AAT1126 600mA, 1MHz Step-Down Converter General Description Features The AAT1126 SwitchReg™ is a member of AnalogicTech's Total Power Management IC™ (TPMIC™) product family. It is a 1MHz step-down converter with an input voltage range of 2.7V to 5.5V and output as low as 0.6V. Its low supply current, small size, and high switching frequency make the AAT1126 the ideal choice for portable applications. • • • • • • • • • • • • • • The AAT1126 is available in either a fixed version with internal feedback or a programmable version with external feedback resistors. It can deliver up to 600mA of load current while maintaining a low 25µA no load quiescent current. The 1MHz switching frequency minimizes the size of external components while keeping switching losses low. The AAT1126 feedback and control delivers excellent load regulation and transient response with a small output inductor and capacitor. SwitchReg™ VIN Range: 2.7V to 5.5V VOUT Adjustable Down to 0.6V — Fixed or Adjustable Version Fast Turn-On Time (100µs Typical) 25µA No Load Quiescent Current Up to 97% Efficiency Output Current Up to 600mA 1MHz Switching Frequency Soft Start Over-Temperature Protection Current Limit Protection 100% Duty Cycle Low-Dropout Operation 0.1µA Shutdown Current SOT23-5 Package Temperature Range: -40°C to +85°C Applications The AAT1126 is designed to maintain high efficiency throughout the operating range and provides fast turn-on time. • • • • • • The AAT1126 is available in a Pb-free, space-saving SOT23-5 package and is rated over the -40°C to +85°C temperature range. Cellular Phones Digital Cameras Handheld Instruments Microprocessor / DSP Core / IO Power PDAs and Handheld Computers USB Devices Typical Application (Fixed Output Voltage) VO VIN U1 AAT1126 5 C2 4.7µF 2 1 1126.2006.05.1.1 VIN LX 3 L1 4.7µH EN GND OUT 4 C1 10µF 1 AAT1126 600mA, 1MHz Step-Down Converter Pin Descriptions Pin # Symbol Function 1 GND Ground pin. 2 EN Enable pin. 3 LX Switching node. Connect the inductor to this pin. It is internally connected to the drain of both high- and low-side MOSFETs. 4 OUT Feedback input pin. This pin is connected either directly to the converter output or to an external resistive divider for an adjustable output. 5 VIN Input supply voltage for the converter. Pin Configuration 2 SOT23-5 (Top View) GND 1 EN 2 LX 3 5 VIN 4 OUT 1126.2006.05.1.1 AAT1126 600mA, 1MHz Step-Down Converter Absolute Maximum Ratings1 Symbol VIN VLX VOUT VEN TJ TLEAD Description Input Voltage GND LX to GND OUT to GND EN to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units 6.0 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to 6.0 -40 to 150 300 V V V V °C °C Value Units 667 150 mW °C/W Thermal Information Symbol PD θJA Description Maximum Power Dissipation (SOT23-5) Thermal Resistance2 ( SOT23-5) 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Mounted on an FR4 board. 1126.2006.05.1.1 3 AAT1126 600mA, 1MHz Step-Down Converter Electrical Characteristics1 TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V. Symbol Description Conditions Step-Down Converter VIN Input Voltage VUVLO UVLO Threshold VOUT Output Voltage Tolerance VOUT Output Voltage Range IQ ISHDN IOUT_X RDS(ON)H RDS(ON)L ILXLEAK ΔVLinereg Quiescent Current Shutdown Current Maximum Load Current High Side Switch On Resistance Low Side Switch On Resistance LX Leakage Current Line Regulation VOUT Out Threshold Voltage Accuracy IOUT ROUT Out Leakage Current Out Impedance TS Start-Up Time FOSC TSD THYS Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis VEN(L) VEN(H) IEN Enable Threshold Low Enable Threshold High Input Low Current Min Typ Max Units 5.5 2.6 V V mV V -3.5 +3.5 % 0.6 VIN V 50 µA 1.0 µA mA Ω Ω 1 µA 0.5 %/V 609 mV 0.2 µA kΩ 2.7 VIN Rising Hysteresis VIN Falling IOUT = 0 to 600mA, VIN = 2.7V to 5.5V 100 1.8 No Load, 0.6V Adjustable Version EN = AGND = PGND 25 600 0.45 0.40 VIN = 5.5V, VLX = 0 to VIN, EN = GND VIN = 2.7V to 5.5V 0.6V Output, No Load TA = 25°C 0.6V Output >0.6V Output From Enable to Output Regulation TA = 25°C 591 600 250 100 0.7 1.0 140 15 µs 1.5 MHz °C °C 0.6 V V µA EN VIN = VFB = 5.5V 1.4 -1.0 1.0 1. The AAT1126 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 1126.2006.05.1.1 AAT1126 600mA, 1MHz Step-Down Converter Typical Characteristics Efficiency vs. Load DC Regulation (VOUT = 3.3V; L = 10μ μH) (VOUT = 3.3V; L = 10μ μH) 3.0 90 VIN = 3.9V VIN = 4.2V 80 2.0 Output Error (%) Efficiency (%) 100 70 VIN = 4.2V 1.0 0.0 -1.0 VIN = 3.9V -2.0 -3.0 60 0.1 1 10 100 0.1 1000 1 Efficiency vs. Load 1000 DC Regulation (VOUT = 2.5V; L = 10μ μH) (VOUT = 2.5V; L = 10μ μH) 3.0 100 Output Error (%) VIN = 3.3V Efficiency (%) 100 Output Current (mA) Output Current (mA) 90 VIN = 3.0V VIN = 3.6V 80 70 VIN = 3.3V 2.0 VIN = 3.6V 1.0 0.0 VIN = 3.0V -1.0 -2.0 -3.0 60 0.1 1 10 100 1000 0.1 1 10 100 1000 Output Current (mA) Output Current (mA) Efficiency vs. Load DC Regulation (VOUT = 1.5V; L = 4.7μ μH) (VOUT = 1.5V; L = 4.7μ μH) 3.0 100 VIN = 2.7V VIN = 3.6V Output Error (%) 90 Efficiency (%) 10 80 VIN = 4.2V 70 60 50 VIN = 4.2V 2.0 VIN = 3.6V 1.0 0.0 VIN = 2.7V -1.0 -2.0 -3.0 0.1 1 10 Output Current (mA) 1126.2006.05.1.1 100 1000 0.1 1 10 100 1000 Output Current (mA) 5 AAT1126 600mA, 1MHz Step-Down Converter Typical Characteristics Frequency vs. Input Voltage Output Voltage Error vs. Temperature (VOUT = 1.8V) (VIN = 3.6V; VO = 2.5V) 2.0 1.5 0.5 Output Error (%) Frequency Variation (%) 1.0 0.0 -0.5 -1.0 -1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 -2.0 -40 5.5 -20 0 20 60 80 100 Temperature (°°C) Input Voltage (V) Switching Frequency vs. Temperature Quiescent Current vs. Input Voltage (VIN = 3.6V; VO = 1.5V) (VO = 1.8V) 0.20 35 Supply Current (μ μA) Variation (%) 40 0.10 0.00 -0.10 85°C 30 25°C 25 20 -40°C -0.20 -40 15 -20 0 40 60 80 3.0 3.5 4.0 4.5 5.0 5.5 Input Voltage (V) P-Channel RDS(ON) vs. Input Voltage N-Channel RDS(ON) vs. Input Voltage 750 750 700 700 650 100°C RDS(ON) (mΩ Ω) 120°C 600 550 85°C 500 450 25°C 400 120°C 6.0 100°C 600 550 500 85°C 450 400 350 25°C 350 300 300 2.5 3.0 3.5 4.0 4.5 Input Voltage (V) 6 2.5 100 Temperature (°°C) 650 RDS(ON) (mΩ Ω) 20 5.0 5.5 6.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Input Voltage (V) 1126.2006.05.1.1 AAT1126 600mA, 1MHz Step-Down Converter Typical Characteristics Load Transient Response Load Transient Response (30mA - 300mA; VIN = 3.6V; VOUT = 2.5V; C1 = 22μ μF) 1.3 1.1 300mA 30mA 0.9 0.7 0.5 0.3 0.1 -0.1 2.65 1.5 2.55 Output Voltage (top) (V) 1.5 1.3 0.9 30mA 2.35 0.7 2.25 0.5 0.3 2.15 0.1 2.05 -0.1 Time (25μs/div) Time (25μs/div) Line Transient Line Regulation (VOUT = 2.5V @ 500mA) (VOUT = 1.5V) 7.0 2.55 6.5 2.50 6.0 2.45 5.5 2.40 5.0 2.35 4.5 2.30 2.25 4.0 2.20 3.5 2.15 3.0 2 1.5 Accuracy (%) 2.60 Input Voltage (bottom) (V) Output Voltage (top) (V) 1.1 300mA 2.45 Load and Inductor Current (200mA/div) (bottom) 1.65 1.60 1.55 1.50 1.45 1.40 1.35 1.30 1.25 1.20 1.15 1.10 1.05 1.00 Load and Inductor Current (200mA/div) (bottom) Output Voltage (top) (V) (30mA - 300mA; VIN = 3.6V; VOUT = 1.5V; C1 = 22μ μF) IOUT = 600mA 1 0.5 IOUT = 100mA 0 IOUT = 10mA -0.5 -1 2.5 Time (25μ μs/div) 3 3.5 4 4.5 5 5.5 6 Input Voltage (V) Soft Start Output Ripple (VIN = 3.6V; VOUT = 1.5V; L = 4.7μ μH) 0.8 0 0.7 0.6 -20 0.5 -40 0.4 -60 0.3 -80 0.2 -100 0.1 -120 Time (250ns/div) 1126.2006.05.1.1 4.0 3.5 3.0 3.0 2.0 2.5 1.0 2.0 0.0 1.5 -1.0 1.0 -2.0 0.5 -3.0 0.0 -4.0 -0.5 Inductor Current (bottom) (A) 20 Enable and Output Voltage (top) (V) 0.9 40 Inductor Current (bottom) (A) Output Voltage (AC Coupled) (top) (mV) (VIN = 3.6V; VOUT = 1.8V; 400mA) Time (50μs/div) 7 AAT1126 600mA, 1MHz Step-Down Converter Functional Block Diagram VIN OUT See note Err Amp . DH Voltage Reference LX Logic DL EN INPUT GND Note: For adjustable version, the internal feedback divider is omitted and the OUT pin is tied directly to the internal error amplifier. Functional Description can also be added to the external feedback to provide improved transient response (see Figure 1). The AAT1126 is a high performance 600mA 1MHz monolithic step-down converter. It has been designed with the goal of minimizing external component size and optimizing efficiency over the complete load range. Apart from the small bypass input capacitor, only a small L-C filter is required at the output. Typically, a 4.7µH inductor and a 10µF ceramic capacitor are recommended (see Table of Values). At dropout, the converter duty cycle increases to 100% and the output voltage tracks the input voltage minus the RDSON drop of the P-channel highside MOSFET. The fixed output version requires only three external power components (CIN, COUT, and L). The adjustable version can be programmed with external feedback to any voltage, ranging from 0.6V to the input voltage. An additional feed-forward capacitor The internal error amplifier and compensation provides excellent transient response, load, and line regulation. Soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. 8 The input voltage range is 2.7V to 5.5V. The converter efficiency has been optimized for all load conditions, ranging from no load to heavy load. 1126.2006.05.1.1 AAT1126 600mA, 1MHz Step-Down Converter JP1 VIN 1 2 1 3 Enable L1 4.7µH VOUT = 1.8V C1 10µF C4 100pF R1 118K 2 3 GND VIN EN OUT LX AAT1126 5 4 C2 4.7µF U1 AAT1126 SOT23-5 L1 CDRH3D16-4R7 C1 10μF 10V 0805 X5R C2 4.7μF 10V 0805 X5R C3 n/a R2 59K GND LX Figure 1: Enhanced Transient Response Schematic. Control Loop The AAT1126 is a peak current mode step-down converter. 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 compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The peak current mode loop appears as a voltage-programmed current 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. For fixed voltage versions, the error amplifier reference voltage is internally set to program the converter output voltage. For the adjustable output, the error amplifier reference is fixed at 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 AAT1126 into a low-power, non-switching state. The total 1126.2006.05.1.1 input current during shutdown is less than 1µA. The AAT1126 provides turn-on within 100µs (typical) of the enable input transition. Current Limit and Over-Temperature Protection For overload conditions, the peak input current is limited. 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 hysteresis. 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 VIN input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation. 9 AAT1126 600mA, 1MHz Step-Down Converter Applications Information Inductor Selection The step-down converter uses peak current mode control with slope compensation to maintain stability for duty cycles greater than 50%. The output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. The internal slope compensation for the adjustable and low-voltage fixed versions of the AAT1126 is 0.24A/µsec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 4.7µH inductor. 0.75 ⋅ VO 0.75 ⋅ 1.5V A m= = = 0.24 L 4.7μH μsec This is the internal slope compensation for the adjustable (0.6V) version or low-voltage fixed versions. When externally programming the 0.6V version to 2.5V, the calculated inductance is 7.5µH. 0.75 ⋅ VO L= = m =3 μsec 0.75 ⋅ VO ≈ 3 A ⋅ VO A 0.24A μsec μsec ⋅ 2.5V = 7.5μH A In this case, a standard 10µH value is selected. For high-voltage fixed versions (2.5V and above), m = 0.48A/µsec. Table 1 displays inductor values for the AAT1126 fixed and adjustable options. 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 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 4.7µH CDRH3D16 series inductor selected from Sumida has a 105mΩ DCR and a 900mA DC current rating. At full load, the inductor DC loss is 17mW which gives a 2.8% loss in efficiency for a 400mA, 1.5V output. Input Capacitor Select a 4.7µF to 10µF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for C. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. CIN = VO ⎛ V ⎞ · 1- O VIN ⎝ VIN ⎠ ⎛ VPP ⎞ - ESR · FS ⎝ IO ⎠ VO ⎛ V ⎞ 1 · 1 - O = for VIN = 2 × VO VIN ⎝ VIN ⎠ 4 CIN(MIN) = 1 ⎛ VPP ⎞ - ESR · 4 · FS ⎝ IO ⎠ Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10µF, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6µF. Configuration Output Voltage Inductor Slope Compensation 0.6V Adjustable With External Resistive Divider 0.6V to 2.0V 4.7µH 0.24A/µsec 2.5V to 3.3V 10µH 0.24A/µsec 0.6V to 2.0V 4.7µH 0.24A/µsec 2.5V to 3.3V 4.7µH 0.48A/µsec Fixed Output Table 1: Inductor Values. 10 1126.2006.05.1.1 AAT1126 600mA, 1MHz Step-Down Converter The maximum input capacitor RMS current is: IRMS = IO · VO ⎛ V ⎞ · 1- O VIN ⎝ 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 ⎛ V ⎞ · 1- O = VIN ⎝ VIN ⎠ D · (1 - D) = 0.52 = for VIN = 2 x VO IRMS(MAX) = 1 2 VO ⎛ VO ⎞ The term VIN · ⎝1 - VIN ⎠ appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when VO is twice VIN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at 50% duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT1126. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. The proper placement of the input capacitor (C2) can be seen in the evaluation board layout in Figure 2. IO 2 Figure 2: AAT1126 Evaluation Board Top Side. Figure 3: Exploded View of Evaluation Board Top Side Layout. Figure 4: AAT1126 Evaluation Board Bottom Side. 1126.2006.05.1.1 11 AAT1126 600mA, 1MHz Step-Down Converter A laboratory test set-up typically consists of two long wires running from the bench power supply to the evaluation board input voltage pins. The inductance of these wires, along with the low-ESR ceramic input capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. Errors in the loop phase and gain measurements can also result. Since the inductance of a short PCB trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. In applications where the input power source lead inductance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or aluminum electrolytic should be placed in parallel with the low ESR, ESL bypass ceramic. This dampens the high Q network and stabilizes the system. Output Capacitor The output capacitor limits the output ripple and provides holdup during large load transitions. A 22µF X5R or X7R ceramic capacitor provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL characteristics necessary for low output ripple. The output voltage droop due to a load transient is dominated by the capacitance of the ceramic output capacitor. During a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. Within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. The relationship of the output voltage 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 12 above equation establishes a limit on the minimum value for the output capacitor with respect to load transients. The internal voltage loop compensation limits the minimum output capacitor value to 10µF. This is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. Increased output capacitance will reduce the crossover frequency with greater phase margin. The maximum output capacitor RMS ripple current is given by: IRMS(MAX) = 1 VOUT · (VIN(MAX) - VOUT) L · F · VIN(MAX) 2· 3 · Dissipation due to the RMS current in the ceramic output capacitor ESR is typically minimal, resulting in less than a few degrees rise in hot-spot temperature. Adjustable Output Resistor Selection For applications requiring an adjustable output voltage, the 0.6V version can be externally programmed. Resistors R1 and R2 of Figure 5 program the output to regulate at a voltage higher than 0.6V. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for R2 is 59kΩ. Although a larger value will further reduce quiescent current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. Table 2 summarizes the resistor values for various output voltages with R2 set to either 59kΩ for good noise immunity or 221kΩ for reduced no load input current. ⎛ VOUT ⎞ ⎛ 1.5V ⎞ R1 = V -1 · R2 = 0.6V - 1 · 59kΩ = 88.5kΩ ⎝ REF ⎠ ⎝ ⎠ The adjustable version of the AAT1126, combined with an external feedforward capacitor (C4 in Figure 1), delivers enhanced transient response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a larger output capacitor C1 for stability. 1126.2006.05.1.1 AAT1126 600mA, 1MHz Step-Down Converter Ω R2 = 59kΩ Ω R2 = 221kΩ VOUT (V) Ω) R1 (kΩ Ω) R1 (kΩ 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 75 113 150 187 221 261 301 332 442 464 523 715 1000 Conduction losses are associated with the RDS(ON) characteristics of the power output switching devices. Switching losses are dominated by the gate charge of the power output switching devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the losses is given by: PTOTAL = IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN - VO]) VIN + (tsw · F · IO + IQ) · VIN IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load stepdown converter switching losses. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: Table 2: Adjustable Resistor Values For Use With 0.6V Step-Down Converter. Thermal Calculations PTOTAL = IO2 · RDSON(HS) + IQ · VIN There are three types of losses associated with the AAT1126 step-down converter: switching losses, conduction losses, and quiescent current losses. JP1 VIN 1 2 3 Enable 1 L1 4.7µH VOUT C1 10µF R1 118K R2 59K GND 2 3 GND EN VIN OUT LX AAT1126 5 4 C2 4.7µF U1 AAT1126 SOT23-5 L1 CDRH3D16-4R7 C2 4.7µF 10V 0805 X5R C1 10µF 6.3V 0805 X5R LX Figure 5: AAT1126 Adjustable Evaluation Board Schematic. 1126.2006.05.1.1 13 AAT1126 600mA, 1MHz Step-Down Converter Since RDS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. Given the total losses, the maximum junction temperature can be derived from the θJA for the SOT23-5 package which is 150°C/W. TJ(MAX) = PTOTAL · ΘJA + TAMB Layout The suggested PCB layout for the AAT1126 is shown in Figures 2, 3, and 4. The following guidelines should be used to help ensure a proper layout. 14 1. The input capacitor (C2) should connect as closely as possible to VIN (Pin 3) and GND (Pin 1). 2. C1 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. 3. The feedback trace or OUT pin (Pin 4) 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. If external feedback resistors are used, they should be placed as closely as possible to the OUT pin (Pin 4) to minimize the length of the high impedance feedback trace. 4. The resistance of the trace from the load return to GND (Pin 1) should be kept to a minimum. This will help to minimize any error in DC regulation due to differences in the potential of the load return and the AAT1126 ground. 1126.2006.05.1.1 AAT1126 600mA, 1MHz Step-Down Converter Step-Down Converter Design Example Specifications VO = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA VIN = 2.7V to 4.2V (3.6V nominal) FS = 1.0MHz TAMB = 85°C 1.8V Output Inductor L1 = 3 μsec μsec ⋅ VO2 = 3 ⋅ 1.8V = 5.4μH A A (see Table 1) For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ. ΔIL1 = ⎛ 1.8V⎞ VO V ⎞ 1.8V ⎛ ⋅ 1- O = ⋅ 1- ⎝ = 218mA VIN ⎠ 4.7μH ⋅ 1.0MHz 4.2V⎠ L1 ⋅ F ⎝ IPKL1 = IO + ΔIL1 = 0.4A + 0.11A = 0.51A 2 PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW 1.8V Output Capacitor VDROOP = 0.05V COUT = 3 · ΔILOAD 3 · 0.3A = = 18.0μF 0.05V · 1MHz VDROOP · FS IRMS = (VO) · (VIN(MAX) - VO) 1 1.8V · (4.2V - 1.8V) · = 63mArms = 4.7μH · 1.0MHz · 4.2V L1 · F · V 2· 3 2· 3 IN(MAX) 1 · Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20μW 1126.2006.05.1.1 15 AAT1126 600mA, 1MHz Step-Down Converter Input Capacitor Input Ripple VPP = 25mV CIN = IRMS = ⎛ VPP ⎝ IO 1 1 = = 4.75μF ⎞ ⎛ 25mV ⎞ - 5mΩ · 4 · 1MHz - ESR · 4 · FS ⎠ ⎝ 0.4A ⎠ IO = 0.2Arms 2 P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW AAT1126 Losses PTOTAL = IO2 · (RDSON(HS) · VO + RDSON(LS) · [VIN -VO]) VIN + (tsw · F · IO + IQ) · VIN = 0.42 · (0.45Ω · 1.8V + 0.4Ω · [4.2V - 1.8V]) 4.2V + (5ns · 1.0MHz · 0.4A + 50μA) · 4.2V = 76mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (150°C/W) · 76mW = 96.4°C 16 1126.2006.05.1.1 AAT1126 600mA, 1MHz Step-Down Converter VOUT (V) Ω) R1 (kΩ Ω) R1 (kΩ Adjustable Version (0.6V device) Ω R2 = 59kΩ Ω1 R2 = 221kΩ 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 75.0 113 150 187 221 261 301 332 442 464 523 715 1000 VOUT (V) Ω) R1 (kΩ Fixed Version R2 Not Used 0.6-3.3V 0 L1 (µH) 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 or 6.8 10 10 L1 (µH) 4.7 Table 3: Evaluation Board Component Values. Manufacturer Sumida Sumida MuRata MuRata Coilcraft Coilcraft Coiltronics Coiltronics Coiltronics Coiltronics Part Number Inductance (µH) Max DC Current (A) DCR Ω) (Ω Size (mm) LxWxH Type CDRH3D16-4R7 CDRH3D16/HP-100 LQH32CN4R7M33 LQH32CN4R7M53 LPO6610-472 LPO3310-472 SDRC10-4R7 SDR10-4R7 SD3118-4R7 SD18-4R7 4.7 10 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 0.90 0.84 0.65 0.65 1.10 0.80 1.53 1.30 0.98 1.77 0.11 0.23 0.15 0.15 0.20 0.27 0.117 0.122 0.122 0.082 4.0x4.0x1.8 4.0x4.0x1.8 2.5x3.2x2.0 2.5x3.2x1.55 5.5x6.6x1.0 3.3x3.3x1.0 4.5x3.6x1.0 5.7x4.4x1.0 3.1x3.1x1.85 5.2x5.2x1.8 Shielded Shielded Non-Shielded Non-Shielded 1mm 1mm 1mm Shielded 1mm Shielded Shielded Shielded Table 4: Typical Surface Mount Inductors. 1. For reduced quiescent current R2 = 221kΩ. 1126.2006.05.1.1 17 AAT1126 600mA, 1MHz Step-Down Converter Manufacturer MuRata MuRata Part Number Value Voltage Temp. Co. Case GRM21BR60J226ME39 GRM21BR60J106KE19 22µF 10µF 6.3V 6.3V X5R X5R 0805 0805 Table 5: Surface Mount Capacitors. 18 1126.2006.05.1.1 AAT1126 600mA, 1MHz Step-Down Converter Ordering Information Output Voltage1 Package Marking2 Part Number (Tape and Reel)3 Adj. ≥ 0.6 SOT23-5 QPXYY AAT1126IGV-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/pbfree. Package Information SOT23-5 2.85 ± 0.15 1.90 BSC 0.40 ± 0.10 0.075 ± 0.075 0.15 ± 0.07 4° ± 4° 10° ± 5° 1.10 ± 0.20 0.60 REF 1.20 ± 0.25 2.80 ± 0.20 1.575 ± 0.125 0.95 BSC 0.60 REF 0.45 ± 0.15 GAUGE PLANE 0.10 BSC All dimensions in millimeters. 1. Contact Sales for other voltage options. 2. XYY = assembly and date code. 3. Sample stock is generally held on part numbers listed in BOLD. 1126.2006.05.1.1 19 AAT1126 600mA, 1MHz Step-Down Converter © 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 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. Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 20 1126.2006.05.1.1