PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter General Description Features The AAT1149 SwitchReg is a 3.0MHz step-down converter with an input voltage range of 2.7V to 5.5V and output voltage as low as 1.0V. It is optimized to react quickly to load variations and operate with a tiny 0603 inductor that is only 1mm tall. • • • • • • • • • • • • • • • The AAT1149 output voltage is programmable via external feedback resistors. It can deliver 400mA of load current while maintaining a low 45μA no load quiescent current. The 3.0MHz switching frequency minimizes the size of external components while keeping switching losses low. The AAT1149 maintains high efficiency throughout the operating range, which is critical for portable applications. The AAT1149 is available in a Pb-free, space-saving 2.0x2.1mm SC70JW-8 package or a 5-pin wafer-level chip scale (WLCSP) package and is rated over the -40°C to +85°C temperature range. Ultra-Small 0603 Inductor (Height = 1mm) VIN Range: 2.7V to 5.5V VOUT Adjustable from 1.0V to VIN 400mA Max Output Current Up to 98% Efficiency 45μA No Load Quiescent Current 3.0MHz Switching Frequency 70μs Soft Start Fast Load Transient Over-Temperature Protection Current Limit Protection 100% Duty Cycle Low-Dropout Operation <1μA Shutdown Current SC70JW-8 or 0.9x1.2mm WLCSP 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 VIN = 3.6V C2 4.7µF 1149.2008.08.1.3 VOUT = 1.8V U1 AAT1149 L1 1.8µH IN LX EN FB AGND PGND PGND PGND www.analogictech.com R1 118k R2 59k C1 4.7µF 1 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Pin Descriptions Pin # SC70JW-8 WLCSP Symbol 1 2 EN 2 1 FB 3 4 IN 4 5 LX 5 6, 7, 8 3 AGND PGND Function Enable pin. Feedback input pin. This pin is connected 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 pins. Connect to the output and input capacitor return. Pin Configuration SC70JW-8 (Top View) 2 WLCSP-5 (Top View) EN 1 8 PGND FB 2 7 PGND IN 3 6 PGND LX 4 5 AGND FB AGND/PGND IN www.analogictech.com 1 2 EN 5 LX 3 4 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Absolute Maximum Ratings1 Symbol VIN VLX VFB VEN TJ TLEAD Description Input Voltage to GND LX to GND FB 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 Thermal Information Symbol Description PD Maximum Power Dissipation θJA Thermal Resistance2 SC70JW-8 WLCSP-52, 4 SC70JW-8 WLCSP-5 2, 3 625 352 160 284 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; for the WLCSP package, use the NSMD (none-solder mask defined) pad style for tighter control on the copper etch process. 3. Derate 6.25mW/°C above 25°C. 4. Derate 3.52 mW/°C above 25°C. 1149.2008.08.1.3 www.analogictech.com 3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Electrical Characteristics1 VIN = 3.6V, TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C. Symbol Description Conditions Min Typ Max Units 5.5 2.7 V V mV V % V μA μA mA Step-Down Converter VIN VUVLO UVLO Threshold VOUT VOUT IQ ISHDN ILIM Output Voltage Tolerance Adjustable Output Voltage Range Quiescent Current Shutdown Current P-Channel Current Limit RDS(ON)H High Side Switch On Resistance RDS(ON)L Low Side Switch On Resistance ILXLEAK ΔVLinereg VOUT IOUT TS FOSC TSD THYS EN VEN(L) VEN(H) IEN 2.7 Input Voltage VIN Rising Hysteresis VIN Falling IOUT = 0 to 400mA, VIN = 2.7V to 5.5V No Load VEN = GND 45 3.0 VIN 70 1.0 600 LX Leakage Current Line Regulation Out Threshold Voltage Accuracy Out Leakage Current Start-Up Time Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Input Low Current 100 1.8 -3.0 1.0 SC70JW-8 WLCSP-5 SC70JW-8 WLCSP-5 VIN = 5.5V, VLX = 0 to VIN, VEN = GND VIN = 2.7V to 5.5V 0.6V Output, No Load, TA = 25°C 0.6V Output From Enable to Output Regulation TA = 25°C 0.45 0.40 0.40 0.35 Ω Ω 1 591 0.1 600 609 0.2 70 3.0 140 15 0.6 VIN = VOUT = 5.5V 1.4 -1.0 1.0 μA %/V mV μA μs MHz °C °C V V μA 1. The AAT1149 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 4 www.analogictech.com 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Typical Characteristics Efficiency vs. Load Current Load Regulation (VOUT = 3V; L = 3µH) (VOUT = 3V; L = 3µH) 1.00 100 VIN = 3.3V 0.75 Output Error (%) Efficiency (%) 90 80 VIN = 4.2V 70 VIN = 5V 60 VIN = 4.2V 0.50 VIN = 5V 0.25 0.00 -0.25 -0.50 VIN = 3.3V -0.75 50 -1.00 0.1 1 10 100 0.1 1000 1 Load Current (mA) Load Regulation (VOUT = 1.8V; L = 2.2µH) (VOUT = 1.8V; L = 2.2µH) VIN = 3V 1.00 VIN = 2.7V 0.75 VIN = 3.6V 80 VIN = 5V 70 VIN = 4.2V 60 1000 Load Current (mA) Output Error (%) Efficiency (%) 100 Efficiency vs. Load Current 100 90 10 0.50 VIN = 3V 0.25 VIN = 4.2V 0.00 -0.25 VIN = 5V VIN = 3.6V -0.50 VIN = 2.7V -0.75 50 0.1 1 10 100 -1.00 0.1 1000 1 Load Current (mA) 85°C Frequency Variation (%) Supply Current (µA) 2 25°C 50 40 -40°C 20 10 0 2.5 1000 Switching Frequency vs. Input Voltage 70 30 100 Load Current (mA) No Load Quiescent Current vs. Input Voltage 60 10 1 VOUT = 1.1V 0 -1 -2 VOUT = 1.8V -3 VOUT = 3V -4 3 3.5 4 4.5 5 5.5 6 2.5 Input Voltage (V) 1149.2008.08.1.3 3 3.5 4 4.5 5 5.5 Input Voltage (V) www.analogictech.com 5 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Typical Characteristics Switching Frequency Variation vs. Temperature Output Voltage Error vs. Temperature (VIN = 3.6V; VO = 1.8V; IOUT = 400mA) 2.0 10 8 Output Error (%) Variation (%) 6 4 2 0 -2 -4 -6 1.0 0.0 -1.0 -8 -2.0 -40 -10 -40 -20 0 20 40 60 80 100 120 -20 0 Temperature (°°C) Line Regulation (VOUT = 3V) (VOUT = 1.8V) 1 0.8 0.6 1mA 0.4 0.2 Accuracy (%) Accuracy (%) 0.6 400mA 300mA -0.4 100mA 0mA 600mA -0.6 0mA 0.2 100mA 0 -0.2 -0.4 600mA -1 3 3.5 4 4.5 5 2.5 5.5 Input Voltage (V) 3 3.5 4 4.5 5 5.5 Line Regulation Line Transient (VOUT = 1.1V) (VOUT = 1.8; 400mA Load; No Feedforward Capacitor) 1.90 4.25 1.88 4.00 1.86 3.75 1.84 3.50 1.82 3.25 1.80 3.00 1.78 2.75 1.76 2.50 1.74 Input Voltage (top) (V) 4.50 0.6 0mA 0.2 0 -0.2 400mA 600mA -0.4 -0.6 -0.8 -1 2.5 3 3.5 4 4.5 5 5.5 Output Voltage (bottom) (V) 1 1mA 6 Input Voltage (V) 0.8 0.4 100 -0.8 -1 2.5 Accuracy (%) 80 400mA 0.4 -0.6 -0.8 6 Input Voltage (V) 6 60 Line Regulation 1 -0.2 40 Temperature (°°C) 0.8 0 20 Time (50µs/div) www.analogictech.com 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Line Transient (VOUT = 1.8; CFF = 100pF) 1.94 4.25 1.92 4.00 1.90 3.75 1.88 3.50 1.86 3.25 1.84 3.00 1.82 2.75 1.80 2.50 1.78 1.86 4.50 1.85 4.25 1.84 4.00 1.83 3.75 1.82 3.50 1.81 3.25 1.80 3.00 1.79 2.75 1.78 2.50 Time (50µs/div) Time (20µs/div) N-Channel RDS(ON) vs. Input Voltage P-Channel RDS(ON) vs. Input Voltage (SC70JW-8) (SC70JW-8) 750 750 700 700 120°C 600 650 100°C RDS(ON) (mΩ Ω) RDS(ON) (mΩ Ω) 650 550 500 85°C 450 400 120°C 100°C 600 550 85°C 500 450 25°C 400 25°C 350 350 300 300 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 2.5 4.0 4.5 5.0 5.5 N-Channel RDS(ON) vs. Input Voltage P-Channel RDS(ON) vs. Input Voltage (WLCSP-5) (WLCSP-5) 750 700 700 650 RDS(ON) (mΩ Ω) 100°C 120°C 600 550 500 450 85°C 400 550 500 85°C 450 400 3.5 4 4.5 5 5.5 6 250 2.5 Input Voltage (V) 1149.2008.08.1.3 100°C 120°C 25°C 300 25°C 3 6.0 600 350 350 250 2.5 3.5 Input Voltage (V) 750 300 3.0 Input Voltage (V) 650 RDS(ON) (mΩ Ω) Input Voltage (top) (V) 4.50 Output Voltage (bottom) (V) Line Transient (VOUT = 1.8; No Load; No Feedforward Capacitor) Output Voltage (bottom) (V) Input Voltage (top) (V) Typical Characteristics 3 3.5 4 4.5 5 5.5 6 Input Voltage (V) www.analogictech.com 7 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Load Transient (VOUT = 1.1V; CFF = 100pF) 2.00 1.20 1.75 1.10 1.00 1.50 400mA 1.25 0.90 1.00 1mA 0.80 0.75 0.70 0.50 0.60 0.25 0.50 0.00 1.30 2.00 1.20 1.75 1.10 1.00 0.90 0.75 0.70 0.50 0.60 0.25 0.50 0.00 1.75 1.75 1.50 400mA 1.25 1.25 1.00 10mA 0.75 0.75 0.50 0.25 0.25 0.00 2.00 2.00 1.90 1.75 1.80 1.50 1.70 1.60 1.40 0.50 1.30 0.25 1.20 0.00 Load Transient (VOUT = 1.8V; CFF = 100pF) 2.00 2.00 1.75 1.75 1.50 400mA 1.25 1mA 1.00 1.00 0.75 0.75 0.50 0.50 0.25 0.25 0.00 2.00 2.00 1.90 1.75 1.50 1.80 1.70 400mA 1.25 1.00 1.60 1mA 1.50 0.75 1.40 0.50 1.30 0.25 1.20 0.00 Time (50µs/div) Load and Inductor Current (bottom) (A) 2.25 Output Voltage (top) (V) Load Transient (VOUT = 1.8V; No Feedforward Capacitor) 1.25 0.75 Time (50µs/div) Load and Inductor Current (bottom) (A) Output Voltage (top) (V) 1.00 10mA 1.50 Time (50µs/div) 8 1.25 400mA Load and Inductor Current (bottom) (A) 2.00 2.00 Output Voltage (top) (V) Load Transient (VOUT = 1.8V; CFF = 100pF) Load and Inductor Current (bottom) (A) Output Voltage (top) (V) Load Transient (VOUT = 1.8V; No Feedforward Capacitor) 1.00 1.00 1mA Time (50µs/div) 2.25 1.50 1.25 0.80 Time (50µs/div) 1.50 1.50 400mA Load and Inductor Current (bottom) (A) 1.30 Output Voltage (top) (V) Load Transient (VOUT = 1.1V; No Feedforward Capacitor) Load and Inductor Current (bottom) (A) Output Voltage (top) (V) Typical Characteristics Time (50µs/div) www.analogictech.com 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Soft Start (VOUT = 1.8V; CFF = 100pF) 2.00 3.00 1.75 2.00 1.50 1.00 1.25 0.00 1.00 -1.00 0.75 -2.00 0.50 -3.00 0.25 -4.00 0.00 2.50 2.00 2.00 1.75 1.50 1.50 1.00 1.25 0.50 1.00 0.00 0.75 -0.50 0.50 -1.00 0.25 -1.50 0.00 Time (50µs/div) Soft Start (VOUT = 1.1V; No Feedforward Capacitor) 2.00 3.00 1.75 2.00 1.50 1.00 1.25 0.00 1.00 -1.00 0.75 -2.00 0.50 -3.00 0.25 -4.00 0.00 Time (50µs/div) 1149.2008.08.1.3 3.50 1.25 3.00 1.00 2.50 0.75 2.00 0.50 1.50 0.25 1.00 0.00 0.50 -0.25 0.00 -0.50 -0.50 -0.75 Inductor Current (bottom) (250mA/div) 4.00 Enable and Output Voltage (top) (V) Soft Start (VOUT = 3V; No Feedforward Capacitor) Inductor Current (bottom) (250mA/div) Enable and Output Voltage (top) (V) Time (50µs/div) Inductor Current (bottom) (250mA/div) 4.00 Enable and Output Voltage (top) (V) Soft Start (VOUT = 1.8V; No Feedforward Capacitor) Inductor Current (bottom) (250mA/div) Enable and Output Voltage (top) (V) Typical Characteristics Time (20µs/div) www.analogictech.com 9 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Functional Block Diagram IN FB Err Amp . DH Voltage Reference EN LX Logic DL INPUT PGND AGND Functional Description The AAT1149 is a high performance 400mA 3.0MHz monolithic step-down converter. It minimizes external component size, enabling the use of a tiny 0603 inductor that is only 1mm tall, and optimizes 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 1.8μH inductor and a 4.7μF ceramic capacitor are recommended (see table of values). Only three external power components (CIN, COUT, and L) are required. Output voltage is programmed with external feedback resistors, ranging from 1.0V to the input voltage. An additional feed-forward capacitor can also be 10 added to the external feedback to provide improved transient response (see Figure 4). At dropout, the converter duty cycle increases to 100% and the output voltage tracks the input voltage minus the RDS(ON) drop of the P-channel high-side 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. www.analogictech.com 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Applications Information Control Loop The AAT1149 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 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 AAT1149 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. Under-Voltage Lockout Internal bias of all circuits is controlled via the IN input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation. 1149.2008.08.1.3 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. Table 1 displays suggested inductor values for various output voltages. 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 1.8μH Sumida has rent rating. which gives output. CDRH2D09 series inductor selected from a 131mW DCR and a 400mA saturation curAt full load, the inductor DC loss is 21mW a 2.8% loss in efficiency for a 400mA, 1.8V 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 = V ⎞ VO ⎛ · 1- O VIN ⎝ VIN ⎠ ⎛ VPP ⎞ - ESR · FS ⎝ IO ⎠ VO ⎛ V ⎞ 1 · 1 - O = for VIN = 2 · VO VIN ⎝ VIN ⎠ 4 1 CIN(MIN) = ⎛ 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. www.analogictech.com 11 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Configuration Output Voltage Typical Inductor Value 0.6V Adjustable With External Feedback 1V, 1.2V 1.5V, 1.8V 2.5V 3.3V 1.0μH to 1.2μH 1.5μH to 1.8μH 2.2μH to 2.7μH 3.3μH Table 1: Inductor Values. The maximum input capacitor RMS current is: IRMS = IO · from the bench power supply, most applications do not exhibit this problem. 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 = 1 2 for VIN = 2 · VO IRMS(MAX) = VO IO 2 ⎛ V ⎞ · 1- O The term V ⎝ V ⎠ 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. IN IN The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT1149. 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 1. 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. 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 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: COUT = 3 · ΔILOAD VDROOP · FS 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. Since the inductance of a short PCB trace feeding the input voltage is significantly lower than the power leads 12 www.analogictech.com 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Figure 1: AAT1149IJS Evaluation Board Top Side. Figure 2: Exploded View of Evaluation Board Top Side. Figure 3: AAT1149IJS Evaluation Board Bottom Side. 1149.2008.08.1.3 www.analogictech.com 13 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter 1 2 3 Enable VIN C3 U1 AAT1149 1 R1 8 EN PGND FB PGND IN PGND LX AGND 2 VOUT 7 3 L1 C1 4.7μF 6 4 R2 59k 5 C2 4.7μF GND GND LX U1 AAT1149 SC70JW-8 L1 CDRH2D09 or SD3112 C1,C2 4.7μF 10V 0805 X5R Improved Transient Response Version C3 100pF C1 10μF 10V 0805 X5R Figure 4: AAT1149IJS Evaluation Board Schematic. Figure 5: AAT1149IUV Evaluation Board Top Side. 14 Figure 6: AAT1149IUV Evaluation Board Bottom Side. www.analogictech.com 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter VIN U1 4 5 IN VOUT C3 AAT1149IUV EN L1 LX R1 adj 3 2 2 1 EN FB 1 R2 59k C1 4.7μF C2 4.7μF GND 3 WLCSP-5 Figure 7: AAT1149IUV Evaluation Board Schematic. The maximum output capacitor RMS ripple current is given by: IRMS(MAX) = 1 VOUT · (VIN(MAX) - VOUT) L · FS · 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. Feedback Resistor Selection Resistors R1 and R2 of Figure 4 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 AAT1149, combined with an external feedforward capacitor (C3 in Figure 4), delivers enhanced transient response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a larger output capacitor C1 for stability. VOUT (V) R2 = 59kΩ R1 (kΩ) R2 = 221kW R1 (kΩ) 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 113K 150K 187K 221K 261K 301K 332K 442K 464K 523K 715K 1.00M Table 2: Feedback Resistor Values. 1149.2008.08.1.3 www.analogictech.com 15 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Thermal Calculations 1. There are three types of losses associated with the AAT1149 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: 2. PTOTAL = 3. IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO]) VIN 4. + (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 converter switching losses. 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 5. The input capacitor (C2) should connect as closely as possible to IN (Pin 3) and PGND (Pins 6-8). C1 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. The feedback trace or FB pin (Pin 2) should be sepaate from any power trace and connect as closely as possible to the load point. Sensing along a highcurrent load trace will degrade DC load regulation. If external feedback resistors are used, they should be placed as closely as possible to the FB pin (Pin 2) to minimize the length of the high impedance feedback trace. The resistance of the trace from the load return to the PGND (Pins 6-8) 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. The pad on the PCB for the WLCSP-5 package should use NSMD (non-solder mask defined) configuration due to its tighter control on the copper etch process. A pad thickness of less than 1oz is recommended to achieve higher stand-off. A high density, small footprint layout can be achieved using an inexpensive, miniature, non-shielded, high DCR inductor, as shown in Figure 8. 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 WLCSP Package Light Sensitivity The electrical performance of the WLCSP package can be adversely affected by exposing the device to certain light sources such as direct sunlight or a halogen lamp whose wavelengths are red and infra-reds. However, fluorescent lighting has very little effect on the electrical performance of the WLCSP package. Figure 8: Minimum Footprint Evaluation Board Using 2.0x1.25x1.0mm Inductor. Layout The suggested PCB layout for the AAT1149 is shown in Figures 1, 2, and 3. The following guidelines should be used to help ensure a proper layout. 16 www.analogictech.com 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Step-Down Converter Design Example Specifications VO = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load DILOAD = 300mA VIN = 2.7V to 4.2V (3.6V nominal) FS = 3.0MHz TAMB= 85°C 1.8V Output Inductor L1 = 1 µs µs ⋅ VO = 1 ⋅ 1.8V = 1.8µH (use 2.2μH; see Table 1) A A For Taiyo Yuden inductor CBC2518T2R2M, 2.2μH, DCR = 130mΩ. ΔIL1 = ⎛ VO V ⎞ 1.8V 1.8V⎞ ⎛ ⋅ 1- O = ⋅ 1= 156mA L1 ⋅ FS ⎝ VIN ⎠ 2.2µH ⋅ 3.0MHz ⎝ 4.2V⎠ IPKL1 = IO + ΔIL1 = 0.4A + 0.078A = 0.478A 2 PL1 = IO2 ⋅ DCR = 0.4A2 ⋅ 130mΩ = 21mW 1.8V Output Capacitor VDROOP = 0.1V COUT = IRMS = 3 · ΔILOAD 3 · 0.3A = = 3.0µF; use 4.7µF VDROOP · FS 0.1V · 3.0MHz 1 2· 3 · (VO) · (VIN(MAX) - VO) 1 1.8V · (4.2V - 1.8V) · = 45mArms = L1 · FS · VIN(MAX) 2 · 3 2.2µH · 3.0MHz · 4.2V Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10µW 1149.2008.08.1.3 www.analogictech.com 17 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Input Capacitor Input Ripple VPP = 25mV CIN = IRMS = ⎛ VPP ⎝ IO 1 1 = = 1.45µF; use 2.2µF ⎞ ⎛ 25mV ⎞ - 5mΩ · 4 · 3.0MHz - ESR · 4 · FS ⎠ ⎝ 0.4A ⎠ IO = 0.2Arms 2 P = esr · IRMS2 = 5mΩ · (0.2A)2 = 0.2mW AAT1149 Losses (SC70JW-8 Package) PTOTAL = IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN -VO]) VIN + (tsw · FS · IO + IQ) · VIN = 0.42 · (0.725Ω · 1.8V + 0.7Ω · [4.2V - 1.8V]) 4.2V + (5ns · 3MHz · 0.4A + 70µA) · 4.2V = 140mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (160°C/W) · 140mW = 107°C 18 www.analogictech.com 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Adjustable Version (0.6V device) VOUT (V) R2 = 59kΩ1 R1 (kΩ) R2 = 221kΩ1 R1 (kΩ) L1 (μH) 1.0 1.2 1.5 1.8 2.5 3.3 39.2 59.0 88.7 118 187 267 150 221 332 442 715 1000 1.0 1.2 1.5 1.8 2.2 3.3 Table 3: Evaluation Board Component Values. Manufacturer Part Number/Type Inductance (μH) Rated Current (mA) DCR (Ω) 0.77 1.0 1.5 1.5 2.2 3.3 1.0 2.2 1.2 1.5 1.8 2.5 3.0 1.0 1.5 2.2 3.3 0.68 0.82 1.2 1.5 2.2 3.3 660 520 410 600 550 450 1000 890 590 520 480 440 400 485 445 425 375 980 830 720 630 510 430 110 180 300 200 250 350 80 130 97.5 110 131 150 195 300 400 480 600 31 54 75 104 116 139 BRC1608 Taiyo Yuden BRL2012 CBC2518 Wire Wound Chip Sumida CDRH2D09 Shielded Murata LQH2MCN4R7M02 Unshielded Coiltronics SD3118 Shielded Size (mm) LxWxH 0603 (HMAX = 1mm) 0805 (HMAX = 1mm) 2.5x1.8x1.8 3.2x3.2x1.0 2.0x1.6x0.95 3.15x3.15x1.2 Table 4: Typical Surface Mount Inductors. Manufacturer Part Number Value Voltage Temp. Co. Case Murata Murata Murata GRM219R61A475KE19 GRM21BR60J106KE19 GRM185R60J475M 4.7μF 10μF 4.7μF 10V 6.3V 6.3V X5R X5R X58 0805 0805 0603 Table 5: Surface Mount Capacitors. 1. For reduced quiescent current, R2 = 221kΩ. 1149.2008.08.1.3 www.analogictech.com 19 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter Ordering Information Output Voltage1 Package Marking2 Part Number (Tape and Reel)3 0.6; Adj ≥ 1.0 0.6; Adj ≥ 1.0 SC70JW-8 WLCSP-5 RGXYY RGYW4 AAT1149IJS-0.6-T1 AAT1149IUV-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 SC70JW-8 2.20 ± 0.20 1.75 ± 0.10 0.50 BSC 0.50 BSC 0.50 BSC 0.225 ± 0.075 2.00 ± 0.20 0.100 7° ± 3° 0.45 ± 0.10 4° ± 4° 0.05 ± 0.05 0.15 ± 0.05 1.10 MAX 0.85 ± 0.15 0.048REF 2.10 ± 0.30 All dimensions in millimeters. 1. 2. 3. 4. Contact Sales for other voltage options. XYY = assembly and date code. Sample stock is generally held on part numbers listed in BOLD. YW = date code (year, week) for WLCSP-5 package. 20 www.analogictech.com 1149.2008.08.1.3 PRODUCT DATASHEET AAT1149 SwitchRegTM 3MHz Fast Transient 400mA Step-Down Converter WLCSP-5 0.910 ± 0.035 0.400 BSC 0.180 0.300 0.380 + 0.030 - 0.025 Line_1: Part Code Line_2: Year Code + Date Code 0.300 0.070 1.235 ± 0.035 Line_2 0.4 00 BS C 60° 0.693 BSC Line_1 0.140 0.200 ± 0.030 Top View Side View + 0.030 0.580 -0.070 Bottom View ø 0.2 (Ref.) Pin 1 indication End View Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611 © Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. 1149.2008.08.1.3 www.analogictech.com 21