the output voltage ripple and improve load transient response. When choosing this value, it is also important to account for the loss of capacitance due to output voltage dc bias. Ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior over temperature and applied voltage. Capacitors must have a dielectric adequate to ensure the minimum capacitance over the necessary temperature range and dc bias conditions. X5R or X7R dielectrics with a voltage rating of 6.3 V or 10 V are recommended for best performance.
Rev. A | Page 13 of 16
VRIPPLE =
(2 x f SW ) x 2 x L x C OUT
V IN
=
I RIPPLE 8 x f SW x C OUT
Capacitors with lower equivalent series resistance (ESR) are preferred to guarantee low output voltage ripple, as shown in the following equation:
ESRCOUT VRIPPLE I RIPPLE
07375-007
0
ADP2108
The effective capacitance needed for stability, which includes temperature and dc bias effects, is 7 F.
Table 6. Suggested 10 F Capacitors
Vendor Murata Taiyo Yuden TDK Type X5R X5R X5R Model GRM188R60J106 JMK107BJ106 C1608JB0J106K Case Size 0603 0603 0603 Voltage Rating (V) 6.3 6.3 6.3
The junction temperature of the die is the sum of the ambient temperature of the environment and the temperature rise of the package due to power dissipation, as shown in the following equation: TJ = TA + TR where: TJ is the junction temperature. TA is the ambient temperature. TR is the rise in temperature of the package due to power dissipation. The rise in temperature of the package is directly proportional to the power dissipation in the package. The proportionality constant for this relationship is the thermal resistance from the junction of the die to the ambient temperature, as shown in the following equation: TR = JA x PD where: TR is the rise in temperature of the package. JA is the thermal resistance from the junction of the die to the ambient temperature of the package. PD is the power dissipation in the package.
Input Capacitor
Higher value input capacitors help to reduce the input voltage ripple and improve transient response. Maximum input capacitor current is calculated using the following equation:
I CIN I LOAD( MAX ) VOUT (VIN - VOUT ) VIN
To minimize supply noise, place the input capacitor as close to the VIN pin of the ADP2108 as possible. As with the output capacitor, a low ESR capacitor is recommended. The list of recommended capacitors is shown in Table 7.
Table 7. Suggested 4.7 F Capacitors
Vendor Murata Taiyo Yuden TDK Type X5R X5R X5R Model GRM188R60J475 JMK107BJ475 C1608X5R0J475 Case Size 0603 0603 0603 Voltage Rating (V) 6.3 6.3 6.3
PCB LAYOUT GUIDELINES
Poor layout can affect ADP2108 performance, causing electromagnetic interference (EMI) and electromagnetic compatibility (EMC) problems, ground bounce, and voltage losses. Poor layout can also affect regulation and stability. A good layout is implemented using the following rules:
*
THERMAL CONSIDERATIONS
Because of the high efficiency of the ADP2108, only a small amount of power is dissipated inside the ADP2108 package, which reduces thermal constraints. However, in applications with maximum loads at high ambient temperature, low supply voltage, and high duty cycle, the heat dissipated in the package is great enough that it may cause the junction temperature of the die to exceed the maximum junction temperature of 125C. If the junction temperature exceeds 150C, the converter goes into thermal shutdown. It recovers when the junction temperature falls below 130C.
* * *
Place the inductor, input capacitor, and output capacitor close to the IC using short tracks. These components carry high switching frequencies, and large tracks act as antennas. Route the output voltage path away from the inductor and SW node to minimize noise and magnetic interference. Maximize the size of ground metal on the component side to help with thermal dissipation. Use a ground plane with several vias connecting to the component side ground to further reduce noise interference on sensitive circuit nodes.
Rev. A | Page 14 of 16
ADP2108 EVALUATION BOARD
ADP2108
TB1 VIN TB2 EN TB5 GND IN VIN CIN 4.7F A1 A2 C1 VIN GND EN U1 FB C2 SW B 1 L1 1H 2 VOUT COUT 10F GND OUT
07375-004
TB3 VOUT
EN
TB4
Figure 30. Evaluation Board Schematic
Figure 31. Recommended Top Layer
Figure 32. Recommended Bottom Layer
Rev. A | Page 15 of 16
07375-006
07375-005
ADP2108 OUTLINE DIMENSIONS
1.06 1.02 0.98 0.022 REF 0.657 0.602 0.546 SEATING PLANE 0.50 REF
2 1 A
BALL 1 IDENTIFIER
1.49 1.45 1.41
0.330 0.310 0.290
1.00 REF
0.50
B
C
TOP VIEW
(BALL SIDE DOWN)
0.355 0.330 0.304
COPLANARITY 0.04 0.280 0.250 0.220
BOTTOM VIEW
(BALL SIDE UP)
Figure 33. 5-Ball Wafer Level Chip Scale Package [WLCSP] (CB-5-3) Dimensions shown in millimeters
ORDERING GUIDE
Model ADP2108ACBZ-1.0-R7 1 ADP2108ACBZ-1.1-R71 ADP2108ACBZ-1.2-R71 ADP2108ACBZ-1.3-R71 ADP2108ACBZ-1.5-R71 ADP2108ACBZ-1.8-R71 ADP2108ACBZ-1.82-R71 ADP2108ACBZ-2.3-R71 ADP2108ACBZ-2.5-R71 ADP2108ACBZ-3.0-R71 ADP2108ACBZ-3.3-R71 ADP2108-1.0-EVALZ1 ADP2108-1.1-EVALZ1 ADP2108-1.2-EVALZ1 ADP2108-1.3-EVALZ1 ADP2108-1.5-EVALZ1 ADP2108-1.8-EVALZ1 ADP2108-1.82-EVALZ1 ADP2108-2.3-EVALZ1 ADP2108-2.5-EVALZ1 ADP2108-3.0-EVALZ1 ADP2108-3.3-EVALZ1
1
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Output Voltage (V) 1.0 1.1 1.2 1.3 1.5 1.8 1.82 2.3 2.5 3.0 3.3 1.0 1.1 1.2 1.3 1.5 1.8 1.82 2.3 2.5 3.0 3.3
Package Description 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] 5-Ball Wafer Level Chip Scale Package [WLCSP] Evaluation Board for 1.0 V Evaluation Board for 1.1 V Evaluation Board for 1.2 V Evaluation Board for 1.3 V Evaluation Board for 1.5 V Evaluation Board for 1.8 V Evaluation Board for 1.82 V Evaluation Board for 2.3 V Evaluation Board for 2.5 V Evaluation Board for 3.0 V Evaluation Board for 3.3 V
Package Option CB-5-3 CB-5-3 CB-5-3 CB-5-3 CB-5-3 CB-5-3 CB-5-3 CB-5-3 CB-5-3 CB-5-3 CB-5-3
111808-A
Branding LA6 LA7 LA8 LA9 LAA LAD LAE LAF LAG LD9 LAH
Z = RoHS Compliant Part.
(c)2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D07375-0-12/08(A)
Rev. A | Page 16 of 16

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