PAM2312 1A Step-Down DC-DC Converter Features n n n n n n n n n n n General Description The PAM2312 is a step-down current-mode, DCDC 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 PA M 2 3 1 2 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. 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 Packages Pb-Free Package The PAM2312 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 PAM2312XX 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 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 PAM2312 is available in SOT23-5 packages. Typical Application Fixed Output Voltage V IN CIN 10µF L VIN SW GND EN Adjustable Output Voltage Vo V IN Co 10µF C IN 10µF VOUT /FB L VIN Vo SW R1 GND VOUT/FB CFW Co 10µF R2 EN R1 ö æ VO = 0.6 ´ ç 1 + ÷ è R2 ø Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 1 PAM2312 1A Step-Down DC-DC Converter Block Diagram 1.5M OSC SLOPE COMP FREQ SHIFT OSC + IAMP - VIN VOUT/FB S Q R1 R Q RS LATCH EA R2 + VIN SWITCHING LOGIC AND BLANKING CIRCUIT MAIN SWITCH( PCH) ANTI SHOOT THRU COMP 0.6VREF EN SW SYNCHRONOUS RECTIFIER (NCH ) + IRCMP - SHUTDOWN GND Pin Configuration & Marking Information Top View SOT23 - 5 EN 1 5 VOUT/FB GND 2 SW 3 4 VIN CG: Product Code of PAM2312 V: Output Voltage Y: Year W: Week X: Internal Code Pin Description Name VIN GND EN F unction Chip main power supply pin Ground Enable control input. Forc e this pin voltage above 1.5V, enables the chip, and below 0.3V shuts down the device. VOUT: Output voltage feedback pin, an internal resis tive divider divides the output VOUT/FB voltage down for comparison to the internal reference voltage. FB: Feedback voltage to internal error amplifier, the threshold voltage is 0.6V. SW The drains of the internal main and synchronous power MOSFET. Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 2 PAM2312 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 ( VIN +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 Thermal Resistance (Junc tion to Case) Thermal Resistance (Junction to Ambient) Internal Power Dissipation Package Note SOT23-5 Symbol Maximum θJ C 130 Unit °C/W SOT23-5 θJA 250 SOT23-5 PD 400 mW 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 05/2010 Rev1.0 3 PAM2312 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 VIN 2.5 Regulated Feedback Voltage V FB 0.588 Reference Voltage Line Regulation ΔVFB Regulated Output Voltage Accuary VO Peak Inductor Current IP K TYP 0.6 MAX UNITS 5.5 V 0.612 V 0.3 IO = 100mA -3 V IN= 3V,VFB = 0.5V or %/V +3 1.5 V O=90% % A Output Voltage Line Regulation LNR V IN = 2.5V to 5V, IO=10mA 0.2 0.5 %/V Output Voltage Load Regulation LDR IO=1mA to 800mA 0.5 1.5 % 40 70 µA 1 µA 1.8 MHz Quiescent Current IQ No load Shutdown Current IS D V EN = 0V Oscillator Frequency fOS C Drain-Source On-State Res istance SW Leakage Current High Effic iency V O = 100% 1.2 V FB = 0V or VO = 0V 1.5 500 k Hz P MOSFET 0.3 0.45 Ω N MOSFET 0.35 0.5 Ω ILSW ±0.01 1 µA η 96 RDS (O N) IDS=100mA % EN Threshold High V EH 1.5 V EN Threshold Low VE L EN Leakage Current IE N ±0.01 µA Over Temperature Protection OTP 150 °C OTP Hysteresis OTH 30 °C 0.3 V Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 4 PAM2312 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) 100 90 80 70 60 50 40 30 20 10 0 Efficiency vs Output Current (Vo=1.5V) 100 90 80 70 60 50 40 Vi n=3.6V Vi n=5V 1 2.5V 3.6V 4.2V 30 Vi n=4.2V 20 10 100 1000 1 Efficiency vs Output Current (Vo=1.8V ) 10 0 100 90 90 80 80 70 70 60 60 50 50 2.5V 3.6V 30 100 100 0 Outp ut Curren t(mA) Output C urrent(m A) 40 10 4.2V Efficiency vs Output Current (Vo=2.5V ) 40 3V 30 3.6V 4.2V 20 20 1 10 1 00 Output Cu rrent(m A) 1 10 00 10 0 90 80 70 60 50 40 30 20 10 0 90 80 70 60 50 40 3V 30 3.6V 4.2V 20 1 10 100 1000 Output Current(mA) Efficiency vs Output Current (Vo=2.8V) 10 0 10 1 00 10 00 Eifficiency VS Output Current (Vo=3.3V) Vin=3.6V Vin=4.2V Vin=5V 1 10 1 00 10 00 Ou tpu t Curren t(mA) Output Cu rrent(m A) Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 5 PAM2312 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 Input Voltage (Vo=1.2V ) 100 100 90 90 80 80 70 70 60 60 Efficiency vs Input Voltage ( Vo=1.5V ) 50 50 10mA Io=10mA 40 40 Io=100mA Io=800mA 30 100mA 800mA 30 3 3.5 4 4 .5 5 2.5 5.5 3 3.5 4 4.5 5 5.5 Input Voltage(V) Inp ut Volta ge(V) Efficiency vs Input Voltage ( Vo=1.8V ) 100 100 90 90 80 80 70 70 60 60 Efficiency vs Input Voltage ( Vo=2.5V ) 50 50 10mA 10mA 40 40 100mA 30 30 2.5 3 100mA 800mA 800mA 3.5 4 4.5 5 3 5.5 3.5 4 5 5.5 Input Voltage(V) Input Voltage(V) Eifficiency VS Input Voltage (Vo=3.3V) Efficiency vs Input Voltage ( Vo=2.8V ) 1 00 4.5 100 90 90 80 80 70 70 60 50 60 40 30 20 50 10mA 40 100mA I o=1 0mA I o=1 00mA 10 800mA I o=8 00mA 30 0 3 3.5 4 4 .5 5 3.5 5.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 Input Voltage(V) In put Volta ge(V) Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 6 PAM2312 1A Step-Down DC-DC Converter Typical Performance Characteristics TA =25 °C , CIN =10μF, CO =10μF, L=4.7 μH, unless otherwise noted. Output Voltage VS Load Current Reference Voltage VS Input Voltage 0.602 1.215 0.600 1.210 0.598 1.205 0.596 1.200 0.594 1.195 0.592 1.190 0.590 0.588 I=1 00mA I=6 00mA 0.586 1.185 Vo=1.2V 1.180 Vin=3.6V I=8 00mA 1.175 0.584 2 3 4 Input Voltage 5 6 0 400 600 800 Load Current(mA ) Output Voltage VS Temperature Reference Voltage VS Temperature 0.620 200 1.194 0.615 1.193 0.610 1.192 0.605 1.191 0.600 1.19 0.595 1.189 0.590 1.188 20 Vo=1.2V Vin=3.6V Io=100mA 0 50 100 150 40 60 80 100 120 140 Temperatur e(℃） Temperature(℃） Reference Voltage VS Load Current 0.604 Output Voltage VS Output Current 1.205 Vo=1.2V 1.203 0.6 1.201 0.596 1.199 0.592 1.197 1.195 0.588 0.584 2.5V 1.193 Vin=2. 7V 3.6V 1.191 Vin=3. 6V 4.2V Vin=4. 2V 0.58 5V 1.189 0 200 400 600 800 10 Load Current 110 210 310 410 510 610 710 810 Output Current(mA) Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 7 PAM2312 1A Step-Down DC-DC Converter Typical Performance Characteristics TA =25 C, CIN =10 μF, CO =10 μF, L=4.7μH, unless otherwise noted. O Dynamic Supply Current VS Input Voltage 50 Dynamic Supply Current VS Temperature 60 Vo=1.2V 45 40 50 ILoad=0A 35 40 30 25 30 20 15 20 10 5 10 0 0 Vo=1.2V Vin=3.6V ILoad=0A 2.5 3.5 4.5 40 5.5 60 80 R dson VS Input Voltage 0.4 100 120 140 Temperature(℃） Input Voltage(V ) Rdson VS Temperature 0.6 Vin=3.6V 0.35 0.5 0.3 0.4 0.25 0.3 0.2 0.2 0.15 0.1 0.1 0 Vi n=4.2V Vi n=3.6V Vi n=2.7V 2 3 4 Input Voltage 5 6 20 Oscillator Frequency VS Supply Voltage 70 Temperature(℃) 120 Oscillator Frequency VS Temperature 1.8 1.58 Vin=3.6V 1.6 1.4 1.56 1.2 1 1.54 0.8 0.6 1.52 0.4 Vo=1.2V Vo=1.5V 0.2 1.50 0 2 3 4 5 20 6 40 60 80 100 120 140 Temperature(℃） Input Voltage (V) Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 8 PAM2312 1A Step-Down DC-DC Converter Typical Performance Characteristics TA =25 °C ,CIN =10μF, CO =10μF, L=4.7 μH, 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 Enable Voltage Output Inductor Current Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 9 PAM2312 1A Step-Down DC-DC Converter Application Information The basic PAM2312 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 æ VOUT ö V OUT ç1÷ V IN ø (f )(L ) è 1 ö æ V VOUT @VI L ç ESR+ ÷ 8fCO UT 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 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 4.7µH 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: éë VOUT (VIN - VO UT )ùû C IN required IRMS @ IOMAX VIN 1 Thermal protection limits power dissipation in the PAM2312. 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 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 05/2010 Rev1.0 10 PAM2312 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: 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: PD =IO2 RDSON H +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 = 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 TJ(MAX) -TA The reference and the circuit remain reset until the VIN crosses its UVLO threshold. θJA Where TJ(max) is the maximum allowable junction temper ature 125°C.TA 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: The PAM2312 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 500kHz and minimum duty cycle, therefore the average input current is typically 200mA. P D=(125°C-25°C)/250°C/W=0.4W Setting the Output Voltage The internal reference is 0.6V (Typical). The output voltage is calculated as below: Thermal Shutdown æ R1ö VO=0.6×1+ ç R2 ÷ è ø 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. Table 1: Resistor selection for output voltage setting Vo R1 R2 1.2V 100k 100k 1.5V 150k 100k 1.8V 200k 100k 2.5V 380k 120k 3.3V 540k 120k Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 11 PAM2312 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 PAM2312. 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. Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 12 PAM2312 1A Step-Down DC-DC Converter Ordering Information PAM 2312 X X X xxx Output Voltage Number of Pins Package Type Pin Configuration Pin Configuration A Type Package Type Number of Pins A: SOT-23 B: 5 Output Voltage 330: 3.3V 1. E N 280: 2.8V 2. GND 250: 2.5V 3. SW 180: 1.8V 4. V IN 150: 1.5V 5. V OUT/FB 120: 1.2V ADJ: Adjustable Power Analog Microelectronics, Inc www.poweranalog.com 05/2010 Rev1.0 13 PAM2312 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 05/2010 Rev1.0 14