AAT2688

PRODUCT DATASHEET AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters General Description 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. 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. 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. Features • 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 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. 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) 0.8 1.0 1.2 1.5 1.8 2.0 2.5 3.0 3.3 5.0 R3 (kΩ) 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). 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: 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. 3: FZ1 = Eq. 4: FZ2 = Eq. 5: FP1 = 1 2 · π · R1 · C5 1 2 · π · (R3 + R5) · C10 1 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. 2 · π · R1 · Eq. 6: FP2 = C5 · C6 C5 + C6 1 2 · π · R5 · C10 Channel 1 Feedback and Compensation Networks C6 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. VOUT =3.3V VIN=6V-24V 1.96kΩ 9.09kΩ 2.2nF 150Ω 2.2nF 150pF 3.92kΩ 220nF 2kΩ Open 0 Open Network C5 R1 C10 R5 VOUT1 Components R4 R3 C10 R5 C5 C6 R1 C4 R2 R6 R7 R8 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 = 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. 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 www.analogictech.com 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Over-Current Protection 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. Channel 2 Input Capacitor 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. 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. L1 LX1 4.7μH V OUT1 3.3V/4.5A R2 2k RS1 C4 220nF R7 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. 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 VOUT1 3.3V/4.5A R2 2k RS1 OS1 C4 220nF R6 R7 Channel 2 Enable Function 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- 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 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. 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. 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. 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: 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. 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 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 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. TJ(MAX) = PTOTAL · θJA + TAMB 14 www.analogictech.com 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Layout Considerations 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. 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. 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. 5. 2. 3. 4. C3 0.1μF D1 BAS16 2 1 U1 LX1 LX1 BST1 VL1 VL1 IN N/C EP COMP1 OUT2 N/C GND GND2 N/C LX1 LX1 DL FB1 RS1 OS1 24 L1 4.7μH C10 2.2nF R5 150 VOUT1 3.3V/4.5A 2 23 5 20 R2 2k Q1 C4 220nF R6 open R3 9.09k J1 1 D1 18 16 VIN1 6.0V - 24.0V 19 13 AAT2688 22 3 14 15 R7 0 C7 22μF C6 R1 150pF 3.92K R4 1.96k C5 2.2nF C8 C9 22μF 22μF C14 2.2μF 3 2 1 4 N/C EN1 IN2 N/C EN2 11 6 12 VOUT2 1.8V/0.6A R8 open C12 2.2μF C11 open EN1 C1 220μF 25V + C15 open C13 1μF 25V VIN2 10 17 9 7 C2 2.2μF EN2 3 2 1 8 21 TQFN 45-24 U1 C1 C2, C12, C14 C3 C4 C5, C6, C10, C11 C7, C8, C9 C13 D1 Q1 L1 R1-R5 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 AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters 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. 16 www.analogictech.com 2688.2008.06.1.0 PRODUCT DATASHEET AAT2688 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 ΔI = 4.5A + 1A = 5.5A 2 IPK1 = IOUT1 + 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 1 2· 3 IRMS(MAX) = · 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 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 R2 · R 8 2kΩ · 165kΩ = = 2kΩ 165kΩ - 2kΩ R8 - R 2 R7 = 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 AAT2688 SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters Ordering Information Voltage Package TQFN45-24 Channel 1 Adjustable Channel 2 1.8 Marking1 3WXYY Part Number (Tape and Reel)2 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 Adjustable 1.8 Code A I Package Information TQFN45-243 Pin 1 Dot by Marking 4.000 ± 0.050 0.400 ± 0.050 2.800 ± 0.050 Pin 1 Identification Chamfer 0.400 x 45° 5.000 ± 0.050 3.800 ± 0.050 3.000 REF 0.750 ± 0.050 0.203 REF 0.000 - 0.050 Side View 0.500 BSC 2.000 REF 0.250 ± 0.050 Top View All dimensions in millimeters. Bottom View 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 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