AAT2153

AAT2153 ANALOGICTECH | Alldatasheet

Document overview

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Technical content

Features

• 2.5A Maximum Output Current
• Input Voltage: 2.7V to 5.5V
• Output Voltage: 0.6V to V IN
• Up to 95% Efficiency
• Low Noise Light Load Mode
• 42 μA No Load Quiescent Current
• No External Compensation Required
• 1.4MHz Switching Frequency
• 100% Duty Cycle Low-Dropout Operation
• Internal Soft Start
• Over-Temperature and Current Limit Protection
• <1 μA Shutdown Current
• 16-Pin 3x3mm QFN Package
• Temperature Range: -40°C to +85°C

Applications

• Cellular Phones
• Digital Cameras
• Hard Disk Drives
• MP3 Players
• PDAs and Handheld Computers
• Portable Media Players
• USB Devices Typical Application 2.2µH 22µF 10µF 2.5V3.3V 187k 59k LX 14 N/C6 EN7 VCC9 VP10 N/C8 LX 13 PGND 3 VP12 VP11 FB 4 LX 15 PGND 2 PGND 1SGND5 N/C 16 AAT2153

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Pin Descriptions Pin # Symbol Function 1, 2, 3 PGND Main power ground return pin. Connect to the output and input capacitor return. (See board layout rules.) 4F B Feedback input pin. For an adjustable output, connect an external resistive divider to this pin. For fi xed output voltage versions, FB is the output pin of the converter. 5 SGND Signal ground. Connect the return of all small signal components to this pin. (See board layout rules.) 6, 8, 16 N/C Not internally connected. 7E N Enable input pin. A logic high enables the converter; a logic low forces the AAT2153 into shutdown mode reducing the supply current to less than 1μA. The pin should not be left fl oating. 9 VCC Bias supply. Supplies power for the internal circuitry. Connect to input power. 10, 11, 12 VP Input supply voltage for the converter power stage. Must be closely decoupled to PGND. 13, 14, 15 LX Connect inductor to these pins. Switching node internally connected to the drain of both high- and low-side MOSFETs. EP Exposed paddle (bottom); connect to PGND directly beneath package. Pin Configuration QFN33-16 (Top View) VP VP VP N/C PGND PGND PGND N/CSGNDEN N/C VCC LX LX LX FB

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Absolute Maximum Ratings1 Symbol Description Value Units VCC, VP VCC, VP to GND 6V VLX LX to GND -0.3 to VP + 0.3 V VFB FB to GND -0.3 to VCC + 0.3 V VEN EN to GND -0.3 to -6 V TJ Operating Junction Temperature Range -40 to150 °C Thermal Characteristics Symbol Description Value Units θJA Maximum Thermal Resistance 50 °C/W θJC Maximum Thermal Resistance 4.2 °C/W PD Maximum Power Dissipation (TA = 25°C)2, 3 2.0 W Recommended Operating Conditions Symbol Description Value Units TA Ambient Temperature Range -40 to 85 °C 1. Stresses above those listed in Absolute Maximum Ratings may cause damage to the device. Functional operation at conditions o ther than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Mounted on a demo board (FR4, in still air). Exposed pad must be mounted to PCB. 3. Derate 20mW/°C above 25°C.

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Electrical Characteristics1 VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are T A = 25°C. Symbol Description Conditions Min Typ Max Units VIN Input Voltage 2.7 5.5 V VOUT Output Voltage Range 0.6 V IN V VUVLO UVLO Threshold VIN Rising 2.7 V Hysteresis 250 mV V IN Falling 1.8 V IQ Quiescent Current No Load 42 90 μA ISHDN Shutdown Current V EN = GND 1.0 μA ILIM Current Limit 2.8 3.5 A RDS(ON)H High Side Switch On-Resistance 0.120 Ω RDS(ON)L Low Side Switch On-Resistance 0.085 Ω ΔVLOADREG Load Regulation I LOAD = 0A to 2.5A 0.5 % ΔVLINEREG/ΔVIN Line Regulation V IN = 2.7V to 5.5V 0.2 %/V VFB Feedback Threshold Voltage Accuracy (Adjustable Version) No Load, TA = 25°C 0.591 0.60 0.609 V IFB FB Leakage Current V OUT = 1.0V 0.2 μA FOSC Internal Oscillator Frequency 1.12 1.4 1.68 MHz TS Start-Up Time From Enable to Output Regulation; CFF = 100pF 150 μs TSD Over-Temperature Shutdown Threshold 140 °C THYS Over-Temperature Shutdown Hysteresis 15 °C EN VIL Enable Threshold Low 0.6 V VIH Enable Threshold High 1.4 V IEN Enable Leakage Current V IN = VEN = 5.5V -1.0 1.0 μA 1. The AAT2153 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assu red by design, characterization, and correla- tion with statistical process controls.

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Typical Characteristics Efficiency vs. Output Current (VOUT = 3.3V) Output Current (mA) Efficiency (%)30 100 0 1 10 100 1000 10000 VIN = 5.0V VIN = 4.5V VIN = 4.2V Load Regulation (VOUT = 3.3V) Output Current (mA) Load Regulation (%) -0.6 -0.4 -0.2 -1.0 -0.8 0.0 0.2 0.4 0.6 0.8 1.0 0.1 1 10 100 1000 10000 VIN = 5.0V VIN = 4.5V VIN = 4.2V Efficiency vs. Output Current (VOUT = 1.8V) Output Current (mA) Efficiency (%) 0 1 10 100 1000 10000 100 VIN = 4.2V VIN = 3.6V VIN = 2.7V Load Regulation (VOUT = 1.8V) Output Current (mA) Load Regulation (%) -0.6 -0.4 -0.2 -1.0 -0.8 0.0 0.2 0.4 0.6 0.8 1.0 0.1 1 10 100 1000 10000 VIN = 4.2V VIN = 3.6V VIN = 2.7V Efficiency vs. Output Current (VOUT = 1.2V) Output Current (mA) Efficiency (%) 0 1 10 100 1000 10000 100 VIN = 4.2V VIN = 3.6V VIN = 2.7V Load Regulation (VOUT = 1.2) Output Current (mA) Load Regulation (%) 0.1 1 10 100 1000 10000 -0.6 -0.4 -0.2 -1.0 -0.8 0.0 0.2 0.4 0.6 0.8 1.0 VIN = 4.2V VIN = 3.6V VIN = 2.7V

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Typical Characteristics Quiescent Current vs. Input Voltage (VOUT = 1.8V; No Load) Input Voltage (V) Quiescent Current (µA) 85°C 25°C -40°C Output Voltage vs. Temperature (VOUT = 1.8V; IOUT = 2.5A) Temperature (°C) Output Voltage Error (%) - 4 0 - 3 0 - 2 0 - 1 00 1 02 03 04 05 06 07 08 09 0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Output Voltage vs. Input Voltage (VOUT = 1.8V; IOUT = 1A) Input Voltage (V) Output Voltage (V) 1.73 1.74 1.75 1.76 1.77 1.78 1.79 1.80 1.81 1.82 85°C 25°C -40°C Switching Frequency vs. Temperature (VOUT = 1.8V; IOUT = 2.5A) Temperature (°C) Switching Frequency Variation (%)- 4 0 - 3 0 - 2 0 - 1 0 0 1 02 03 04 05 06 07 08 09 0 Load Transient Response (VOUT = 1.8V) Time (100µs/div) Output Voltage (AC coupled) (top)(mV) Output Current (bottom) (A) -0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 Load Transient Response (VOUT = 1.8V; CFF = 100pF) Time (100µs/div) Output Voltage (AC coupled) (top)(mV) Output Current (bottom) (A) -0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Typical Characteristics Load Transient Response (IOUT = 1A to 2.5A; VOUT = 1.8V; R1 = 0Ω; COUT = 2x22μF) Time (100μs/div) Output Voltage (top) (V) Load Current (bottom) (A) 1.6 1.7 1.8 1.9 2.0 Load Transient Response (IOUT = 1A to 2.5A; VOUT = 1.8V; R1 = 10Ω; COUT = 22μF) Time (100μs/div) Output Voltage (top) (V) Load Current (bottom) (A) 1.6 1.7 1.8 1.9 2.0 Load Transient Response (IOUT = 250mA to 2.5A; VOUT = 1.8V; R1 = 0Ω; COUT = 2x22μF) Time (100μs/div) Output Voltage (top) (V) Load Current (bottom) (A) 1.6 1.7 1.8 1.9 2.0 Load Transient Response (IOUT = 250mA to 2.5A; VOUT = 1.8V; R1 = 10Ω; COUT = 22μF) Time (100μs/div) Output Voltage (top) (V) Load Current (bottom) (A) 1.6 1.7 1.8 1.9 2.0 Load Transient Response (IOUT = 100mA to 2.5A; VOUT = 1.8V; R1 = 0Ω; COUT = 2x22μF) Time (100μs/div) Output Voltage (top) (V) Load Current (bottom) (A) 1.6 1.7 1.8 1.9 2.0 Load Transient Response (IOUT = 100mA to 2.5A; VOUT = 1.8V; R1 = 10Ω; COUT = 22μF) Time (100μs/div) Output Voltage (top) (V) Load Current (bottom) (A) 1.6 1.7 1.8 1.9 2.0

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Typical Characteristics Load Transient Response (IOUT = 10mA to 2.5A; VOUT = 1.8V; R1 = 0Ω; COUT = 2x22μF) Time (100μs/div) Output Voltage (top) (V) Load Current (bottom) (A) 1.6 1.7 1.8 1.9 2.0 Load Transient Response (IOUT = 10mA to 2.5A; VOUT = 1.8V; R1 = 10Ω; COUT = 22μF) Time (100μs/div) Output Voltage (top) (V) Load Current (bottom) (A) 1.6 1.7 1.8 1.9 2.0 Line Transient Response (VOUT = 1.8V; IOUT = 1.5A; CFF = 100pF) Time (100µs/div) Input Voltage (top) (V) Output Voltage (AC coupled) (bottom) (V) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 Line Regulation (VOUT = 1.8V; IOUT = 1A) Input Voltage (V) VOUT Error (%) -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40 Enable Soft Start (VIN = 3.6V; VOUT = 1.8V; IOUT = 2.5A; CFF = 100pF) Time (100μs/div) VOUT (1V/div) EN (2V/div) IIN (1A/div) Enable Soft Start (VIN = 3.6V; VOUT = 1.8V; IOUT = 2.5A; CFF = 1nF) Time (100μs/div) VOUT (1V/div) EN (2V/div) IIN (1A/div)

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Typical Characteristics Heavy Load Switching Waveform (VIN = 3.6V; VOUT = 1.8V; IOUT = 2.5A; R1 = 10Ω; COUT = 22μF) Time (400ns/div) Output Voltage (AC Coupled) (top) (mV) Inductor Ripple Current (bottom) (A) -10 2.2 2.4 2.6 2.8 Heavy Load Switching Waveform (VIN = 3.6V; VOUT = 1.8V; IOUT = 2.5A; R1 = 0Ω; COUT = 2x22μF) Time (400ns/div) Output Voltage (AC Coupled) (top) (mV) Inductor Ripple Current (bottom) (A) -10 2.2 2.4 2.6 2.8 Light Load Switching Waveform (VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA; CFF = 0pF) Time (5µs/div) Output Voltage (AC coupled) (top)(mV) Inductor Ripple Current (bottom) (A) -240 -200 -160 -120 -80 -40 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Light Load Switching Waveform (VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA; CFF = 0pF) Time (200µs/div) Output Voltage (AC coupled) (top)(mV) Inductor Ripple Current (bottom) (A) -240 -200 -160 -120 -80 -40 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Light Load Switching Waveform (VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA; CFF = 100pF) Time (5µs/div) Output Voltage (AC coupled) (top)(mV) Inductor Ripple Current (bottom) (A) -240 -200 -160 -120 -80 -40 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Light Load Switching Waveform (VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA; CFF = 100pF) Time (500µs/div) Output Voltage (AC coupled) (top)(mV) Inductor Ripple Current (bottom) (A) -240 -200 -160 -120 -80 -40 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Functional Description The AAT2153 is a high performance 2.5A monolithic step-down converter operating at a 1.4MHz switching frequency. It minimizes external component size, opti- mizes efficiency over the complete load range, and pro- duces reduced ripple and spectral noise. Apart from the small bypass input capacitor, only a small L-C filter is required at the output. Typically, a 3.3μH inductor and a 22μF ceramic capacitor are recommended for a 3.3V output (see table of recommended values). At dropout, the converter duty cycle increases to 100% and the output voltage tracks the input voltage minus the R DS(ON) drop of the P-channel high-side MOSFET (plus the DC drop of the external inductor). The device inte- grates extremely low R DS(ON) MOSFETs to achieve low dropout voltage during 100% duty cycle operation. This is advantageous in applications requiring high output voltages (typically > 2.5V) at low input voltages. The integrated low-loss MOSFET switches can provide greater than 95% efficiency at full load. Light load opera- tion maintains high efficiency, low ripple and low spectral noise even at lower currents (typically <150mA). In battery-powered applications, as V IN decreases, the converter dynamically adjusts the operating frequency prior to dropout to maintain the required duty cycle and provide accurate output regulation. Output regulation is maintained until the dropout voltage, or minimum input voltage, is reached. At 2.5A output load, dropout voltage headroom is approximately 200mV. The AAT2153 typically achieves better than ±0.5% out- put regulation across the input voltage and output load range. A current limit of 3.5A (typical) protects the IC and system components from short-circuit damage. Typical no load quiescent current is 42μA. Thermal protection completely disables switching when the maximum junction temperature is detected. The Functional Block Diagram VPVCC ENSGND PGND LOGIC 0.6V REF Temp. Sensing OSC OP. AMP LX FB DH DL CMP 1MΩ

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET junction over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault condition is removed, the output voltage automati- cally recovers. Peak current mode control and optimized internal com- pensation provide high loop bandwidth and excellent response to input voltage and fast load transient events. Soft start eliminates output voltage overshoot when the enable or the input voltage is applied. Under-voltage lockout prevents spurious start-up events. Control Loop The AAT2153 is a peak current mode step-down con- verter. The current through the P-channel MOSFET (high side) is sensed for current loop control, as well as short- circuit and overload protection. A fixed slope compensa- tion signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The peak cur- rent mode loop appears as a voltage-programmed cur- rent source in parallel with the output capacitor. The output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. Internal loop compensation terminates the transconductance voltage error amplifier output. The reference voltage is internally set to program the con- verter output voltage greater than or equal to 0.6V. Soft Start/Enable Soft start limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the AAT2153 into a low-power, non-switching state. The total input current during shut- down is less than 1μA. Current Limit and Over-Temperature Protection For overload conditions, the peak input current is limit- ed. To minimize power dissipation and stresses under current limit and short-circuit conditions, switching is terminated after entering current limit for a series of pulses. Switching is terminated for seven consecutive clock cycles after a current limit has been sensed for a series of four consecutive clock cycles. Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature threshold is 140°C with 15°C of hys- teresis. Once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. Under-Voltage Lockout Internal bias of all circuits is controlled via the VCC input. Under-voltage lockout (UVLO) guarantees suffi- cient V IN bias and proper operation of all internal cir- cuitry prior to activation. 3.0μH 2x22μF 10μF 0.1μF C1 Murata 10μF 6.3V X5R GRM42-6X5R106K6.3 C3 Murata 22μF 6.3V GRM21BR60J226ME39L X5R 0805 L1 see Table 2 R1 and C2 are an optional noise filter for internal V CC. R6, C4, C5-C7 are not populated C8 100 pF to 1nF feed-forward capacitor for enhanced transient response VOUT+VIN+ LX N/C EN VCC VP N/C LX PGND VP VP FB LX PGND PGND SGND N/C AAT2153 59.0k 100K Enable LX GNDGND VOUT(V) R3 (kΩ) 0.8 19.6 0.9 29.4 1.0 39.2 1.1 49.9 1.2 59.0 1.3 68.1 1.4 78.7 1.5 88.7 1.8 118 2.0 137 2.5 187 3.3 267 Figure 1: AAT2153 Evaluation Schematic.

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Component Selection Inductor Selection The step-down converter uses peak current mode con- trol 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 inductor should be set equal to the output voltage numeric value in μH. This guarantees that there is suf- ficient internal slope compensation. Manufacturer’s specifications list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the satura- tion 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 3.3 μH CDRH4D28 series Sumida inductor has a 49.2mΩ worst case DCR and a 1.57A DC current rating. At full 2.5A load, the inductor DC loss is 97mW which gives less than 1.5% loss in efficiency for a 2.5A, 3.3V output. Input Capacitor Select a 10μF to 22μF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (V PP) and solve for C. The calculated value varies with input voltage and is a maximum when V IN is double the output voltage. VO VIN CIN = VO VIN VPP IO VO VIN VO VIN CIN(MIN) = 1 VPP IO Always examine the ceramic capacitor DC voltage coef- ficient characteristics when selecting the proper value. For example, the capacitance of a 10μF, 6.3V, X5R ceram- ic capacitor with 5.0V DC applied is actually about 6 μF. Some examples of DC bias voltage versus capacitance for different package sizes are shown in Figure 2. DC Bias Voltage (V) Capacitance (F) 000.0E+0 5.0E+6 10.0E+6 15.0E+6 20.0E+6 25.0E+6 Figure 2: Capacitance vs. DC Bias Voltage for Different Package Sizes. The maximum input capacitor RMS current is: VO VIN VO VIN 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. VO VIN VO VIN for VIN = 2 · VO IO RMS(MAX)I 2= The term VO VIN VO VIN appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when V O is twice V IN. 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 AAT2153. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capaci- tor 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 (C1) can be seen in the evaluation board layout in the Layout section of this datasheet (see Figure 3).

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET A laboratory test set-up typically consists of two long wires running from the bench power supply to the evalu- ation 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 dur- ing 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 induc- tance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or alu- minum electrolytic should be placed in parallel with the low ESR/ESL bypass ceramic capacitor. This dampens the high Q network and stabilizes the system. Output Capacitor The output capacitor limits the output ripple and pro- vides holdup during large load transitions. A 10 μF to 22μF X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL charac- teristics necessary for low output ripple. The output voltage droop due to a load transient is dom- inated 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- 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 equa- tion 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 10 μF. This is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. Increased output capac- itance will reduce the crossover frequency with greater phase margin. Adjustable Output Resistor Selection The output voltage on the AAT2153 is programmed with external resistors R3 and R4. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum sug- gested value for R4 is 59kΩ. Although a larger value will further reduce quiescent current, it will also increase the impedance of the feedback node, making it more sensi- tive to external noise and interference. Table 1 summa- rizes the resistor values for various output voltages with R4 set to either 59kΩ for good noise immunity or 221kΩ for reduced no load input current. The external resistor R3, combined with an external 100pF feed forward capacitor (C8 in Figure 1), delivers enhanced transient response for extreme pulsed load applications and reduces ripple in light load conditions. The addition of the feed forward capacitor typically requires a larger output capacitor C3-C4 for stability. The external resistors set the output voltage according to the following equation: R4VOUT = 0.6V 1 + or ⎡⎤⎣⎦ VOUT VREF R3 = - 1 R 4 VOUT (V) R4 = 59kΩ R3 (kΩ) R4 = 221kΩ R3 (kΩ) 0.8 19.6 75 0.9 29.4 113 1.0 39.2 150 1.1 49.9 187 1.2 59.0 221 1.3 68.1 261 1.4 78.7 301 1.5 88.7 332 1.8 118 442 1.85 124 464 2.0 137 523 2.5 187 715 3.0 237 887 3.3 267 1000 Table 1: AAT2153 Resistor Values for Various Output Voltages.

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Thermal Calculations There are three types of losses associated with the AAT2153 step-down converter: switching losses, conduc- tion losses, and quiescent current losses. Conduction losses are associated with the R DS(ON) characteristics of the power output switching devices. Switching losses are dominated by the gate charge of the power output switch- ing devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the losses is given by: PTOTAL IO 2 · (RDS(ON)H · VO + RDS(ON)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 con- verter switching losses. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: PTOTAL IO 2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO]) VIN + (tsw · FS · IO + IQ) · VIN Since RDS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be inves- tigated over the complete input voltage range. Given the total losses, the maximum junction tempera- ture can be derived from the θ JA for the QFN33-16 pack- age, which is 50°C/W. TJ(MAX) = PTOTAL · ΘJA + TAMB Layout The suggested PCB layout for the AAT2153 is shown in Figures 3 and 4. The following guidelines should be used to help ensure a proper layout. 1. The input capacitor (C1) should connect as closely as possible to VP and PGND. 2. C2 and L1 should be connected as closely as possi- ble. The connection of L1 to the LX pin should be as short as possible. 3. The feedback trace or FB pin should be separate from any power trace and connect as closely as pos- sible to the load point. Sensing along a high-current load trace will degrade DC load regulation. 4. The resistance of the trace from the load return to PGND should be kept to a minimum. This will help to minimize any error in DC regulation due to differ- ences in the potential of the internal signal ground and the power ground. 5. Connect unused signal pins to ground to avoid unwanted noise coupling. Figure 3: AAT2153 Evaluation Board Figure 4: AAT2153 Evaluation Board Top Side Layout. Bottom Side Layout.

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Design Example Specifications VO 3.3V @ I O = 2.5A, Pulsed Load ΔILOAD = 2.4A VIN 2.7V to 4.2V (3.6V nominal) FS 1.4MHz TAMB 85°C in QFN33-16 Package Output Inductor L = VO (μH) = 3.3μH; see Table 2. For Wurth inductor 7447789003 3.3μH DCR = 30mΩ max. IPK = IO + ΔI = 2.5A + 0.077A = 2.577A2 PL = IO 2 · DCR = 2.5A2 · 30mΩ = 188mW Output Capacitor VDROOP = 0.2V 3.3µH · 1.4MHz · 4.2V 23 RMS(MAX)I L · FS · VIN(MAX) = · 3 · ΔILOAD VDROOP · FS 3 · 2.4A 0.2V · 1.4MHz COUT = = = 25.7µF; use 2x22µF

• = 44mArms (VOUT) · (VIN(MAX) - VOUT) = Pesr = esr · IRMS 2 = 5mΩ · (44mA)2 = 9.8µW Input Capacitor Input Ripple VPP = 50mV CIN = = = 11.9µF; use 2x10µF1 - ESR · 4 · FS VPP IO1 + IO2 - 5mΩ · 4 · 1.2MHz50mV 1.4A IO RMS(MAX)I P = esr · IRMS 2= = 1.25Arms

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 Losses Total losses can be estimated by calculating the dropout (V IN = VO) losses where the power MOSFET R DS(ON) will be at the maximum value. All values assume an 85°C ambient temperature and a 120°C junction temperature with the QFN 50°C/W package. PLOSS = IO 2 · RDS(ON)H = 2.5A2 · 0.12Ω = 750mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 750mW = 122.5°C The total losses are also investigated at the nominal lithium-ion battery voltage (3.6V). The simplified version of the RDS(ON) losses assumes that the N-channel and P-channel R DS(ON) are equal. PTOTAL = IO 2 · RDS(ON) + [(tsw · FS · IO + IQ) · VIN] TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 813mW = 125.6°C VOUT (V) Inductance (μH) Part Number Manufacturer Size (mm) Rated Current (A) ISAT (A) DCR (mΩ) 3.3 3.0 CDRH5D28RHPNP Sumida 6x6x3 2.4 31.8 1.8 1.8 CDRH4D28 Sumida 6x6x2 2.5 46.0 Table 2: Surface Mount Inductors. Manufacturer Part Number Value Voltage Temp. Co. Case Murata GRM21BR60J106KE19 10 μF 6.3V X5R 0805 Murata GRM21BR60J226ME39 22 μF 6.3V X5R 0805 Murata GRM31CR60J226KE19 22 μF 6.3V X5R 1206 Table 3: Surface Mount Capacitors.

2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET AAT2153 2.5A Low Noise Step-Down ConverterSwitchReg TM PRODUCT DATASHEET Advanced Analogic Technologies, Inc.

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Package Marking 1 Part Number (Tape and Reel)2 QFN33-16 5QXYY AAT2153IVN-0.6-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.

Package Information

3.000 ± 0.050 Pin 1 Dot By Marking 1.250 ± 0.050 0.400 ± 0.100 1.250 ± 0.0503.000 ± 0.050 0.500 ± 0.050 0.900 ± 0.100 Pin 1 Identification C0.3 0.025 ± 0.025 0.214 ± 0.036 0.230 ± 0.050 Top View Bottom View Side View 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 c onnection.