AAT2552_08

PRODUCT DATASHEET AAT2552178 SystemPowerTM General Description Total Power Solution for Portable Applications Features • Battery Charger: ▪ Input Voltage Range: 4V to 7.5V ▪ Programmable Charging Current up to 500mA ▪ Highly Integrated Battery Charger • Charging Device • Reverse Blocking Diode • Current Sensing • Step-Down Converter: ▪ Input Voltage Range: 2.7V to 5.5V ▪ Output Voltage Range: 0.6V to VIN ▪ 300mA Output Current ▪ Up to 96% Efficiency ▪ 45μA Quiescent Current ▪ 1.5MHz Switching Frequency ▪ 120μs Start-Up Time • Linear Regulator: ▪ 300mA Output Current ▪ Low Dropout: 400mV at 300mA ▪ Fast Line and Load Transient Response ▪ High Accuracy: ±1.5% ▪ 85μA Quiescent Current • Short-Circuit, Over-Temperature, and Current Limit Protection • TDFN34-16 Package • -40°C to +85°C Temperature Range The AAT2552 is a fully integrated 500mA battery charger, a 300mA step-down converter, and a 300mA low dropout (LDO) linear regulator. The input voltage range is 4V to 7.5V for the battery charger and 2.7V to 5.5V for the step-down converter and linear regulator, making it ideal for applications operating with single-cell lithiumion/polymer batteries. The battery charger is a complete constant current/constant voltage linear charger. It offers an integrated pass device, reverse blocking protection, high accuracy current and voltage regulation, charge status, and charge termination. The charging current is programmable via external resistor from 30mA to 500mA. In addition to these standard features, the device offers over-voltage, current limit, and thermal protection. The step-down converter is a highly integrated converter operating at a 1.5MHz switching frequency, minimizing the size of external components while keeping switching losses low. The output voltage ranges from 0.6V to the input voltage. The AAT2552 linear regulator is designed for high speed turn-on and turn-off performance, fast transient response, and good power supply ripple rejection. Delivering up to 300mA of load current, it includes short-circuit protection and thermal shutdown. The AAT2552 is available in a Pb-free, thermallyenhanced TDFN34-16 package and is rated over the -40°C to +85°C temperature range. Applications • • • • • • • Bluetooth™ Headsets Cellular Phones GPS Handheld Instruments MP3 and Portable Music Players PDAs and Handheld Computers Portable Media Players Typical Application Adapter/USB Input Enable VOUTB RFBB1 COUTB 4.7μF RFBB2 VOUTA RFBA1 COUTA RFBA2 FBA GND FBB OUTA L1 LX ADP STAT EN_BAT INB ENB INA ENA AAT2552 MODE BAT ISET System BATT+ C OUT R SET Battery Pack BATT- 2552.2008.02.1.2 www.analogictech.com 1 PRODUCT DATASHEET AAT2552178 AAT2552178 SystemPowerTM Pin Descriptions Pin # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 EP Total Power Solution for Portable Applications Symbol EN_BAT ISET AGND FBB ENB MODE ENA FBA OUTA INA INB LX PGND BAT ADP STAT Function Enable pin for the battery charger. When connected to logic low, the battery charger is disabled and consumes less than 1μA of current. When connected to logic high, the charger operates normally (pulled down internally). Charge current set point. Connect a resistor from this pin to ground. Refer to typical characteristics curves for resistor selection. Analog ground. Feedback input for the step-down converter. This pin must be connected directly to an external resistor divider. Nominal voltage is 0.6V. Enable pin for the step-down converter. When connected to logic low, the step-down converter is disabled and consumes less than 1μA of current. When connected to logic high, the converter operates normally (pulled up internally). Pulled down internally for automatic PWM/LL operation. Connect to logic high for forced PWM. Drive with external clock signal to synchronize step-down converter to external clock in PWM mode. Enable pin for the linear regulator. When connected to logic low, the regulator is disabled and consumes less than 1μA of current. When connected to logic high, the LDO operates normally (pulled up internally). Feedback input for the LDO. This pin must be connected directly to an external resistor divider. Nominal voltage is 1.24V. Linear regulator output. Connect a 2.2μF capacitor from this pin to ground. Linear regulator input voltage. Connect a 1μF or greater capacitor from this pin to ground. Input voltage for the step-down converter. Output of the step-down converter. Connect the inductor to this pin. Internally, it is connected to the drain of both high- and low-side MOSFETs. Power ground. Battery charging and sensing. Connect to positive terminal of Lithium-ion/polymer battery. Input from USB port or AC wall adapter. Open drain status pin for charger. Exposed paddle (bottom): connect to ground directly beneath the package. Pin Configuration TDFN34-16 (Top View) EN_BAT ISET AGND FBB ENB MODE ENA FBA 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 STAT ADP BAT PGND LX INB INA OUTA 2 www.analogictech.com 2552.2008.02.1.2 PRODUCT DATASHEET AAT2552178 AAT2552178 Units V V V V V V °C °C SystemPowerTM Absolute Maximum Ratings1 Symbol VINA, VINB VADP VLX VFB VEN VX TJ TLEAD Total Power Solution for Portable Applications Description Input Voltage to GND Adapter Voltage to GND LX to GND FB to GND ENA, ENB, EN_BAT to GND BAT, ISET, STAT Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value 6.0 -0.3 to 7.5 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to 6.0 -0.3 to VADP + 0.3 -40 to 150 300 Thermal Information Symbol PD θJA Description Maximum Power Dissipation Thermal Resistance2 Value 2.0 50 Units W °C/W 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Mounted on an FR4 board. 2552.2008.02.1.2 www.analogictech.com 3 PRODUCT DATASHEET AAT2552178 AAT2552178 SystemPowerTM Electrical Characteristics1 Total Power Solution for Portable Applications VINB = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C. Symbol Description Conditions Min 2.7 VINB Rising Hysteresis IOUTB = 0 to 300mA, VINB = 2.7V to 5.5V No Load VENB = GND 300 0.3 0.5 VINB = 5.5V, VLX = 0 to VINB IOUTB = 0mA to 300mA VINB = 2.7V to 5.5V VINB = 3.6V VOUTB = 1.0V From Enable to Output Regulation 1.0 0.4 0.1 0.6 1.5 120 140 15 0.6 VINB = VENB = 5.5V IOUTA = 1mA to 300mA TA = 25°C TA = -40°C to +85°C 1.4 -1.0 -1.5 -2.5 1.2 1.22 VOUT + VDO3 1.0 1.5 2.5 3.3 1.26 5.5 650 0.09 300 400 85 1kHz 10kHz 1MHz 70 50 30 140 15 95 8 0.6 1.4 VINA = VENA = 5.5V 1.0 150 1.0 250 -3.0 0.6 45 3.0 VINB 90 1.0 Typ Max 7.5 2.6 Units V V mV % V μA μA mA Ω Ω μA % %/V V μA MHz μs °C °C V V μA % V V V mV %/V mA mA μA μA dB °C °C μVRMS/√Hz ppm/°C V V μA Step-Down Converter Input Voltage VIN VUVLO UVLO Threshold Output Voltage Tolerance2 VOUT Output Voltage Range VOUT Quiescent Current IQ Shutdown Current ISHDN P-Channel Current Limit ILIM High-Side Switch On Resistance RDS(ON)H RDS(ON)L Low-Side Switch On Resistance ILXLEAK LX Leakage Current ΔVOUT/ΔVOUT Load Regulation ΔVLinereg/ΔVIN Line Regulation Feedback Threshold Voltage Accuracy VFB FB Leakage Current IFB Oscillator Frequency FOSC Startup Time TS Over-Temperature Shutdown Threshold TSD Over-Temperature Shutdown Hysteresis THYS Enable Threshold Low VEN(L) Enable Threshold High VEN(H) Input Low Current IEN Linear Regulator VOUT VOUT VFB VIN VDO ΔVOUT/ VOUT*ΔVIN IOUT ISC IQ ISHDN PSRR TSD THYS eN TC VEN(L) VEN(H) IEN Output Voltage Tolerance Output Voltage Range Feedback Voltage Accuracy Input Voltage Dropout Voltage4 Line Regulation Output Current Short-Circuit Current Quiescent Current Shutdown Current Power Supply Rejection Ratio Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Output Noise Output Voltage Temperature Coefficient Enable Threshold Low Enable Threshold High Enable Input Current 0.591 0.609 0.2 1.24 400 IOUTA = 300mA; VOUT = 3.3V VINA = VOUTA + 1 to 5.0V VOUTA > 2.0V VOUTA < 0.4V VINA = 5V; VENA = VIN VINA = 5V; VENA = 0V IOUTA =10mA eNBW = 100Hz to 100kHz 1. The AAT2552 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Output voltage tolerance is independent of feedback resistor network accuracy. 3. VDO is defined as VIN - VOUT when VOUT is 98% of nominal. 4. For VOUT VUVLO Yes Shut Down Yes Fault Conditions Monitoring OV, OT Charge Control No Preconditioning Test V MIN > VBAT Yes Preconditioning (Trickle Charge) No No Recharge Test V RCH > VBAT Yes Current Phase Test V BAT_EOC > VBAT Yes Constant Current Charge Mode No Voltage Phase Test IBAT > ITERM Yes Constant Voltage Charge Mode No Charge Completed 2552.2008.02.1.2 www.analogictech.com 17 PRODUCT DATASHEET AAT2552178 SystemPowerTM Application Information Soft Start / Enable Total Power Solution for Portable Applications stant current levels from 30mA to 500mA may be set by selecting the appropriate resistor value from Table 1. Normal ICHARGE (mA) 500 400 300 250 200 150 100 50 40 30 20 15 The EN_BAT pin is internally pulled down. When pulled to a logic high level, the battery charger is enabled. When left open or pulled to a logic low level, the battery charger is shut down and forced into the sleep state. Charging will be halted regardless of the battery voltage or charging state. When it is re-enabled, the charge control circuit will automatically reset and resume charging functions with the appropriate charging mode based on the battery charge state and measured cell voltage from the BAT pin. Separate ENA and ENB inputs are provided to independently enable and disable the LDO and step-down converter, respectively. This allows sequencing of the LDO and step-down outputs during startup. The LDO is enabled when the ENA pin is pulled high. The control and feedback circuits have been optimized for high-speed, monotonic turn-on characteristics. The step-down converter is enabled when the ENB pin is pulled high. Soft start increases the inductor current limit point in discrete steps when the input voltage or ENB input is applied. It limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the ENB input forces the AAT2552 into a low-power, non-switching state. The step-down converter input current during shutdown is less than 1μA. Set Resistor Value R1 (kΩ) 3.24 4.12 5.36 6.49 8.06 10.7 16.2 31.6 38.3 53.6 78.7 105 Table 1: RSET Values. 1000 ICH (mA) 100 10 1 1 10 100 1000 RSET (kΩ) Adapter or USB Power Input Constant current charge levels up to 500mA may be programmed by the user when powered from a sufficient input power source. The battery charger will operate from the adapter input over a 4.0V to 7.5V range. The constant current fast charge current for the adapter input is set by the RSET resistor connected between ISET and ground. Refer to Table 1 for recommended RSET values for a desired constant current charge level. Figure 2: Constant Charging Current vs. Set Resistor Values. Charge Status Output The AAT2552 provides battery charge status via a status pin. This pin is internally connected to an N-channel open drain MOSFET, which can be used to drive an external LED. The status pin can indicate several conditions, as shown in Table 2. Event Description No battery charging activity Battery charging via adapter or USB port Charging completed Programming Charge Current The fast charge constant current charge level is user programmed with a set resistor placed between the ISET pin and ground. The accuracy of the fast charge, as well as the preconditioning trickle charge current, is dominated by the tolerance of the set resistor used. For this reason, a 1% tolerance metal film resistor is recommended for the set resistor function. Fast charge con- Status OFF ON OFF Table 2: LED Status Indicator. The LED should be biased with as little current as necessary to create reasonable illumination; therefore, a bal- 18 www.analogictech.com 2552.2008.02.1.2 PRODUCT DATASHEET AAT2552178 SystemPowerTM Total Power Solution for Portable Applications Figure 3 shows the relationship of maximum power dissipation and ambient temperature of the AAT2552. 3.00 2.50 PD(MAX) (mW) last resistor should be placed between the LED cathode and the STAT pin. LED current consumption will add to the overall thermal power budget for the device package, hence it is good to keep the LED drive current to a minimum. 2mA should be sufficient to drive most lowcost green or red LEDs. It is not recommended to exceed 8mA for driving an individual status LED. The required ballast resistor values can be estimated using the following formulas: 2.00 1.50 1.00 0.50 R6 = Example: (VADP - VF(LED)) ILED 0.00 0 20 40 60 80 100 TA (°C) Figure 3: Maximum Power Dissipation. (5.5V - 2.0V) = 1.75kΩ R6 = 2mA Note: Red LED forward voltage (VF) is typically 2.0V @ 2mA. Next, the power dissipation of the battery charger can be calculated by the following equation: PD = [(VADP - VBAT) · ICH + (VADP · IOP)] Where: PD VADP VBAT ICH IOP = = = = Total Power Dissipation by the Device ADP/USB Voltage Battery Voltage as Seen at the BAT Pin Constant Charge Current Programmed for the Application = Quiescent Current Consumed by the Charger IC for Normal Operation [0.5mA] Thermal Considerations The AAT2552 is offered in a TDFN34-16 package which can provide up to 2W of power dissipation when it is properly bonded to a printed circuit board and has a maximum thermal resistance of 50°C/W. Many considerations should be taken into account when designing the printed circuit board layout, as well as the placement of the charger IC package in proximity to other heat generating devices in a given application design. The ambient temperature around the IC will also have an effect on the thermal limits of a battery charging application. The maximum limits that can be expected for a given ambient condition can be estimated by the following discussion. First, the maximum power dissipation for a given situation should be calculated: By substitution, we can derive the maximum charge current before reaching the thermal limit condition (thermal cycling). The maximum charge current is the key factor when designing battery charger applications. ICH(MAX) = (PD(MAX) - VIN · IOP) VIN - VBAT (TJ(MAX) - TA) PD(MAX) = θJA Where: PD(MAX) = Maximum Power Dissipation (W) θJA = Package Thermal Resistance (°C/W) TJ(MAX) = Maximum Device Junction Temperature (°C) [135°C] TA = Ambient Temperature (°C) (TJ(MAX) - TA) - V · I IN OP θJA ICH(MAX) = VIN - VBAT In general, the worst condition is the greatest voltage drop across the IC, when battery voltage is charged up to the preconditioning voltage threshold. Figure 4 shows the maximum charge current in different ambient temperatures. 2552.2008.02.1.2 www.analogictech.com 19 PRODUCT DATASHEET AAT2552178 SystemPowerTM 500 450 400 Total Power Solution for Portable Applications Capacitor Selection TA = 25°C TA = 60°C TA = 45°C Linear Regulator Input Capacitor (C6) An input capacitor greater than 1μF will offer superior input line transient response and maximize power supply ripple rejection. Ceramic, tantalum, or aluminum electrolytic capacitors may be selected for CIN. There is no specific capacitor ESR requirement for CIN. However, for 300mA LDO regulator output operation, ceramic capacitors are recommended for CIN due to their inherent capability over tantalum capacitors to withstand input current surges from low impedance sources such as batteries in portable devices. ICH(MAX) (mA) 350 300 250 200 150 100 50 0 4.25 4.5 4.75 5 5.25 5.5 5.75 6 6.25 6.5 6.75 7 TA = 85°C VIN (V) Figure 4: Maximum Charging Current Before Thermal Cycling Becomes Active. There are three types of losses associated with the stepdown converter: switching losses, conduction losses, and quiescent current losses. Conduction losses are associated with the RDS(ON) characteristics of the power output switching devices. Switching losses are dominated by the gate charge of the power output switching devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the losses is given by: Battery Charger Input Capacitor (C1) In general, it is good design practice to place a decoupling capacitor between the ADP pin and GND. An input capacitor in the range of 1μF to 22μF is recommended. If the source supply is unregulated, it may be necessary to increase the capacitance to keep the input voltage above the under-voltage lockout threshold during device enable and when battery charging is initiated. If the adapter input is to be used in a system with an external power supply source, such as a typical AC-to-DC wall adapter, then a CIN capacitor in the range of 10μF should be used. A larger input capacitor in this application will minimize switching or power transient effects when the power supply is “hot plugged” in. PTOTAL = IO2 · (RDSON(H) · VO + RDSON(L) · [VIN - VO]) VIN + (tsw · FS · IO + 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. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: 2 Step-Down Converter Input Capacitor (C6) Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for CIN. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. CIN = PTOTAL = IO · 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. Given the total losses, the maximum junction temperature can be derived from the θJA for the TDFN34-16 package which is 50°C/W. VO ⎛ V⎞ · 1- O VIN ⎝ VIN ⎠ ⎛ VPP ⎞ - ESR · FS ⎝ IO ⎠ VO ⎛ V⎞ 1 · 1 - O = for VIN = 2 · VO VIN ⎝ VIN ⎠ 4 CIN(MIN) = 1 ⎛ VPP ⎞ - ESR · 4 · FS ⎝ IO ⎠ TJ(MAX) = PTOTAL · ΘJA + TAMB Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10μF, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6μF. 20 www.analogictech.com 2552.2008.02.1.2 PRODUCT DATASHEET AAT2552178 SystemPowerTM The maximum input capacitor RMS current is: Total Power Solution for Portable Applications the converter performance, a high ESR tantalum or aluminum electrolytic capacitor should be placed in parallel with the low ESR, ESL bypass ceramic capacitor. This dampens the high Q network and stabilizes the system. The linear regulator and the step-down convertor share the same input capacitor on the evaluation board. VO ⎛ V⎞ · 1- O = VIN ⎝ VIN ⎠ D · (1 - D) = 0.52 = 1 2 The input capacitor RMS ripple current varies with the input and output voltage and will always be less than or equal to half of the total DC load current. Linear Regulator Output Capacitor (C5) For proper load voltage regulation and operational stability, a capacitor is required between OUT and GND. The COUT capacitor connection to the LDO regulator ground pin should be made as directly as practically possible for maximum device performance. Since the regulator has been designed to function with very low ESR capacitors, ceramic capacitors in the 1.0μF to 10μF range are recommended for best performance. Applications utilizing the exceptionally low output noise and optimum power supply ripple rejection should use 2.2μF or greater for COUT. In low output current applications, where output load is less than 10mA, the minimum value for COUT can be as low as 0.47μF. IRMS = IO · for VIN = 2 · VO VO ⎛ V⎞ · 1- O VIN ⎝ VIN ⎠ IRMS(MAX) = IO 2 The term appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when VO is twice VIN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at 50% duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the step-down converter. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. The proper placement of the input capacitor (C6) can be seen in the evaluation board layout in Figure 7. A laboratory test set-up typically consists of two long wires running from the bench power supply to the evaluation board input voltage pins. The inductance of these wires, along with the low-ESR ceramic input capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. Errors in the loop phase and gain measurements can also result. Since the inductance of a short PCB trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. In applications where the input power source lead inductance cannot be reduced to a level that does not affect Battery Charger Output Capacitor (C2) The battery charger of the AAT2552 only requires a 1μF ceramic capacitor on the BAT pin to maintain circuit stability. This value should be increased to 10μF or more if the battery connection is made any distance from the charger output. If the AAT2552 is to be used in applications where the battery can be removed from the charger, such as with desktop charging cradles, an output capacitor greater than 10μF may be required to prevent the device from cycling on and off when no battery is present. Step-Down Converter Output Capacitor (C3) The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7μF to 10μF X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL characteristics necessary for low output ripple. For enhanced transient response and low temperature operation applications, a 10μF (X5R, X7R) ceramic capacitor is recommended to stabilize extreme pulsed load conditions. The output voltage droop due to a load transient is dominated by the capacitance of the ceramic output capacitor. During a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. Within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. The relationship of the output volt- 2552.2008.02.1.2 www.analogictech.com 21 PRODUCT DATASHEET AAT2552178 SystemPowerTM Total Power Solution for Portable Applications peak current rating, which is determined by the saturation characteristics. The inductor should not show any appreciable saturation under normal load conditions. Some inductors may meet the peak and average current ratings yet result in excessive losses due to a high DCR. Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. The 3.0μH CDRH2D09 series inductor selected from Sumida has a 150mΩ DCR and a 470mA DC current rating. At full load, the inductor DC loss is 9.375mW which gives a 2.08% loss in efficiency for a 250mA, 1.8V output. age droop during the three switching cycles to the output capacitance can be estimated by: COUT = 3 · ΔILOAD VDROOP · FS Once the average inductor current increases to the DC load level, the output voltage recovers. The above equation establishes a limit on the minimum value for the output capacitor with respect to load transients. The internal voltage loop compensation also limits the minimum output capacitor value to 4.7μF. This is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. Increased output capacitance will reduce the crossover frequency with greater phase margin. The maximum output capacitor RMS ripple current is given by: Adjustable Output Voltage for the Step-down Converter Resistors R2 and R3 of Figure 5 program the output of the step down converter and regulate at a voltage higher than 0.6V. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the suggested value for R3 is 59kΩ. Decreased resistor values are necessary to maintain noise immunity on the FBB pin, resulting in increased quiescent current. Table 3 summarizes the resistor values for various output voltages. IRMS(MAX) = 1 2· 3 · VOUT · (VIN(MAX) - VOUT) L · FS · VIN(MAX) Dissipation due to the RMS current in the ceramic output capacitor ESR is typically minimal, resulting in less than a few degrees rise in hot-spot temperature. Inductor Selection The step-down converter uses peak current mode control with slope compensation to maintain stability for duty cycles greater than 50%. The output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. The internal slope compensation for the AAT2552 is 0.45A/μsec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.8V output and 3.0μH inductor. ⎛ VOUT ⎞ ⎛ 3.3V ⎞ R2 = V -1 · R3 = 0.6V - 1 · 59kΩ = 267kΩ ⎝ REF ⎠ ⎝ ⎠ With enhanced transient response for extreme pulsed load application, an external feed-forward capacitor (C8 in Figure 5) can be added. R3 = 59kΩ R2 (kΩ) 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 VOUT (V) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 R3 = 221kΩ R2 (kΩ) 75 113 150 187 221 261 301 332 442 464 523 715 1000 m= L= 0.75 ⋅ VO 0.75 ⋅ 1.8V A = = 0.45 L 3.0µH µsec µsec 0.75 ⋅ VO ≈ 1.67 A ⋅ VO A 0.45A µsec 0.75 ⋅ VO = m For most designs, the step-down converter operates with inductor values from 1μH to 4.7μH. Table 6 displays inductor values for the AAT2552 for various output voltages. Manufacturer’s specifications list both the inductor DC current rating, which is a thermal limitation, and the Table 3: Adjustable Resistor Values For Step-Down Converter. 22 www.analogictech.com 2552.2008.02.1.2 PRODUCT DATASHEET AAT2552178 SystemPowerTM Adjustable Output Voltage for the LDO Total Power Solution for Portable Applications Printed Circuit Board Layout Considerations For the best results, it is recommended to physically place the battery pack as close as possible to the AAT2552 BAT pin. To minimize voltage drops on the PCB, keep the high current carrying traces adequately wide. Refer to the AAT2552 evaluation board for a good layout example (see Figures 6 and 7). The following guidelines should be used to help ensure a proper layout. 1. The input capacitors (C1, C6) should connect as closely as possible to ADP, INA, and INB. It is possible to use two input capacitors for INA and INB. C4 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. Do not make the node small by using narrow trace. The trace should be kept wide, direct, and short. The feedback pin should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high-current load trace will degrade DC load regulation. Feedback resistors should be placed as closely as possible to the FBB pin to minimize the length of the high impedance feedback trace. If possible, they should also be placed away from the LX (switching node) and inductor to improve noise immunity. The resistance of the trace from PGND should be kept to a minimum. This will help to minimize any error in DC regulation due to differences in the potential of the internal signal ground and the power ground. A high density, small footprint layout can be achieved using an inexpensive, miniature, non-shielded, high DCR inductor. The output voltage for the LDO can be programmed by an external resistor divider network. As shown below, the selection of R4 and R5 is a straightforward matter. R5 is chosen by considering the tradeoff between the feedback network bias current and resistor value. Higher resistor values allow stray capacitance to become a larger factor in circuit performance whereas lower resistor values increase bias current and decrease efficiency. To select appropriate resistor values, first choose R5 such that the feedback network bias current is reasonable. Then, according to the desired VOUT, calculate R4 according to the equation below. An example calculation follows. 2. R4 = ⎛ VOUT ⎞ - 1 · R5 ⎝ VREF ⎠ 3. An R5 value of 59kΩ is chosen, resulting in a small feedback network bias current of 1.24V/59kΩ ≈ 21μA. The desired output voltage is 1.8V. From this information, R4 is calculated from the equation below. The result is R4 = 26.64kΩ. Since 26.64kΩ is not a standard 1%-value, 26.7kΩ is selected. From this example calculation, for VOUT = 1.8V, use R5 = 59kΩ and R4 = 26.7kΩ. Example output voltages and corresponding resistor values are provided in Table 4. R4 Standard 1% Values VOUT (V) 3.3 2.8 2.5 2.0 1.8 1.5 4. (R5 = 59kΩ) R4 (kΩ) 97.6 75.0 60.4 36.5 26.7 12.4 5. Table 4: Adjustable Resistor Values for the LDO. 2552.2008.02.1.2 www.analogictech.com 23 PRODUCT DATASHEET AAT2552178 AAT2552178 SystemPowerTM JP1 21 Total Power Solution for Portable Applications EN_BAT ADP 321 Power Selection BAT D1 RED LED Sync/Mode R6 1.5K C1 10μF U1 15 16 1 6 C6 10μF (at bottom layer) 10 11 7 5 14 2 JP2 1 2 EN_LDO JP3 1 2 VoB C4 100pF R2 (Optional) C3 4.7μF ADP STAT EN_BAT MODE LX FBB AGND PGND INA INB ENA ENB BAT ISET OUTA FBA EN_BUCK L1 12 4 3 13 VoA 9 8 C2 10μF R1 8.06K C5 4.7μF R4 R3 59k R5 59k VOUTB (V) R2 (Ω) 0.6 13 1.2 1.8 2.5 3.0 3.3 R2 short, R3 open 9.2K 59K 118K 187K 237K 267K L1 1.5μH (CDRH2D09/HP; DCR 88mΩ; 730mA @ 20°C) 2.2μH (CDRH2D09/HP; DCR 115mΩ; 600mA @ 20°C) 3.0μH (CDRH2D09/HP; DCR 150mΩ; 470mA @ 20°C) 3.9μH (CDRH2D09/HP; DCR 180mΩ; 450mA @ 20°C) 4.7μH (CDRH2D09/HP; DCR 230mΩ; 410mA @ 20°C) 5.6μH (CDRH2D09/HP; DCR 260mΩ; 370mA @ 20°C) VOUTA (V) 1.24 1.5 1.8 2.0 2.5 2.8 3.0 R4 (Ω) R4 short, R5 open 12.4K 26.7K 36.5K 60.4K 75.0K 97.6K Figure 5: AAT2552 Evaluation Board Schematic. Figure 6: AAT2552 Evaluation Board Top Side Layout. Figure 7: AAT2552 Evaluation Board Bottom Side Layout. 24 www.analogictech.com 2552.2008.02.1.2 PRODUCT DATASHEET AAT2552178 AAT2552178 Manufacturer AnalogicTech Panansonic Murata Murata Murata Sumida Vishay Vishay Vishay Vishay Vishay Sullins Electronics Chicago Miniature Lamp SystemPowerTM Component U1 C1, C2 C3, C5 C6 C4 L1 R6 R1 R2 R3, R5 R4 JP1, JP2, JP3, JP4 D1 Total Power Solution for Portable Applications Part Number AAT2552IRN ECJ-1VB0J106M GRM188R60J475KE19 GRM319R61A106KE19 GRM1886R1H101JZ01J CDRH2D09 Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor PRPN401PAEN CMD15-21SRC/TR8 Description Total Power Solution for Portable Applications CER 10μF 6.3V X5R 0603 CER 4.7μF 6.3V X5R 0603 CER 10μF 10V X5R 1206 CER 100pF 50V 5% R2H 0603 Shielded SMD, 3x3x1mm 1.5KΩ, 5%, 1/4W 0603 8.06KΩ, 1%, 1/4W 0603 118KΩ, 1%, 1/4W 0603 59KΩ, 1%, 1/4W 0603 60.4KΩ, 1%, 1/4W 0603 Conn. Header, 2mm zip Red LED 1206 Table 5: AAT2552 Evaluation Board Component Listing. 2552.2008.02.1.2 www.analogictech.com 25 PRODUCT DATASHEET AAT2552178 AAT2552178 SystemPowerTM Total Power Solution for Portable Applications Step-Down Converter Design Example (to be updated) Specifications VO VIN FS TAMB = = = = 1.8V @ 250mA, Pulsed Load ΔILOAD = 200mA 2.7V to 4.2V (3.6V nominal) 1.5MHz 85°C 1.8V Output Inductor L1 = 1.67 µsec µsec ⋅ VO2 = 1.67 ⋅ 1.8V = 3µH (use 3.0μH; see Table 3) A A For Sumida inductor CDRH2D09-3R0, 3.0μH, DCR = 150mΩ. ΔIL1 = ⎛ VO V⎞ 1.8V 1.8V ⎞ ⎛ ⋅ 1- O = ⋅ 1= 228mA L1 ⋅ FS ⎝ VIN⎠ 3.0µH ⋅ 1.5MHz ⎝ 4.2V ⎠ IPKL1 = IO + ΔIL1 = 250mA + 114mA = 364mA 2 PL1 = IO2 ⋅ DCR = 250mA2 ⋅ 150mΩ = 9.375mW 1.8V Output Capacitor VDROOP = 0.1V COUT = 3 · ΔILOAD 3 · 0.2A = = 4µF (use 4.7µF) 0.1V · 1.5MHz VDROOP · FS (VO) · (VIN(MAX) - VO) 1 1.8V · (4.2V - 1.8V) · = 66mArms = L1 · FS · VIN(MAX) 2 · 3 3.0µH · 1.5MHz · 4.2V 2· 3 1 · IRMS = Pesr = esr · IRMS2 = 5mΩ · (66mA)2 = 21.8µW Input Capacitor Input Ripple VPP = 25mV CIN = ⎛ VPP ⎝ IO 1 1 = = 1.38µF (use 4.7µF) ⎞ ⎛ 25mV ⎞ - 5mΩ · 4 · 1.5MHz - ESR · 4 · FS ⎠ ⎝ 0.2A ⎠ IRMS = IO = 0.1Arms 2 P = esr · IRMS2 = 5mΩ · (0.1A)2 = 0.05mW 26 www.analogictech.com 2552.2008.02.1.2 PRODUCT DATASHEET AAT2552178 AAT2552178 SystemPowerTM AAT2552 Losses PTOTAL = IO2 · (RDSON(H) · VO + RDSON(L) · [VIN -VO]) VIN Total Power Solution for Portable Applications + (tsw · FS · IO + IQ) · VIN = 0.22 · (0.59Ω · 1.8V + 0.42Ω · [4.2V - 1.8V]) 4.2V + (5ns · 1.5MHz · 0.2A + 30µA) · 4.2V = 26.14mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 26.14mW = 86.3°C 2552.2008.02.1.2 www.analogictech.com 27 PRODUCT DATASHEET AAT2552178 AAT2552178 L1 (μH) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2.2 2.7 3.0/3.3 3.0/3.3 3.0/3.3 3.9/4.2 4.9 5.6 SystemPowerTM Output Voltage VOUTB (V) 0.6 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3 3.3 Total Power Solution for Portable Applications R3 = 59kΩ R3 (kΩ) R2 short, R3 open 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 237 267 R3 = 221kΩ R1 (kΩ) R2 short, R3 open 75 113 150 187 221 261 301 332 442 464 523 715 887 1000 Table 6: Step-Down Converter Component Values. Inductance (μH) 1.5 2.2 2.5 3.0 3.9 4.7 5.6 1.5 2.2 3.3 4.7 1.5 2.2 3.3 4.7 1.5 2.2 3.0 4.2 Manufacturer Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Taiyo Yuden Taiyo Yuden Taiyo Yuden Taiyo Yuden FDK FDK FDK FDK Part Number CDRH2D09-1R5 CDRH2D09-2R2 CDRH2D09-2R5 CDRH2D09-3R0 CDRH2D09-3R9 CDRH2D09-4R7 CDRH2D09-5R6 CDRH2D11-1R5 CDRH2D11-2R2 CDRH2D11-3R3 CDRH2D11-4R7 NR3010T1R5N NR3010T2R2M NR3010T3R3M NR3010T4R7M MIPWT3226D-1R5 MIPWT3226D-2R2 MIPWT3226D-3R0 MIPWT3226D-4R2 Max DC Current (mA) 730 600 530 470 450 410 370 900 780 600 500 1200 1100 870 750 1200 1100 1000 900 DCR (mΩ) 110 144 150 194 225 287 325 68 98 123 170 80 95 140 190 90 100 120 140 Size (mm) LxWxH 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.2x2.6x0.8 3.2x2.6x0.8 3.2x2.6x0.8 3.2x2.6x0.8 Type Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Chip shielded Chip shielded Chip shielded Chip shielded Table 7: Suggested Inductors and Suppliers. 1. For reduced quiescent current, R3 = 221kΩ. 28 www.analogictech.com 2552.2008.02.1.2 PRODUCT DATASHEET AAT2552178 AAT2552178 Case Size 0805 0603 0603 0603 0603 0603 SystemPowerTM Manufacturer Murata Murata Murata Murata Murata Murata Total Power Solution for Portable Applications Part Number GRM21BR61A106KE19 GRM188R60J475KE19 GRM188R61A225KE34 GRM188R60J225KE19 GRM188R61A105KA61 GRM185R60J105KE26 Value (μF) 10 4.7 2.2 2.2 1.0 1.0 Voltage Rating 10 6.3 10 6.3 10 6.3 Temp. Co. X5R X5R X5R X5R X5R X5R Table 8: Surface Mount Capacitors. 2552.2008.02.1.2 www.analogictech.com 29 PRODUCT DATASHEET AAT2552178 AAT2552178 SystemPowerTM Ordering Information Package TDFN34-16 Total Power Solution for Portable Applications Marking1 UVXYY Part Number (Tape and Reel)2 AAT2552IRN-CAE-T1 All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/about/quality.aspx. Legend Voltage Adjustable (0.6) 0.9 Adjustable (1.2) 1.5 1.8 1.9 2.5 2.6 2.7 2.8 2.85 2.9 3.0 3.3 4.2 Code A B E G I Y N O P Q R S T W C 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 30 www.analogictech.com 2552.2008.02.1.2 PRODUCT DATASHEET AAT2552178 AAT2552178 SystemPowerTM Package Information1 Total Power Solution for Portable Applications TDFN34-16 3.000 ± 0.050 1.600 ± 0.050 Detail "A" Index Area 4.000 ± 0.050 3.300 ± 0.050 0.350 ± 0.100 Top View Bottom View C0.3 0.230 ± 0.050 (4x) 0.850 MAX 0.050 ± 0.050 0.229 ± 0.051 Side View Detail "A" All dimensions in millimeters. 1. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611 © Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. 2552.2008.02.1.2 www.analogictech.com 0.450 ± 0.050 Pin 1 Indicator (optional) 31