AAT1157 ANALOGICTECH | Alldatasheet

Document overview

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Technical content

Features

  • V IN Range: 2.7V to 5.5V
  • Up to 95% Efficiency
  • 110 m Ω R DS(ON) Internal Switches
  • <1µA Shutdown Current
  • 1MHz Buck Switching Frequency
  • Fixed or Adjustable V OUT ≥ 0.8V
  • Integrated Power Switches
  • Current Mode Operation
  • Internal Compensation
  • Stable with Ceramic Capacitors
  • Constant PWM Operation for Low Output Ripple
  • Internal Soft Start
  • Over-Temperature Protection
  • Current Limit Protection
  • 16-Pin QFN 3x3mm Package
  • -40°C to +85°C Temperature Range

Applications

  • HDD MP3 Players
  • Notebook Computers
  • PDAs
  • Point-of-Load Regulation
  • Set Top Boxes
  • Smart Phones
  • Wireless Notebook Adapters Typical Application 3.0µH 2x 22µF C3-C4 10µF 100 0.1µF 2.5V3.3V 187kR3 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 AAT1157

1MHz 1.2A Buck DC/DC Converter 2 1157.2005.11.1.4 Pin Descriptions Pin Configuration QFN33-16 (Top View) VP VP VP N/C PGND PGND PGND N/CSGNDEN N/C VCC LX LX LX FB Pin # Symbol Function 1, 2, 3 PGND Main power ground return pin. Connect to the output and input capacitor return. (See board layout rules.) 4 FB Feedback input pin. This pin is connected to the converter output. It is used to set the output of the converter to regulate to the desired value via an internal resistive divider. For an adjustable output, an external resistive divider is con- nected to this pin. 5 SGND Signal ground. Connect the return of all small signal components to this pin. (See board layout rules.) 7 EN Enable input pin. A logic high enables the converter; a logic low forces the AAT1157 into shutdown mode reducing the supply current to less than 1µA. The pin should not be left floating. 6, 8, 16 N/C Not internally connected. 9 VCC Bias supply. Supplies power for the internal circuitry. Connect to input power via low pass filter with decoupling to SGND. 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.

1MHz 1.2A Buck DC/DC Converter 1157.2005.11.1.4 3 Absolute Maximum Ratings1 Thermal Characteristics Recommended Operating Conditions Symbol Description Value Units T Ambient Temperature Range -40 to 85 °C Symbol Description Value Units θJA Maximum Thermal Resistance (QFN33-16)3 50 °C/W θJC Maximum Thermal Resistance (QFN33-16) 4.2 °C/W PD Maximum Power Dissipation (QFN33-16) (TA = 25°C)3, 4 2.0 W Symbol Description Value Units VCC, VP VCC, VP to GND 6 V VLX LX to GND -0.3 to V P + 0.3 V VFB FB to GND -0.3 to V CC + 0.3 V VEN EN to GND -0.3 to -6 V TJ Operating Junction Temperature Range -40 to150 °C VESD ESD Rating2 - HBM 3000 V 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. Human body model is 100pF capacitor discharged through a 1.5k Ω resistor into each pin. 3. Mounted on a demo board (FR4, in still air). Exposed pad must be mounted to PCB. 4. Derate 20mW/°C above 25°C.

1MHz 1.2A Buck DC/DC Converter 4 1157.2005.11.1.4 Electrical Characteristics1 VIN = VCC = VP = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at T A = 25°C. Symbol Description Conditions Min Typ Max Units VIN Input Voltage Range 2.7 5.5 V VOUT Output Voltage Tolerance VIN = VOUT + 0.2 to 5.5V, -4 +4 %IOUT = 0 to 1.2A ∆VOUT/VOUT Load Regulation V IN = 4.2V, ILOAD = 0 to 1.2A ±2.5 % ∆VOUT(VOUT*∆VIN) Line Regulation V IN =2.7 to 5.5V ±0.1 %/V IQ Quiescent Supply Current No Load 160 300 µA ISHDN Shutdown Current V EN = 0V, VIN = 5.5V 1.0 µA ILIM Current Limit T A = 25°C 1.7 A VUVLO Under-Voltage Lockout VIN Rising, VEN = VCC 2.5 VVIN Falling, VEN = VCC 1.2 VUVLO(HYS) Under-Voltage Lockout Hysteresis 250 mV VIL Input Low Voltage 0.6 V VIH Input High Voltage 1.4 V IIL Input Low Current V IN = VFB = 5.5V 1.0 µA IIH Input High Current V IN = VFB = 0V 1.0 µA RDS(ON)H High Side Switch On Resistance T A = 25°C 110 150 m Ω RDS(ON)L Low Side Switch On Resistance T A = 25°C 100 150 m Ω FOSC Oscillator Frequency T A = 25°C 750 1000 1250 kHz TSD Over-Temperature Shutdown 140 °CThreshold THYS Over-Temperature Shutdown 15 °CHysteresis 1. The AAT1157 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assu red by design, characterization, and correlation with statistical process controls.

1MHz 1.2A Buck DC/DC Converter 1157.2005.11.1.4 5 Typical Characteristics Frequency vs. Input Voltage (VOUT = 1.8V) Input Voltage (V) Frequency (MHz) 1.2 1.22 1.24 1.26 1.28 1.3 Output Voltage vs. Temperature (VIN = 3.6V; VOUT = 2.5V; IOUT = 1.0A) Temperature (°°C) Output Voltage Error (%)-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.1 -40 -20 0 20 40 60 80 100 N-Channel RDSON vs. Input Voltage Input Voltage (V) RDSON (mΩΩ) 100 120 140 160 180 200 2.5 3 3.5 4 4.5 5 5.5 120°C100°C 25°C85°C P-Channel RDSON vs. Input Voltage Input Voltage (V) RDSON (mΩΩ) 100 120 140 160 180 200 2.5 3 4 3.5 4.5 5 5.5 120°C100°C 25°C85°C DC Regulation (VOUT = 2.5V) Output Current (mA) Output Error (%) -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 1 10 100 1000 10000 VIN = 3.0V VIN = 3.3V VIN = 3.6V No Load Supply Current vs. Input Voltage Input Voltage (V) Supply Current (µµA) 100 150 200 250 300 2.5 3 4 3.5 4.5 5.5 5 -40°C 25°C 85°C

1MHz 1.2A Buck DC/DC Converter 6 1157.2005.11.1.4 Typical Characteristics Load Transient Response (400mA-1.2A; VIN = 3.3V; VOUT = 2.5V) Output Voltage (AC Coupled) (V) (top) Time (20µµs/div) Load Current (A) (bottom) -0.16 -0.13 -0.10 -0.07 -0.04 -0.01 0.02 0.05 0.08 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 400mA 1.2A Line Transient (IOUT = 1.2A; VO = 2.5V) Input Voltage (top) (V) Output Voltage (AC coupled) (bottom) (V) Time (25µµs/div) 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 -0.08 -0.04 0.00 0.04 0.08 0.12 0.16 0.20 0.24 Output Ripple (VOUT = 2.5V; IOUT = 1.2A; VIN = 3.6V) Time (500ns/div) Output Voltage (AC coupled) (top) (V) Inductor Current (bottom) (A) -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0.01 0.02 0.5 1.5 2.5 Soft Start (VOUT = 2.5V; IOUT = 1.2A; VIN = 3.6V) Time (250µµs/div) Enable and Output Voltage (top) (V) Inductor Current (bottom) (A) -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

1MHz 1.2A Buck DC/DC Converter 1157.2005.11.1.4 7 Functional Block Diagram VP = 2.7V to 5.5VVCC ENSGND PGND LOGIC 1.0V REF Temp. Sensing OSC OP. AMP LX FB DH DL CMP 1MΩ Applications Information Control Loop The AAT1157 is a peak current mode buck converter. The inner wide bandwidth loop controls the inductor peak current. The inductor current is sensed through the P-channel MOSFET (high side) and is also used for short-circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The loop appears as a voltage-programmed current source in parallel with the output capacitor. The voltage error amplifier output programs the current loop for the necessary inductor current to force a constant output voltage for all load and line conditions. The external voltage feedback resistive divider divides the output voltage to the error ampli- fier reference voltage of 0.6V. The low-DC gain voltage error amplifier eliminates the need for external compensation components while provid- ing sufficient DC loop gain for good load regulation. The voltage loop crossover frequency and phase margin are set by the output capacitor. Soft Start/Enable Soft start increases the inductor current limit point in discrete steps once the input voltage or enable input is applied. It limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the AAT1157 into a non-switching shutdown state. The total input current during shutdown is less than 1µA. Power and Signal Source Separate small signal ground and power supply pins isolate the internal control circuitry from the noise associated with the output power MOSFET switching. The low-pass filter R1 and C2 shown in the Figure 1 schematic filters the input noise asso- ciated with the power switching. Current Limit and Over-Temperature Protection For overload conditions, the peak input current sensed through the high-side P-channel MOSFET is limited. Thermal protection completely disables switching when internal dissipation becomes excessive, protecting the device from damage. The junction over-temperature threshold is 140°C with 15°C of hysteresis. Once the over-temperature or over-current fault is removed, the AAT1157 auto- matically recovers.

1MHz 1.2A Buck DC/DC Converter 8 1157.2005.11.1.4 Inductor The output inductor should limit the ripple current to 330mA at the maximum input voltage. This match- es the inductor current downslope with the fixed internal slope compensation. For a 2.5V output and the ripple set to a maximum input voltage of 4.2V, the inductance value required to limit the ripple cur- rent to 330mA is 3.0µH. From this calculated value, a standard value can be selected. 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 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 loss- es 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. For a maximum ripple current of 330mA, the peak switch and inductor current at 1.2A is 1.365A. A stan- dard value of 3.0µH can be used in this example. The 3.0µH Sumida series CDRH5D28 inductor has a 24mΩ maximum DCR and a 2.4A DC current rating. Input Capacitor The primary function of the input capacitor is to pro- vide a low impedance loop for the edges of pulsed current drawn by the AAT1157. A low ESR/ESL ceramic capacitor is ideal for this function. To mini- mize 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 radiated and conducted EMI while facilitating optimum performance of the AAT1157. Ceramic X5R or X7R capacitors are ideal for this function. The size required will vary depending on the load, output voltage, and input voltage source impedance characteristics. Values range from 1µF to 10µF. The input capacitor RMS current varies with the input voltage and the output voltage. The equation for the RMS current in the input capacitor is: The input capacitor RMS ripple current reaches a maximum when V IN is two times the output volt- age where it is approximately one half of the load current. Losses associated with the input ceramic capacitor are typically minimal and are not an issue. The proper placement of the input capaci- tor can be seen in the evaluation board layout (C1 in Figure 2). VO ⎛ VO ⎞IRMS = IO ⋅ ⋅ 1 - VIN ⎝ VIN ⎠VOUT VOUT 2.5V 2.5V L = ⋅ 1 - = 3.07µH = ⋅ 1 - ∆IPP ⋅ F VIN(MAX) 0.33A ⋅ 1MHz 4.2V Figure 1: AAT1157 Evaluation Board Schematic Lithium-Ion to 2.5V Converter. 3.0µH 2x 22µF C3-C4 10µF 100 0.1µF C1 Murata 10µF 6.3V X5R GRM42-6X5R106K6.3 C3,C4 MuRata 22µF 6.3V GRM21BR60J226ME39L X5R 0805 VOUT+VIN+ L1 Sumida CDRH5D28-3R0NC LX N/C EN VCC VP N/C LX PGND VP VP FB LX PGND PGND SGND N/C AAT1157 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

1MHz 1.2A Buck DC/DC Converter 1157.2005.11.1.4 9 Output Capacitor Since there are no external compensation compo- nents, the output capacitor has a strong effect on loop stability. Larger output capacitance reduces the crossover frequency while increasing the phase mar- gin. For the 2.5V 1.2A design using the 3.0µH induc- tor, a 40µF capacitor provides a stable output. Table 1 provides a list of suggested output capacitor values for various output voltages. In addition to assisting in stability, the output capacitor limits the output ripple and provides holdup during large load transitions. The output capacitor RMS ripple current is given by: For an X7R or X5R ceramic capacitor, the ESR is very low and the dissipation due to the RMS current of the capacitor is not a concern. Tantalum capaci- tors with sufficiently low ESR to meet output voltage ripple requirements also have an RMS current rating well beyond that actually seen in this application. Layout Figures 2 and 3 display the suggested PCB layout for the AAT1157. The following guidelines should be used to help insure a proper layout. 1. The input capacitor (C1) should connect as closely as possible to V P (Pins 10, 11, and 12) and PGND (Pins 1, 2, and 3). 2. C3-C4 and L1 should be connected as close- ly as possible. The connection from L1 to the LX node should be as short as possible. 3. The trace connecting the FB pin to resistors R3 and R4 should be as short as possible by plac- ing R3 and R4 immediately next to the AAT1157. The sense trace connection R3 to the output voltage 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. 4. The resistance of the trace from the load return to the PGND (Pins 1, 2, and 3) and SGND (Pin 5) 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. SGND (Pin 5) can also be used to remotely sense the output ground at the point of load to improve regulation. 5. A low pass filter (R1 and C2) provides a clean- er bias source for the AAT1157 active circuitry. C2 should be placed as closely as possible to SGND (Pin 5) and V CC (Pin 9). 6. For good heat transfer, four 15 mil vias spaced on a 26 mil grid connect the QFN central pad- dle to the bottom side ground plane, as shown in Figures 2 and 3. Thermal Calculations There are three types of losses associated with the AAT1157: MOSFET switching losses, conduction losses, and quiescent current losses. The conduc- tion losses are due to the R DSON characteristics of the internal P- and N-channel MOSFET power devices. At full load, assuming continuous conduc- tion mode (CCM), a simplified form of the total loss- es is given by: VOUT ⋅ (VIN - VOUT)1IRMS = ⋅ L ⋅ F ⋅ VIN2 ⋅ 3 Figure 2: Evaluation Board Top Side. Figure 3: Evaluation Board Bottom Side.

1MHz 1.2A Buck DC/DC Converter 1157.2005.11.1.4 11 Design Example Specifications IOUT 1.2A IRIPPLE 330mA VOUT 2.5V VIN 3.0V to 4.2V FS 1MHz TAMB = 85°C Maximum Input Capacitor Ripple: Inductor Selection: Select Sumida inductor CDRH5D28 3.0µH. Output Capacitor Ripple Current: 3.0µH · 1MHz · 4.2V 23 RMS IN I LFV=· ·· ·

  • = 97.4mArms (VOUT) · (VIN - VOUT) = Pesr = esr · IRMS 2 = 5mΩ · (97.4mA)2 = 47.4µW VO VO 2.5V 2.5V ∆I = ⋅ 1 - = ⋅ 1- = 340mAL ⋅ F VIN 3.0µH ⋅ 1MHz 4.2V IPK = IOUT + ∆I = 1.2A + 0.17A = 1.37A2 P = IO 2 ⋅ DCR = (1.2A)2 ⋅ 31mΩ = 45mW 1 0.59ArmsOO RMS O IN IN VVII VV P = esr · IRMS 2 = 5mΩ · 0.592 A = 1.7mW

1MHz 1.2A Buck DC/DC Converter 12 1157.2005.11.1.4 AAT1157 Dissipation and Junction Temperature Estimate: Surface Mount Inductors Surface Mount Capacitors Value Voltage Manufacturer Part Number (µF) (V) T emp. Co. Case MuRata GRM21BR60J106ME01L 10 6.3 X5R 0805 MuRata GRM21BR60J226ME01L 22 6.3 X5R 0805 MuRata GRM31CR60J106KA01L 10 6.3 X5R 1206 Value Max DC DCR Size (mm) Manufacturer Part Number (µH) Current (A) (m ΩΩ) L x W x H Type TJ(MAX) = TAMB + ΘJA · PTOTAL = 85°C + 50°C/W · 0.341W = 102°C PTOTAL + (tsw · F · IO + IQ) · VIN IO 2 · (RDSON(HS) · VO + RDSON(LS) · (VIN -VO)) VIN = 341mW 4.2V

1MHz 1.2A Buck DC/DC Converter 1157.2005.11.1.4 13

Ordering Information

Package Information

All dimensions in millimeters. 3.000 ± 0.05 Pin 1 Dot By Marking 1.55 ± 0.15 0.400 ± 0.05 3.000 ± 0.05 0.500 ± 0.05 0.850 ± 0.05 Pin 1 Identification 0.025 ± 0.025 0.203 ± 0.0254 0.230 ± 0.05 Top View Bottom View Side View 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/pbfree. Output Voltage Package Marking 1 Part Number (Tape and Reel)2 FB = 0.8V, Adjustable ≥ 0.8V QFN33-16 OEXYY AAT1157IVN-T1 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.

1MHz 1.2A Buck DC/DC Converter 14 1157.2005.11.1.4 Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 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. Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. Testing and other quality con- trol 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.