PAM2305D 1A Step-Down DC-DC Converter Features General Description n n n n n n n n n n The PAM2305D is a step-down current-mode, DC-DC converter. At heavy load, the constantfrequency P WM control per for ms exc ellent stability and transient response. To ensure the longest battery life in portable applications, the PAM2305D provides a power-saving PulseSkipping Modulation (PSM) mode to reduce quiescent current under light load operation to save power. Efficiency up to 96% Only 40 μA(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 The PAM2305D 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 adjustab le from 0.6V to the input voltage. 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 μA. Other key features include under-voltage lockout to prevent deep battery discharge. 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 The PAM2305D is available in SOT23-5, DFN2x2 6-Pin and QFN3x3 16-Pin packages. Typical Application V IN C IN 10µF L VIN Vo SW R1 GND CFW Co 10µF FB R2 EN R1 V O = 0.6 1+ R2 Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 1 PAM2305D 1A Step-Down DC-DC Converter Block Diagram 1.5M OSC SLOPE COMP FREQ SHIFT OSC + IAMP - VIN FB S Q R1 R Q RS LATCH EA R2 + VIN MAIN SWITCH( PCH) SWITCHING LOGIC AND BLANKING CIRCUIT ANTI SHOOT THRU SW SYNCHRONOUS RECTIFIER (NCH ) COMP 0.6VREF EN + IRCMP - SHUTDOWN GND Pin Configuration & Marking Information Top View SOT23 - 5 Top View QFN 3x3 16L Top View DFN 2x2 6L 5 SW VIN 1 16 15 14 13 NC GND 2 EN 3 4 FB 1 6 FB EN 2 5 GND VIN 3 4 SW GND GND GND 1 FB 4 P2305D XXXYW 2 3 12 VIN 11 VIN VIN VIN 10 9 5 6 7 BK: Product Code of PAM2305D Y: Year W: Week X: Internal Code 8 Pin Description Name Function VIN Chip main power supply pin GND Ground EN Enable control input. Force this pin voltage above 1.5V, enables the chip, and below 0.3V shuts down the device. FB Feedback voltage to internal error amplifier, the threshold voltage is 0.6V. SW The drains of the internal main and s ynchronous power MOSFET. NC No connection Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 2 PAM2305D 1A Step-Down DC-DC Converter 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 6.0V EN, FB Pin Voltage.............................-0.3V to V IN SW Pi n Voltage.....................-0.3V to ( V IN+0.3V ) Junction Temperature................................150°C Storage Temperature Range........-65°C to 150°C Soldering Temperature......................300°C , 5sec Recommended Operating Conditions Supply Voltage................................2.5V to 5.5V Operation Temperature Range.........-40 °C to 85 °C Junction Temperature Range........-40 °C to 125 °C Thermal Information Parameter Package Symbol Note Thermal Resistance (Junc tion to Case) Thermal Resistance (Junction to Ambient) Internal Power Dissipation SOT23-5 DFN 2x2-6 Maximum 130 θJ C 25 QFN 3x3-16 14 SOT23-5 250 DFN 2x2-6 θJA 35 SOT23-5 400 QFN 3x3-16 PD °C/W 68 QFN 3x3-16 DFN 2x2-6 Unit 980 mW 1470 Note: The maximun output current for SOT23-5 package is limited by internal power dissipation capacity as described in Application Information hereinafter. Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 3 PAM2305D 1A Step-Down DC-DC Converter Electrical Characteristic TA =25 °C , VIN =3.6V, VO =1.8V, CIN =10µF, CO =10µF, L=4.7µH, unless otherwise noted. PARAMETER SYMBOL Test Conditions MIN Input Voltage Range VI N 2.5 Regulated Feedback Voltage V FB 0.588 Reference Voltage Line Regulation ΔV FB Regulated Output Voltage Accuary VO Peak Induc tor Current IPK TYP 0.6 MAX UNITS 5.5 V 0.612 V 0.3 IO = 100mA -3 VIN =3V,VFB = 0.5V or %/V +3 1.5 VO=90% Output Voltage Line Regulation LNR VIN = 2.5V to 5V, IO= 10mA 0.2 Output Voltage Load Regulation LDR IO=1mA to 1A 1.5 % A 0.5 %/V % Quiescent Current IQ No load 40 70 µA Shutdown Current ISD VEN = 0V 0.1 1 µA 1.5 1.8 MHz Oscillator Frequency Drain-Source On-State Res istance fOSC R DS(O N) VO = 100% 1.2 VFB = 0V or VO = 0V IDS=100mA 500 kHz P MO SFET 0.3 0.45 Ω N MOSFET 0.35 0.5 Ω ±0.01 1 µA SW Leakage Current ILS W EN Threshold High VEH EN Threshold Low V EL EN Leakage Current IEN ±0.01 µA Over Temperature Protection OTP 150 °C OTP Hysteresis OTH 30 °C 1.5 V 0.3 V Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 4 PAM2305D 1A Step-Down DC-DC Converter Typical Performance Characteristics TA =25 °C , CIN =10μF, CO =10μF, L=4.7 μH, unless otherwise noted. Efficiency vs Output Current (Vo=1.2V) Efficiency vs Input Voltage (Vo=1.2V) 100 95 90 90 85 80 80 70 75 60 Vin=3.6V Vin=4.2V Vin=5.0V 50 70 40 1 10 100 Io=10mA Io=100mA Io=1000mA 65 60 2.5 1000 3.0 3.5 4.0 4.5 5.0 5.5 Input Voltage(V) Output Current(mA) Efficiency vs Output Current (Vo=1.5V ) Efficiency vs Input Voltage (Vo=1.5V) 100 95 90 90 85 80 80 70 75 60 70 Vin=3.6V Vin=4.2V Vin=5.0V 50 65 60 2.5 40 1 10 100 Io=10mA Io=100mA Io=1000mA 1000 3.0 3.5 Output Current(mA) 4.0 4.5 Input Voltage(V) 5.0 5.5 Eifficiency vs Input Voltage (Vo=1.8V) Efficiency vs Output Current (Vo=1.8V) 95 100 90 90 85 80 80 70 75 60 70 Vin=3.6V Vin=4.2V Vin=5.0V 50 60 2.5 40 1 10 100 Io=10mA Io=100mA Io=1000mA 65 1000 Output Current(mA) 3.5 4.5 5.5 Input Voltage(V) Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 5 PAM2305D 1A Step-Down DC-DC Converter Typical Performance Characteristics TA =25 °C , CIN =10μF, CO =10μF, L=4.7 μH, unless otherwise noted. Efficiency vs Output Current (Vo=2.5V) Efficiency vs Input Voltage (Vo=2.5V) 100 96 92 90 88 80 84 80 70 76 60 72 Vin=3.6V Vin=4.2V Vin=5.0V 50 64 40 1 10 100 Output Current(mA) 60 2.5 1000 100 95 95 90 90 85 85 80 80 75 75 5.5 65 60 4.0 60 10 100 Output Current(mA) Io=10mA Io=100mA Io=1000mA 70 Vin=4.2V Vin=5.0V Vin=5.5V 1 4.5 Efficiency vs Input Voltage (Vo=3.3V) 100 65 3.5 Input Voltage(V) Efficiency vs Output Current (Vo=3.3V ) 70 Io=10mA Io=100mA Io=1000mA 68 1000 4.5 5.0 Input Voltage(V) 5.5 Rdson vs Input Voltage Quiescent Current vs Input Voltage 43 0.36 42 0.34 41 Vout=1.2V Vout=2.5V Vout=3.3V 0.32 40 0.3 39 0.28 38 Vout=1.2V Vout=1.8V Vout=3.3V 37 0.26 36 2.5 3 3.5 4 4.5 Input Votage(V) 5 0.24 2.5 5.5 3 3.5 4 4.5 Input Votage(V) 5 5.5 Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 6 PAM2305D 1A Step-Down DC-DC Converter Typical Performance Characteristics TA =25 °C , CIN =10μF, CO =10μF, L=4.7 μH,Vo=1.2V, unless otherwise noted. Reference Voltage vs Load Current Output Voltage vs Load Current 614 1. 235 612 1. 230 610 1. 225 608 1. 220 606 1. 215 604 602 1. 210 Vin=3.6V Vin=4.2V Vin=5.0V 600 Vin=3.6V Vin=4.2V Vin=5.0V 1. 205 598 1. 200 0 200 400 6 00 800 0 1000 200 400 600 800 1000 Output Current(m A ) Output Current(mA) Oscillator Frequency vs Supply Voltage Oscillator Frequency vs Temperature 1.58 1.8 Vo=1.2V 1.7 1.56 1.6 1.5 1.54 1.4 1.52 1.3 1.2 1.50 2 3 4 5 Supply Voltage(V) 6 7 20 40 60 80 100 120 140 Temperature(℃） Load Transient Io=0-1A, Vo=3.3V, Vin=5V Load Transient Io=0-1A, Vo=1.2V, Vin=5V Output Current Output Current Output Voltage Output Voltage Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 7 PAM2305D 1A Step-Down DC-DC Converter Application Information The basic PAM2305D application circuit is shown in Page 1. External component selection is determined by the load requirement, selecting L first and then Cin and Cout. 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: 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 VOUT V OUT 1 (f )(L ) V IN 1 V VOUT @VI L ESR+ 8fCO UT 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 ΔIL increases with input voltage. (1) 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. 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 1.2V 1.5V 1.8V 2.5V 3.3V L 2.2µH 2.2µH 2.2µH 4.7µH 4.7µH 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. C IN and C OUT Selection Thermal consideration 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: Thermal protection limits power dissipation in the PAM2305D. 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. 2 VOUT (VIN - VO UT ) C IN required IRMS @ IOMAX VIN 1 For continuous operation, the junction temperature should be maintained below 125°C. The power dissipation is defined as: This formula has a maximum at V IN =2Vout, w h e r e IR MS = IOU T / 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. PD =IO 2 VORDSONH + (VIN -VO )RDSONL VIN + (tSW FSIO +IQ )VIN IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses. Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 8 PAM2305D 1A Step-Down DC-DC Converter For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dis sipation reduces to: Table 1: Resistor selection for output voltage setting 2 PD =IO R DSONH +IQ VIN Since RDS(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 de pend s on th e ther ma l r esi sta nc e 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 = Vo R1 R2 1.2V 100k 100k 1.5V 150k 100k 1.8V 200k 100k 2.5V 380k 120k 3.3V 540k 120k 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 th e voltag e d rop ac ros s the P - c hannel transistor: TJ(MAX) -TA θJA Where TJ(max) is the maximum allowable junction temperature 125°C.T A is the ambient temperature and θJA 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 θJA 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: V OUT = V IN –I LOAD (R dson + R L ) where Rdson = P-channel switch ON resistance, IL O A D = O ut pu t c u rr e n t, RL = I nd uc t or DC resistance UVLO and Soft-Start The reference and the circuit remain reset until the VIN crosses its UVLO threshold. SOT-25 package: The PAM2305D 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). 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: Short Circuit Protection P D=(125°C-25°C)/68°C/W=1.47W 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. Setting the Output Voltage The internal reference is 0.6V (Typical). The output voltage is calculated as below: R1 V O=0.6×1+ R2 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. The output voltage is given by Table 1. Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 9 PAM2305D 1A Step-Down DC-DC Converter PCB Layout Check List When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the PAM2305D. 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 :PAM2305D Suggested Layout Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 10 PAM2305D 1A Step-Down DC-DC Converter Ordering Information PAM 2305D X X xxx Output Voltage Number of Pins Package Type Package Type Number of Pins A: SOT-23 B: 5 J: QFN 3x3 E: 16 G: DFN 2x2 F: 6 Output Voltage ADJ: Adjustable Package Part Number Output Voltage Marking PAM2305DABADJ ADJ B KAYW SOT23-5 3,000Units /Tape&Reel PAM2305DJEADJ ADJ P2305D QFN3x3 3,000Units /Tape&Reel PAM2305DGFADJ ADJ B KAYW DFN2x2-6 3,000Units /Tape&Reel Type Standard Package Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 11 PAM2305D 1A Step-Down DC-DC Converter Outline Dimensions SOT23-5 D e1 θ L REF. e L1 (REF.) b REF. A A1 A2 c D E E1 L L1 θ b e e1 Millimeter Min Max 1.10 MAX 0 0.10 0.70 1 0.12 REF. 2.70 3.10 2.60 3.00 1.40 1.80 0.45 REF. 0.60 REF. 0º 10º 0.30 0.50 0.95 REF. 1.90 REF. Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 12 PAM2305D 1A Step-Down DC-DC Converter Outline Dimensions DFN 2x2 Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 13 PAM2305D 1A Step-Down DC-DC Converter Outline Dimensions 3x3 mm QFN 16 DIMENSIONS (Millieters) MIN TYP MAX A 0.70 0.75 0.80 A1 0.00 0.02 0.05 A2 0.20 b 0.18 0.25 0.30 D 2.90 3.00 3.10 D1 1.55 1.70 1.80 E 2.90 3.00 3.10 E1 1.55 1.70 1.80 e L 0.50BSC 0.30 0.40 N 16 aaa 0.08 bbb 0.10 0.50 Power Analog Microelectronics, Inc www.poweranalog.com 02/2012 Rev1.1 14