AAT1143IJS-1.5-T1

1MHz 400mA Step-Down Converter General Description The AAT1143 SwitchReg™ 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 AAT1143 the ideal choice for portable applications. The AAT1143 is available in either a fixed version with internal feedback or a programmable version with external feedback resistors. It can deliver 400mA 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 AAT1143 feedback and control delivers excellent load regulation and transient response with a small output inductor and capacitor. The AAT1143 is designed to maintain high efficiency throughout the operating range, which is critical for portable applications. The AAT1143 is available in a space-saving 2.0x2.1mm SC70JW-8 package and is rated over the -40°C to +85°C temperature range. AAT1143 Features • • • • • • • • • • • • • SwitchReg™ VIN Range: 2.7V to 5.5V VOUT Adjustable Down to 0.6V — Fixed or Adjustable Version 25μA No Load Quiescent Current Up to 95% Efficiency 400mA Max Output Current 1MHz Switching Frequency Soft Start Over-Temperature Protection Current Limit Protection 100% Duty Cycle Low-Dropout Operation 0.1μA Shutdown Current SC70JW-8 Package Temperature Range: -40°C to +85°C Applications • • • • • • Cellular Phones Digital Cameras Handheld Instruments Microprocessor / DSP Core / IO Power PDAs and Handheld Computers USB Devices Typical Application (Fixed Output Voltage) VIN 3 1 VO U1 AAT1143 VIN EN AGND PGND LX OUT PGND PGND 4 2 7 6 Efficiency vs. Load Current (VOUT = 2.5V; VIN = 3.3V) 100 95 L1 4.7μH C1 4.7μF Efficiency (%) 90 85 80 75 70 65 60 0.1 1 10 100 1000 C2 4.7μF 5 8 Output Current (mA) 1143.2006.07.1.10 1 1MHz 400mA Step-Down Converter Pin Descriptions Pin # 1 2 3 4 5 6, 7, 8 AAT1143 Symbol EN OUT VIN LX AGND PGND Function Enable pin. Feedback input pin. This pin is connected either directly to the converter output or to an external resistive divider for an adjustable output. Input supply voltage for the converter. Switching node. Connect the inductor to this pin. It is internally connected to the drain of both high- and low-side MOSFETs. Non-power signal ground pin. Main power ground return pin. Connect to the output and input capacitor return. Pin Configuration SC70JW-8 (Top View) EN OUT VIN LX 1 2 3 4 8 7 6 5 PGND PGND PGND AGND 2 1143.2006.07.1.10 1MHz 400mA Step-Down Converter Absolute Maximum Ratings1 Symbol VIN VLX VOUT VEN TJ TLEAD AAT1143 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 6.0 -0.3 to VP + 0.3 -0.3 to VP + 0.3 -0.3 to 6.0 -40 to 150 300 Units V V V V °C °C Thermal Information Symbol PD θJA Description Maximum Power Dissipation (SC70JW-8) Thermal Resistance2 (SC70JW-8) Value 625 160 Units mW °C/W 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. 1143.2006.07.1.10 3 1MHz 400mA 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 Min 2.7 VIN Rising Hysteresis VIN Falling IOUT = 0 to 400mA, VIN = 2.7V to 5.5V Fixed Output Version Adjustable Output Version2 No Load, 0.6V Adjustable Version EN = AGND = PGND 100 1.8 -3.0 0.6 0.6 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 TA = 25°C 1 0.2 597 250 0.7 600 615 0.2 1.0 140 15 1.5 +3.0 4.0 2.5 50 1.0 AAT1143 Typ Max 5.5 2.6 Units V V mV V % V μA μA mA Ω Ω μA %/V mV μA kΩ MHz °C °C V V μA Step-Down Converter VIN Input Voltage VUVLO VOUT VOUT IQ ISHDN ILIM RDS(ON)H RDS(ON)L ILXLEAK ΔVLinereg VOUT IOUT ROUT FOSC TSD THYS EN VEN(L) VEN(H) IEN Enable Threshold Low Enable Threshold High Input Low Current UVLO Threshold Output Voltage Tolerance Output Voltage Range Quiescent Current Shutdown Current P-Channel Current Limit High Side Switch On Resistance Low Side Switch On Resistance LX Leakage Current Line Regulation Out Threshold Voltage Accuracy Out Leakage Current Out Impedance Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis 0.6 VIN = VFB = 5.5V 1.4 -1.0 1.0 1. The AAT1143 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. 2. For adjustable version with higher than 2.5V output, please consult your AnalogicTech representative. 4 1143.2006.07.1.10 1MHz 400mA Step-Down Converter Typical Characteristics Efficiency vs. Load (VOUT = 2.5V; L = 4.7μH) VIN = 3.3V 100 2.0 AAT1143 (VOUT = 2.5V; L = 4.7μH) Load Regulation VIN = 3.0V Efficiency (%) 90 Output Error (%) 1.0 VIN = 3.0V 0.0 80 VIN = 3.6V VIN = 3.3V -1.0 70 VIN = 3.6V 60 0.1 -2.0 1 10 100 1000 0.1 1 10 100 1000 Output Current (mA) Output Current (mA) Efficiency vs. Load (VOUT = 1.8V; L = 4.7μH) VIN = 3.6V 100 90 2.0 (VOUT = 1.8V; L = 4.7μH) DC Regulation VIN = 2.7V Output Error (%) Efficiency (%) 1.0 VIN = 4.2V 80 70 60 50 0.1 1 10 100 1000 VIN = 4.2V 0.0 VIN = 2.7V -1.0 VIN = 3.6V -2.0 0.1 1 10 100 1000 Output Current (mA) Output Current (mA) Frequency vs. Input Voltage (VOUT = 1.8V) 1.0 2.0 Output Voltage Error vs. Temperature (VIN = 3.6V; VO = 1.5V) Frequency Variation (%) Output Error (%) 0.5 0.0 -0.5 -1.0 -1.5 -2.0 2.7 1.0 INTERNAL DOCUMENT DO NOT COPY 0.0 -1.0 -2.0 3.1 3.5 3.9 4.3 4.7 5.1 5.5 -40 -20 0 20 40 60 80 100 Input Voltage (V) Temperature (°C) 1143.2006.07.1.10 5 1MHz 400mA Step-Down Converter Typical Characteristics Switching Frequency vs. Temperature (VIN = 3.6V; VO = 1.5V) 0.20 35 AAT1143 Quiescent Current vs. Input Voltage (VO = 1.8V) 85°C 30 Variation (%) 0.10 Supply Current (μA) 25°C 25 0.00 -0.10 20 -40°C 15 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 -0.20 -40 -20 0 20 40 60 80 100 Temperature (°C) Input Voltage (V) P-Channel RDS(ON) vs. Input Voltage 750 700 650 Load Transient Response (30mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10μF) 2.0 1.9 1.4 1.2 1.0 300mA 30mA 0.8 0.6 0.4 0.2 0.0 -0.2 Load and Inductor Current (200mA/div) (bottom) Output Voltage (top) (V) 5.0 5.5 6.0 RDS(ON) (mΩ) 120°C 100°C 600 550 500 450 400 350 300 2.5 3.0 3.5 4.0 4.5 25°C 85°C 1.8 1.7 1.6 1.5 1.4 1.3 1.2 Time (25μs/div) Input Voltage (V) N-Channel RDS(ON) vs. Input Voltage Output Voltage (AC Coupled) (top) (V) 750 700 650 120°C 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 Load Transient Response (30mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10μF; C4 = 100pF; see Figure 1) 1.4 1.2 300mA 30mA 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 Load and Inductor Current (200mA/div) (bottom) RDS(ON) (mΩ) 100°C 600 550 500 450 400 350 300 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 25°C 85°C Input Voltage (V) Time (25μs/div) 6 1143.2006.07.1.10 1MHz 400mA Step-Down Converter Typical Characteristics Load Transient Response (30mA to 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7μF) 2.0 1.9 1.4 1.2 1.0 300mA 30mA 0.8 0.6 0.4 0.2 0.0 -0.2 1.90 1.85 AAT1143 Line Transient (VOUT = 1.8V @ 400mA) 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 Load and Inductor Current (200mA/div) (bottom) Output Voltage (top) (V) Output Voltage (top) (V) 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.80 1.75 1.70 1.65 1.60 1.55 1.50 Input Voltage (bottom) (V) Time (25μs/div) Time (25μs/div) Line Regulation (VOUT = 1.8V) 0.05 0 Soft Start (VIN = 3.6V; VOUT = 1.8V; 400mA) Enable and Output Voltage (top) (V) 4.0 3.0 2.0 1.0 0.0 -1.0 -2.0 -3.0 -4.0 3.5 3.0 0.1 IOUT = 100mA Inductor Current (bottom) (A) Accuracy (%) 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -0.05 -0.1 -0.15 -0.2 -0.25 -0.3 -0.35 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 IOUT = 10mA IOUT = 400mA Input Voltage (V) Time (250μs/div) Output Ripple (VIN = 3.6V; VOUT = 1.8V; 400mA) Output Voltage (AC Coupled) (top) (mV) 40 20 0 -20 -40 -60 -80 -100 -120 0.9 0.8 Inductor Current (bottom) (A) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Time (250ns/div) 1143.2006.07.1.10 7 1MHz 400mA Step-Down Converter Functional Block Diagram OUT VIN AAT1143 See note Err Amp . DH Voltage Reference Logic LX DL EN INPUT PGND AGND Note: For adjustable version, the internal feedback divider is omitted and the FB pin is tied directly to the internal error amplifier. Functional Description The AAT1143 is a high performance 400mA 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 4.7μF ceramic capacitor are recommended (see table of values). 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 can also be added to the external feedback to provide improved transient response (see Figure 1). 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 input voltage range is 2.7V to 5.5V. The converter efficiency has been optimized for all load conditions, ranging from no load to 400mA. 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 1143.2006.07.1.10 1MHz 400mA Step-Down Converter 1 2 3 AAT1143 Enable VIN C4 100pF 1 U1 AAT1143 R1 EN PGND 8 7 6 5 2 3 4 VOUT =1.8V 118k L1 C1 10μF 4.7μH R2 59k OUT PGND VIN LX PGND AGND C2 4.7μF GND LX GND2 U1 AAT1143 SC70JW-8 L1 CDRH3D16-4R7 C2 4.7μF 10V 0805 X5R C1 10μF 6.3V 0805 X5R Figure 1: Enhanced Transient Response Schematic. Control Loop The AAT1143 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. into a low-power, non-switching state. The total input current during shutdown is less than 1μA. 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. 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 AAT1143 1143.2006.07.1.10 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 1MHz 400mA 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 AAT1143 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. AAT1143 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. 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 μsec 0.75 ⋅ VO ≈ 3 A ⋅ VO A 0.24A μsec CIN = VO ⎛ V⎞ · 1- O VIN ⎝ VIN ⎠ ⎛ VPP ⎞ - ESR · FS ⎝ IO ⎠ =3 μsec ⋅ 2.5V = 7.5μH A VO ⎛ V⎞ 1 · 1 - O = for VIN = 2 · VO VIN ⎝ VIN ⎠ 4 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 AAT1143 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 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 0.6V Adjustable With External Resistive Divider Fixed Output Output Voltage 0.6V to 2.0V 2.5V 0.6V to 2.0V 2.5V to 3.3V Inductor 4.7μH 10μH 4.7μH 4.7μH Slope Compensation 0.24A/μsec 0.24A/μsec 0.24A/μsec 0.48A/μsec Table 1: Inductor Values. 10 1143.2006.07.1.10 1MHz 400mA Step-Down Converter The maximum input capacitor RMS current is: AAT1143 IRMS = IO · VO ⎛ V⎞ · 1- O VIN ⎝ VIN ⎠ 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. 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 ⎠ for VIN = 2 · VO D · (1 - D) = 0.52 = 1 2 Output Capacitor The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7μF to 10μF X5R or X7R ceramic capacitor typically 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: 3 · ΔILOAD VDROOP · FS IRMS(MAX) = VO ⎛ IO 2 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 AAT1143. 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. 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. VO ⎞ COUT = Once the average inductor current increases to the DC load level, the output voltage recovers. The above equation 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 4.7μF. 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. 1143.2006.07.1.10 11 1MHz 400mA Step-Down Converter AAT1143 Figure 2: AAT1143 Evaluation Board Top Side. Figure 3: Exploded View of Evaluation Board Top Side Layout. Figure 4: AAT1143 Evaluation Board Bottom Side. The maximum output capacitor RMS ripple current is given by: VOUT · (VIN(MAX) - VOUT) L · FS · VIN(MAX) 2· 3 · 1 IRMS(MAX) = 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. 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 ⎠ ⎝ ⎠ 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 12 1143.2006.07.1.10 1MHz 400mA Step-Down Converter The adjustable version of the AAT1143, 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. R2 = 59kΩ VOUT (V) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 AAT1143 Thermal Calculations There are three types of losses associated with the AAT1143 step-down converter: switching losses, conduction losses, and quiescent current losses. 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: IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO]) VIN R2 = 221kΩ R1 (kΩ) 75 113 150 187 221 261 301 332 442 464 523 715 R1 (kΩ) 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 PTOTAL = + (tsw · FS · 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. Table 2: Adjustable Resistor Values For Use With 0.6V Step-Down Converter. 1 2 3 VIN Enable 1 U1 AAT1143 EN OUT VIN LX PGND PGND PGND AGND 8 7 6 5 2 3 4 R1 118k VOUT C1 4.7μF L1 4.7μH R2 59k C2 4.7μF GND GND2 LX U1 AAT1143 SC70JW-8 L1 CDRH3D16-4R7 C1, C2 4.7μF 10V 0805 X5R Figure 5: AAT1143 Adjustable Evaluation Board Schematic. 1143.2006.07.1.10 13 1MHz 400mA Step-Down Converter For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: PTOTAL = IO2 · RDS(ON)H + IQ · VIN AAT1143 Layout The suggested PCB layout for the AAT1143 is shown in Figures 2, 3, and 4. The following guidelines should be used to help ensure a proper layout. 1. The input capacitor (C2) should connect as closely as possible to VIN (Pin 3) and PGND (Pins 6 through 8). 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 2) 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 2) to minimize the length of the high impedance feedback trace. 4. The resistance of the trace from the load return to PGND (Pins 6 through 8) should be kept to a minimum. This will help to minimize any error in DC regulation due to differences in the potential of the internal signal ground and the power ground. 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 SC70JW-8 package which is 160°C/W. For the condition where the buck converter is in dropout at 100% duty cycle, the total device dissipation reduces to: PTOTAL = IO2 · RDS(ON)H + IQ · VIN 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 SC70JW-8 package which is 160°C/W. TJ(MAX) = PTOTAL · ΘJA + TAMB 14 1143.2006.07.1.10 1MHz 400mA Step-Down Converter Step-Down Converter Design Example Specifications VO VIN FS TAMB = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ΔILOAD = 300mA = 2.7V to 4.2V (3.6V nominal) = 1.0MHz = 85°C AAT1143 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. ⎛ 1.8V⎞ VO 1.8V ⎛ V⎞ ⋅ 1- O = ⋅ 1-⎝ = 218mA 4.2V⎠ L1 ⋅ FS ⎝ VIN ⎠ 4.7μH ⋅ 1.0MHz ΔIL1 = IPKL1 = IO + ΔIL1 = 0.4A + 0.11A = 0.51A 2 PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW 1.8V Output Capacitor VDROOP = 0.2V 3 · ΔILOAD 3 · 0.3A = = 4.5μF 0.2V · 1MHz VDROOP · FS (VO) · (VIN(MAX) - VO) 1 1.8V · (4.2V - 1.8V) · = 63mArms = 4.7μH · 1.0MHz · 4.2V L1 · FS · VIN(MAX) 2· 3 2· 3 1 · COUT = IRMS = Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20μW 1143.2006.07.1.10 15 1MHz 400mA Step-Down Converter Input Capacitor Input Ripple VPP = 25mV AAT1143 CIN = ⎛ VPP ⎝ IO 1 1 = = 4.75μF ⎞ ⎛ 25mV ⎞ - 5mΩ · 4 · 1MHz - ESR · 4 · FS ⎠ ⎝ 0.4A ⎠ IRMS = IO = 0.2Arms 2 P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW AAT1143 Losses IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN -VO]) VIN PTOTAL = + (tsw · FS · IO + IQ) · VIN = 0.42 · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V]) 4.2V + (5ns · 1.0MHz · 0.4A + 50μA) · 4.2V = 122mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 122mW = 104.5°C 16 1143.2006.07.1.10 1MHz 400mA Step-Down Converter VOUT (V) Adjustable Version (0.6V device) AAT1143 R1 (kΩ) R2 = 59kΩ R1 (kΩ) R2 = 221kΩ1 L1 (μH) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 75.0 113 150 187 221 261 301 332 442 464 523 715 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 VOUT (V) Fixed Version R1 (kΩ) R2 Not Used L1 (μH) 4.7 0.6-3.3V 0 Table 3: Evaluation Board Component Values. Manufacturer Sumida Sumida MuRata MuRata MuRata Coilcraft Coilcraft Coiltronics Coiltronics Coiltronics Coiltronics Part Number CDRH3D16-4R7 CDRH3D16-100 LQH32CN4R7M23 LQH32CN4R7M33 LQH32CN4R7M53 LPO6610-472 LPO3310-472 SDRC10-4R7 SDR10-4R7 SD3118-4R7 SD18-4R7 Inductance (μH) 4.7 10 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 4.7 Max DC Current (A) 0.90 0.55 0.45 0.65 0.65 1.10 0.80 1.53 1.30 0.98 1.77 DCR (Ω) 0.11 0.21 0.20 0.15 0.15 0.20 0.27 0.117 0.122 0.122 0.082 Size (mm) LxWxH 3.8x3.8x1.8 3.8x3.8x1.8 2.5x3.2x2.0 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 Type Shielded Shielded Non-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. 1143.2006.07.1.10 17 1MHz 400mA Step-Down Converter Manufacturer MuRata MuRata MuRata MuRata AAT1143 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 5: Surface Mount Capacitors. 18 1143.2006.07.1.10 1MHz 400mA Step-Down Converter Ordering Information Output Voltage1 0.6 1.2 1.5 1.6 1.8 2.5 3.3 AAT1143 Package SC70JW-8 SC70JW-8 SC70JW-8 SC70JW-8 SC70JW-8 SC70JW-8 SC70JW-8 Marking2 NUXYY PBXYY NXXYY PYXYY OKXYY OYXYY PLXYY Part Number (Tape and Reel)3 AAT1143IJS-0.6-T1 AAT1143IJS-1.2-T1 AAT1143IJS-1.5-T1 AAT1143IJS-1.6-T1 AAT1143IJS-1.8-T1 AAT1143IJS-2.5-T1 AAT1143IJS-3.3-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 SC70JW-8 0.50 BSC 0.50 BSC 0.50 BSC 1.75 ± 0.10 0.225 ± 0.075 2.00 ± 0.20 2.20 ± 0.20 0.048REF 0.85 ± 0.15 1.10 MAX 0.15 ± 0.05 0.100 7° ± 3° 0.45 ± 0.10 2.10 ± 0.30 4° ± 4° 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. 1143.2006.07.1.10 0.05 ± 0.05 19 1MHz 400mA Step-Down Converter AAT1143 © 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 1143.2006.07.1.10