PAM2305
1A Step-Down DC-DC Converters
F eatures
n n n n n n n n n n
General Description
The PAM2305 is a step-down current-mode, DCDC converter. At heavy load, the constantfrequency PWM control performs excellent stability and transient response. To ensure the longest battery life in portable applications, the PA M 2 3 0 5 p r o v i d e s a p o w e r - s a v i n g P u l s e Skipping Modulation (PSM) mode to reduce quiescent current under light load operation to save power. The PAM2305 supports a range of input voltages from 2.5V to 5.5V, allowing the use of a single Li+/Li-polymer cell, multiple Alkaline/NiMH cell, USB, and other standard power sources. The output voltage is adjustable from 0.6V to the input voltage, while the part number suffix PAM2305XX indicates pre-set output voltage of 3.3V, 2.8V, 2.5V, 1.8V, 1.5V, 1.2V or adjustable. All versions employ internal power switch and synchronous rectifierfor to minimize external part count and realize high efficiency. During shutdown, the input is disconnected from the output and the shutdown current is less than 0.1 μ A. Other key features include under-voltage lockout to prevent deep battery discharge. The PAM2305 is available in SOT23-5, DFN2x2 6Pin and QFN3x3 16-Pin packages.
Efficiency up to 96% Only 40 μ A(TYP.) Quiescent Current Output Current: Up to 1A Internal Synchronous Rectifier 1.5MHz Switching Frequency Soft Start Under-Voltage Lockout Short Circuit Protection Thermal Shutdown 5-pin Small SOT23-5, DFN2x2 6-Pin and QFN3x3 16-Pin Packages n Pb-Free Package
Applications
n n n n n n n n
Cellular Phone Portable Electronics Wireless Devices Cordless Phone Computer Peripherals Battery Powered Widgets Electronic Scales Digital Frame
Typical Application
Fixed Output Voltage Adjustable Output Voltage
V IN C IN 10μF
1
VIN GND
SW
5
L
Vo
Co 10μF
V IN C IN 10μF
1
VIN
SW
5
L
R1 C FW
Vo
Co 10μF
2 VOUT 4 /FB
GND 4 2 VOUT/FB
R2
3 EN
3 EN
R1 ö æ VO = 0.6 ´ ç1 + ÷ è R2 ø
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PAM2305
1A Step-Down DC-DC Converters
B lock Diagram
1.5M OSC SLOPE COMP + IAMP VIN
FB FREQ SHIFT R1 R2
VIN OSC
SQ RQ
RS LATCH
+-+
PWM COMP
+
EA
COMP
SWITCHING LOGIC AND BLANKING CIRCUIT
MAIN SWITCH ( PCH )
ANTI SHOOT THRU
SW
SYNCHRONOUS RECTIFIER ( NCH )
EN
0.6VREF
SHUTDOWN
+ IRCMP -
GND
Pin Configuration& Marking Information
Top View SOT23 - 5
VIN 1
BEV YW
Top View DFN 2x2 6L
Top View
QFN 3x3 16L
SW SW NC SW
16 15 14 13
5 SW
NC EN 1 6
VOUT/FB GND SW
GND 2 EN 3
2 3
5 4
GND GND GND VOUT/FB
1 2 3 4 5 6 7 8
12
VIN VIN VIN VIN
P2305V XXXYW
11 10 9
4 VOUT/FB
VIN
BE: Product Code of PAM2305 V: Output Voltage Y: Year W: Week X: Internal Code
GND
Pin Description
Name VIN GND EN Chip main power supply pin Ground Enable control input. Force this pin voltage above 1.5V, enables the chip, and below 0.3V shuts down the device. VOUT: Output voltage feedback pin, an internal resistive divider divides the output VOUT/FB SW NC voltage down for comparison to the internal reference voltage. FB: Feedback voltage to internal error amplifier, the threshold voltage is 0.6V. The drains of the internal main and synchronous power MOSFET. No connection Function
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EN NC
NC
BEV YW
PAM2305
1A Step-Down DC-DC Converters
Absolute Maximum Ratings
These are stress ratings only and functional operation is not implied . Exposure to absolute maximum ratings for prolonged time periods may affect device reliability . All voltages are with respect to ground . Input Voltage..................................-0.3V to 6.6V EN, FB Pin Voltage.............................- 0.3V to V IN SW Pi n Voltage......................- 0.3V to ( V IN+0.3V ) Junction Temperature................................125°C Storage Temperature Range........-65°C to 150°C Soldering Temperature......................300°C , 5sec
Recommended Operating Conditions
Supply Voltage................................2.5V to 5.5V Max. Supply Voltage (for Max. duration of 30 minutes)................................................6.0V Ambient Temperature Range..........-40 °C to 85 °C
Thermal Information
Parameter Thermal Resistance (Junction to Case) Thermal Resistance (Junction to Ambient) Package SOT23-5
Note
Symbol θJC
Maximum 130 20 12 102
Unit
DFN 2x2 QFN 3x3 SOT23-5 DFN 2x2 QFN 3x3 SOT23-5 DFN 2x2 QFN 3x3
°C/W
θJA
68 34 400
Internal Power Dissipation
PD
980 1470
mW
Note: The maximun output current for SOT23-5 package is limited by internal power dissipation capacity as described in Application Information hereinafter.
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PAM2305
1A Step-Down DC-DC Converters
E lectrical Characteristic
T A=25 °C , V IN=3.6V, V O=1.8V, C IN=10μF, C O=10μF,L=4.7μH, unless otherwise noted.
PARAMETER Input Voltage Range Regulated Feedback Voltage Reference Voltage Line Regulation Regulated Output Voltage Accuary Peak Inductor Current Output Voltage Line Regulation Output Voltage Load Regulation Quiescent Current Shutdown Current Oscillator Frequency Drain-Source On-State Resistance SW Leakage Current High Efficiency EN Threshold High EN Threshold Low EN Leakage Current Over Temperature Protection OTP Hysteresis SYMBOL VIN V FB ΔVFB VO IPK LNR LDR IQ ISD fOSC RDS(O N) ILSW η VEH VEL IEN OTP OTH ±0.01 150 30 1.5 0.3 IO = 100mA VIN=3V,VFB = 0.5V or VO=90% VIN = 2.5V to 5V, IO=10mA IO=1mA to 800mA No load VEN = 0V VO = 100% VFB = 0V or VO = 0V IDS=100mA P MOSFET N MOSFET 1.2 -3 1.5 0.2 0.5 40 0.1 1.5 500 0.3 0.35 ±0.01 96 0.45 0.5 1 0.5 1.5 70 1 1.8 Test Conditions MIN 2.5 0.588 0.6 0.3 +3 TYP MAX 5.5 0.612 UNITS V V %/V % A %/V % μA μA MHz kHz Ω Ω μA % V V μA °C °C
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PAM2305
1A Step-Down DC-DC Converters
Typical Performance Characteristics
T A=25 °C , C IN=10 μ F, C O=10uF, L=4.7 μ H, unless otherwise noted. Efficiency vs Output Current (Vo=1.2V) Efficiency vs Output Current (Vo=1.5V)
100 90 80 70 60 50 40 30 20 10 0
100 90
Efficiency(%)
Efficiency(%)
80 70 60 50 40 30 20
2.5V 3.6V 4.2V
Vin=3.6V Vin=4.2V Vin=5V
1
10
100
1000
1
10
100
1000
Output Current(mA)
Output Current(mA)
Efficiency vs Output Current ( Vo=1.8V )
100 90
100 90 80
Efficiency vs Output Current ( Vo=2.5V )
Efficiency(%)
80 70 60 50 40 30 20 1 10 100 Output Current(mA) 1000
2.5V 3.6V 4.2V
Efficiency(%)
70 60 50 40 30 20 1 10 100 1000 Output Current(mA)
3V 3.6V 4.2V
100 90
Efficiency vs Output Current (Vo=2.8V)
70 60 50 40 30 20 1 10 100 Output Current(mA)
3V 3.6V 4.2V
Efficiency(%)
Efficiency(%)
80
100 90 80 70 60 50 40 30 20 10 0
Eifficiency VS Output Current (Vo=3.3V)
Vin=3.6V Vin=4.2V Vin=5V
1000
1
10
100
1000
Output Current(mA)
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PAM2305
1A Step-Down DC-DC Converters
Typical Performance Characteristics
T A=25 °C , C IN=10 μ F, C O=10uF, L=4.7 μ H, unless otherwise noted. Efficiency VS Input Voltage ( Vo=1.2V )
100 90
Efficiency(%)
Efficiency(%)
100 90 80 70 60 50
Io=10mA
Efficiency vs Input Voltage ( Vo=1.5V )
80 70 60 50 40 30 3 3.5 4 4.5 5 5.5 Input Voltage(V)
Io=100mA Io=800mA
10mA
40 30 2.5 3
100mA 800mA
3.5
4
4.5
5
5.5
Input Voltage(V)
Efficiency vs Input Voltage ( Vo=1.8V )
100 90
100 90
Efficiency vs Input Voltage ( Vo=2.5V )
Efficiency(%)
Efficiency(%)
80 70 60 50
10mA
80 70 60 50
10mA
40 30 2.5 3
100mA 800mA
40 30
100mA 800mA
3.5
4
4.5
5
5.5
3
3.5
4
4.5
5
5.5
Input Voltage(V)
Input Voltage(V)
100 90
Efficiency vs Input Voltage ( Vo=2.8V )
Eifficiency VS Input Voltage (Vo=3.3V)
100 90 80 70 60 50 40 30 20 10 0
Io=10mA Io=100mA Io=800mA
Efficiency(%)
70 60 50
10mA
40 30 3
100mA 800mA
Eifficiency(%)
80
3.5
4
4.5
5
5.5
3.5
3.75
4
4.25
4.5
4.75
5
5.25
5.5
Input Voltage(V)
Input Voltage(V)
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PAM2305
1A Step-Down DC-DC Converters
Typical Performance Characteristics
T A=25 °C , C IN=10 μ F, C O=10uF,L=4.7 μ H, unless otherwise noted. Reference Voltage VS Input Voltage
0.602 0.600 0.598 0.596
Vfb(V)
1.215
Output Voltage VS Load Current
1.210
Vin=3.6V
Output Voltage(V)
1.205 1.200 1.195 1.190 1.185 1.180 1.175
0.594 0.592 0.590 0.588 0.586 0.584 2 3 4 Input Voltage(V) 5 6
I=100mA I=600mA I=800mA
Vo=1.2V Vin=3.6V
0 200 400 Load Current(mA) 600 800
Reference Voltage VS Temperature
0.620
1.194 1.193
Output Voltage VS Temperature
Reference Voltage(V)
0.615 0.610 0.605 0.600 0.595 0.590 0 50 100 150 Tem perature(°C)
Output Voltage(V)
1.192 1.191 1.19 1.189 1.188 20 40 60 80 100 120 140 Temperature(°C)
Vo=1.2V Vin=3.6V Io=100mA
Reference Voltage VS Load Current
0.604 0.6 0.596
Vfb
Output Voltage VS Output Current
1.205 1.203 1.201
Output Voltage(V)
Vo=1.2V
1.199 1.197 1.195 1.193
2.5V 3.6V 4.2V 5V
0.592 0.588 0.584 0.58 0 200 400 Load Current(mA) 600 800
Vin=2.7V Vin=3.6V Vin=4.2V
1.191 1.189 10 110
210
310
410
510
610
710
810
Output Current(mA)
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PAM2305
1A Step-Down DC-DC Converters
Typical Performance Characteristics
T A=25 C, C IN=10 μ F, C O=10uF,L=4.7 μ H, unless otherwise noted. Dynamic Supply Current VS Input Voltage
50
O
Dynamic Supply Current VS Temperature
60
Dynamic Supply Current(uA)
Dynamic Supply Current(uA)
45 40 35 30 25 20 15 10 5 0
Vo=1.2V ILoad =0A
50 40 30
Vo=1.2V
20 10 0
Vin=3.6V ILoad=0A
2.5
3
3.5 4 4.5 Input Voltage(V)
5
5.5
40
60
80
100
120
140
Temperature(°C)
R dson VS Input Voltage
0.4
Rdson VS Temperature
0.6
Vin=3.6V
0.35
RDS(ON)
Vin=3.6V
0.5 0.4
0.3 0.25 0.2 0.15 0.1 2 3 4 Input Voltage(V) 5 6
Rds(on)
0.3 0.2 0.1 0 20 70 Temperature(°C) 120
Vin=4.2V Vin=3.6V Vin=2.7V
Oscillator Frequency VS Supply Voltage
1.8
Oscillator Frequency(MHz)
1.58
Oscillator Frequency VS Temperature
Vin=3.6V
Oscillator Frequency(MHz)
1.56
Vin=3.6V
1.7 1.6 1.5 1.4 1.3 1.2 2 3 4 5 Supply Voltage(V) 6 7
1.54
1.52
1.50 20 40 60 80 100 120 140 Temperature(°C)
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PAM2305
1A Step-Down DC-DC Converters
Typical Performance Characteristics
T A=25 °C ,C IN=10 μ F, C O=10uF,L=4.7 μ H, unless otherwise noted. Load Transient Io=0-500mA Vo=3.3V Vin=5V Load Transient Io=0-1A Vo=1.2V Vin=3.6V
Output Current
Output Current
Voltage Output
Voltage Output
Start-up from Shutdown Vo=1.8V,Vin=3.6V
Voltage Output
Enable
Inductor Current
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PAM2305
1A Step-Down DC-DC Converters
Application Information
The basic PAM2305 application circuit is shown in Page 1. External component selection is determined by the load requirement, selecting L first and then Cin and Cout. Inductor Selection For most applications, the value of the inductor will fall in the range of 1μH to 4.7μH. Its value is chosen based on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V IN or Vout also increases the ripple current as shown in equation 1. A reasonable starting point for setting ripple current is △I L = 400mA (40% of 1A).
DIL = 1 æ VOUT ö VOUT ç 1÷ f )(L ) VIN ø ( è
The selection of Cout is driven by the required effective series resistance (ESR). Typically, once the ESR requirement for Cout has been met, the RMS current rating generally far exceeds the I RIPPLE(P-P) requirement. The output ripple △Vout is determined by:
1ö æ VVOUT @VIL ç ESR+ ÷ 8fCOUT ø è
Where f = operating frequency, C OUT =output capacitance and Δ I L = ripple current in the inductor. For a fixed output voltage, the output ripple is highest at maximum input voltage since Δ I L increases with input voltage. Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. Using ceramic capacitors can achieve very low output ripple and small circuit size. When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage charac teristics of all the ceramics for a given value and size. Thermal consideration Thermal protection limits power dissipation in the PAM2305. When the junction temperature exceeds 150°C, the OTP (Over Temperature Protection) starts the thermal shutdown and turns the pass transistor off. The pass transistor resumes operation after the junction temperature drops below 120°C. For continuous operation, the junction temperature should be maintained below 125°C. The power dissipation is defined as:
PD =IO 2 VORDSONH + (VIN -VO )RDSONL VIN + (t SW FSIO +IQ )VIN
(1)
The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 1.4A rated inductor should be enough for most applications (1A + 400mA). For better efficiency, choose a low DC-resis tance inductor.
Vo L 1.2V 2.2μH 1.5V 2.2μH 1.8V 2.2μH 2.5V 4.7μH 3.3V 4.7μH
C IN and C OUT Selection In continuous mode, the source current of the top MOSFET is a square wave of duty cycle Vout/Vin. To prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by:
é VOUT (VIN - VOUT )ù û CIN required IRMS @ IOMAX ë VIN
1 2
This formula has a maximum at V IN =2Vout, w h e r e I RMS= I OUT/ 2 . T h i s s i m p l e w o r s t - c a s e condition is com monly used for design because even significant deviations do not offer much relief. Note that the capacitor manufacturer's ripple current ratings are often based on 2000 hours of life. This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Consult the manufac turer if there is any question.
I Q is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses.
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PAM2305
1A Step-Down DC-DC Converters
For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dis sipation reduces to:
PD =IO RDSONH +IQ VIN
2
Table 1: Resistor selection for output voltage setting
Vo 1.2V 1.5V 1.8V 2.5V 3.3V R1 100k 150k 200k 380k 540k R2 100k 100k 100k 120k 120k
Since R DS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surrounding airflow and temperature difference between junction and ambient. The maximum power dissipation can be calculated by the following formula:
PD = TJ(MAX) -TA θJA
100% Duty Cycle Operation As the input voltage approaches the output voltage, the converter turns the P-chan nel transistor continuously on. In this mode the output voltage is equal to the input voltage minus the voltage drop across the P - channel transistor: V OUT = V IN – I LOAD (R dson + R L) where R dson = P-channel switch ON resistance, I L O A D = Output current, R L = Inductor DC resistance UVLO and Soft-Start The reference and the circuit remain reset until the VIN crosses its UVLO threshold. The PAM2305 has an internal soft-start circuit that limits the in-rush current during start-up. This prevents possible voltage drops of the input voltage and eliminates the output voltage overshoot. The soft-start acts as a digital circuit to increase the switch current in several steps to the P-channel current limit (1500mA). Short Circuit Protection The switch peak current is limited cycle-by-cycle to a typical value of 1500mA. In the event of an output voltage short circuit, the device operates with a frequency of 400kHz and minimum duty cycle, therefore the average input current is typically 200mA. Thermal Shutdown When the die temperature exceeds 150°C, a reset occurs and the reset remains until the temperature decrease to 120°C, at which time the circuit can be restarted.
Where TJ(max) is the maximum allowable junction temperature 125°C.T A is the ambient temperature and θ JA is the thermal resistance from the junction to the ambient. Based on the standard JEDEC for a two layers thermal test board, the thermal resistance θ JA of SOT23-5 package is 250°C/W, DFN2X2 102°C/W, and QFN3X3 68°C/W, respectively. The maximum power dissipation at T A = 25°C can be calculated by following formula: SOT-25 package: P D=(125°C-25°C)/250°C/W=0.4W DFN2*2 package: P D=(125°C-25°C)/102°C/W=0.984W QFN3*3 package: P D=(125°C-25°C)/68°C/W=1.47W Setting the Output Voltage The internal reference is 0.6V (Typical). The output voltage is calculated as below:
æ R1 ö VO=0.6×1+ ç R2 ÷ è ø
The output voltage is given by Table 1.
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PAM2305
1A Step-Down DC-DC Converters
PCB Layout Check List When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the PAM2305. These items are also illustrated graphically in Figure 1. Check the following in your layout: 1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct and wide. 2. Does the V FB pin connect directly to the feedback resistors? The resistive divider R1/R2 must be con nected between the (+) plate of C OUT and ground. 3. Does the (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to the internal power MOSFETs. 4. Keep the switching node, SW, away from the sensitive VFB node. 5. Keep the (–) plates of C IN and C OUT as close as possible.
Figure 1 :PAM2305 Suggested Layout
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PAM2305
1A Step-Down DC-DC Converters
O rdering Information
PAM 2305 X X X xxx
Output Voltage Number of Pins Package Type Pin Configuration
Pin Configuration A Type 1. VIN 2. GND 3. EN 4. VOUT/FB 5. SW B Type : 16 pins C Type: 1. NC 2. EN 3. VIN 4. SW 5. GND 6 : VOUT/FB Package Type A: SOT-23 J: QFN 3x3 G: DFN 2x2 Number of Pins B: 5 E: 16 F: 6 Output Voltage 330: 3.3V 280: 2.8V 250: 2.5V 180: 1.8V 150: 1.5V 120: 1.2V ADJ: Adjustable
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PAM2305
1A Step-Down DC-DC Converters
Ordering Information
Part Number PAM2305AAB330 PAM2305AAB280 PAM2305AAB250 PAM2305AAB180 PAM2305AAB150 PAM2305AAB120 PAM2305AABADJ PAM2305BJE330 PAM2305BJE280 PAM2305BJE250 PAM2305BJE180 PAM2305BJE150 PAM2305BJE120 PAM2305BJEADJ PAM2305CGF330 PAM2305CGF280 PAM2305CGF250 PAM2305CGF180 PAM2305CGF150 PAM2305CGF120 PAM2305CGFADJ Output Voltage 3.3V 2.8V 2.5V 1.8V 1.5V 1.2V ADJ 3.3V 2.8V 2.5V 1.8V 1.5V 1.2V ADJ 3.3V 2.8V 2.5V 1.8V 1.5V 1.2V ADJ Marking BEKYW BEHYW BEGYW BEEYW BECYW BEBYW BEAYW P2305K P2305H P2305G P2305E P2305C P2305B P2305A BEKYW BEHYW BEGYW BEEYW BECYW BEBYW BEAYW Package Type SOT23-5 SOT23-5 SOT23-5 SOT23-5 SOT23-5 SOT23-5 SOT23-5 QFN3x3 QFN3x3 QFN3x3 QFN3x3 QFN3x3 QFN3x3 QFN3x3 DFN2x2-6 DFN2x2-6 DFN2x2-6 DFN2x2-6 DFN2x2-6 DFN2x2-6 DFN2x2-6 Standard Package 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel 3,000Units/Tape&Reel
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PAM2305
1A Step-Down DC-DC Converters
O utline Dimensions
c (REF.) 0.25
θ L REF. L1 (REF.)
SOT23-5
D e1
E1
E
REF. A A1 A2 c D E E1 L L1 θ b e e1
Min 0 0.70 2.70 2.60 1.40
0º 0.30
Millimeter Nom 1.10MAX 0.05 1.00 0.12REF. 2.90 2.80 1.60 0.45REF. 0.60REF. 5º 0.40 0.95REF. 1.90REF.
A1
A2
A
Max 0.10 1.295 3.10 3.00 1.80
10º 0.50
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PAM2305
1A Step-Down DC-DC Converters
Outline Dimensions
D FN 2x2
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PAM2305
1A Step-Down DC-DC Converters
Outline Dimensions
3x3 mm QFN 16
DIMENSIONS (Millieters) MIN A A1 A2 b D D1 E E1 e L N aaa bbb 0.30 0.18 2.90 1.55 2.90 1.55 0.70 0.00 TYP 0.75 0.02 0.20 0.25 3.00 1.70 3.00 1.70 0.50BSC 0.40 16 0.08 0.10 0.50 0.30 3.10 1.80 3.10 1.80 MAX 0.80 0.05
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