PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters General Description Features The AAT2687 provides two independently regulated DC outputs; consisting of a high voltage step-down regulator and a low input voltage low dropout (LDO) regulator. The PMIC is optimized for low-cost 12V adapter inputs, making the device the ideal system-on-a-chip power solution for consumer communications equipment. • 2-Output Step-Down Converters: ▪ Channel 1 Step-Down: VIN1 = 6V to 24V • VOUT1 Adjustable from 1.5V to 5.5V • IOUT1 up to 4.5A • High Switching Frequency • Voltage Mode Control • PWM Fixed Frequency for Low-Ripple ▪ Channel 2 (LDO): VIN2 = 2.7V to 5.5V • IOUT2 up to 600mA • 1V Dropout Voltage at 600mA • High Accuracy ±1.5% • Small Solution Size ▪ System On a Chip ▪ Ultra-small External L/C • Shutdown Current <35μA • Independent Enable Pins • Programmable Over-Current Protection • Over-Temperature Protection • Internal Soft Start • 4x5mm 24-Pin TQFN Low Profile Thermally Enhanced Package • -40°C to 85°C Temperature Range Channel 1 is a step-down regulator with an input voltage range 6.0 to 24V, providing up to 4.5A output current. 490kHz fixed switching frequency allows small L/C filtering components. Channel 1 utilizes voltage mode control configured for optimum performance across the entire output voltage and load range. Channel 2 is a low-dropout (LDO) regulator providing up to 600mA output current. The device provides extremely low output noise, low quiescent current and excellent transient response. The controller includes integrated cycle-by-cycle overcurrent protection, soft-start and over-temperature disable features. Independent input and enable pins provide maximum design flexibility. The AAT2687 is available in the Pb-free, 4x5mm 24-pin TQFN package. The rated operating temperature range is -40°C to 85°C. Applications • • • • DSL and Cable Modems Notebook Computers Satellite Settop Box Wireless LAN Systems Typical Application C3 0.1µF J1 VIN1 6.0V - 24.0V D1 BAS16 2 1 C14 2.2µF VL1 RS1 AAT2687 EN1 IN2 2687.2008.06.1.0 C1 220µF 25V C13 1µF 25V C2 2.2µF C10 2.2nF R5 450 R3 8.87k C8 C9 C7 22µF 22µF 22µF FB1 COMP1 VIN2 R2 C4 2k 220nF OS1 IN1 + 4.7µH 5.3A D2 BST VOUT1 3.3V/4.5A L1 LX1 OUT2 R1 3.92K C5 2.2nF C6 R4 VOUT2 150pF 1.8V/600mA 1.96k C12 2.2µF EN2 GND TQFN45-24 www.analogictech.com 1 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Pin Descriptions Pin # Symbol 1 LX1 2 LX1 3, 4 N/C 5 BST1 6 EN1 7 GND2 8 EN2 9 N/C 10 IN2 11 OUT2 12 N/C 13 RS1 14 OS1 15 COMP1 16 FB1 17 GND1 18 VL1 19 20 21 VL1 N/C N/C 22 IN1 23 LX1 24 LX1 EP EP 2 Function Channel 1 step-down converter switching pin. Connect output inductor to this pin. Connect all four LX1 pins together. Channel 1 step-down converter switching pin. Connect output inductor to this pin. Connect all four LX1 pins together. No Connect. Can be used to route IN1 and EP. Channel 1 step-down regulator boost drive input pin. Connect the cathode of fast rectifier from this pin and connect a 100nF capacitor from this pin to the channel 1 switching node (LX1) for internal high-side MOSFET gate drive. Channel 1 step-down regulator enable input pin. Active high enables the channel 1 output. It can be tied to VIN1. Ground pin for Channel 2. Power return pin for channel 2. Connect return of channel 2 input and output capacitors close to this pin for best noise performance. Channel 2 linear low dropout (LDO) enable input pin. Active high enables the channel 2 output. It can be tied to VOUT1. No Connect. Can be used to route IN2. Input supply voltage pin for channel 2 linear low dropout (LDO) regulator. Connect 2.2μF ceramic input capacitor close to this pin. Output of channel 2 of linear low dropout (LDO) regulator. Connect a 2.2μF ceramic capacitor from this pin to GND pin. No Connect. Can be used to route OUT2. Channel 1 output current sense pin. Connect a small signal resistor from this pin to channel 1 switching node (LX) to enable over-current sense for step-down converter. Channel 1 output sense voltage pin. Connect to the output capacitor to enable over-current sense for stepdown converter. Compensation pin for channel 1 step-down regulator. Connect a series resistor, capacitor network to compensate the voltage mode control loop. Feedback input pin for channel 1 step-down converter. Connect an external resistor divider to this pin to program the output voltage to the desired value. Ground pin for Channel 1. Power return pin for channel 1. Connect return of channel 1 input and output capacitors close to this pin for best noise performance. Internal linear regulator for channel 1 step-down converter. Connect a 2.2μF/6.3V capacitor from this pin to GND1 pin. Internal linear regulator for channel 1 step-down converter. Connect to pin 18. No Connect. Do not connect to any node on the PCB. No Connect. Can be connected to GND. Input supply voltage pin for channel 1 step-down regulator. Connect both IN1 pins together. Connect the input capacitor close to this pin for best noise performance. Channel 1 step-down converter switching pin. Connect output inductor to this pin. Connect all four LX1 pins together. Channel 1 step-down converter switching pin. Connect output inductor to this pin. Connect all four LX1 pins together. Exposed paddle tied to IN1. Connect to PCB heatsink for optimum thermal performance of internal LDO device. www.analogictech.com 2687.2008.06.1.0 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Pin Configuration TQFN45-24 (Top View) N/C N/C IN1 LX1 LX1 20 21 22 23 24 LX1 LX1 N/C N/C BST1 EN1 GND2 1 19 2 18 3 17 4 16 5 15 6 14 7 13 VL1 VL1 GND1 FB1 COMP1 OS1 RS1 12 11 10 9 8 N/C OUT2 IN2 N/C EN2 Absolute Maximum Ratings1 Symbol Description VIN1, VEN1 VIN2 VBST1-LX1 VCONTROL VEN2 IIN1(PULSED) TJ TLEAD IN1, LX, EN1 to GND IN2, VL1, OUT2 to GND BST1 to LX1 FB1, COMP1, RS1, OS1, OUT2 to GND EN2 to GND IN1 to LX1 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 VIN2 + 0.3 12.0 -40 to 150 300 V V V V V A °C °C Value Units 33 3.0 °C/W W Thermal Information Symbol ΘJA PD Description Thermal Resistance2 Maximum Power Dissipation3 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 with exposed paddle connected to ground plane. 3. Derate 30 mW/°C above 25°C ambient temperature. 2687.2008.06.1.0 www.analogictech.com 3 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Electrical Characteristics1 VIN1 = 12.0V, VIN2 =3.3V; TA = -40°C to 85°C, unless noted otherwise. Typical values are at TA = 25°C. Symbol Description Conditions Channel 1: Step-Down Converter VIN1 Input Voltage VUVLO1 UVLO Threshold Min Typ 6.0 VIN1 Rising VIN1 Hysteresis VIN1 Falling VOUT1 Output Voltage Range VFB1 Feedback Pin Voltage TA = 25°C VOUT Output Voltage Accuracy IOUT1 = 0A to 4.5A ΔVOUT/VOUT Line Regulation VIN1 = 6V to 24V, VOUT1 = 3.3V, IOUT1 = 4.5A ΔVIN ΔVOUT/VOUT Load Regulation VIN1 = 12V, VOUT1 = 3.3V, IOUT1 = 0A to 4.5A ΔIOUT IQ1 Quiescent Current VEN1 = High, No load ISHDN1 Shutdown Current VEN1 = Low, VL1 = 0V VOCP1 Over-Current Offset Voltage VEN1 = High, VIN1 = 6.0V to 24.0V, TA = 25°C ILX1 LX Pin Leakage Current VIN1 = 24.0V, VEN1 = Low DMAX Maximum Duty Cycle TON(MIN) Minimum On-Time VIN1 = 6.0 to 24.0V High Side On-Resistance VL1 = 4.5V RDSON(H) FOSC1 Oscillator Frequency FFOLDBACK1 Short Circuit Foldback Frequency Current Limit Triggered TS1 Start-Up Time From Enable Channel 1 to Output Regulation Channel 2: 600mA Linear Low Dropout (LDO) Regulator VIN2 Input Voltage VDO2 Dropout Voltage 98% x VOUT2(NOM), IOUT2 = 600mA IQ2 Quiescent (Ground) Current No load ISHDN2 Shutdown Current VEN2 = GND IOUT2 = 1mA to 600mA, VIN2 = 2.7V to 5.5V, TA = 25°C Output Voltage Tolerance VOUT2(TOL) IOUT2 = 1mA to 600mA, VIN2 = 2.7V to 5.5V, TA = -40°C to 85°C Output Noise BW = 300Hz to 50kHz eN 1kHz PSRR Power Supply Rejection Ratio IOUT2 = 10mA 10kHz 1MHz ILIMIT2 Current Limit Enable Start-Up Delay From Enable Channel 2 to Output Regulation TS2 Over-Temperature, EN Logic Over-Temperature Shutdown Threshold TSD1,2 Over-Temperature Shutdown Hysteresis VEN1,EN2(L) Enable Threshold Low Enable Threshold High VEN1(H) VEN2(H) Enable Threshold High IEN1,EN2 Input Low Current Max Units 24.0 5.0 V V mV V V V % 300 3.0 1.5 0.591 -2.5 0.600 5.5 0.609 2.5 0.06 %/V 0.18 %/A 0.6 80 -1.0 350 35.0 120 1.0 100 85 100 35 490 100 2.5 650 2.7 mA μA mV μA % ns mΩ kHz kHz ms 5.5 1300 125 1.0 V mV μA μA -2.0 +2.0 % -3.5 +3.5 % 1000 70 700 250 67 47 45 800 15 μVRMS 135 °C 15 °C dB mA μs 0.6 2.5 1.4 -1.0 1.0 V V V μA 1. The AAT2687 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 2687.2008.06.1.0 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Typical Characteristics—Channel 1 100 90 Efficiency (%) 80 70 60 50 VIN1 = 6V VIN1 = 7V VIN1 = 8V VIN1 = 12V VIN1 = 18V VIN1 = 24V 40 30 20 10 0 0.001 0.01 0.1 1 10 Step-Down Converter Load Regulation vs. Load Current Output Voltage Difference (%) Step-Down Converter Efficiency vs. Load Current 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 0.001 VIN1 = 6V VIN1 = 7V VIN1 = 8V VIN1 = 12V VIN1 = 18V VIN1 = 24V 0.01 Load Current (A) 2 0.5 625 0 -0.5 -1 -1.5 -2 10 650 IOUT1 = 0.1µA IOUT1 = 2.25A IOUT1 = 3.5A IOUT1 = 4mA IOUT1 = 4.5A 1 1 No Load Step-Down Converter Input Current vs. Input Voltage Input Current (µA) Output Voltage Difference (%) Step-Down Converter Line Regulation vs. Load Current 1.5 0.1 Load Current (A) 600 575 550 525 500 85°C 25°C -40°C 475 6 9 12 15 18 21 450 24 6 9 12 Input Voltage (V) 15 18 21 24 Input Voltage (V) (VOUT1 = 3.3V; IOUT1 = 4.5A) (VOUT = 3.3V; IOUT1 = 4.5A; COUT1 = 66µF; L = 4.7µH; VIN1 = 12V) 8 Output Voltage Difference (%) Step-Down Converter Output Voltage vs. Temperature Frequency Variation (%) Step-Down Converter Switching Frequency vs. Input Voltage 85°C 25°C -40°C 6 4 2 0 -2 -4 -6 -8 6 8 10 12 14 16 18 20 22 1 0.75 0.5 0.25 0 -0.25 -0.5 -0.75 24 Input Voltage (V) 2687.2008.06.1.0 -1 -40 -15 10 35 60 85 Temperature (°C) www.analogictech.com 5 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Step-Down Converter Load Transient Step-Down Converter Load Transient (VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH) (VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH) 14 3.55 12 3.30 10 3.05 8 2.80 6 4.5A 2.55 2.30 2.05 4 2 450mA 0 3.7 Output Voltage (top) (V) 16 3.80 16 3.5 14 3.3 12 3.1 10 2.9 8 2.7 6 4.5A 2.5 2.3 2.1 0 Time (100µs/div) Time (100µs/div) Step-Down Converter Load Transient Step-Down Converter Line Transient 3.4 9 3.3 8 3.2 7 3.1 6 3 4.5A 2.8 3.375A 5 4 3 2 2.7 3.36 22 3.34 20 3.32 18 3.3 16 3.28 14 3.26 12 3.24 10 3.22 8 3.2 6 Time (100µs/div) Input Voltage (bottom) (V) 10 Output Voltage (top) (V) (VOUT1 = 3.3V; COUT1 = 66µF; L = 4.7µH) 3.5 Load Current (bottom) (A) Output Voltage (top) (V) (VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH) 2.9 4 2 2.25A Load Current (bottom) (A) 4.05 Load Current (bottom) (A) Output Voltage (top) (V) Typical Characteristics—Channel 1 Time (100µs/div) 30 3.3 25 3.28 20 3.26 15 3.24 10 3.22 5 3.2 0 3.18 -5 3.36 35 3.34 30 3.32 25 3.3 20 3.28 15 3.26 10 3.24 5 3.22 0 3.2 -5 Time (1µs/div) 6 LX Voltage (bottom) (V) 35 3.32 LX Voltage (bottom) (V) 3.34 Output Voltage (top) (V) Step-Down Converter Output Voltage Ripple (VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH; IOUT1 = 1mA) Output Voltage (top) (V) Step-Down Converter Output Voltage Ripple (VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH; IOUT1 = 4.5A) Time (2µs/div) www.analogictech.com 2687.2008.06.1.0 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Typical Characteristics—Channel 2 LDO Input Current vs. Input Voltage LDO Dropout Voltage vs. Temperature (VEN1 = 0V; VEN2 = VIN2) 1400 Dropout Voltage (mV) Input Current (µA) 100 80 60 40 85°C 25°C -40°C 20 0 2 2.5 3 3.5 4 4.5 1200 IOUT2 = 600mA IOUT2 = 500mA IOUT2 = 300mA IOUT2 = 150mA IOUT2 = 50mA 1000 800 600 400 200 0 -40 5 -15 10 Input Voltage (V) LDO Dropout Voltage vs. Output Current 60 85 LDO VIH and VIL vs. Input Voltage 1500 1.30 1.25 1200 VIH and VIL (V) Dropout Voltage (V) 35 Temperature (°C) 900 600 85°C 25°C -40°C 300 1.20 1.15 1.10 1.05 0 1.00 0 100 200 300 400 500 600 VIH VIL 2.5 3 Output Current (mA) 3.5 4 4.5 5 Input Voltage (V) LDO Output Voltage Error vs. Temperature LDO Dropout Characteristic (VIN2 = 3.3V; VOUT2 = 1.8V; IOUT2 = 600mA) (VOUT2 = 1.8V) 1.84 IOUT2 = 0.1mA IOUT2 = 300mA IOUT2 = 600mA 2.0 Output Voltage (V) Output Voltage Error (%) 3.0 1.0 0.0 -1.0 -2.0 -3.0 -50 -25 0 25 50 75 100 1.82 1.80 1.78 1.76 IOUT2 = 0.1mA IOUT2 = 50mA IOUT2 = 100mA IOUT2 = 300mA IOUT2 = 600mA 1.74 1.72 1.70 1.5 Temperature (°C) 2687.2008.06.1.0 5.5 2 2.5 3 3.5 4 4.5 Input Voltage (V) www.analogictech.com 7 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Typical Characteristics—Channel 2 LDO Turn-Off Response Time LDO Turn-On Time from Enable (VIN2 = 3.3V; VEN2 = 3.3V; VOUT2 = 1.8V; IOUT2 = 600mA) (VIN2 = 3.3V; VEN2 = 3.3V; VOUT2 = 1.8V; IOUT2 = 600mA) 1 0 2.0 1.0 0.0 -1.0 Enable Voltage (top) (V) Enable Voltage (top) (V) 2 4 3 2 1 3 0 2 1 0 Time (5µs/div) Output Voltage (bottom) (V) 3 Output Voltage (bottom) (V) 4 Time (5µs/div) LDO Load Transient Response (IOUT2 = 0.3 to 0.6A; VIN2 = 3.3V; VOUT2 = 1.8V; COUT2 = 2.2µF) 3 2 1.85 VOUT 1.80 1.75 1.70 Output Current (top) (A) VIN 4 0.7 0.6 0.5 0.4 0.3 1.90 1.85 1.80 1.75 Time (200µs/div) Output Voltage (bottom) (V) 5 Output Voltage (bottom) (V) Input Voltage (top) (V) LDO Line Transient Response (VIN2 = 3V to 4V; VOUT2 = 1.8V; IOUT2 = 600mA; COUT2 = 2.2µF) Time (40µs/div) LDO Power Supply Rejection Ratio, PSRR LDO Output Voltage Noise (IOUT2 = 10mA; BW: 100KHz to 300KHz) (IOUT2 = 10mA; Power BW: 300~50KHz) 10 70 Magnitude (dB) Noise (µVRMS) 60 5 50 40 30 20 10 0 100 1000 10000 100000 0 100 10000 100000 Frequency (Hz) Frequency (Hz) 8 1000 www.analogictech.com 2687.2008.06.1.0 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Functional Block Diagram VINT Reg. VL1 IN1 OT FB1 Error Amp OSC Comp. Comp. BST1 COMP1 Logic LX1 Control Logic EN1 20Ω Voltage Ref Ref1 Comp VOCP1 = 0.1V OT RS1 OS1 IN2 OCP FB_LDO Error Amp OUT2 Logic FB_LDO Voltage Ref 2 EN2 Control Logic GND Functional Description The AAT2687 provides two independently regulated DC outputs, consisting of a high voltage step-down regulator and a low input voltage linear low dropout (LDO) regulator. The PMIC is optimized for low cost 12V adapter inputs, making the device an ideal system-on-a-chip power solution for consumer communications equipment. Channel 1 is a step-down regulator with an input voltage range 6.0 to 24V, providing up to 4.5A output current. The 490kHz fixed switching frequency allows small L/C filtering components. Channel 1 utilizes voltage mode control configured for optimum performance across the entire output voltage and load range. The controller includes integrated overcurrent, soft-start and over-temperature protection. Overcurrent is sensed through the output inductor DC winding 2687.2008.06.1.0 resistance (DCR). An external resistor network adjusts the current limit according to the DCR of the desired inductor and the desired output current limit. Frequency reduction limits over-current stresses during short-circuit events. The operating frequency returns to the nominal setting when over-current conditions are removed. Channel 2 is a linear low-dropout (LDO) regulator providing up to 600mA output current at a factory set output voltage. The device provides extremely low output noise, low quiescent current and excellent transient response. The controller includes integrated over-current, softstart and over-temperature protection. Independent input and enable pins provide maximum design flexibility. The AAT2687 is available in the Pb-free, 4x5mm 24-pin TQFN package. The rated operating temperature range is -40°C to 85°C. www.analogictech.com 9 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Applications Information Output 1 is a high voltage DC/DC step-down converter providing an output voltage from 1.5V to 85% of the minimum input voltage (85% · VIN). The integrated highside n-channel MOSFET device provides up to 4.5A output current. Input voltage range is 6.0V to 24.0V. The step-down converter utilizes constant frequency (PWMmode) 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 2 is a low voltage, low dropout (LDO) linear regulator providing 1.8V with up to 600mA output current. The input voltage range is 2.7V to 5.5V. The LDO provides very low noise output which can be derived directly from the Output 1 channel. Channel 1 Output Voltage and Current Output 1 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) R4 = 1.96kΩ R3 (kΩ) 1.5 1.8 1.85 2.0 2.5 3.0 3.3 5.0 2.94 3.92 4.02 4.53 6.19 7.87 8.87 14.3 Three 22μF ceramic output capacitors are required to filter the inductor current ripple and supply the load transient current for IOUT = 4.5A. The 1206 package with 10V minimum voltage rating is recommended for the output capacitors to maintain a minimum capacitance drop with DC bias. Channel 1 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. Channel 1 Rectifier Selection When the high-side switch is on, the input voltage will be applied to the cathode of the Shottky 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. Table 1: Feedback Resistor Values. Alternatively, the feedback resistor may be calculated using the following equation: R3 = Channel 1 Regulator Output Capacitor Selection (VOUT - 0.6) · R4 0.6 Channel 1 Input Capacitor Selection For low cost applications, a 220μF/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. R3 is rounded to the nearest 1% resistor value. 10 www.analogictech.com 2687.2008.06.1.0 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Channel 1 Feedback and Compensation Networks stability. Equation 3, 4, 5 and 6 relate the compensation network’s poles and zeros to the components R1, R3, R5, C5, C6, and C10: C6 Eq. 3: FZ1 = C5 C10 R1 R5 VOUT1 Eq. 4: FZ1 = 1 2 · π · (R3 + R5) · C10 Eq. 5: FP1 = 1 COMP1 R3 1 2 · π · R1 · C5 2 · π · R1 · FB1 Eq. 6: FP2 = R4 REF Figure 1: AAT2687 Feedback and Compensation Networks for Type III Voltage-Mode Control Loop. 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 = Eq. 2: FESR = 1 2 · π · L · COUT 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 Network Feedback Feed-forward Compensation Current Limit C5 · C6 C5 + C6 1 2 · π · R5 · C10 Components of the feedback, feed forward, compensation, and current limit networks need to be adjusted to maintain the systems stability for different input and output voltages applications as shown in Table 1. Channel 1 Thermal Protection The AAT2687 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. Components VOUT =3.3V VIN = 6V-24V VOUT = 5.0V VIN = 6V-24V R4 R3 C10 R5 C5 C6 R1 C4 R2 R6 R7 R8 1.96kΩ 8.87kΩ 2.2nF 453Ω 2.2nF 150pF 3.92kΩ 220nF 2kΩ Open 2kΩ 165kΩ 1.96kΩ 8.87kΩ 2.2nF 453Ω 2.2nF 150pF 3.92kΩ 220nF 2kΩ Open 2kΩ 165kΩ Table 1: AAT2687 Feedback, Compensation, and Current Limit Components For VOUT = 3.3V and VOUT = 5.0V. 2687.2008.06.1.0 www.analogictech.com 11 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Over-Current Protection Channel 2 Input Capacitor The output 1 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. Typically, a 1μF or larger capacitor is recommended for CIN in most applications. A CIN capacitor is not required for basic LDO regulator operation. However, if the AAT2687 is physically located more than three centimeters from an input power source, a CIN capacitor will be needed for stable operation. The preset current limit threshold is triggered when the differential voltage from RS1 to OS1 exceeds 100mV (nominal). L1 LX1 V OUT1 3.3V/4.5A 4.7μH C4 220nF R2 2k Channel 2 Output Capacitor RS1 R7 OS1 R8 Figure 2: Optional Resistor Network to Adjust the Current Limit Less than the Pre-Set Over-Current Threshold (Add R7 and R8). L1 LX1 RS1 VOUT1 3.3V/4.5A 4.7μH R2 2k C4 220nF R6 For proper load voltage regulation and operational stability, a capacitor is required between pins VOUT and GND. The COUT capacitor connection to the LDO regulator ground pin should be connected as close as possible for maximum device performance. The AAT2687 LDO has been specifically designed to function with very low ESR ceramic capacitors. For best performance, ceramic capacitors are recommended. Typical output capacitor values for maximum output current conditions range from 1μF to 10μF. Applications utilizing the exceptionally low output noise and optimum power supply ripple rejection characteristics of the channel 2 should use 2.2μF or greater for COUT. If desired, COUT may be increased without limit. In low output current applications where output load is less than 10mA, the minimum value for COUT can be as low as 0.47μF. Channel 2 Enable Function R7 OS1 Figure 3: Optional Resistor Network to Adjust the Current Limit Greater than the Pre-Set OverCurrent Level (Add R6 and R7). 12 CIN should be located as close to the device VIN pin as possible. CIN values greater than 1μF will offer superior input line transient response and will assist in maximizing the highest possible power supply ripple rejection. Ceramic, tantalum, or aluminum electrolytic capacitors may be selected for CIN. There is no specific capacitor ESR requirement for CIN. However, for 150mA LDO regulator output operation, ceramic capacitors are recommended for CIN due to their inherent capability over tantalum capacitors to withstand input current surges from low impedance sources, such as batteries in portable devices. The AAT2687 features an LDO regulator enable/disable function. This pin (EN) is active high and is compatible with CMOS logic. To assure the LDO regulator will switch on, the EN turn-on control level must be greater than 1.5V. The LDO regulator will go into the disable shutdown mode when the voltage on the EN pin falls below 0.6V. If the enable function is not needed in a specific application, it may be tied to VIN to keep the LDO regulator in a continuously on state. When the LDO regulator is in shut- www.analogictech.com 2687.2008.06.1.0 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters down mode, an internal 1.5kΩ resistor is connected between VOUT and GND. This is intended to discharge COUT when the LDO regulator is disabled. The internal 1.5kΩ has no adverse effect on device turn-on time. Channel 2 Short-Circuit Protection The AAT2687 LDO contains an internal short-circuit protection circuit that will trigger when the output load current exceeds the internal threshold limit. Under shortcircuit conditions, the output of the LDO regulator will be current limited until the short-circuit condition is removed from the output or LDO regulator package power dissipation exceeds the device thermal limit. Channel 2 Thermal Protection The AAT2687 LDO has an internal thermal protection circuit which will turn on when the device die temperature exceeds 150°C. The internal thermal protection circuit will actively turn off the LDO regulator output pass device to prevent the possibility of over temperature damage. The LDO regulator output will remain in a shutdown state until the internal die temperature falls back below the 150°C trip point. The combination and interaction between the short circuit and thermal protection systems allows the LDO regulator to withstand indefinite short-circuit conditions without sustaining permanent damage. Channel 2 No-Load Stability The AAT2687 is designed to maintain output voltage regulation and stability under operational no load conditions. This is an important characteristic for applications where the output current may drop to zero. Channel 2 Reverse Output-to-Input Voltage Conditions and Protection Under normal operating conditions, a parasitic diode exists between the output and input of the LDO regulator. The input voltage should always remain greater than the output load voltage, maintaining a reverse bias on the internal parasitic diode. Conditions where VOUT might exceed VIN should be avoided since this would forward bias the internal parasitic diode and allow excessive current flow into the VOUT pin, possibly damaging the LDO regulator. In applications where there is a possibility of VOUT exceeding VIN for brief amounts of time during normal operation, the use of a larger value CIN capacitor is 2687.2008.06.1.0 highly recommended. A larger value of CIN with respect to COUT will effect a slower CIN decay rate during shutdown, thus preventing VOUT from exceeding VIN. In applications where there is a greater danger of VOUT exceeding VIN for extended periods of time, it is recommended to place a Schottky diode across VIN to VOUT (connecting the cathode to VIN and anode to VOUT). The Schottky diode forward voltage should be less than 0.45V. Thermal Calculations There are three types of losses associated with the AAT2687 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 and LDO losses is given by: PTOTAL = IOUT12 · (RDS(ON)H · VOUT1 + RDS(ON)L · [VIN1 - VOUT1 ]) VIN1 + (tSW · FS · IOUT1 + IQ1 ) · VIN1 + (VIN2 - VOUT2) · IOUT2 IQ1 and IQ2 are the step-down converter and LDO quiescent currents respectively. 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. The total package losses for the AAT2687 reduce to the following equation: PTOTAL = IOUT12 · RDS(ON)H · D + (tSW · FS · IOUT1 + IQ) · VIN + (VIN2 - VOUT2) · IOUT2 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 TQFN45-24 package, which is 33°C/W. www.analogictech.com TJ(MAX) = PTOTAL · θJA + TAMB 13 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Layout Considerations 5. The suggested PCB layout for the AAT2687 is shown in Figures 5, 6, 7, and 8. The following guidelines should be used to help ensure a proper layout. 6. 1. 2. 3. 4. 14 The power input capacitors (C1 and C15) should be connected as close as possible to high voltage input pin (IN1) and power ground. C1, L1, D2, C7, C8, and C9 should be place 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 FB1 pin should be separated from any power trace and connected as close as possible to the load point. Sensing along a high-current 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. 7. 8. 9. Connect unused signal pins to ground or input to avoid unwanted noise coupling. The critical small signal components include feedback components, and compensation components should be placed close to the FB1 and COMP1 pins. The feedback resistors should be located as close as possible to the FB1 pin with its ground tied straight to the signal ground plane which is separated from power ground plane. C4 should be connected close to the RS1 and OS1 pins, while R2 should be connected directly to the output pin of the inductor. For the best current limit performance, C4 and R2 should be placed at the bottom layer to avoid noise coupling from the inductor. R7 should be connected directly to the output pin of inductor L1 to sense precisely its DCR. For good thermal coupling, a 4-layer PCB layout is recommended and PCB vias are required from the exposed pad (EP) for the TQFN45-24 paddle to the middle plans and bottom plane. The EP is internally connected to IN. www.analogictech.com 2687.2008.06.1.0 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters VOUT1 U1 C3 0.1μF J1 2 1 D1 3.3V/4.5A L1 1 LX1 LX1 24 2 LX1 LX1 23 5 BST N/C 20 18 VL1 FB1 16 VL1 RS1 4.7μH 5.3A C4 2k D2 220nF R6 open 19 22 OS1 14 COMP1 15 3 N/C 4 N/C OUT2 11 6 EN1 N/C 12 10 IN2 GND 17 9 N/C GND2 8 EN2 N/C 3 2 13 C15 open C13 1μF 25V VIN2 7 R3 8.87k C7 R1 22μF 3.92K R4 1.96k C8 C9 22μF 22μF C5 2.2nF VOUT2 1.8V/0.6A 1 EN1 C6 150pF R7 2k AAT2687 IN1 EP C14 2.2μF + R5 453 BAS16 VIN1 6.0V - 24.0V C1 220μF 25V C10 2.2nF R2 R8 165k C12 2.2μF C11 open 3 C2 2.2μF 2 21 1 EN2 U1 C1 C2, C12, C14 C3 C4 C5, C6, C10 C7, C8, C9 C13 D1 D2 L1 R1 - R5 TQFN45-24 AAT2687 Analogic Technologies, Hi-Voltage Buck/LDO, TQFN45-24 Cap, MLC, 220μF/25V, Electrolytic cap Cap, MLC, 2.2μF, 6.3V, 0805 Cap, MLC, 0.1μF/6.3V, 0603 Cap, MLC, 220nF/6.3V, 0402 Cap, MLC, misc, 0603 Cap, MLC, 22μF/10V, 1206 Cap, MLC, 1μF, 25V, 0805 BAS16, Generic, Rectifier, 0.2A/85V, Ultrafast, SOT23 B540C, Generic, Schottky Rectifier, 5A/40V, SMC RCH108NP-4R7M, Sumida, 4.7μH, ISAT = 5.7A, DCR = 11.7mΩ or Wurth 744 771 004, 4.7μH, ISAT = 6.8A, DCR = 11mΩ Carbon film resistor, 0402 Figure 4: AAT2687IFK Evaluation Board Schematic For VIN = 6V - 24V and VOUT = 3.3V. 2687.2008.06.1.0 www.analogictech.com 15 PRODUCT DATASHEET AAT2687 SystemPowerTM 16 PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Figure 5: AAT2687IFK Evaluation Board Top Layer. Figure 6: AAT2687IFK Evaluation Board MID1 Layer. Figure 7: AAT2687IFK Evaluation Board MID2 Layer. Figure 8: AAT2687IFK Evaluation Board Bottom Layer. www.analogictech.com 2687.2008.06.1.0 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters AAT2687 Design Example Specifications VO1 = 3.3V @ 4.5A, Pulsed Load ΔILOAD = 4.5A VO2 = 1.8V @ 600mA VIN1 = 12V FS = 490kHz TAMB = 85°C in TQFN45-24 Package Channel 1 Output Inductor For Sumida inductor RCH108NP-4R7M, 4.7μH, DCR = 11.7mΩ max. ΔI = VOUT1 VOUT1 3.3V 3.3V · 1= · 1= 1A L1 · FS VIN1 4.7μH · 490kHz 12V IPK1 = IOUT1 + ΔI = 4.5A + 1A = 5.5A 2 PL1 = IOUT12 · DCR = 5.5A2 · 11.7mΩ = 354mW Channel 1 Output Capacitor VDROOP = 0.4V COUT = 3 · ΔILOAD 3 · 4.5A = = 69μF; use 3x22μF 0.4V · 490kHz VDROOP · FS IRMS(MAX) = 1 2· 3 · VOUT1 · (VIN(MAX) - VOUT1) 1 3.3V · (24V - 3.3V) · = 357mARMS = L · FS · VIN1(MAX) 2 · 3 4.7μH · 490kHz · 24V PRMS = ESR · IRMS2 = 5mΩ · (357mA)2 = 0.6W Channel 1 Input Capacitor Input Ripple VPP = 33mV CIN1 = 1 VPP - ESR · 4 · FS IOUT1 = 1 5.5mV - 5mΩ · 4 · 490kHz 4.5A = 219μF For low cost applications, a 220μF/25V electrolytic capacitor in parallel with a 1μF/25V ceramic capacitor is used to reduce ESR. IRMS = IOUT1 = 2.25A 2 P = ESR · (IRMS)2 = 5mΩ · (2.25A)2 = 25.3mW 2687.2008.06.1.0 www.analogictech.com 17 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Channel 1 Current Limit Voltage sense VS = 100mV Total trace parasitic resister and inductor DCR is 10mΩ ILIMIT = 5A. IPRESET = VS 100mV = = 10A > ILIMIT 10mΩ DCR R8 = VOUT · R2 3.3V · 2kΩ = 165kΩ = 0.1V - 6A · 10mΩ VS - ILIMIT · DCR R7 = R2 · R 8 2kΩ · 165kΩ = = 2kΩ 165kΩ - 2kΩ R8 - R 2 AAT2687 Losses All values assume 25°C ambient temperature and thermal resistor of 50°C/W in the TQFN45-24 package. PTOTAL = IOUT12 · RDS(ON)H · D + (tSW · FS · IOUT1 + IQ) · VIN1 + (VIN2 - VOUT2) · IOUT2 2 PTOTAL = 4.5A · 70mΩ · 3.3V + (5ns · 490kHz · 4.5A + 70μA) · 12V + (3.3 - 1.8) · 600mA 12V PTOTAL = 1.42W TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (33°C/W) · 1.42W = 131°C 18 www.analogictech.com 2687.2008.06.1.0 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Ordering Information Voltage Package Channel 1 Channel 2 Marking1 Part Number (Tape and Reel)2 TQFN45-24 Adj (0.6) 1.8 3PXYY AAT2687IFK-AI-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. Legend Voltage Code Adjustable (0.6) 1.8 A I 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 2687.2008.06.1.0 www.analogictech.com 19 PRODUCT DATASHEET AAT2687 SystemPowerTM PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters Package Information1 TQFN45-24 Pin 1 Identification Chamfer 0.400 x 45° 2.800 ± 0.050 3.000 REF 3.800 ± 0.050 0.400 ± 0.050 0.750 ± 0.050 4.000 ± 0.050 5.000 ± 0.050 Pin 1 Dot by Marking 0.203 REF 0.000 - 0.050 Side View 0.250 ± 0.050 0.500 BSC 2.000 REF Top View Bottom View All dimensions in millimeters. 1. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. 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. 20 www.analogictech.com 2687.2008.06.1.0