PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters General Description Features The AAT2688 provides two independently regulated DC outputs: a high voltage synchronous step-down (Buck) regulator and a low input voltage step-down low dropout (LDO) regulator. The PMIC is optimized for low cost 12V adapter inputs, making the device the ideal system-ona-chip power solution for consumer communications equipment. • 2-Output Step-Down Converters: • Channel 1 (Buck): VIN1 = 6.0 to 24.0V ▪ VOUT1 Adjustable from 0.8V to 5.5V ▪ IOUT1 up to 4.5A ▪ High Switching Frequency ▪ Voltage Mode Control ▪ High Accuracy ±1.5% ▪ PWM Fixed Frequency for Low Ripple • Channel 2 (LDO): VIN2 = 2.7V to 5.5V ▪ IOUT2 up to 600mA ▪ 1V Dropout Voltage at 600mA IOUT • Small Solution Size • System on a Chip • Ultra-small External L/C • Shutdown Current <35μA • Independent Enable Pins • Over-Current and Over-Temperature Protection • Internal Soft Start • 4x5mm 24-Pin TQFN Low Profile Package • -40°C to 85°C Temperature Range Channel 1 is a step-down regulator with an input voltage range of 6.0V 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 low output noise, low quiescent current, and excellent transient response. The step-down regulator includes integrated over-current, soft-start and over-temperature protection. Independent input and enable pins provide maximum design flexibility. Applications • • • • The AAT2688 is available in the Pb-free 4mm x 5mm 24-pin TQFN package. The rated operating temperature range is -40°C to 85°C. DSL and Cable Modems Notebook Computers Satellite Set-top Boxes Wireless LAN Systems Typical Application VOUT1 3.3V/4.5A L1 4.7μH/5.3A LX1 C3 0.1μF BST1 D1 BAS16 J1 VL1 2 C14 2.2μF 1 VIN1 6.0V -24.0V DL Q1 R2 2K C4 220nF RS1 R3 9.09k C7 22μF C8 22μF C9 22μF R5 150 OS1 IN1 C10 2.2nF FB1 COMP1 AAT2688 C6 150pF EN1 VIN2 + C1 220μF 25V C13 1μF 25V C2 2.2μF C5 2.2nF R1 3.92k IN2 OUT2 EN2 GND VOUT2 R4 1.96k C12 2.2μF TQFN45-24 2688.2008.06.1.0 www.analogictech.com 1 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Pin Descriptions Pin # Symbol 1, 2, 23, 24 LX1 3, 4, 9, 12 N/C 5 BST1 6 EN1 7 GND2 8 EN2 10 IN2 11 OUT2 13 RS1 14 OS1 15 COMP1 16 FB1 17 GND1 18, 19 VL1 20 DL1 21 PGND 22 IN1 EP EP 2 Function Channel 1 step-down (Buck) converter switching pin. Connect output inductor to this pin. Connect both LX1 pins together. No connect. For optional routing reasons, pins 3 and 4 can be connected to VIN, pin 9 to pin 10 (IN2), and pin 12 to pin 11 (OUT2). 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 hi-side MOSFET gate drive. Channel 1 step-down regulator enable input pin. Active high enables internal linear regulator and channel 1 output. 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 low dropout (LDO) enable input pin. Active high. 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. Channel 1 output current sense pin. Connect a small signal resistor from this pin to switching node (LX1) to enable over-current sense for step-down converter. The current limit threshold varies with sense resistor sizing. Channel 1 output sense voltage pin. Connect to the output capacitor to enable over-current sense for step-down 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. Connect a 2.2μF capacitor from this pin to GND pin. Channel 1 gate drive for low side MOSFET. Connect to the gate pin of an external N type MOSFET (see the "MOSFET Selection" section of this product datasheet). Ground pin for both channels. Power return pin for both channels. Connect returns of both channels’ input and output capacitors close to this pin for best noise performance. 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. Exposed Paddle. Tie to IN1. Connect to PCB heatsink for optimum thermal performance. www.analogictech.com 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Pin Configuration TQFN45-24 (Top View) DL1 PGND IN1 LX1 LX1 20 21 22 23 24 LX1 LX1 N/C N/C BST1 EN1 GND2 1 19 2 18 3 17 EP 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 VIN(HI) VIN(LO) VBST1-LX1 VCONTROL VEN2 TJ TLEAD Description IN1, EN1, LX1 to GND IN2, VL1 to GND BST1 to LX1 FB1, COMP1, RS1, OS1, OUT2, DL1 to GND EN2 to GND 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 -40 to 150 300 V V V V V °C °C Value Units 3.0 33 W °C/W Thermal Information Symbol PD ΘJA Description Maximum Power Dissipation2 Thermal Resistance3 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 30mW/°C above 25°C ambient temperature. 2688.2008.06.1.0 www.analogictech.com 3 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Electrical Characteristics1 VIN1 = 12.0V, VIN2 =3.3V; TA = -40°C to 85°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol Description Conditions Channel 1: 4.5A Step-Down (Buck) Converter VIN1 Input Voltage VUVLO1 VOUT1 VFB1 VOUT (ΔVOUT/VOUT)/ ΔVIN (ΔVOUT/VOUT)/ ΔIOUT IQ1 ISHDN1 VOCP1 ILX1 DMAX RDL1 UVLO Threshold Min Typ 6.0 VIN1 Rising VIN1 Hysteresis VIN1 Falling Max Units 24.0 5.0 V V mV V V V % 300 3.0 0.8 0.576 -3.0 Output Voltage Range Feedback Pin Voltage Output Voltage Accuracy IOUT1 = 0 to 4.5A Line Regulation VIN1 = 6V to 24V, VOUT1 = 3.3V, IOUT1 = 4.5A 0.05 %/V Load Regulation VIN1 = 12V, VOUT1 = 3.3V, IOUT1 = 0A to 4.5A 0.2 %/A Quiescent Current Shutdown Current Over-Current Offset Voltage LX1 Pin Leakage Current Maximum Duty Cycle VEN1 = Low, No load, VFB1 = 1.2V VEN1 = High, VL1 = 0V VEN1 = Low, VIN1 = 6.0V to 24.0V, TA = 25°C VIN1 = 24.0V, VEN1 = 5.0V 600 Low Side Drive Source Resistance 80 -1.0 Pull-Up, VL1 = 4.5V Pull-Down, VL1 = 4.5V VL1 = 4.5V RDSON(H) Hi Side On-Resistance 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 Low Dropout (LDO) Regulator Input Voltage VIN2 VDO2 Dropout Voltage 98% · VOUT2(NOM), IOUT2 = 600mA IQ2 Quiescent (Ground) Current No load ISHDN2 Shutdown Current VEN2 = GND IOUT2= 1mA to 600mA, VIN2 = 2.7 to 5.5V, TA = 25°C Output Voltage Tolerance VOUT2(TOL) IOUT2= 1mA to 600mA, VIN2 = 2.7 to 5.5V, TA = -40°C to 85°C eN Output Noise BW = 300Hz to 50kHz 1kHz PSRR Power Supply Rejection Ratio IOUT2 = 10mA 10kHz 1MHz Current Limit ILIMIT2 tS2 Enable Start-Up Delay From Enable Channel 2 to Output Regulation Over-Temperature, EN Logic Over-Temperature Shutdown Threshold TSD1,2 Over-Temperature Shutdown Hysteresis Enable Threshold Low VEN1,EN2(L) VEN1(H) Enable Threshold High VEN2(H) IEN1,EN2 Input Low Current 350 0.585 100 85 5.0 1.7 35 490 100 2.5 2.7 5.5 0.594 +3.0 35 120 1.0 μA μA mV μA % Ω 650 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 V V 1.0 μA 1. The AAT2688 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 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Typical Characteristics–Channel 1 Step-Down Converter Efficiency vs. Output Current Step-Down Converter DC Regulation (VOUT1 = 3.3V; L = 4.7µH) (VOUT1 = 3.3V; L = 4.7µH) 2.0 Output Voltage Error (%) 100 90 Efficiency (%) 80 70 60 50 VIN1 = 6V VIN1 = 8V VIN1 = 12V VIN1 = 18V VIN1 = 24V 40 30 20 10 0 0.1 1 10 100 1000 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0.1 10000 VIN1 = 6V VIN1 = 8V VIN1 = 12V VIN1 = 18V VIN1 = 24V 1 Output Current (mA) Step-Down Converter Output Voltage Error vs. Input Voltage Switching Frequency (kHz) Output Voltage Error (%) 0 -1 -2 6 8 10 12 14 16 18 10000 20 22 510 500 490 480 470 -40 24 -15 10 35 60 85 Temperature (°C) Input Voltage (V) Step-Down Converter Switching Frequency vs. Input Voltage No Load Step-Down Converter Input Current vs. Input Voltage (VOUT1 = 3.3V; IOUT1 = 4.5A) (VEN1 = VIN1) 0.70 3 Input Current (mA) Switching Frequency Variation (%) 1000 (VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 4.5A) IOUT1 = 0.10mA IOUT1 = 100mA IOUT1 = 1000mA IOUT1 = 2250mA IOUT1 = 3500mA IOUT1 = 4500mA 1 100 Step-Down Converter Switching Frequency vs. Temperature (VOUT1 = 3.3V; L = 4.7µH) 2 10 Output Current (mA) 2 1 0 -1 -2 0.65 0.60 0.55 0.50 0.45 85°C 25°C -40°C 0.40 0.35 0.30 -3 6 8 10 12 14 16 18 20 22 24 Input Voltage (V) Input Voltage (V) 2688.2008.06.1.0 www.analogictech.com 5 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Typical Characteristics–Channel 1 Step-Down Converter Output Voltage Error vs. Temperature Step-Down Converter Output Ripple (VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 4.5A) 3.30 IOUT1 = 0.10mA IOUT1 = 10mA IOUT1 = 2250mA IOUT1 = 4500mA 0.4 0.2 Output Voltage (top) (V) Output Voltage Error (%) 3.31 0.6 0.0 -0.2 3.29 12V 0V 5 4 -0.4 3 -0.6 -40 -15 10 35 60 85 Temperature (°C) Time (1µs/div) Step-Down Converter Load Transient Response (VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 1mA) (IOUT1 = 3.375A to 4.5A; VIN1 = 12V; COUT1 = 3x22µF) Output Voltage (top) (V) 12V 0V 1 0 -1 6 5 4.5A 4 3.375A 3 3.4 3.3 3.2 Output Current (top) (A) 3.29 LX Voltage (middle) (V) Inductor Current (bottom) (A) 3.30 Output Voltage (bottom) (V) Step-Down Converter Output Ripple 3.31 Time (100µs/div) Time (1µs/div) (IOUT1 = 0.45A to 4.5A; VIN1 = 12V; COUT1 = 3x22µF) 3 2.25A 2 3.5 3.3 3.1 4.5A 6 4 2 0.45A 0 3.7 3.5 3.3 3.1 Output Current (top) (A) 4 Output Current (top) (A) 4.5A 5 Output Voltage (bottom) (V) Step-Down Converter Load Transient Response (IOUT1 = 2.25 to 4.5A; VIN1 = 12V; COUT1 = 3x22µF) Output Voltage (bottom) (V) Step-Down Converter Load Transient Response 2.9 Time (100µs/div) 6 LX Voltage (middle) (V) Inductor Current (bottom) (A) (VIN1 = 12V; VOUT1 = 3.3V) Time (100µs/div) www.analogictech.com 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Typical Characteristics–Channel 1 (VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 4.5A) 5 3.35 3.30 3.25 Time (100ms/div) 2688.2008.06.1.0 15 10 5 0 6 4 2 Output Current (bottom) (A) 10 Output Voltage (bottom) (V) 15 Enable Voltage (top) (V) Output Voltage (middle) (V) Step-Down Converter Soft Start (VIN1 = 6V to 10V; VOUT1 = 3.3V; IOUT1 = 4.5A) Input Voltage (top) (V) Step-Down Converter Line Transient Response 0 Time (500µs/div) www.analogictech.com 7 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output 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 2.5 3 3.5 4 4.5 IOUT2 = 600mA IOUT2 = 500mA IOUT2 = 300mA IOUT2 = 150mA IOUT2 = 50mA 1000 800 600 400 200 0 -40 0 2 1200 5 -15 10 Input Voltage (V) 1.30 1.25 1200 VIH and VIL (V) Dropout Voltage (V) 85 LDO VIH and VIL vs. Input Voltage 1500 900 600 85°C 25°C -40°C 300 1.20 1.15 1.10 1.05 0 VIH VIL 1.00 0 100 200 300 400 500 2.5 600 3 Output Current (mA) 3.5 4 4.5 5 5.5 Input Voltage (V) LDO Output Voltage Error vs. Temperature LDO Dropout Characteristics (VOUT2 = 1.8V) (VIN2 = 3.3V; VOUT2 = 1.8V; IOUT2 = 600mA) 1.84 IOUT2 = 0.1mA IOUT2 = 300mA IOUT2 = 600mA 2.0 1.0 0.0 -1.0 -2.0 -3.0 -50 -25 0 25 50 75 100 Output Voltage (V) 3.0 Output Voltage Error (%) 60 Temperature (°C) LDO Dropout Voltage vs. Output Current 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) 8 35 2 2.5 3 3.5 4 4.5 Input Voltage (V) www.analogictech.com 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output 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) 4 3 2 1.85 VOUT 1.80 1.75 1.70 Output Current (top) (A) VIN 0.7 0.6 0.5 0.4 0.3 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 Output Voltage Noise LDO Power Supply Rejection Ratio, PSRR (IOUT2 = 10mA; Power BW: 300~50KHz) (IOUT2 = 10mA; BW: 100KHz to 300KHz) 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) 2688.2008.06.1.0 1000 www.analogictech.com 9 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Functional Block Diagram VINT Reg. VL1 IN1 OT OSC Comp. Comp. FB 1 BST1 Error Amp 30mΩ COMP1 Logic LX1 Control Logic EN 1 Voltage Ref 20Ω PGND GND1 DL1 RS1 OS1 Comp OT IN 2 OCP FB_LDO Error Amp OUT 2 Logic FB_LDO Voltage Ref 2 EN2 Control Logic GND2 Functional Description The AAT2688 provides two independently regulated DC outputs; consisting of a high voltage synchronous stepdown (Buck) regulator and a low input voltage linear 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. Channel 1 is a step-down (Buck) 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. The regulator includes integrated overcurrent, soft-start and over-temperature protection. Over-current is sensed through the output inductor DC 10 winding resistance. An external resistor network adjusts the current limit according to the DC winding resistance 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 low-dropout (LDO) regulator providing up to 600mA output current at a factory set output voltage. The device provides low output noise, low quiescent current, and excellent transient response. The regulators include integrated over-current, soft-start and over-temperature protection. Independent input and enable pins provide maximum design flexibility. The AAT2688 is available in the Pb-free 4x5 mm 24-pin TQFN package. The rated operating temperature range is -40°C to 85°C. www.analogictech.com 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Applications Information Output 1 is a high voltage DC/DC step-down converter providing an output voltage from 0.8V to 5.5V. The integrated high-side 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 (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 and an optional feed forward capacitor 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 Output 1. Output Voltage—Channel 11 The output voltage is set using an external resistor divider as shown in Table 1. Minimum output voltage is 0.8V and maximum output voltage is 5.5V. Typical maximum duty cycle is 85%. Example: with R4 = 1.96KΩ, R3 = (VOUT - 0.585) · R4 0.585 VOUT1 (V) R3 (kΩ) 0.8 1.0 1.2 1.5 1.8 2.0 2.5 3.0 3.3 5.0 0.715 1.37 2.05 3.09 4.02 4.75 6.49 8.06 9.09 14.7 Table 1: External Resistor Values (Standard 1% Resistors are Substituted for Calculated Values). Channel 1 Regulator Output Capacitor Selection 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 or the MOSFETs. Channel 1 MOSFET Selection The step-down (buck) converter utilizes synchronous rectification (Q1) for constant frequency (PWM mode) voltage mode control. The synchronous rectifier is selected based on the desired RDS(ON) value and QG (total gate charge), these two critical parameters are weighed against each other. To get a low RDS(ON) value, the MOSFET must be of a very large size and a larger MOSFET will have a large QG. Conversely to get a low QG, the MOSFET must be small and thus have a large RDS(ON) value. In addition to the trade off between RDS(ON) and QG, the maximum voltage rating for the external synchronous MOSFET must exceed the maximum application input voltage value (VDS[MAX] > VIN[MAX]). The QG affects the turn-on/turn-off time of the synchronous MOSFET, the longer the turn-on/turn-off time the more likely the step-down converter will have “shoot through” current issues. “Shoot through” current occurs when the AAT2688 internal top-side MOSFET and the external synchronous MOSFET are conducting current at the same time. This will result in a low impedance path to ground from the input voltage through the two MOSFETs, and the current may exceed the maximum current rating of the AAT2688 and external synchronous MOSFET. Exceeding the maximum current ratings will lead to the destructive derating of the AAT2688 and external synchronous MOSFET. 1. The R3 and R4 feedback resistors are separate from the compensation network. When changing either R3 and/or R4, the compensation network will have to be altered. Contact the Applications Engineering department for compensation network recommendations for specific output voltages. 2688.2008.06.1.0 www.analogictech.com 11 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters The critical parameter recommendations for the external synchronous minimum 25V MOSFET are as follows: Eq. 3: FZ1 = QG (Total Gate Charge) = 5nC to 15nC (max) (VGS: 4.5V to 5V) RDS(ON) = 10mΩ to 30mΩ (max) (VGS: 4.5V to 5V) Eq. 4: FZ2 = 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. Channel 1 Feedback and Compensation Networks 1 2 · π · R1 · C5 1 2 · π · (R3 + R5) · C10 1 Eq. 5: FP1 = 2 · π · R1 · Eq. 6: FP2 = 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 voltage applications as shown in Table 2. Components VOUT =3.3V VIN=6V-24V R4 R3 C10 R5 C5 C6 R1 C4 R2 R6 R7 R8 1.96kΩ 9.09kΩ 2.2nF 150Ω 2.2nF 150pF 3.92kΩ 220nF 2kΩ Open 0 Open C6 Network C5 C10 R1 R5 VOUT1 Feedback Feed Forward COMP1 R3 Compensation FB1 R4 Current Limit REF Figure 1: AAT2688 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 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: 12 C5 · C6 C5 + C6 Table 2: AAT2688 Feedback, Compensation, and Current Limit Components for VOUT =3.3V. Channel 1 Thermal Protection The AAT2688 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. www.analogictech.com 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Over-Current Protection Channel 2 Input Capacitor The regulator 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. The regulator reduces the operating frequency when an over-current condition is detected; limiting stresses and preventing inductor saturation. This allows the smallest possible inductor for the given application. A small resistor divider may be necessary to adjust the over-current threshold and compensate for variation in inductor DC resistance. 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 AAT2688 is physically located more than three centimeters from an input power source, a CIN capacitor will be needed for stable operation. L1 LX1 V OUT1 3.3V/4.5A 4.7μH C4 220nF R2 2k RS1 R7 OS1 R8 Figure 2: Resistor Network to Adjust the Current Limit Less than the Pre-Set Over-Current Threshold (Add R7, R8). L1 LX1 4.7μH R2 2k RS1 VOUT1 3.3V/4.5A C4 220nF R6 Channel 2 Output Capacitor 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 AAT2688 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: Resistor Network to Adjust the Current Limit Greater than the Pre-Set Over-Current Level (Add R6, R7). 2688.2008.06.1.0 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 AAT2688 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 13 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output 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 AAT2688 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 AAT2688 LDO 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 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 135°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 AAT2688 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 14 highly recommended. A larger value of CIN with respect to COUT will affect 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 AAT2688 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 a synchronous Step-Down converter, the power dissipation occurs in the internal high side MOSFET during the on time and the external low side MOSFET during the off time. When the internal high side switch is off, the power dissipates on the external low side switch. The total package losses for AAT2688 reduce to the following equation: PTOTAL = IOUT12 · RDS(ON)H · D + (tSW · FS · IOUT1 + IQ1) · 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 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Layout Considerations 5. Connect unused signal pins to ground or input to avoid unwanted noise coupling. 6. 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. 7. C4 should be connected close to the RS1 and OS1 pins, while R2 should be connected close to the inductor. 8. R7 should be connected directly to the output pin of inductor L1 to sense precisely its DCR. 9. 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. The suggested PCB layout for the AAT2688 is shown in Figures 5 through 8. The following guidelines should be used to help ensure a proper layout. 1. 2. 3. 4. 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, Q1, 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 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. 1 C3 0.1μF 2 LX1 BST1 DL 18 VL1 FB1 16 19 VL1 RS1 13 5 D1 J1 LX1 1 VIN1 6.0V - 24.0V 4.7μH 3 C14 2.2μF IN 20 OS1 14 COMP1 15 N/C EP R2 2k Q1 C4 220nF 4 N/C OUT2 11 6 EN1 N/C 12 C1 220μF 25V + C15 open C13 1μF 25V VIN2 10 IN2 GND 17 9 N/C GND2 8 EN2 N/C 7 C7 22μF C6 R1 150pF 3.92K R4 1.96k C8 C9 22μF 22μF C5 2.2nF VOUT2 1.8V/0.6A 1 EN1 R3 9.09k R5 150 R6 open R7 0 3 2 C10 2.2nF 23 AAT2688 22 VOUT1 3.3V/4.5A L1 24 LX1 2 D1 BAS16 U1 LX1 R8 open C12 2.2μF C11 open 3 C2 2.2μF 2 21 1 EN2 U1 C1 C2, C12, C14 C3 C4 C5, C6, C10, C11 C7, C8, C9 C13 D1 Q1 L1 R1-R5 TQFN 45-24 AAT2688 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 SOP8 MOSFET, Si4686DY, Vishay or FDS8884, Fairchild RCH108NP-4R7M, Sumida, 4.7μH, ISAT = 5.7A, DCR = 11.7mΩ; Unshielded or Wurth 744 771 004, 4.7μH, ISAT = 6.8A, DCR = 11mΩ, Shielded Carbon film resistor, 0402 Figure 4: AAT2688 Evaluation Board Schematic for VIN = 6V-24V and VOUT = 3.3V. 2688.2008.06.1.0 www.analogictech.com 15 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters 16 Figure 5: AAT2688IFK Evaluation Board Top Layer. Figure 6: AAT2688IFK Evaluation Board Mid1 Layer. Figure 7: AAT2688IFK Evaluation Board Mid2 Layer. Figure 8: AAT2688IFK Evaluation Board Bottom Layer. www.analogictech.com 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters AAT2688 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 = 219μF 33mV - 5mΩ · 4 · 490kHz 4.5A For low cost applications, a 220μF/25V electrolytic capacitor in parallel with a 1μF/25V ceramic capacitor is used to reduce the ESR. IRMS = IOUT1 = 2.25A 2 P = ESR · (IRMS)2 = 5mΩ · (2.25A)2 = 25.3mW 2688.2008.06.1.0 www.analogictech.com 17 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Channel 1 Current Limit Voltage sense VS = 100mV Total trace parasitic resistor and inductor DCR = 10mΩ 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 AAT2688 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) · VIN + (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 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Ordering Information Voltage Package Channel 1 Channel 2 Marking1 Part Number (Tape and Reel)2 TQFN45-24 Adjustable 1.8 3WXYY AAT2688IFK-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 1.8 A I Package Information TQFN45-243 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. XYY = Assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. 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. 2688.2008.06.1.0 www.analogictech.com 19 PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters 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 2688.2008.06.1.0