PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch General Description Features The AAT1275 SwitchReg is a 2MHz, 500mA synchronous boost converter with an integrated current-limiting load switch controlled output. The AAT1275 operates from a single-cell Lithium-ion/ polymer battery source and provides a regulated 5V, current limit controlled output to support USB port VBUS applications in portable consumer electronic products. The AAT1275 can support both USB 2.0 host port and USB on-the-go operation, as well as general purpose applications where a 5V supply with a user programmable current limit is needed. • High Frequency Boost With 5V / 500mA Output Capability From a Single-Cell Lithium-Ion/Polymer Battery • Input Voltage Range: 2.7V to 5V • VOUT1 Adjustable or Fixed (5V) • >90% Efficiency • Up to 2MHz Switching Frequency • True Load Disconnect • Load Switch With Programmable Current Limit • Over-Temperature, Over-Current Protection • Inrush Current Limit • Fault Report • Low Shutdown Current < 1µA Typical • -40°C to +85°C Temperature Range • TSOPJW-12 and TDFN34-16 Packages The high efficiency boost converter section of the AAT1275 is typically set for a 5V output and can deliver up to 500mA load current to support USB VBUS operation from an input supply as low as 2.7V. The high boost converter switching frequency (up to 2.0MHz) provides fast load transient and allows the use of small external components. Fully integrated control circuitry simplifies system design and reduces total solution size. Applications • • • • • • The integrated, programmable current limiting load switch provides USB port protection for portable devices allowing the AAT1275 to supply a 5V USB VBUS up to 500mA. The load switch provides an active low fault flag to alert the system in the event of an over-current condition applied to the AAT1275 output. USB On-the-Go Cell Phones Digital Still Cameras PDAs and Portable Media Players Smart Phones Other Hand-Held Devices The AAT1275 is available in the Pb-free, space-saving 12-pin TSOPJW and 16-pin TDFN34 packages and is rated over the -40°C to +85°C operating temperature range. Typical Application L1 2.2µH LIN VIN SW OUT1 IN CIN 4.7µF RFB1 432k VCC FB 10k AAT1275 Fault RFB2 59k FLT Enable EN VBUS Output OUT2 SET RSET 1275.2008.04.1.7 COUT1 4.7µF COUT2 1µF GND www.analogictech.com 1 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Pin Descriptions Pin TSOPJW-12 TDFN34-16 Symbol 1 2 3 4 5 6 1, 16 3, 15 13, 14 11, 12 10 9 LIN IN PGND SW OUT1 OUT2 7 8 SET 8 7 FLT 9 10 11 12 6 5 4 2 FB GND VCC EN EP Function Switched power input. Connect an inductor between this pin and the SW pin. Supply input. Connect to VCC for proper operation. Power ground. Switch pin. Boost inductor is connected between SW and LIN. Boost converter output. Load switch output. Load switch current limit programming pin. Connect a set resistor between this pin and ground. Load switch over-current or over-temperature fault flag. Active low, open-drain output. A 10kΩ external pull-up resistor is recommended. Boost converter voltage feedback pin. Ground. Bias supply for the internal circuitry. Connect to IN for proper operation. Enable pin, active high. Exposed paddle (bottom); connect to ground directly beneath the package. Pin Configuration TSOPJW-12 (Top View) 2 TDFN34-16 (Top View) LIN 1 16 LIN EN 2 15 IN IN 3 14 PGND VCC 4 13 PGND GND 5 12 SW FLT FB 6 11 SW SET FLT 7 10 OUT1 SET 8 9 OUT2 LIN 1 12 EN IN 2 11 VCC PGND 3 10 GND SW 4 9 FB OUT1 5 8 OUT2 6 7 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Absolute Maximum Ratings Symbol VCC, IN, OUT SW LIN, FB EN, SET, FLT TJ TLEAD Description IN, OUTx to GND SW to GND LIN, FB to GND EN, SET, FLT to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units 6.0 -0.3 to VOUT + 0.3 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -40 to 150 300 V V V V °C °C Value Units Thermal Characteristics1 Symbol Description θJA Maximum Thermal Resistance PD Maximum Power Dissipation @ TA = 25°C TSOPJW-12 TDFN34-16 TSOPJW-12 TDFN34-16 110 50 909 2.0 °C/W mW W 1. Mounted on an FR4 board. 1275.2008.04.1.7 www.analogictech.com 3 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Electrical Characteristics1 VCC = VIN = 3.6V, VOUT1 = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol VIN, VCC VOUTx VUVLO IQ Description Conditions Operating Input Voltage Range Maximum Output Voltage Range Under-Voltage Lockout FOSC Typ 2.7 No Load, Switching No Load, Not Switching, VFB = 1.5V EN = GND Quiescent Supply Current ISHDN Shutdown Current Boost Converter Continuous Output Current IO ILIMIT Input Switch Current Limit VFB FB Pin Regulation VOUT Output Voltage Tolerance ∆VOUT Load Regulation (VOUT*∆VIN) ∆VOUT/VOUT Line Regulation RDS(ON)H High Side Switch On Resistance RDS(ON)L Low Side Switch On Resistance RDS(ON)_IN Input Disconnect Switch TSS Soft-Start Time η Min 100 45 3V < VIN < 5V, VO = 5V No Load, TA = 25°C ILOAD = 0 to 500mA, VIN = 2.7V to 5V 0.591 -3 VIN = 2.7V to 5V VOUT1 = 5V, IOUT1 = 500mA VOUT1 = 5V, IOUT1 = 500mA VOUT1 = 5V, IOUT1 = 500mA From Enable to Output Regulation IOUT1 = 250mA, L = 2.2µH, VIN = 3.6V, VOUT1 = 5V TA = 25°C, IOUT1 = 500mA, VIN = 3.6V, VOUT1 = 5V Switching Frequency Load Switch RDS(ON) Current Limit Switch On Resistance Current Limit ILIM ILIM(MIN) Minimum Current Limit TRESP Current Limit Response Time TON Turn-On Delay Time TOFF Turn-Off Delay Time VFLT_LOW FLT Logic Output Low IFLT FLT Logic Output High Leakage Current Fault Blanking Time TBLANK Control VTH-L EN Threshold Low VTH-H EN Threshold High IEN EN Input Leakage TJ-TH TJ Thermal Shutdown Threshold TJ-HYS TJ Thermal Shutdown Hysteresis Units 5.0 5.5 2.7 V V V 90 1.0 500 ILOAD = 0 to 500mA Efficiency Max VOUT1 = 5V, TA = 25°C RSET = 16.9kΩ RSET = 40kΩ VOUT1 = 5V VOUT1 = 5V, RL = 10Ω VOUT1 = 5V, RL = 10Ω ISINK = 1mA VFAULT = 5V Rising and Falling Edge 2.5 0.6 0.609 3 µA mA A V % 0.005 %/mA 0.2 200 170 170 300 %/V mΩ mΩ mΩ µs 90 % 2.0 MHz 500 100 0.4 4 10 0.5 4 0.2 625 0.4 1 0.4 VEN = 5V, VIN = 5V µA 1.4 -1 1 140 15 Ω mA mA µs ms µs V µA ms V V µA °C °C 1. The AAT1275 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. 4 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Typical Characteristics Efficiency vs. Load DC Regulation (VOUT = 5.0V) 1.5 80 60 VIN = 4.2V VIN = 3.6V VIN = 2.7V Output Error (%) Efficiency (%) 100 40 20 0 0.1 1 10 100 VIN = 4.2V 1.0 0.5 0.0 -1.0 -1.5 0.1 1000 1 Line Regulation 100 1000 Output Voltage vs. Temperature (VIN = 3.6V; 50Ω Ω Load) (IOUT = 300mA) 4.960 0.1 4.958 Output Voltage (V) Output Voltage Accuracy (%) 10 Output Current (mA) Output Current (mA) 4.956 4.954 4.952 4.950 4.948 4.946 4.944 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 4.942 4.940 VIN = 3.6V VIN = 2.7V -0.5 3.6 3.7 3.8 3.9 4.0 4.1 -0.7 4.2 -50 -25 0 Input Voltage (V) 25 50 75 100 Temperature (°C) No Load Current vs. Supply Voltage No Load Current vs. Temperature (VIN = 3.6V; VOUT = 5.0V) 140 120 No Load Current (µA) No Load Current (µA) 140 85°C 100 80 -40°C 60 25°C 40 20 0 2.7 2.9 3.2 3.4 3.6 3.9 4.1 4.3 4.5 4.8 5.0 120 100 80 60 40 20 0 0 50 100 150 Temperature (°°C) Supply Voltage (V) 1275.2008.04.1.7 -50 www.analogictech.com 5 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Typical Characteristics Light Load Switching Waveform Heavy Load Switching Waveform (VIN = 3.6V; VOUT = 5.0V; 10mA Load) (VIN = 3.6V; VOUT = 5.0V; 500mA Load) VLX (2V/div) VLX (2V/div) VOUT1 (25mV/div) VOUT1 (100mV/div) VOUT2 (100mV/div) ILX (500mA/div) VOUT2 (25mV/div) ILX (500mA/div) Time (5µs/div) Time (500ns/div) Load Transient Response Load Transient Response (VIN = 3.6V; VOUT = 5.0V) (VIN = 3.6V; VOUT = 5.0V) 5.062V 5.0V VOUT (100mV/div) VOUT (50mV/div) 4.87V 500mA 4.92V 500mA IOUT (400mA/div) IOUT (200mA/div) 1mA 250mA Time (100µs/div) Time (100µs/div) Load Switch RDS(ON) vs. Input Voltage Line Transient Response (16Ω Ω Load) 250 85°C 4.2V VIN (500mV/div) RDS(ON) (mΩ Ω) 3.6V 5.064V VOUT (200mV/div) 150 100 -40°C 25°C 50 4.752V 0 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 Supply Voltage (V) Time (100µs/div) 6 120°C 200 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Typical Characteristics P-Channel RDS(ON) vs. Supply Voltage N-Channel RDS(ON) vs. Supply Voltage 350 320 100°C 260 85°C 240 220 25°C 200 100°C 300 125°C 280 RDS(ON) (mΩ Ω) RDS(ON) (mΩ Ω) 300 125°C 250 85°C 200 25°C 150 180 100 160 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 2.5 4.5 Supply Voltage (V) 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 Supply Voltage (V) Enable Soft Start Enable Soft Start (VIN = 3.6V; 500mA Load) (VIN = 4.2V; 500mA Load) EN (2V/div) EN (2V/div) VOUT2 (2V/div) VOUT2 (2V/div) VOUT1 (2V/div) VOUT1 (2V/div) IIN (500mA/div) IIN (500mA/div) Time (1ms/div) Time (1ms/div) Enable Soft Start Shutdown (VIN = 3.6V; CVOUT2 = 120µF; 16Ω Ω Load) (VIN = 3.6V; CVOUT2 = 120µF; 16Ω Ω Load) EN (2V/div) EN (2V/div) VOUT1 (1V/div) VOUT1 (2V/div) VOUT2 (2V/div) VOUT2 (2V/div) Time (100µs/div) 1275.2008.04.1.7 2.7 Time (50ms/div) www.analogictech.com 7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Typical Characteristics Current Limit vs. RSET Current Limit vs. Temperature (RSET = 20.3kΩ Ω) 6.0 RSET (kΩ Ω) Current Limit (%) 100 10 100 4.0 2.0 0.0 -2.0 -4.0 -6.0 -50 1000 -25 Switching Frequency vs. Input Voltage 50 75 100 Switching Frequency vs. Temperature (VIN = 3.6V; 16.5Ω Ω Load; L = 2.2µH) (24W Load; L = 2.2µH) 1000 940 800 920 FS (kHz) FS (kHz) 25 Temperature (°C) Current Limit (mA) 600 400 200 900 880 860 840 820 0 3.0 3.2 3.4 3.6 3.8 4.0 4.2 Input Voltage (V) 8 0 -50 -25 0 25 50 75 100 Temperature (°C) www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Functional Block Diagram LIN SW OUT1 IN VCC Boost Regulator Control FB EN OUT2 SET Load Switch Control FLT GND Functional Description Control Scheme The AAT1275 is a 500mA synchronous boost converter with a current-limited load switch targeted for single-cell Lithium-ion/polymer devices acting as a portable host for USB power. The control circuit uses hysteretic current mode control with internal inductor current sensing for very high efficiency over a wide output current range. For heavy load, the boost converter operates in continuous conduction mode (CCM). This minimizes the RMS current and optimizes the efficiency at load conditions where the losses are dominated by the power MOSFET RDS(ON). This also keeps the ripple current to a minimum and minimizes the output voltage ripple and the output capacitor size. A zero current comparator senses the inductor current and prevents reverse current flow for optimum light load efficiency. The AAT1275 has integrated control and synchronous MOSFETs, minimizing the cost and the number of external components. Additional features include a soft-start function which allows the load voltage to ramp up in a controlled manner, eliminating output voltage overshoot and minimizing inrush current. Typical soft-start time for the boost converter is approximately 300µs. The AAT1275 also has a load switch with user-programmable current limiting. The load switch reports overcurrent and over-temperature conditions through an open-drain fault reporting signal (FLT). The fault reporting signal has a 4ms turn-on delay. 1275.2008.04.1.7 www.analogictech.com 9 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Step-Up Converter Application Information Soft Start / Enable The AAT1275 step-up converter provides the benefits of current mode control with a simple hysteretic feedback loop. The device maintains exceptional DC regulation, transient response, and cycle-by-cycle current limit without additional compensation components. The AAT1275 modulates the power MOSFET switching current in response to changes in output voltage. The voltage loop programs the required inductor current in response to changes in the output load and input voltage. The switching cycle initiates when the N-channel MOSFET is turned ON and the inductor current ramps up. The ON interval is terminated when the inductor current reaches the programmed peak current level. During the OFF interval, the input current decays until the lower threshold, or zero inductor current is reached. The lower current is equal to the peak current minus a preset hysteresis threshold, which determines the inductor ripple current. The peak current is adjusted by the controller until the output current requirement is met. The magnitude of the feedback error signal determines the average input current. Therefore, the AAT1275 boost controller implements a programmed current source connected to the output capacitor and load resistor. There is no right-half plane zero, and loop stability is achieved with no additional external compensation components. At light load, the inductor OFF interval current goes to zero and the boost converter enters discontinuous mode operation. Further reduction in the load results in a corresponding reduction in the switching frequency, which reduces switching losses and maintains high efficiency at light loads. The operating frequency varies with changes in the input voltage, output voltage, and inductor size. Once the boost converter has reached continuous mode, increasing the output load will not significantly change the operating frequency. A small 2.2µH (± 20%) inductor is selected to maintain high frequency operation for the 5V USB output voltage. Input Current Limit and Over-Temperature Protection The switching of the N-channel MOSFET terminates when input current limit of 2.5A (typical) is exceeded. This minimizes the power dissipation and component stresses under overload and short-circuit conditions. Switching resumes when the current decays below the limit. Thermal protection disables the AAT1275 boost converter when the internal power dissipation becomes excessive. The junction over-temperature threshold is 140°C with 15°C of temperature hysteresis. The output voltage automatically recovers when the over-temperature or over-current fault condition is removed. Shutdown and Output Disconnect A typical synchronous step-up (boost) converter has a conduction path from the input to the output via the body diode of the P-channel MOSFET. The AAT1275 design disconnects this body diode from the output and eliminates this conduction path. This enables the AAT1275 to provide true load disconnect during shutdown and inrush current limit at turn-on. Short-Circuit Protection The P-channel synchronous MOSFET body diode disconnect feature also gives the AAT1275 the ability to provide output short-circuit current limit protection. Under-Voltage Lockout Output Voltage Programming The output voltage is programmed through a resistor divider network located from the OUT1 output capacitor to the FB pin to ground. 10 The input disconnect switch is activated when a valid input voltage is present and the EN pin is pulled high. The slew rate control on the P-channel MOSFET ensures minimal inrush current as the output voltage is charged to the input voltage prior to switching of the N-channel power MOSFET. The soft-start circuitry guarantees monotonic turn-on and eliminates output voltage overshoot across the full input voltage range for all load conditions. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to soft start. Internal bias of all circuits is controlled via the VCC input, which is connected to VIN. www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Selecting the Boost Inductor The AAT1275 boost controller utilizes hysteretic control and the switching frequency varies with output load and input voltage. The value of the inductor determines the maximum switching frequency of the boost converter. Increasing output inductance decreases the switching frequency, resulting in higher peak currents and increased output voltage ripple. To maintain the 2MHz switching frequency and stable operation, an output inductor sized from 1.5µH to 2.7µH is recommended. Manufacturer’s specifications list both the inductor DC current rating, which is a thermal limitation, and peak inductor current rating, which is a function of the saturation characteristics. Measure the inductor current at full load and high ambient temperature to ensure that the inductor does not saturate or exhibit excessive temperature rise. Select the output inductor (L) to avoid saturation at the minimum input voltage and maximum load. The RMS current flowing through the boost inductor is equal to the DC plus AC ripple components. The maximum inductor RMS current occurs at the minimum input voltage and the maximum load. Use the following equations to calculate the maximum peak and RMS current: DMAX = VO - VIN(MIN) VO VIN(MIN) · D L · FS IPP = IP = Shielded inductors provide decreased EMI and may be required in noise sensitive applications. Unshielded chip inductors provide significant space savings at a reduced cost compared to shielded inductors. In general, chiptype inductors have increased winding resistance (DCR) when compared to shielded, wound varieties. Selecting the Step-Up Converter Capacitors The high output ripple inherent in the boost converter necessitates low impedance output filtering. Multi-layer ceramic (MLC) capacitors provide small size, adequate capacitance, with low parasitic equivalent series resistance (ESR) and equivalent series inductance (ESL). This makes them well suited for use with the AAT1275. MLC capacitors of type X7R or X5R ensure good capacitance stability over the full operating range. MLC capacitors exhibit significant capacitance reduction with an applied DC voltage. Output ripple measurements can confirm that the capacitance used meets the specific ripple requirements. Voltage derating minimizes this factor, but results may vary with package size and among specific manufacturers. Use a 4.7µF 10V ceramic output capacitor to minimize output ripple for the 5V output. Small 0805 sized ceramic capacitors are available which meet these requirements. IO 1-D IPK = IP + Compare the RMS current values with the manufacturer’s temperature rise, or thermal derating guidelines. For a given inductor type, smaller inductor size leads to an increase in DCR winding resistance and, in most cases, increased thermal impedance. Winding resistance degrades boost converter efficiency and increases the inductor’s operating temperature. IPP 2 Estimate the output capacitor required at the minimum switching frequency (FS) of 800kHz (worst-case). IV = IP - IPP IRMS = 2 PK I COUT = 2 + IPK · IV + IV 3 PLOSS(INDUCTOR) = I2RMS · DCR At light load and low output voltage, the controller reduces the operating frequency to maintain maximum efficiency. As a result, further reduction in output load does not reduce the peak current. The minimum peak current ranges from 0.5A to 0.75A. 1275.2008.04.1.7 IOUT · DMAX FS · ∆VOUT The boost converter input current flows during both ON and OFF switching intervals. The input ripple current is less than the output ripple and, as a result, less input capacitance is required. A ceramic output capacitor from 1µF to 4.7µF is recommended. Minimum 6.3V rated capacitors are required at the input. Ceramic capacitors sized as small as 0603 are available which meet these requirements. www.analogictech.com 11 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Setting the Output Voltage Program the output voltage through a resistive divider located from the output to the FB pin to ground. The internal error amplifier reference voltage is 0.6V. A 59.0kΩ programming resistor value from VFB to GND with a 432kΩ resistor from FB to the output will set the output voltage to 5V. R2⎞ ⎛ VOUT = VREF · 1 + R3 ⎝ ⎠ load is removed, power is removed, or until a logic low level is applied to the EN pin. A fault flag indicates when the OUT2 pin load current has exceeded the current limit level set by RSET. The fault flag is an active low, open-drain pin that requires 10kΩ pullup to VIN. The fault signal has a 4ms blanking time to prevent false over current indicator during the charging of the USB bus capacitor. Steady-State Maximum Power Dissipation 432kΩ ⎞ ⎛ = 0.6V · 1 + 59.0kΩ ⎝ ⎠ The maximum power dissipation for the AAT1275 occurs at the minimum input voltage, where it operates in continuous conduction mode (CCM). The total power dissipation at full load is dominated by the RDS(ON) losses of the power MOSFET. The dissipation includes the losses in the input and output switch, as well as both synchronous switches. = 5.0V USB Load Switch Application Information Setting the Load Switch Current Limit In most applications, the variation in ILIM must be taken into account when determining RSET. The ILIM variation is due to processing variations from part to part, as well as variations in the voltages at OUT1 and OUT2, plus the operating temperature. The typical RSET value for a 300mA load is in the range of 20 to 22kΩ. RSET (kΩ) IOUT (mA) 11 12 14 16 18 20 30 40 740 690 590 550 450 420 160 100 Due to the magnitude of the inductor ripple current, it cannot be neglected when analyzing the RDS(ON) power dissipation. Once the ripple current has been determined, the RMS current during the on and the off period can be calculated. DMAX = IPP = VO - VIN(MIN) VO VIN(MIN) · DMAX L · FS IP = IO 1-D IPK = IP + IV = IP - IPP Table 1: Load Switch Current Limit vs. RSET. Operation in Current Limit IRMS(ON) = When a heavy load is applied to OUT2 of the AAT1275, the load current is limited to the value of ILIM (determined by RSET) causing a drop in the output voltage. This increases the AAT1275 power dissipation and die temperature. When the die temperature exceeds the overtemperature limit, the AAT1275 shuts down until it has cooled sufficiently, at which point it will start up again. The AAT1275 will continue to cycle on and off until the IPP 2 IRMS(OFF) = (IP2 + IPK · IV + IV2) · DMAX 3 (IP2 + IPK · IV + IV2) · (1 - DMAX) 3 PTOTAL = IRMS(ON)2 · (RDS(ON)IN + RDS(ON)N) + IRMS(OFF)2 · (RDS(ON)IN + RDS(ON)P + RDS(ON)) TJ(MAX) = PTOTAL · θJA + TAMB 12 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch RDS(ON)IN is the input disconnect switch, RDS(ON)N is the high-side synchronous switch, RDS(ON)P is the low-side synchronous switch, and RDS(ON) is the current limit load switch. PCB Layout Guidelines The step-up converter performance can be adversely affected by poor layout. Possible impact includes high input and output voltage ripple, poor EMI performance, and reduced operating efficiency. Every attempt should be made to optimize the layout in order to minimize parasitic PCB effects (stray resistance, capacitance, inductance) and EMI coupling from the high frequency SW node. Figure 1: AAT1275 TSOPJW-12 Package Evaluation Board Top Side Layout. 1275.2008.04.1.7 A suggested PCB layout for the AAT1275 is shown in Figures 1 and 2. The following PCB layout guidelines should be considered: 1. Minimize the distance from capacitors C2 and C3 to the IC. This is especially true for the output capacitor C2, which conducts high ripple current associated with the step-up converter output capacitor. 2. Place the feedback resistor close to the output terminals. Route the output pin directly to resistor R2 to maintain good output regulation. R3 should be routed close to the output GND pin and should not share a significant return path with output capacitor C2. 3. Minimize the distance between L1 and the switching pin SW; minimize the size of the PCB area connected to the SW pin. 4. Maintain a ground plane and connect to the IC RTN pin(s), as well as the GND terminals of C1 and C2. Figure 2: AAT1275 TSOPJW-12 Package Evaluation Board Bottom Side Layout. www.analogictech.com 13 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch VIN L1 2.2µH 4 1 GND R4 7 16.9kΩ C6 120µF CCase SW LIN SET FLT 8 OUT2 6 OUT1 5 10 GND EN 12 11 VCC FB 9 PGND 3 2 VIN R1 10K U1 AAT1275 VIN FLT VO2 VO1 J5 R2 432k R3 59k C3 4.7µF 10V C2 4.7µF 10V C1 4.7µF GND VIN 3 2 GND 1 Enable Figure 3: AAT1275 TSOPJW-12 Package Evaluation Board Schematic. Figure 4: AAT1275 TDFN34-16 Package Evaluation Board Top Side Layout. 14 Figure 5: AAT1275 TDFN34-16 Package Evaluation Board Bottom Side Layout. www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch AAT1275-TDFN34-16 L1 2.2µH U1 1 3 VIN 4 C6 120µF R1 10K 15 3 2 1 LIN LIN VIN SW VCC SW VIN OUT2 2 EN OUT1 7 FLT 16 12 11 Feedback Option 1 2 3 9 VOUT2 10 Enable R5 1k 1 FB 6 PGND SET GND PGND GND 8 R2 432k FLT 13 C3 4.7µF 10V 14 C4 100pF VOUT1 C2 4.7µF 10V C1 4.7µF 10V 5 R4 16.9k R3 59k Figure 6: AAT1275 TDFN34-16 Package Evaluation Board Schematic. Manufacturer Part Number Value Voltage Temp. Co. Case Murata Murata Murata Murata GRM21BR61A475KA73L GRM18BR60J475KE19D GRM21BR60J106KE19 GRM21BR60J226ME39 4.7µF 4.7µF 10µF 22µF 10V 6.3V 6.3V 6.3V X5R X5R X5R X5R 0805 0603 0805 0805 Table 2: Typical Surface Mount Capacitors. Manufacturer Part Number Inductance (µH) Max DC Current (A) DCR (Ω) Size (mm) LxWxH Type Sumida Sumida Coiltronics Coiltronics CDRH2D14-2R2 CDRH4D11/HP-2R4 SD3112-2R2 SD3114-2R2 2.2 2.4 2.2 2.2 1.6 1.7 1.12 1.48 0.094 0.105 0.140 0.086 3.2x3.2x1.55 4.8x4.8x1.2 3.1x3.1x1.2 3.1x3.1x1.4 Shielded Shielded Shielded Shielded Table 3: Typical Surface Mount Inductors. 1275.2008.04.1.7 www.analogictech.com 15 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Step-Up Converter Design Example Specifications VOUT = 5V IOUT = 300mA VIN = 2.7V to 4.2V (3.6V nominal) TAMB = 50°C Output Inductor DMAX = VOUT - VIN(MIN) 5V - 2.7V = = 0.46 VOUT 5V From the characterization curves, the switching frequency at room temperature with a 300mA load and 2.2µH inductor is about 800kHz. IPP = IP = VIN(MIN) · DMAX L · FS IO 1-D IPK = IP + IPP 2 IV = IP - IPP IV = IP - IPP = 0.9A - 0.7A = 0.20A IRMS = IPK2 + IPK · IV + IV2 = 3 0.9A2 + 0.9A · 0.2A + 0.2A2 = 0.59A 3 For the Sumida CDRH2D14-2R2 inductor, ISAT = 1.0A, IDC(MAX) = 1.6A and DCR = 94mΩ. PLOSS(INDUCTOR) = I2RMS · DCR = (590mA)2 · 94mΩ = 32mW 5V Output Capacitor ∆VOUT = 0.05V COUT(MIN) = 16 IOUT · DMAX 0.3A · 0.46 = = 3.0µF; use 4.7µF 10V MLC FS · ∆VOUT 800kHz · 0.05V www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch AAT1275 Losses IRMS(ON) = IRMS(OFF) = (IPK2 + IPK · IV + IV2) · DMAX = 3 (0.9A2 + 0.9A · 0.2A + 0.2A2) · 0.46 = 0.4A 3 (IPK2 + IPK · IV + IV2) · (1 - DMAX) = 3 (0.9A2 + 0.9A · 0.2A + 0.2A2) · (1 - 0.46) = 0.43A 3 PTOTAL = IRMS(ON)2 · (RDS(ON)IN + RDS(ON)N) + IRMS(OFF)2 · (RDS(ON)IN + RDS(ON)P + RDS(ON)) = 0.4A2 · (0.25Ω + 0.3Ω) + 0.422 · (0.25Ω + 0.3Ω + 0.2Ω) = 0.22W TJ(MAX) = PTOTAL · θJA + TAMB = 0.22W · 1275.2008.04.1.7 110°C + 85°C = 109°C W www.analogictech.com 17 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch Ordering Information Package Marking1 Part Number (Tape and Reel)2 TSOPJW-12 TDFN34-16 USXYY USXYY AAT1275ITP-5.0-T1 AAT1275IRN-5.0-T1 Package Information3 TSOPJW-12 2.85 ± 0.20 2.40 ± 0.10 0.20 + 0.10 - 0.05 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 7° NOM 0.04 REF 0.055 ± 0.045 0.15 ± 0.05 + 0.10 1.00 - 0.065 0.9625 ± 0.0375 3.00 ± 0.10 4° ± 4° 0.45 ± 0.15 0.010 2.75 ± 0.25 All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. 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. 18 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch TDFN34-16 3.000 ± 0.050 1.600 ± 0.050 Detail "A" 3.300 ± 0.050 4.000 ± 0.050 Index Area 0.350 ± 0.100 Top View 0.230 ± 0.050 Bottom View C0.3 (4x) 0.050 ± 0.050 0.450 ± 0.050 0.850 MAX Pin 1 Indicator (optional) 0.229 ± 0.051 Side View Detail "A" All dimensions in millimeters. 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. 1275.2008.04.1.7 www.analogictech.com 19