PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter General Description Features The AAT2146 SwitchReg is a 2MHz step-down converter with an input voltage range of 2.7V to 5.5V and output voltage as low as 0.6V. It is optimized to react quickly to a load variation. The AAT2146 incorporates a unique low noise architecture which reduces ripple and spectral noise. * * * * * * * * * * * * * * * * The AAT2146 is available in fixed voltage versions with internal feedback and a programmable version with external feedback resistors. It can deliver 600mA of load current while maintaining a low 37A no load quiescent current. The 2MHz switching frequency minimizes the size of external components while keeping switching losses low. The AAT2146 is designed to maintain high efficiency throughout the operating range, which is critical for portable applications. The AAT2146 is available in the Pb-free, space-saving 2.0x2.1mm SC70JW-8 package and is rated over the -40C to +85C temperature range. VIN Range: 2.7V to 5.5V Low Noise Light Load Mode Low Ripple PWM Mode VOUT Fixed or Adjustable from 0.6V to VIN 37A No Load Quiescent Current Up to 98% Efficiency 600mA Max Output Current 2MHz Switching Frequency 150s Soft Start Fast Load Transient Over-Temperature Protection Current Limit Protection 100% Duty Cycle Low-Dropout Operation <1A Shutdown Current SC70JW-8 Package Temperature Range: -40C to +85C Applications * * * * * * Cellular Phones Digital Cameras Handheld Instruments Microprocessor / DSP Core / IO Power PDAs and Handheld Computers USB Devices Typical Application (Fixed Output Voltage) U1 AAT2146 VIN C2 2.2F 2146.2008.04.1.1 VIN LX EN OUT AGND PGND PGND PGND www.analogictech.com L1 4.7H VO C1 4.7F 1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Pin Descriptions Pin # Symbol 1 EN 2 OUT 3 VIN 4 LX 5 6, 7, 8 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 pins. Connect to the output and input capacitor return. Pin Configuration SC70JW-8 (Top View) 2 EN 1 8 PGND OUT 2 7 PGND VIN 3 6 PGND LX 4 5 AGND www.analogictech.com 2146.2008.04.1.1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA 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 VIN + 0.3 -40 to 150 300 V V V V C C Value Units 625 160 mW C/W Thermal Information Symbol PD JA Description Maximum Power Dissipation Thermal Resistance2 2, 3 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. 3. Derate 6.25mW/C above 25C. 2146.2008.04.1.1 www.analogictech.com 3 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Electrical Characteristics1 TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C, VIN = 3.6V. Symbol Description Conditions Min Typ Max Units 5.5 2.7 V V mV V % V A A mA %/V mV A k s MHz C C Step-Down Converter VIN VUVLO VOUT VOUT IQ ISHDN ILIM RDS(ON)H RDS(ON)L VLinereg VOUT IOUT ROUT TS FOSC TSD THYS EN VEN(L) VEN(H) IEN 2.7 Input Voltage 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 Line Regulation Out Threshold Voltage Accuracy Out Leakage Current Out Impedance Start-Up Time Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Input Low Current VIN Rising Hysteresis VIN Falling IOUT = 0 to 600mA, VIN = 2.7V to 5.5V 100 1.8 -3.0 0.6 No Load, 0.6V Adjustable Version EN = AGND = PGND +3.0 VIN 70 1.0 37 800 VIN = 2.7V to 5.5V; IOUT = 600mA 0.6V Output, No Load; TA = 25C 0.6V Output >0.6V Output From Enable to Output Regulation TA = 25C 591 0.35 0.30 0.1 600 609 0.2 250 0.9 150 2.0 140 15 2.6 0.6 VIN = VOUT = 5.5V 1.4 -1.0 1.0 V V A 1. The AAT2146 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 4 www.analogictech.com 2146.2008.04.1.1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Typical Characteristics Efficiency vs. Output Current Load Regulation (VOUT = 1.8V) (VOUT = 1.8V) 100 1 0.8 Output Error (%) Efficiency (%) 90 80 70 60 50 VIN = 2.7V VIN = 3.6V VIN = 4.2V 40 30 0.1 1 10 100 0.6 0.4 0.2 0 -0.2 -0.4 VIN = 2.7V VIN = 3.6V VIN = 4.2V -0.6 -0.8 -1 1000 0.1 1 10 Output Current (mA) Efficiency vs. Output Current Load Regulation (VOUT = 2.5V) (VOUT = 2.5V) 1 100 Output Error (%) Efficiency (%) 80 70 60 VIN = 3V VIN = 3.6V VIN = 4.2V VIN = 5V 50 40 1 10 100 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0.1 1000 1 10 Output Current (mA) Efficiency vs. Output Current Load Regulation (VOUT = 3.3V) (VOUT = 3.3V) 1 Output Error (%) 80 70 60 50 VIN = 3.6V VIN = 4.2V VIN = 5V 40 1 10 100 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 1000 -1 0.1 Output Current (mA) 2146.2008.04.1.1 1000 VIN = 3.6V VIN = 4.2V VIN = 5V 0.8 90 Efficiency (%) 100 Output Current (mA) 100 30 0.1 1000 VIN = 3V VIN = 3.6V VIN = 4.2V VIN = 5V 0.8 90 30 0.1 100 Output Current (mA) 1 10 100 1000 Output Current (mA) www.analogictech.com 5 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Typical Characteristics Line Regulation Switching Frequency vs. Temperature (VOUT = 1.8V) 1mA 400mA 600mA 0.4 0.3 Accuracy (%) Switching Frequency (MHz) (VOUT = 1.8V; IOUT = 1A) 0.5 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 2.08 2.06 2.04 2.02 2 1.98 1.96 1.94 1.92 -40 -15 10 Input Voltage (V) 35 60 85 Input Voltage (V) Frequency Variation vs. Input Voltage Output Voltage Error vs. Temperature (VIN = 3.6V; VO = 1.8V, IOUT = 400mA) 2.0 Output Voltage Error (%) Frequency Variation (%) 4 3 2 1 0 -1 -2 VOUT = 1.8V VOUT = 3V -3 -4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 1.0 0.0 -1.0 -2.0 -40 5.5 -20 0 550 60 55 45 40 35 30 25 85C 25C -40C 20 15 3.1 3.5 3.9 4.3 80 100 120C 100C 85C 25C 500 50 RDS(ON) (m ) Supply Current (A) 60 P-Channel RDS(ON) vs. Input Voltage No Load Quiescent Current vs. Input Voltage 4.7 5.1 450 400 350 300 250 5.5 200 2.5 3 3.5 4 4.5 5 5.5 6 Input Voltage (V) Input Voltage (V) 6 40 Temperature (C) Input Voltage (V) 10 2.7 20 www.analogictech.com 2146.2008.04.1.1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Typical Characteristics N-Channel RDS(ON) vs. Input Voltage Load Transient (VIN = 3.6V; VOUT = 1.8V; COUT = 10F; CFF = 100pF) RDS(ON) (m ) 500 450 Output Voltage (top) (V) 120C 100C 85C 25C 400 350 300 250 200 2.5 1.8 1.7 1.5 3.5 4 4.5 5 5.5 1.3 300mA 1.2 1mA 6 Time (50s/div) Load Transient Load Transient (VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F; CFF = 0pF) (VIN = 3.6V; VOUT = 1.8V; COUT = 10F; CFF = 0pF) 1.7 400mA 300mA 1.65 1.6 400mA 1.55 300mA 1.5 Output Voltage (top) (V) 1.75 1.85 1.8 1.75 1.7 400mA 300mA 1.65 1.6 1.55 400mA 300mA 1.5 Time (50s/div) Output and Inductor Current (100mA/div) 1.8 Output and Inductor Current (100mA/div) 1.85 Output Voltage (top) (V) 1mA 1.4 Input Voltage (V) Time (50s/div) Line Transient (VOUT = 1.8V; VIN = 3.6V to 4.2V; IOUT = 400mA; CFF = 0pF) 1.7 1.65 400mA 300mA 1.6 1.55 300mA 400mA 1.5 4.8 1.92 4.2 1.9 3.6 1.88 3 1.86 2.4 1.84 1.8 1.82 1.2 1.8 0.6 1.78 0 1.76 Time (50s/div) 2146.2008.04.1.1 Output Voltage (bottom) (V) 1.75 Output and Inductor Current (100mA/div) 1.8 Input Voltage (top) (V) Load Transient (VIN = 3.6V; VOUT = 1.8V; COUT = 10F; CFF = 100pF) 1.85 Output Voltage (top) (V) 300mA 1.6 1.1 3 Output and Inductor Current (100mA/div) 1.9 550 Time (50s/div) www.analogictech.com 7 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Output Ripple (VOUT = 1.8V; VIN = 3.6V; IOUT = 400mA; CFF = 0pF) 0.02 0.35 0.01 0.3 -0.01 0.2 -0.02 0.15 -0.03 0.1 -0.04 0.05 -0.05 0 -0.06 -0.05 0.02 1.4 0.01 1.2 0 1 -0.01 0.8 -0.02 0.6 -0.03 0.4 -0.04 0.2 -0.05 0 -0.06 -0.2 Time (10s/div) Inductor Current (bottom) (A) 0.25 0 Output Voltage (top) (V) Output Ripple (VOUT = 1.8V; VIN = 3.6V; IOUT = 1mA; CFF = 0pF) Inductor Current (bottom) (A) Output Voltage (top) (V) Typical Characteristics Time (10s/div) Soft Start 4 3 2 1 0 0.5 0 -0.5 Input Current (bottom) (A) Enable Voltage (top) (V) Output Voltage (middle) (V) (VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA) Time (100s/div) 8 www.analogictech.com 2146.2008.04.1.1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Functional Block Diagram VIN OUT See note Err Amp . DH Voltage Reference EN LX Logic DL INPUT PGND AGND Note: For adjustable version, the internal feedback divider is omitted and the OUT pin is tied directly to the internal error amplifier. Functional Description The AAT2146 is a high performance 600mA 2MHz monolithic step-down converter. It has been designed with the goal of minimizing external component size and optimizing efficiency over the complete load range, and produces reduced ripple and spectral noise. Apart from the small bypass input capacitor, only a small L-C filter is required at the output. Typically, a 4.7H inductor and a 4.7F 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 addi- 2146.2008.04.1.1 tional 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 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 600mA. 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 9 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter 1 2 3 VIN Enable U1 AAT2146 CFF VOUT C1 10F 1 R1 2 118k 3 L1 4.7H 4 EN PGND OUT PGND VIN PGND LX AGND 8 7 6 5 C2 4.7F R2 59k GND GND2 LX U1 AAT2146 SC70JW-8 L1 CDRH3D16-4R7 C1 10F 10V 0805 X5R C2 4.7F 10V 0805 X5R CFF 100pF 0402 X5R Figure 1: Enhanced Transient Response Schematic. Control Loop The AAT2146 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 AAT2146 into a low-power, non-switching state. The total input current during shutdown is less than 1A. 10 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 140C with 15C 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. www.analogictech.com 2146.2008.04.1.1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Applications Information Input Capacitor 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 AAT2146 is 0.24A/s. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 4.7H inductor. m= CIN = 0.75 VO s 0.75 VO 3 A VO = m A 0.24A s =3 s 2.5V = 7.5H A For high-voltage fixed versions (2.5V), m = 0.48A/s. Table 1 displays inductor values for the AAT2146 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 4.7H CDRH3D16 series inductor selected from Sumida has a 105m 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. 2146.2008.04.1.1 CIN(MIN) = VPP - ESR * FS IO 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 10F, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6F. Configuration In this case, a standard 6.8H value is selected. V VO * 1- O VIN VIN VO V 1 * 1 - O = for VIN = 2 * VO VIN VIN 4 0.75 VO 0.75 1.5V A = = 0.24 L 4.7H s 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 7.5H. L= Select a 2.2F to 10F 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. Output Voltage Inductor 1V, 1.2V 1.5V, 1.8V 2.5V, 3.3V 0.6V to 3.3V 2.2H 4.7H 6.8H 4.7H 0.6V Adjustable With External Feedback Fixed Output Table 1: Inductor Values. 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 www.analogictech.com D * (1 - D) = 0.52 = 1 2 11 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Output Capacitor for VIN = 2 * VO I IRMS(MAX) = O 2 VO 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 AAT2146. 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 output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7F to 10F 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: 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. 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. 12 COUT = 3 * ILOAD 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 4.7F. 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. www.analogictech.com 2146.2008.04.1.1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Figure 2: AAT2146 Evaluation Board Component Side Layout. Figure 3: Exploded View of AAT2146 Evaluation Board Component Side Layout. Figure 4: AAT2146 Evaluation Board Solder Side Layout. 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 59k. 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 2146.2008.04.1.1 R2 set to either 59k for good noise immunity or 221k for reduced no load input current. VOUT 1.5V R1 = V -1 * R2 = 0.6V - 1 * 59k = 88.5k REF The adjustable version of the AAT2146, 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. www.analogictech.com 13 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter R2 = 59k R2 = 221k VOUT (V) R1 (k) R1 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 75K 113K 150K 187K 221K 261K 301K 332K 442K 464K 523K 715K 1.00M 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 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: Table 2: Adjustable Resistor Values For Use With 0.6V Step-Down Converter. PTOTAL = IO2 * RDSON(HS) + 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. Thermal Calculations There are three types of losses associated with the AAT2146 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 Given the total losses, the maximum junction temperature can be derived from the JA for the SC70JW-8 package which is 160C/W. TJ(MAX) = PTOTAL * JA + TAMB 1 2 3 Enable VIN C4 100pF U1 AAT2146 1 VOUT =1.8V R1 2 L1 118k 4.7H 3 4 C1 10F C3 n/a R2 59k EN PGND OUT PGND VIN PGND LX AGND 8 7 6 5 C2 4.7F GND LX GND2 U1 AAT2146 SC70JW-8 L1 CDRH3D16-4R7 C2 4.7F 10V 0805 X5R C1 10F 6.3V 0805 X5R Figure 5: AAT2146 Adjustable Evaluation Board Schematic. 14 www.analogictech.com 2146.2008.04.1.1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Layout The suggested PCB layout for the AAT2146 is shown in Figures 2, 3, and 4. The following guidelines should be used to help ensure a proper layout. 1. 2. 3. 4. The input capacitor (C2) should connect as closely as possible to VIN (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 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. 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. 2146.2008.04.1.1 A high density, small footprint layout can be achieved using an inexpensive, miniature, non-shielded, high DCR inductor. An evaluation board is available with this inductor and is shown in Figure 6. The total solution footprint area is 40mm2. Figure 6: Minimum Footprint Evaluation Board Using 2.0mm x 1.6mm x 0.95mm Inductor. www.analogictech.com 15 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Step-Down Converter Design Example Specifications VO = 1.8V @ 400mA (adjustable using 0.6V version), Pulsed Load ILOAD = 300mA VIN = 2.7V to 4.2V (3.6V nominal) FS = 2MHz TAMB = 85C 1.8V Output Inductor L1 = 3 s s VO2 = 3 1.8V = 5.4H (use 4.7H; see Table 1) A A For Sumida inductor CDRH3D16, 4.7H, DCR = 105m. IL1 = VO V 1.8V 1.8V 1- O = 1 = 109mA L1 FS VIN 4.7H 2.0MHz 4.2V IPKL1 = IO + IL1 = 0.4A + 0.055A = 0.455A 2 PL1 = IO2 DCR = 0.4A2 105m = 17mW 1.8V Output Capacitor VDROOP = 0.1V COUT = 3 * ILOAD 3 * 0.3A = = 4.5F; use 4.7F VDROOP * FS 0.1V * 2.0MHz IRMS = (VO) * (VIN(MAX) - VO) 1 1.8V * (4.2V - 1.8V) * = 32mArms = 4.7H * 2.0MHz * 4.2V L1 * F * V 2* 3 2* 3 IN(MAX) 1 * Pesr = esr * IRMS2 = 5m * (32mA)2 = 6W Input Capacitor Input Ripple VPP = 25mV CIN = IRMS = VPP IO 1 1 = = 2.17F; use 2.2F 25mV - 5m * 4 * 2.0MHz - ESR * 4 * FS 0.4A IO = 0.2Arms 2 P = esr * IRMS2 = 5m * (0.2A)2 = 0.2mW 16 www.analogictech.com 2146.2008.04.1.1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter AAT2146 Losses PTOTAL = IO2 * (RDSON(HS) * VO + RDSON(LS) * [VIN -VO]) VIN + (tsw * F * IO + IQ) * VIN = 0.42 * (0.725 * 1.8V + 0.7 * [4.2V - 1.8V]) 4.2V + (5ns * 2.0MHz * 0.4A + 70A) * 4.2V = 131mW TJ(MAX) = TAMB + JA * PLOSS = 85C + (160C/W) * 131mW = 105.9C 2146.2008.04.1.1 www.analogictech.com 17 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Adjustable Version (0.6V device) VOUT (V) R2 = 59k R1 (k) R2 = 221k1 R1 (k) L1 (H) 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 2.2 2.2 2.2 2.2 2.2 2.2 4.7 4.7 4.7 4.7 6.8 6.8 6.8 Fixed Version VOUT (V) R2, R4 Not Used R1 (k) L1 (H) 0.6-3.3V 0 4.7 Table 3: Evaluation Board Component Values. Manufacturer Sumida Murata Coilcraft Coiltronics TDK Wurth Part Number Inductance (H) Max DC Current (A) DCR () Size (mm) LxWxH Type CDRH3D16-2R2 CDRH3D16-4R7 CDRH3D16-6R8 LQH2MCN4R7M02 LQH32CN4R7M23 LPO3310-472 SD3118-4R7 SD3118-6R8 SDRC10-4R7 VLS3015T-4R7MR99 VLS3015T-6R8MR86 744042006 2.2 4.7 6.8 4.7 4.7 4.7 4.7 6.8 4.7 4.7 6.8 6.8 1.20 0.90 0.73 0.40 0.45 0.80 0.98 0.82 1.30 0.99 0.86 1.25 0.072 0.105 0.170 0.80 0.20 0.27 0.122 0.175 0.122 0.136 0.176 0.100 3.8x3.8x1.8 3.8x3.8x1.8 3.8x3.8x1.8 2.0x1.6x0.95 2.5x3.2x2.0 3.2x3.2x1.0 3.1x3.1x1.85 3.1x3.1x1.85 5.7x4.4x1.0 3.0x3.0x1.5 3.0x3.0x1.5 4.8x4.8x1.8 Shielded Shielded Shielded Non-Shielded Non-Shielded 1mm Shielded Shielded 1mm Shielded Shielded Shielded Shielded Table 4: Typical Surface Mount Inductors. Manufacturer Part Number Value Voltage Temp. Co. Case Murata Murata Murata GRM219R61A475KE19 GRM21BR60J106KE19 GRM21BR60J226ME39 4.7F 10F 22F 10V 6.3V 6.3V X5R X5R X5R 0805 0805 0805 Table 5: Surface Mount Capacitors. 1. For reduced quiescent current, R2 and R4 = 221k. 18 www.analogictech.com 2146.2008.04.1.1 PRODUCT DATASHEET AAT2146 SwitchRegTM Low Noise, Fast Transient 600mA Step-Down Converter Ordering Information Output Voltage1 Package Marking2 Part Number (Tape and Reel)3 Adj 0.6 SC70JW-8 YXXYY AAT2146IJS-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. Contact Sales for other voltage options. 2. XYY = assembly and date code. 3. 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