PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator General Description Features The AAT1184 is a single output step-down (Buck) DC output regulator with an integrated high side MOSFET. The input range is 6V to 24V making it the ideal power IC solution for consumer communications equipment operating from a low cost AC/DC adapter with 12V output. • • • • • • • • • The step-down regulator provides up to 1.2A output current in a small package. 490kHz fixed switching frequency allows small L/C filtering components. Voltage mode control allows for optimum performance across the entire output voltage and load range. The controller includes programmable over-current, integrated soft-start and over-temperature protection. The AAT1184 is available in the Pb-free, low profile 12-pin TSOPJW package. The rated operating temperature range is -40°C to 85°C. • • • • VIN = 6.0 to 24.0V VOUT Adjustable from 1.5V to 5.5V IOUT up to 1.2A Small Solution Size Low-Cost Non-Synchronous Solution Shutdown Current <35μA High Switching Frequency Voltage Mode Control PWM Fixed Frequency for Lowest Noise ▪ Programmable Over-Current Protection Over-Temperature Protection Internal Soft Start Low Profile 3x3mm TSOPJW-12 Package -40°C to 85°C Temperature Range Applications • • • • DSL and Cable Modems Notebook Computers Satellite Set Top Box Wireless LAN Systems Typical Application VIN 6V - 24V TSOPJW -12 IN BST C2 0.1µF L1 4.7µH VOUT 5V/1.2A LX D1 BAS16 + C1 25µF 25V D2 B340A EN C12 1µF 25V RS AAT1184 R4 44.2k R7 499 C4 68nF OS VL C7 330pF R1 2.32K C8 22µF FB C3 2.2µF R2 24.3K COMP GND 1184.2008.07.1.0 C5 220pF www.analogictech.com C6 56pF R5 6.04k 1 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Pin Descriptions Pin # Symbol 1 RS 2 EN 3 BST 4, 5 LX 6, 7 IN 8 VL 9 GND 10 FB 11 COMP 12 OS Function Output current sense pin. Connect a small signal resistor from this pin to switching node (LX) to enable over-current sense for step-down converter. Enable input pin. Active high. Boost drive input pin. Connect the cathode of fast rectifier from this pin and connect a 100nF capacitor from this pin to the switching node (LX) for internal hi-side MOSFET gate drive. Step-down converter switching pin. Connect output inductor to this pin. Connect LX pins together. Input supply voltage pin for step-down regulator. Connect both IN pins together. Connect the input capacitor close to this pin for best noise performance. Internal linear regulator. Connect a 2.2μF/6.3V capacitor from this pin to GND pin. Ground pin for step-down converter. Connect input and output capacitors return terminals close to this pin for best noise performance. Feedback input pin for step-down converter. Connect an external resistor divider to this pin to program the output voltage to the desired value. Compensation pin for step-down regulator. Connect a series resistor, capacitor network to compensate the voltage mode control loop. Output voltage sense pin. Connect to the output capacitor to enable over-current sense for stepdown converter. Pin Configuration TSOPJW-12 (Top View) RS EN BST LX LX IN 2 1 12 2 11 3 10 4 9 5 8 6 7 OS COMP FB GND VL IN www.analogictech.com 1184.2008.07.1.0 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Absolute Maximum Ratings1 Symbol VIN(HI) VIN(LO) VBST1-LX VCONTROL VEN IIN(PULSED) TJ TLEAD Description IN, LX to GND VL to GND BST to LX FB, COMP, OS, RS to GND EN to GND IN to LX Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units -0.3 to 30.0 -0.3 to 6.0 -0.3 to 6.0 -0.3 to VIN(LO) + 0.3 -0.3 to 6.0 12.0 -40 to 150 300 V V V V V A °C °C Value Units 140 0.7 C/W W Thermal Information Symbol ΘJA PD Description Thermal Resistance Maximum Power Dissipation2 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. Derate 7mW/°C above 25°C ambient temperature. 1184.2008.07.1.0 www.analogictech.com 3 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Electrical Characteristics1 VIN = 12V; TA = -40°C to 85°C, unless noted otherwise. Typical values are at TA = 25°C. Symbol Description VIN Input Voltage VUVLO VOUT VFB ΔVLINEREG/ ΔVIN ΔVLOADREG/ ΔIIN IQ ISHDN VOCP ILX DMAX TON(MIN) RDSON(H) FOSC FFOLDBACK TSS TSD VEN(L) VEN(H) IEN Conditions Min Typ 6.0 VIN Rising VIN Hysteresis VIN Falling UVLO Threshold Output Voltage Range Output Voltage Accuracy Feedback Pin Voltage IOUT = 0A to 1.2A Line Regulation Load Regulation Quiescent Current Shutdown Current Over-Current Offset Voltage LX Pin Leakage Current Maximum Duty Cycle Minimum On-Time Hi Side On-Resistance Oscillator Frequency Short Circuit Foldback Frequency Soft-Start Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Input Low Current VIN = 6V to 24V, VOUT = 3.3V, IOUT = 1.2A VIN = 6V to 24V, VOUT = 5.0V, IOUT = 1.2A VIN = 12V, VOUT = 3.3V, IOUT = 0A to 1.2A VIN = 12V, VOUT = 5V, IOUT = 0A to 1.2A VEN = High, No load VEN = Low, VL = 0V VEN = High, VIN = 6.0V to 24.0V, TA = 25°C VIN = 24.0V, VEN = Low Max Units 24.0 5.0 V V mV V V % V 300 3.0 1.5 -2.5 0.591 80 -1.0 VIN = 6.0 to 24.0V VL = 4.5V 350 Current Limit Triggered From Enable to Output Regulation 0.600 0.02 0.2 0.4 2.5 0.6 100 85 100 70 490 100 2.5 135 15 5.5 2.5 0.609 %/V %/A 35.0 120 1.0 650 0.6 2.5 -1.0 1.0 mA μA mV μA % ns mΩ kHz kHz ms °C °C V V μA 1. The AAT1184 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 1184.2008.07.1.0 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Step-Down Converter Efficiency vs. Load Step-Down Converter Efficiency vs. Load (VOUT = 3.3V; L = 4.7µH) (VOUT = 5V; L = 4.7µH) 100 100 90 90 80 80 Efficiency (%) Efficiency (%) Typical Characteristics 70 60 50 40 VIN = 6V VIN = 8V VIN = 12V VIN = 18V VIN = 24V 30 20 10 0 0.1 1 10 100 1000 70 60 50 VIN = 6V VIN = 8V VIN = 12V VIN = 18V VIN = 24V 40 30 20 10 0 0.1 10000 1 10 Output Current (mA) Step-Down Converter DC Regulation Output Error (%) Output Error (%) 1.5 1.0 0.5 0.0 VIN = 6V VIN = 8V VIN = 12V VIN = 18V VIN = 24V -0.5 -1.0 -1.5 10 100 1000 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 10000 VIN = 6V VIN = 8V VIN = 12V VIN = 18V VIN = 24V 0.1 1 10 Output Current (mA) 100 1000 10000 Output Current (mA) Step-Down Converter Line Regulation Step-Down Converter Line Regulation (VOUT = 3.3V; L = 4.7µH) (VOUT = 5V; L = 4.7µH) 1.5 Accuracy (%) 1.0 Accuracy (%) 10000 (VOUT = 5V; L = 4.7µH) 2.0 1 1000 Step-Down Converter DC Regulation (VOUT = 3.3V; L = 4.7µH) -2.0 0.1 100 Output Current (mA) 0.5 0.0 IOUT = 0.1mA IOUT = 10mA IOUT = 100mA IOUT = 600mA IOUT = 1200mA -0.5 -1.0 -1.5 6 8 10 12 14 16 18 20 22 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 -4.0 24 Input Voltage (V) 1184.2008.07.1.0 IOUT = 0.1mA IOUT = 10mA IOUT = 100mA IOUT = 600mA IOUT = 1200mA 6 8 10 12 14 16 18 20 22 24 Input Voltage (V) www.analogictech.com 5 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Step-Down Converter Output Ripple (VIN = 12V; VOUT = 3.3V; IOUT = 1mA) (VIN = 12V; VOUT = 5V; IOUT = 1mA) 0V 0.2 0.1 0.0 3.31 3.30 3.29 12V 0V 0.2 0.1 0.0 5.02 5.00 4.98 Time (2µs/div) Step-Down Converter Output Ripple (VIN = 12V; VOUT = 3.3V; IOUT = 1.2A) (VIN = 12V; VOUT = 5V; IOUT = 1.2mA) 0V 2 1 0 3.31 3.30 3.29 5.0 12V 4.0 0V 3.0 2.0 1.0 0.0 5.02 5.00 4.98 Time (1µs/div) LX Voltage (top) (V) Inductor Current (middle) (A) 12V Output Voltage (AC Coupled) (bottom) (V) Step-Down Converter Output Ripple LX Voltage (top) (V) Inductor Current (middle) (A) Output Voltage (AC Coupled) (bottom) (V) Time (2µs/div) LX Voltage (top) (V) Inductor Current (middle) (A) 12V Output Voltage (AC Coupled) (bottom) (V) Step-Down Converter Output Ripple LX Voltage (top) (V) Inductor Current (middle) (A) Output Voltage (AC Coupled) (bottom) (V) Typical Characteristics Time (1µs/div) Step-Down Converter Load Transient Response (IOUT = 0.12A to 1.2A; VIN = 12V; VOUT = 5V; COUT = 2x22µF) 1.0 0.5 0.12A 0.0 3.7 3.5 3.3 3.1 2.9 Time (100µs/div) 6 1.2A 1.0 0.5 0.12A 0.0 5.2 5.0 4.8 Output Current (top) (A) 1.2A Output Voltage (AC Coupled) (bottom) (V) 1.5 1.5 Output Current (top) (A) Output Voltage (AC Coupled) (bottom) (V) Step-Down Converter Load Transient Response (IOUT = 0.12A to 1.2A; VIN = 12V; VOUT = 3.3V; COUT = 2x22µF) 4.6 Time (100µs/div) www.analogictech.com 1184.2008.07.1.0 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Typical Characteristics (IOUT = 0.6A to 1.2A; VIN = 12V; VOUT = 5V; COUT = 2x22µF) 1.5 1.0 0.5 0.0 3.5 3.4 3.3 3.2 3.1 1.5 1.2A 1.0 0.6A 0.5 0.0 5.1 5.0 4.9 Time (100µs/div) Output Current (top) (A) 0.6A Output Current (top) (A) 1.2A Output Voltage (AC Coupled) (bottom) (V) Step-Down Converter Load Transient Response (IOUT = 0.6A to 1.2A; VIN = 12V; VOUT = 3.3V; COUT = 2x22µF) Output Voltage (AC Coupled) (bottom) (V) Step-Down Converter Load Transient Response Time (100µs/div) (IOUT = 0.9A to 1.2A; VIN = 12V; VOUT = 5V; COUT = 2x22µF) 1.5 0.5 0.0 3.5 3.4 3.3 3.2 3.1 1.5 1.2A 0.9A 1.0 0.5 0.0 -0.5 5.1 5.0 4.9 Output Current (top) (A) 0.9A 1.0 Output Current (top) (A) 1.2A Output Voltage (AC Coupled) (bottom) (V) Step-Down Converter Load Transient Response (IOUT = 0.6A to 1.2A; VIN = 12V; VOUT = 3.3V; COUT = 2x22µF) Output Voltage (AC Coupled) (bottom) (V) Step-Down Converter Load Transient Response Step-Down Converter Line Transient Response Step-Down Converter Line Transient Response (VIN = 6V to 10V; VOUT = 3.3V; IOUT = 1.2A) (VIN = 6V to 10V; VOUT = 5V; IOUT = 1.2A) 5 0 3.35 3.30 3.25 Time (100ms/div) 1184.2008.07.1.0 15 10 5 0 5.2 5.0 4.8 4.6 Output Voltage (AC Coupled) (bottom) (V) 10 Output Voltage (AC Coupled) (bottom) (V) 15 Input Voltage (top) (V) Time (100µs/div) Input Voltage (top) (V) Time (100µs/div) Time (100ms/div) www.analogictech.com 7 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Step-Down Converter Soft Start (VIN = 12V; VEN = 10V; VOUT = 5V; IOUT = 1.2A) 15 10 0 2 1 0 15 10 5 0 2 1 0 Time (500µs/div) Time (500µs/div) Step-Down Converter Switching Frequency vs. Input Voltage Step-Down Converter Output Voltage Error vs. Temperature (VIN = 12V; VOUT = 3.3V) Output Voltage Error (%) Frequency Variation (%) (VIN = 6V to 24V; VOUT = 3.3V; IOUT = 1.2A) 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 8 10 12 14 16 18 20 22 1.5 IOUT = 0.1mA IOUT = 10mA IOUT = 100mA IOUT = 600mA IOUT = 1200mA 1.0 0.5 0.0 -0.5 -1.0 -1.5 -50 -2.0 6 24 -25 Input Voltage (V) 0 0.0 -0.2 -0.4 -0.6 600 550 500 450 400 85°C 25°C -40°C 350 -0.8 300 -1.0 -50 -25 0 25 50 75 100 Temperature (°C) 8 100 (VEN = VIN) IOUT = 0.1mA IOUT = 10mA IOUT = 100mA IOUT = 600mA IOUT = 1200mA 0.2 75 650 Input Current (µA) Output Voltage Error (%) (VIN = 12V; VOUT = 5V) 0.4 50 No Load Step-Down Converter Input Current vs. Input Voltage 1.0 0.6 25 Temperature (°C) Step-Down Converter Output Voltage Error vs. Temperature 0.8 Inductor Current (bottom) (A) 5 Enable Voltage (top) (V) Output Voltage (middle) (V) Step-Down Converter Soft Start (VIN = 12V; VEN = 10V; VOUT = 3.3V; IOUT = 1.2A) Inductor Current (bottom) (A) Enable Voltage (top) (V) Output Voltage (middle) (V) Typical Characteristics 6 9 12 15 18 21 24 Input Voltage (V) www.analogictech.com 1184.2008.07.1.0 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Typical Characteristics VIH and VIL vs. Input Voltage 1.35 VIH and VIL (%) 1.30 VIH 1.25 1.20 1.15 1.10 VIL 1.05 1.00 5 10 15 20 25 Input Voltage (V) 1184.2008.07.1.0 www.analogictech.com 9 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Functional Block Diagram VINT Reg. VL IN OT FB OSC Comp. Comp. Error Amp BST COMP Logic LX Control Logic EN 20Ω Voltage Ref RS OS Comp VOCP = 0.1V GND Functional Description The AAT1184 is a high voltage step-down (Buck) regulator with input voltage range from 6.0V to 24.0V, providing high output current in a small package. The output voltage is user-programmable from 1.5V to 5.5V. The device is optimized for low-cost 12V adapter inputs. The device utilizes voltage mode control configured for optimum performance across the entire output voltage and load range. The controller includes integrated over-current, softstart and over-temperature protection. Over-current is sensed through the output inductor DC winding resistance (DCR). An external resistor and capacitor network adjusts the current limit according to the DCR of the inductor and the desired output current limit. Frequency reduction limits the over-current stress during overload and short-circuit events. The operating frequency returns to the nominal setting when over-current conditions are removed. The AAT1184 is available in the Pb-free 12-pin TSOPJW package with rated operating temperature range of -40°C to 85°C. 10 www.analogictech.com 1184.2008.07.1.0 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Applications Information The high voltage DC/DC step-down converter provides an output voltage from 1.5V to 5.5V. The integrated high-side n-channel MOSFET device provides up to 1.2A output current1. Input voltage range is 6.0V to 24.0V. The step-down converter utilizes constant frequency (PWM-mode) voltage mode control to achieve high operating efficiency while maintaining extremely low output noise across the operating range. High 490kHz (nominal) switching frequency allows small external filtering components, achieving minimum cost and solution size. External compensation allows the designer to optimize the transient response while achieving stability across the operating range. Output Voltage and Current The output voltage is set using an external resistor divider as shown in Table 1. Minimum output voltage is 1.5V and maximum output voltage is 5.5V. Typical maximum duty cycle is 85%. VOUT (V) R5 = 6.04kΩ R4 (kΩ) 1.5 1.8 1.85 2.0 2.5 3.0 3.3 5.0 9.09 12.1 12.4 14.0 19.1 24.3 27.4 44.2 Output Inductor Selection The step-down converter utilizes constant frequency (PWM-mode) voltage mode control. A 4.7μH inductor value is selected to maintain the desired output current ripple and minimize the converter’s response time to load transients. The peak switch current should not exceed the inductor saturation current, the MOSFET or the external Schottky rectifier peak current ratings. Rectifier Selection When the high-side switch is on, the input voltage will be applied to the cathode of the Schottky diode. The rectifier's rated reverse breakdown voltage must be chosen at least equal to the maximum input voltage of the stepdown regulator. When the high-side switch is off, the current will flow from the power ground to the output through the Schottky diode and the inductor. The power dissipation of the Schottky diode during the time-off can be determined by the following equation: PD = IOUT · VD · 1 - VOUT VIN Where VD is the voltage drop across the Schottky diode. Input Capacitor Selection Table 1: Feedback Resistor Values. Alternatively, the feedback resistor may be calculated using the following equation: R4 = capacitors to maintain a minimum capacitance drop with DC bias. (VOUT - 0.6) · R5 0.6 R4 is rounded to the nearest 1% resistor value. Buck Regulator Output Capacitor Selection A 22μF ceramic output capacitor is required to filter the inductor current ripple and supply the load transient current for IOUT = 1.2A. The 1206 package with 10V minimum voltage rating is recommended for the output For low cost applications, a 100μF/25V electrolytic capacitor is selected to control the voltage overshoot across the high side MOSFET. A small ceramic capacitor with voltage rating at least 1.05 times greater than the maximum input voltage is connected as close as possible to the input pin (Pin 14) for high frequency decoupling. Feedback and Compensation Networks The transfer function of the Error Amplifier is dominated by the DC Gain and the L COUT output filter of the regulator. This output filter and its equivalent series resistor (ESR) create a double pole at FLC and a zero at FESR in the following equations: Eq. 1: FLC = 1 2 · π · L · COUT 1. Output current capability may vary and is dependent on package selection, maximum ambient temperature, airflow and PCB heatsinking. 1184.2008.07.1.0 www.analogictech.com 11 PRODUCT DATASHEET AAT1184 SwitchRegTM Eq. 2: FESR = High Voltage Step-Down Regulator 1 2 · π · ESR · COUT The feedback and compensation networks provide a closed loop transfer function with the highest 0dB crossing frequency and adequate phase margin for system stability. Equations 3, 4, 5 and 6 relate the compensation network’s poles and zeros to the components R2, R3, R4, C5, C6, and C7: Eq. 3: FZ1 = 1 2 · π · R2 · C5 Eq. 4: FZ2 = 1 2 · π · ( R 7 + R 4) · C7 Eq. 5: FP1 = 1 2 · π · R2 · Eq. 6: FP2 = C5 · C6 C5 + C6 1 2 · π · R7 · C7 Components of the feedback, feed forward, compensation, and current limit networks need to be adjusted to maintain system stability for different input and output voltage applications as shown in Table 2. C6 C5 C7 R2 R7 VOUT COMP R4 FB R5 REF Figure 1: AAT1184 Feedback and Compensation Networks for Type III Voltage-Mode Control Loop. Network Feedback Feed-forward Compensation Current Limit Components VOUT = 3.3V VOUT = 5.0V R4 R5 C7 R7 C5 C6 R2 C4 R1 R3 R6 R8 27.4kΩ 6.02kΩ 330pF 499Ω 470pF 56pF 24.3kΩ 68nF 2.32kΩ 0kΩ Open Open 44.2kΩ 6.02kΩ 330pF 499Ω 220pF 56pF 24.3kΩ 68nF 2.32kΩ 0kΩ Open Open Table 2: AAT1184 Feedback and Compensation Network Components for VOUT = 3.3V and VOUT = 5.0V. 12 www.analogictech.com 1184.2008.07.1.0 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Thermal Protection The AAT1184 has an internal thermal protection circuit which will turn on when the device die temperature exceeds 135°C. The internal thermal protection circuit will actively turn off the high side regulator output device to prevent the possibility of over temperature damage. The Buck regulator output will remain in a shutdown state until the internal die temperature falls back below the 135°C trip point. The combination and interaction between the short circuit and thermal protection systems allows the Buck regulator to withstand indefinite short-circuit conditions without sustaining permanent damage. Thermal Calculations There are two types of losses associated with the AAT1184 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 synchronous step-down converter losses is given by: PTOTAL = IQ is the step-down converter current. The term tSW is used to estimate the full load step-down converter switching losses. For asynchronous Step-Down converter, the power dissipation is only in the internal high side MOSFET during the on time. When the switch is off, the power dissipates on the external Schottky diode. Total package losses for AAT1184 reduce to the following equation: PTOTAL = IOUT2 · RDS(ON)H · D + (tSW · FS · IOUT + IQ) · VIN where D = VOUT is the duty cycle. 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 TSOPJW-12 package, which is 140°C/W. TJ(MAX) = PTOTAL · θJA + TAMB IOUT2 · (RDS(ON)H · VOUT + RDS(ON)L · [VIN - VOUT]) VIN + (tSW · FS · IOUT + IQ) · VIN VOUT 5V/1.2A V OUT 5.0V/1.2A LX LX L1 4.7µH R1 2.32k C4 68nF L1 4.7µH R1 2.32k RS C4 68nF RS R8 R3 OS R3 OS R6 Figure 2: Resistor Network to Adjust the Current Limit Less than the Pre-Set Over-Current Threshold (Add R6, R7). 1184.2008.07.1.0 Figure 3: Resistor Network to Adjust the Current Limit Greater than the Pre-Set Over-Current Level (Add R6, R8). www.analogictech.com 13 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Over-Current Protection 2. The controller provides true-load DC output current sensing which protects the load and limits component stresses. The output current is sensed through the DC resistance in the output inductor (DCR). The controller reduces the operating frequency when an over-current condition is detected; limiting stresses and preventing inductor saturation. This allows the smallest possible inductor for a given output load. A small resistor divider may be necessary to adjust the over-current threshold and compensate for variation in inductor DCR. 3. The preset current limit threshold is triggered when the differential voltage from RS to OS exceeds 100mV (nominal). Layout Considerations The suggested PCB layout for the AAT1184 is shown in Figures 5 and 6. The following guidelines should be used to help ensure a proper layout. 1. 14 The power input capacitors (C1 and C12) should be connected as close as possible to high voltage input pin (IN) and power ground. 4. 5. 6. 7. C2, L1, D2, and C8 should be placed as close as possible to minimize any parasitic inductance in the switched current path which generates a large voltage spike during the switching interval. The connection of inductor to switching node should be as short as possible. The feedback trace or FB pin should be separated from any power trace and connected as close as possible to the load point. Sensing along a highcurrent load trace will degrade DC load regulation. The resistance of the trace from the load returns to PGND 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. Connect unused signal pins to ground to avoid unwanted noise coupling. The critical small signal components include feedback components, and compensation components should be placed close to the FB and COMP pins. The feedback resistors should be located as close as possible to the FB pin with its ground tied directly to the signal ground plane which is separated from power ground plane. C4 should be connected close to the RS and OS pins, while R1 should be connected directly to the output pin of the inductor. For the best current limit performance, C4 and R1 should be placed on the bottom layer to avoid noise coupling from the inductor. www.analogictech.com 1184.2008.07.1.0 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator U1 4 LX LX 4.7µH C2 0.1µF D2 B340A 3 RS 8 C3 2.2µF 7 + C11 open C12 1µF 25V 2 EN OS 1 12 IN FB IN COMP EN GND C7 330pF R3 0 R7 499 R4 44.2k C8 22µF C9 open C10 open R6 open 10 R5 6.04k 11 R2 24.3K C5 220pF 9 TSOPJW-12 U1 C1 C2 C3 C4,C5,C6,C7 C8 C12 D1 D2 L1 R1-R6 R8 open AAT 1184 6 C1 22µF 25V VL C4 68nF R1 2.32k BST D1 BAS16 VIN 6V - 24V VOUT 5V/1.2A L1 5 C6 56pF AAT1189 Analogic Technologies, Hi-Voltage Buck, TSOPJW-12 Cap, MLC, 100µF/25V, Electrolytic cap Cap, MLC, 0.1µF/6.3V, 0603 Cap, MLC, 2.2µF/6.3V, 0602 Cap, MLC, misc, 0603 Cap, MLC, 22µF/6.3V, 1206 Cap, MLC, 1µF/25V, 1206 BAS16, Generic, Rectifier, 0.2A/85V, Ultrafast, SOT-23 B340A, Generic, Schottky Rectifier, 3A/40V, SMA SLF7045T-4R7M2R0-PF, TDK, 4.7µH, ISAT = 2A, DCR = 30mΩ Carbon film resistor, 0402 Figure 4: AAT1184ITP Evaluation Board Schematic. Figure 5: AAT1184ITP Evaluation Board Top Layer. 1184.2008.07.1.0 Figure 6: AAT1184ITP Evaluation Board Bottom Layer. www.analogictech.com 15 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator AAT1184 Design Example Specifications VOUT = 5.0V @ 1.2A, Pulsed Load ΔILOAD = 1.2A VIN = 12V FS = 490kHz TAMB = 85°C in TSOPJW-12 Package Output Inductor For TDK inductor SLF7045T-4R7M2R0-PF, 4.7μH, DCR = 30mΩ max. ΔI = VOUT VOUT 5V 5V · 1= · 1= 1.2A L1 · FS VIN 4.7µH · 490kHz 12V IPK = IOUT + ΔI = 1.2A + 0.6A = 1.8A 2 PL1 = IOUT2 · DCR = 1.8A2 · 11.7mΩ = 37.9mW Output Capacitor VDROOP = 0.33V (10% Output Voltage) COUT = 3 · ΔILOAD 3 · 1.2A = = 22.3µF; use 22µF 0.33V · 490kHz VDROOP · FS IRMS(MAX) = 1 2· 3 · VOUT · (VIN(MAX) - VOUT1) 1 5.0V · (24V - 5.0V) · = 496mARMS = 4.7µH · 490kHz · 24V L · FS · VIN1(MAX) 2· 3 PRMS = ESR · IRMS2 = 5mΩ · (496mA)2 = 1.2mW Input Capacitor Input Ripple VPP = 25mV CIN = 1 VPP - ESR · 4 · FS IOUT = 1 25mV - 5mW · 4 · 490kHz 1.2A = 32µF For low cost applications, a 100μF/25V electrolytic capacitor in parallel with a 1μF/25V ceramic capacitor is used to reduce the ESR. IRMS = IOUT = 0.6A 2 P = ESR · (IRMS)2 = 5mΩ · (0.6A)2 = 1.8mW 16 www.analogictech.com 1184.2008.07.1.0 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Current Limit Over-Current Offset Voltage: VOCP = 100mV Total trace parasitic resistor and inductor DCR is 30mΩ ILIMIT = 3A IPRESET = VOCP 100mV = = 3.3A DCR 30mΩ AAT1184 Losses All values assume an 85°C ambient temperature and thermal resistance of 50°C/W in the TSOPJW-12 package. PTOTAL = IOUT2 · RDS(ON)H · D + (tSW · FS · IOUT + IQ) · VIN 2 PTOTAL = 1.2A · 70mΩ · 5V + (5ns · 490kHz · 1.2A + 70µA) · 12V 12V PTOTAL = 78mW TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (140°C/W) · 78mW = 96°C 1184.2008.07.1.0 www.analogictech.com 17 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator Ordering Information Package Voltage Marking1 Part Number (Tape and Reel)2 TSOPJW-12 0.6 3QXYY AAT1184ITP-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 TSOPJW-12 2.85 ± 0.20 2.40 ± 0.10 0.20 + 0.10 - 0.05 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 7° NOM 0.04 REF 0.055 ± 0.045 0.15 ± 0.05 + 0.10 1.00 - 0.065 0.9625 ± 0.0375 3.00 ± 0.10 4° ± 4° 0.45 ± 0.15 0.010 2.75 ± 0.25 All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 18 www.analogictech.com 1184.2008.07.1.0 PRODUCT DATASHEET AAT1184 SwitchRegTM High Voltage Step-Down Regulator 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. 1184.2008.07.1.0 www.analogictech.com 19