AAT1275

PRODUCT DATASHEET AAT1275 SwitchRegTM General Description 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. 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. 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. 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. Boost Converter with USB Power Switch Features • 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 Applications • • • • • • USB On-the-Go Cell Phones Digital Still Cameras PDAs and Portable Media Players Smart Phones Other Hand-Held Devices Typical Application L1 2.2µH LIN SW OUT1 VIN CIN 4.7µF 10k IN VCC RFB1 432k FB COUT1 4.7µF AAT1275 Fault Enable FLT EN OUT2 SET RFB2 59k VBUS Output COUT2 1µF RSET GND 1275.2008.04.1.7 www.analogictech.com 1 PRODUCT DATASHEET AAT1275 AAT1275 SwitchRegTM Pin Descriptions Pin TSOPJW-12 1 2 3 4 5 6 7 8 9 10 11 12 TDFN34-16 1, 16 3, 15 13, 14 11, 12 10 9 8 7 6 5 4 2 Boost Converter with USB Power Switch Symbol LIN IN PGND SW OUT1 OUT2 SET FLT 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) TDFN34-16 (Top View) LIN IN PGND SW OUT1 OUT2 1 2 3 4 5 6 12 11 10 9 8 7 EN VCC GND FB FLT SET LIN EN IN VCC GND FB FLT SET 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 LIN IN PGND PGND SW SW OUT1 OUT2 2 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 AAT1275 SwitchRegTM Absolute Maximum Ratings Symbol VCC, IN, OUT SW LIN, FB EN, SET, FLT TJ TLEAD Boost Converter with USB Power Switch 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 6.0 -0.3 to VOUT + 0.3 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -40 to 150 300 Units V V V V °C °C Thermal Characteristics1 Symbol θJA PD Description Maximum Thermal Resistance Maximum Power Dissipation @ TA = 25°C TSOPJW-12 TDFN34-16 TSOPJW-12 TDFN34-16 Value 110 50 909 2.0 Units °C/W mW W 1. Mounted on an FR4 board. 1275.2008.04.1.7 www.analogictech.com 3 PRODUCT DATASHEET AAT1275 AAT1275 SwitchRegTM 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 Boost Converter with USB Power Switch Description Operating Input Voltage Range Maximum Output Voltage Range Under-Voltage Lockout Quiescent Supply Current Conditions Min 2.7 Typ Max 5.0 5.5 2.7 Units V V V µA µA mA A V % %/mA %/V mΩ mΩ mΩ µs % MHz 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 FOSC Efficiency Switching Frequency No Load, Switching No Load, Not Switching, VFB = 1.5V EN = GND 3V < VIN < 5V, VO = 5V No Load, TA = 25°C ILOAD = 0 to 500mA, VIN = 2.7V to 5V ILOAD = 0 to 500mA 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 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 0.591 -3 100 45 90 1.0 500 2.5 0.6 0.005 0.2 200 170 170 300 90 2.0 0.609 3 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 500 100 0.4 4 10 0.5 4 0.2 625 0.4 1 Ω mA mA µs ms µs V µA ms V V µA °C °C 0.4 VEN = 5V, VIN = 5V 1.4 -1 140 15 1 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 AAT1275 SwitchRegTM Typical Characteristics Efficiency vs. Load 100 1.5 Boost Converter with USB Power Switch DC Regulation (VOUT = 5.0V) 60 40 20 0 0.1 VIN = 2.7V VIN = 3.6V VIN = 4.2V Output Error (%) Efficiency (%) 80 1.0 0.5 0.0 -0.5 -1.0 -1.5 0.1 VIN = 4.2V VIN = 2.7V VIN = 3.6V 1 10 100 1000 1 10 100 1000 Output Current (mA) Output Current (mA) Line Regulation (IOUT = 300mA) Output Voltage Accuracy (%) 4.960 4.958 4.956 4.954 4.952 4.950 4.948 4.946 4.944 4.942 4.940 3.6 3.7 3.8 3.9 4.0 4.1 4.2 0.1 Output Voltage vs. Temperature (VIN = 3.6V; 50Ω Load) Output Voltage (V) 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -50 -25 0 25 50 75 100 Input Voltage (V) Temperature (°C) No Load Current vs. Supply Voltage 140 140 No Load Current vs. Temperature (VIN = 3.6V; VOUT = 5.0V) 120 100 80 60 40 20 0 -50 0 50 100 150 No Load Current (µA) 120 100 80 60 40 20 0 2.7 2.9 3.2 3.4 3.6 3.9 4.1 85°C -40°C 25°C 4.3 4.5 4.8 5.0 No Load Current (µA) Supply Voltage (V) Temperature (°C) 1275.2008.04.1.7 www.analogictech.com 5 PRODUCT DATASHEET AAT1275 AAT1275 SwitchRegTM Typical Characteristics Light Load Switching Waveform (VIN = 3.6V; VOUT = 5.0V; 10mA Load) VLX (2V/div) VOUT1 (25mV/div) VOUT2 (25mV/div) ILX (500mA/div) Time (5µs/div) Boost Converter with USB Power Switch Heavy Load Switching Waveform (VIN = 3.6V; VOUT = 5.0V; 500mA Load) VLX (2V/div) VOUT1 (100mV/div) VOUT2 (100mV/div) ILX (500mA/div) Time (500ns/div) Load Transient Response (VIN = 3.6V; VOUT = 5.0V) 5.062V Load Transient Response (VIN = 3.6V; VOUT = 5.0V) 5.0V VOUT (100mV/div) 4.87V 500mA VOUT (50mV/div) 500mA 4.92V IOUT (400mA/div) 1mA IOUT (200mA/div) 250mA Time (100µs/div) Time (100µs/div) Line Transient Response (16Ω Load) 250 4.2V Load Switch RDS(ON) vs. Input Voltage 85°C 200 120°C RDS(ON) (mΩ) VIN (500mV/div) 5.064V 3.6V 150 100 50 VOUT (200mV/div) 4.752V -40°C 25°C 0 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 Time (100µs/div) Supply Voltage (V) 6 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 AAT1275 SwitchRegTM Typical Characteristics P-Channel RDS(ON) vs. Supply Voltage 320 300 350 Boost Converter with USB Power Switch N-Channel RDS(ON) vs. Supply Voltage 100°C RDS(ON) (mΩ) 260 240 220 200 180 160 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 RDS(ON) (mΩ) 280 125°C 300 250 200 150 100 2.5 2.7 2.9 3.1 3.3 3.5 100°C 125°C 85°C 25°C 85°C 25°C 3.7 3.9 4.1 4.3 4.5 Supply Voltage (V) Supply Voltage (V) Enable Soft Start (VIN = 3.6V; 500mA Load) EN (2V/div) VOUT2 (2V/div) VOUT1 (2V/div) IIN (500mA/div) EN (2V/div) VOUT2 (2V/div) VOUT1 (2V/div) IIN (500mA/div) Enable Soft Start (VIN = 4.2V; 500mA Load) Time (1ms/div) Time (1ms/div) (VIN = 3.6V; CVOUT2 = 120µF; 16Ω Load) Enable Soft Start (VIN = 3.6V; CVOUT2 = 120µF; 16Ω Load) Shutdown EN (2V/div) VOUT1 (2V/div) VOUT2 (2V/div) EN (2V/div) VOUT1 (1V/div) VOUT2 (2V/div) Time (100µs/div) Time (50ms/div) 1275.2008.04.1.7 www.analogictech.com 7 PRODUCT DATASHEET AAT1275 AAT1275 SwitchRegTM Typical Characteristics Current Limit vs. RSET 100 6.0 Boost Converter with USB Power Switch Current Limit vs. Temperature (RSET = 20.3kΩ) Current Limit (%) 10 100 4.0 2.0 0.0 -2.0 -4.0 -6.0 -50 RSET (kΩ) 1000 -25 0 25 50 75 100 Current Limit (mA) Temperature (°C) Switching Frequency vs. Input Voltage (24W Load; L = 2.2µH) 1000 800 940 920 Switching Frequency vs. Temperature (VIN = 3.6V; 16.5Ω Load; L = 2.2µH) FS (kHz) 600 400 200 0 3.0 3.2 3.4 3.6 3.8 4.0 4.2 FS (kHz) 900 880 860 840 820 -50 -25 0 25 50 75 100 Input Voltage (V) Temperature (°C) 8 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Functional Block Diagram LIN SW Boost Converter with USB Power Switch IN OUT1 VCC Boost Regulator Control EN FB OUT2 SET Load Switch Control FLT GND Functional Description 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 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. Control Scheme 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. 1275.2008.04.1.7 www.analogictech.com 9 PRODUCT DATASHEET AAT1275 SwitchRegTM Step-Up Converter Application Information 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. Boost Converter with USB Power Switch Soft Start / Enable 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. 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. 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. Under-Voltage Lockout 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. 10 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM 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: Boost Converter with USB Power Switch 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. 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. Estimate the output capacitor required at the minimum switching frequency (FS) of 800kHz (worst-case). DMAX = IPP = VO - VIN(MIN) VO VIN(MIN) · D L · FS IO 1-D IPP 2 IP = IPK = IP + IV = IP - IPP IRMS = I 2 PK + IPK · IV + IV 3 2 COUT = IOUT · DMAX FS · ∆VOUT 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. 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. 1275.2008.04.1.7 www.analogictech.com 11 PRODUCT DATASHEET AAT1275 SwitchRegTM 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. Boost Converter with USB Power Switch 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. R2⎞ ⎛ VOUT = VREF · 1 + R3 ⎝ ⎠ 432kΩ ⎞ ⎛ = 0.6V · 1 + 59.0kΩ ⎝ ⎠ = 5.0V Steady-State Maximum Power Dissipation 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. 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. 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) 11 12 14 16 18 20 30 40 DMAX = IPP = VO - VIN(MIN) VO IOUT (mA) 740 690 590 550 450 420 160 100 VIN(MIN) · DMAX L · FS IP = IO 1-D IPP 2 IPK = IP + Table 1: Load Switch Current Limit vs. RSET. IV = IP - IPP IRMS(ON) = IRMS(OFF) = Operation in Current Limit 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 (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 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. Boost Converter with USB Power Switch A suggested PCB layout for the AAT1275 is shown in Figures 1 and 2. The following PCB layout guidelines should be considered: 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. 1. 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. Figure 2: AAT1275 TSOPJW-12 Package Evaluation Board Bottom Side Layout. 1275.2008.04.1.7 www.analogictech.com 13 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch VIN U1 AAT1275 4 1 R1 10K L1 2.2µH SW LIN SET GND VCC VIN FLT OUT2 OUT1 EN FB PGND 8 6 5 12 9 3 FLT GND R4 16.9kΩ 7 10 11 VO1 J5 R2 432k VO2 VIN C6 120µF CCase C3 4.7µF 10V 2 R3 59k C2 4.7µF 10V C1 4.7µF GND VIN 3 2 1 GND Enable Figure 3: AAT1275 TSOPJW-12 Package Evaluation Board Schematic. Figure 4: AAT1275 TDFN34-16 Package Evaluation Board Top Side Layout. Figure 5: AAT1275 TDFN34-16 Package Evaluation Board Bottom Side Layout. 14 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 SwitchRegTM Boost Converter with USB Power Switch AAT1275-TDFN34-16 U1 1 L1 2.2µH LIN VIN VCC VIN EN FLT LIN SW SW OUT2 OUT1 FB 16 VIN 3 12 4 11 123 Feedback Option C6 120µF R1 10K 3 2 1 15 9 VOUT2 2 10 Enable 1 FLT 13 7 6 R5 1k R2 432k C4 100pF 5 VOUT1 C2 4.7µF 10V C1 4.7µF 10V C3 4.7µF 10V 14 PGND SET GND PGND GND 8 R4 16.9k R3 59k Figure 6: AAT1275 TDFN34-16 Package Evaluation Board Schematic. Manufacturer Murata Murata Murata Murata Part Number GRM21BR61A475KA73L GRM18BR60J475KE19D GRM21BR60J106KE19 GRM21BR60J226ME39 Value 4.7µF 4.7µF 10µF 22µF Voltage 10V 6.3V 6.3V 6.3V Temp. Co. X5R X5R X5R X5R Case 0805 0603 0805 0805 Table 2: Typical Surface Mount Capacitors. Max DC Current (A) 1.6 1.7 1.12 1.48 Manufacturer Sumida Sumida Coiltronics Coiltronics Part Number CDRH2D14-2R2 CDRH4D11/HP-2R4 SD3112-2R2 SD3114-2R2 Inductance (µH) 2.2 2.4 2.2 2.2 DCR (Ω) 0.094 0.105 0.140 0.086 Size (mm) LxWxH 3.2x3.2x1.55 4.8x4.8x1.2 3.1x3.1x1.2 3.1x3.1x1.4 Type Shielded Shielded Shielded Shielded Table 3: Typical Surface Mount Inductors. 1275.2008.04.1.7 www.analogictech.com 15 PRODUCT DATASHEET AAT1275 AAT1275 SwitchRegTM Step-Up Converter Design Example Specifications VOUT = 5V IOUT = 300mA VIN = 2.7V to 4.2V (3.6V nominal) TAMB = 50°C Boost Converter with USB Power Switch 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 = VIN(MIN) · DMAX L · FS IP = IO 1-D IPP 2 IPK = IP + 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) = IOUT · DMAX 0.3A · 0.46 = = 3.0µF; use 4.7µF 10V MLC FS · ∆VOUT 800kHz · 0.05V 16 www.analogictech.com 1275.2008.04.1.7 PRODUCT DATASHEET AAT1275 AAT1275 SwitchRegTM AAT1275 Losses IRMS(ON) = Boost Converter with USB Power Switch (IPK2 + IPK · IV + IV2) · DMAX = 3 (0.9A2 + 0.9A · 0.2A + 0.2A2) · 0.46 = 0.4A 3 (0.9A2 + 0.9A · 0.2A + 0.2A2) · (1 - 0.46) = 0.43A 3 IRMS(OFF) = (IPK2 + 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)) = 0.4A2 · (0.25Ω + 0.3Ω) + 0.422 · (0.25Ω + 0.3Ω + 0.2Ω) = 0.22W TJ(MAX) = PTOTAL · θJA + TAMB = 0.22W · 110°C + 85°C = 109°C W 1275.2008.04.1.7 www.analogictech.com 17 PRODUCT DATASHEET AAT1275 AAT1275 SwitchRegTM Ordering Information Package TSOPJW-12 TDFN34-16 Boost Converter with USB Power Switch Marking1 USXYY USXYY Part Number (Tape and Reel)2 AAT1275ITP-5.0-T1 AAT1275IRN-5.0-T1 Package Information3 TSOPJW-12 0.20 + 0.10 - 0.05 2.40 ± 0.10 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 2.85 ± 0.20 7° NOM 3.00 ± 0.10 0.9625 ± 0.0375 + 0.10 1.00 - 0.065 0.04 REF 0.15 ± 0.05 0.055 ± 0.045 4° ± 4° 0.010 0.45 ± 0.15 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 AAT1275 SwitchRegTM Boost Converter with USB Power Switch 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. 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 0.450 ± 0.050 Pin 1 Indicator (optional) 19