AAT2504_08 ANALOGICTECH | Alldatasheet
Document overview
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Technical content
Features
- 800mA Buck Converter ▪ V IN Range: 2.7V to 5.5V ▪ V OUT Range: 0.9V to VIN, Adjustable ▪ High Efficiency: 95% ▪ 2MHz Switching Frequency ▪ Synchronizable to External Clock ▪ Internal Soft Start
- Two 300mA Linear Regulators ▪ LDO Input Voltage Range: 1.62V to 5.5V ▪ Low Dropout Voltage ▪ High Output Accuracy: ±1.5%
- Low Total Quiescent Current I Q (80μA)
- Independent Enable Pins
- Over-Temperature Protection
- QFN34-20 Package
- -40°C to +85°C Temperature Range
Applications
- Cellular Phones
- Digital Cameras
- Handheld Instruments
- Microprocessor/DSP Core/IO Power
- PDAs and Handheld Computers Typical Application AAT2504 R2B R1B R2A R1A 2.2μF OUTA OUTB POKPOK OUTA OUTB AGND VLDOA VLDOB LX FB L VOUT (Step-down) PGND VIN VP FBB COUT FBA 2.2μF ENB EN ENA VIN 100kΩ MODE/SYNC
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Pin Descriptions Pin # Symbol Function 1 FBB Feedback input pin for LDOB. This pin is used to regulate the output of LDOB to the desired value via an external resistor divider. 2 ENA Enable pin for LDOA. Active high. 3 ENB Enable pin for LDOB. Active high.
4 MODE/SYNC
PWM operation and oscillator synchronization pin. Connect to ground for PWM/Light Load operation and optimized effi ciency throughout the load range. Connect high for low noise PWM operation under all operating conditions. When connected to an external clock, the internal oscillator is disabled and the step-down converter is synchronized to an external clock applied to this pin (PWM only). 5F B Feedback input pin for the step-down converter. This pin is used to see the output of the converter to regulate to the desired value via an external resistor divider. 6 AGND Ground connection pin. 7 PGND Main power ground return pin for the step-down converter. Connect to the output and input capacitor return. 8, 9 LX Connect inductor to this pin. Switching node internally connected to the drain of both high- and low-side MOSFETs. 10 VP Input supply voltage for the converter. Must be closely decoupled. 11, 12 N/C Not connected. 13 VIN Bias supply. Supply power for the internal circuitry. Connect to input power via low pass fi lter with de- coupling to AGND. 14 EN Enable for the step-down converter. Active high. 15 POK Power-OK pin with open drain output. It is pulled low when the OUTA pin is outside the regulation win- dow. Place a pull-up resistor between POK and OUTA. 16 FBA Feedback input pin for LDOA. This pin is used to regulate the output of LDOA to the desired value via an external resistor divider. 17 OUTA LDOA output pin; should be closely decoupled with a low-ESR ceramic capacitor. 18 VLDOA Input voltage pin for linear regulator A; should be closely decoupled. 19 VLDOB Input voltage pin for linear regulator B; should be closely decoupled. 20 OUTB LDOB output pin; should be closely decoupled with a low-ESR ceramic capacitor. EP Exposed paddle; connect to ground directly beneath the package. Pin Configuration QFN34-20 (Top View) FBB ENA ENB MODE/SYNC FB AGND PGND LX LX VP VIN EN N/C N/C POK FBA OUTA VLDOA VLDOB OUTB
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Absolute Maximum Ratings1 Symbol Description Value Units VP, VIN, VLDO Input Voltage and Bias Power to GND 6.0 V VLX LX to GND -0.3 to VP + 0.3 V VFB FB to GND -0.3 to VP + 0.3 V VEN EN and EN_LDO to GND -0.3 to 6.0 V TJ Operating Junction Temperature Range -40 to 150 °C TLEAD Maximum Soldering Temperature (at leads, 10 sec) 300 °C Thermal Information Symbol Description Value Units PD Maximum Power Dissipation (T A = 25°C) 2.0 W θJA Thermal Resistance2 50 °C/W 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at co nditions 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.
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Electrical Characteristics1 VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are T A = 25°C. Symbol Description Conditions Min Typ Max Units Bias Power Supply IQ Quiescent Current ENA = ENB = EN = V IN; ILOAD = 0 80 145 μA ISHDN Shutdown Current ENA = ENB = EN = GND 1.0 μA UVLO Under-Voltage Lockout Voltage VIN Rising 2.2 V Hysteresis 250 mV VIN Falling 1.7 V LDOA, LDOB VLDO Input Voltage 1.62 5.5 V VOUT Output Voltage Tolerance IOUT = 1mA to 300mA VFB Feedback Voltage 0.593 0.6 0.607 V VDO Dropout Voltage2, 3 IOUT = 300mA 300 mV ΔVLINEREG/VIN Line Regulation4 VIN = VOUT + 1 to 5.0V 0.09 %/V VEN(L) Enable Threshold Low 0.6 V VEN(H) Enable Threshold High 1.4 V IOUT Output Current V LDO (MIN) = 2.5 300 mA ISHT Shutdown Current V IN = 5V 1.0 μA TSD Over-Temperature Shutdown Threshold 140 °C THYS Over-Temperature Shutdown Hysteresis 15 °C LDOA VPOK Power-OK Trip Threshold V OUT Rising, TA = 25°C 80 90 98 % of V OUT VPOKHYS Power-OK Hysteresis 1.0 % of V OUT VPOK(LO) Power-OK Output Voltage Low I SINK = 1mA 0.4 V IPOK Power-OK Output Leakage Current V POK <5.5V, VOUT in Regulation 1.0 μA Step-Down Converter VIN Input Voltage 2.7 5.5 V VOUT Output Voltage Tolerance I OUT = 0 to 800mA; VIN = 2.7V to 5.5V -3.0 3.0 % VOUT VOUT Programmable Range 0.9 V IN V VFB Feedback Threshold Voltage 0.891 0.9 0.909 V ISHDN Shutdown Current EN = GND 1.0 μA ILX_LEAK LX Leakage Current V IN = 5.5, VLX = 0 - VIN 1.0 μA IFB Feedback Leakage V FB = 1.0V 0.2 μA ILIM Current Limit 1.2 A RDS(ON)H High Side Switch On Resistance 280 m Ω RDS(ON)L Low Side Switch On Resistance 160 m Ω ΔVLOADREG/VOUT Load Regulation I LOAD = 10 to 800mA 0.2 % ΔVLINEREG/VIN Line Regulation 0.2 %/V FOSC Oscillator Frequency 1.6 2.0 2.4 MHz TSD Over-Temperature Shutdown Threshold 140 °C THYS Over-Temperature Shutdown Hysteresis 15 °C VEN(L) Enable Threshold Low 0.6 V VEN(H) Enable Threshold High 1.4 V IEN EN Input Leakage V EN = 5V, VIN = 5V -1.0 1.0 μA 1. The AAT2504 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assu red by design, characterization, and correla- tion with statistical process controls. 2. VDO is defined as VIN - VOUT when VOUT is 98% of nominal. 3. For VOUT < 1.5V, VDO = 1.8 - VOUT. 4. CIN = 10μF.
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Typical Characteristics–Step-Down Converter Step-Down Converter Efficiency vs. Output Current (VOUT = 1.8V) Output Current (mA) Efficiency (%) 100 0.1 1 10 100 1000 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.5V PWM/Light Load Mode Forced PWM Mode Output Voltage Error vs. Temperature (VIN = 3.6V; VOUT = 2.5V) Temperature (°C) Output Error (%) -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 -40 -15 10 35 60 85 800mA 600mA 400mA 100mA Step-Down Converter Load Regulation (VOUT = 2.5V; Forced PWM) Output Current (mA) Output Voltage Error (%)-0.3 -0.2 -0.1 0.0 0.1 0.2 0.1 1 10 100 1000 VIN = 3V VIN = 3.6V VIN = 5.5V VIN = 4.2V Step-Down Converter Line Regulation (VOUT = 2.5V; Forced PWM) Input Voltage (V) Output Voltage Error (%)-0.2 -0.1 0.0 0.1 0.2 0.3 0.4 800mA600mA 100mA50mA1mA Step-Down Converter Output Ripple (VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA) Time (200ns/div) Inductor Current (bottom) (A) Output Voltage (top) (V) 1.79 1.80 1.81 1.82 0.2 0.4 0.6 0.8 1.0 VOUT IINDUCTOR Step-Down Converter Load Transient (VIN = 3.6V; IOUT = 300mA to 650mA) Time (20µs/div) Output Voltage (top) (V) Load and Inductor Current (bottom) (A) 1.6 1.8 2.0 2.2 0.0 0.3 0.6 0.9 VOUT IOUT IL
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Typical Characteristics–Step-Down Converter Step-Down Converter Line Transient (VOUT = 1.8V; IOUT = 800mA; VIN = 3.6V-4.2V) Time (20µs/div) Input Voltage (top) (V) Output Voltage (AC Coupled) (bottom) (V) 3.5 4.0 4.5 5.0 -0.02 0.00 0.02 No Load Quiescent Current vs. Input Voltage (Step-Down Converter Enabled; Both LDOs Enabled) Input Voltage (V) Quiescent Current (µA) 100 120 140 160 85°C 25°C -40°C No Load Quiescent Current vs. Input Voltage (Step-Down Converter Enabled; Both LDOs Disabled) Input Voltage (V) Quiescent Current (µA) 100 110 85°C 25°C -40°C Step-Down Converter Switching Frequency vs. Temperature (VIN = 3.6V; VOUT = 1.2V) Temperature (ºC) Switching Frequency (MHz)1.75 1.80 1.85 1.90 1.95 2.00 2.05 -40 -15 10 35 60 8 800mA 600mA 400mA Step-Down Converter Soft Start (VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA) Time (50µs/div) Inductor Current (bottom) (A) Enable (top) (V) VOUT (middle) (V) 0.0 0.5 1.0 1.5 EN VOUT IL 1.8V Step-Down Converter Turn-Off (VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA) Time (100µs/div) Inductor Current (bottom) (A) Enable (top) (V) VOUT (middle) (V) 0.0 0.5 1.0 EN VOUT IL 1.8V
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Typical Characteristics–Step-Down Converter High Side Switch On Resistance vs. Input Voltage Input Voltage (V) RDS(ON)H (mΩΩ) 220 240 260 280 300 320 340 360 380 400 120°C 100°C 85°C 25°C Low Side Switch On Resistance vs. Input Voltage Input Voltage (V) RDS(ON)L (mΩΩ) 100 150 200 250 300 350 100°C 85°C 25°C
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Typical Characteristics–LDO Regulator Dropout Voltage vs. Output Current (VOUT = 2.5V) Output Current (mA) Dropout Voltage (mV) 100 120 140 160 180 200 0 50 100 150 200 250 300 25°C 85°C -40°C Output Voltage vs. Input Voltage (VOUT = 2.5V) Input Voltage (V) Output Voltage (V) 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 300mA 250mA 200mA 100mA 50mA Dropout Voltage vs. Output Current (VOUT = 3.3V) Output Current (mA) Dropout Voltage (mV) 100 120 140 160 0 50 100 150 200 250 300 25°C 85°C -40°C Output Voltage vs. Input Voltage (VOUT = 3.3V) Input Voltage (V) Output Voltage (V) 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 300mA 200mA 100mA 50mA 1mA LDO Output Voltage vs. LDO Input Voltage (VOUTA = 1.5V; VIN = VP = 3.6V) LDO Input Voltage (VLDOA/B) (V) LDO Output Voltage (VOUTA) (V) 1.20 1.25 1.30 1.35 1.40 1.45 1.50 1.55 1.60 300mA 200mA 100mA LDO Output Voltage vs. LDO Input Voltage (VOUTA = 1.8V; VIN = VP = 3.6V) LDO Input Voltage (VLDOA/B) (V) LDO Output Voltage (VOUTA) (V) 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90 100mA 200mA 300mA
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Typical Characteristics–LDO Regulator LDO Output Voltage Variation vs. Temperature (VOUT = 2.5V) Temperature (°C) Output Voltage Error (%) -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 -40 -15 10 35 60 85 300mA 200mA 100mA LDO Line Regulation (VOUT = 2.5V) Input Voltage (V) Output Voltage Error (%)-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 300mA200mA50mA 100mA10mA 1mA LDO Load Regulation (VOUT = 2.5V) Output Current (mA) Output Voltage Error (%)-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.1 1 10 100 1000 VIN = 5.5V VIN = 3.6V VIN = 2.7V VIN = 4.2V LDO Load Transient (VOUT = 1.8V) Time (50µs/div) Output Voltage (AC coupled) (top) (mV) Output Current (bottom) (A) -25 0.0 0.1 0.2 0.3 LDO Line Transient (VOUT = 1.8V; IOUT = 300mA) Time (50µs/div) Output Voltage (AC coupled) (top) (mV) Input Voltage (bottom) (V) -50 100 3.0 3.5 4.0 4.5 No Load Quiescent Current vs. Input Voltage (Both LDOs Enabled, Step-Down Converter Disabled) Input Voltage (V) Quiescent Current (µA) 85°C 25°C -40°C
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Typical Characteristics–LDO Regulator Turn-On Time (VIN = 3.6V; VOUT = 1.8V; IOUT = 300mA) Time (25µs/div) Output Voltage (bottom) (V) Enable (top) (V) 0.0 0.5 1.0 1.5 2.0 Turn-Off Time (VIN = 3.6V; VOUT = 1.8V; IOUT = 300mA) Time (25µs/div) Output Voltage (top) (V) Enable (bottom) (V) 0.0 0.5 1.0 1.5 2.0
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Functional Description The AAT2504 is a high performance power management IC comprised of a step-down converter and two linear regulators. The step-down converter operates in both fixed and variable frequency modes for high efficiency performance. The switching frequency is 2MHz, minimiz- ing the size of the inductor. The converter requires only three external power components (C IN, COUT, and L). Each LDO can deliver up to 300mA. Each regulator has inde- pendent input voltage and enable pins and operates with ceramic capacitors. Switch-Mode Step-Down Converter The switching regulator is a monolithic step-down con- verter operating with input voltage range of 2.7V to 5.5V. Power devices are sized for 800mA current capability and achieves over 95% efficiency. The internal oscillator operates at 2MHz, minimizing the cost and size of exter- nal components. Light Load operation maintains high efficiency under light load conditions (typically <50mA) when MODE/SYNC is grounded. The MODE/SYNC pin tied high allows optional “PWM Only” operation. This main- tains constant frequency and low output ripple across all load conditions. Alternatively, by connecting an external clock to the AAT2504’s MODE/SYNC pin, the internal clock is disabled. The external synchronization must stay between 1MHz and 3MHz. The current through the P-channel MOSFET (high side) is sensed for current loop control, as well as short-circuit and overload protection. A fixed slope compensation sig- nal is added to the sensed current to maintain stability for duty cycles greater than 50%. The peak current mode loop appears as a voltage-programmed current source in parallel with the output capacitor. Functional Block Diagram EN VLDOA OUTB MODE/SYNC POK LXLogic DH DL PGND VP AGND OUTA VLDOB FBB FBA ENA ENB VIN Control Logic Voltage Reference Voltage Reference 90% VREF Err. Amp. Err. Amp. Err. Amp. FB
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET The output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. Internal loop compensation terminates the transconductance voltage error amplifier output. The internal error amplifier reference is fixed at 0.9V. A logic low on the EN pin shuts the converter down and makes it consume less than 1μA of current. Soft start increases the inductor current limit point in discrete steps when the input voltage or enable input is applied. It limits the current surge seen at the input and eliminates output voltage overshoot. For overload conditions, the peak input current is limit- ed. As load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. Thermal protection com- pletely disables switching when internal dissipation becomes excessive, protecting the device from damage. The junction over-temperature threshold is 140°C with 15°C of hysteresis. Linear Regulators The two linear regulators are high performance LDOs where each LDO sources 300mA of current. For added flexibility, both regulators have independent input volt- ages operating from 1.8V to 5.5V. An external feedback pin for each LDO allows programming the output voltage from 3.6V to 0.6V. The regulators have thermal protec- tion in case of adverse operating conditions. LDOA features an integrated Power-OK comparator which indicates when the output is out of regulation. The POK is an open drain output and it is held low when the AAT2504 is in shutdown mode. Under-Voltage Lockout Internal bias of all circuits is controlled via the VIN pin. Under-voltage lockout guarantees sufficient V IN bias and proper operation of all internal circuits prior to activation. Over-Temperature Protection Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature threshold is 140°C with 15°C of hys- teresis. Once an over-temperature fault condition is removed, the output voltage automatically recovers. Applications Information Step-Down Converter Inductor Selection The step-down converter uses peak current mode con- trol with slope compensation to maintain stability for duty cycles greater than 50%. The output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. The internal slope compensation for the AAT2504 step- down converter is 0.51A/ μs. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 2.2 μH inductor. 0.75 ⋅ VO m = = = 0.51 L 0.75 ⋅ 1.5V 2.2µH A µs Manufacturer’s specifications list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the satura- tion characteristics. The inductor should not show any appreciable saturation under normal load conditions. Some inductors may meet the peak and average current ratings yet result in excessive losses due to a high DCR. Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. The 2.2 μH CDRH2D14 series Sumida inductor has a 94mΩ DCR and a 1.5A DC current rating. At full 800mA load, the inductor DC loss is 60mW which gives a 4.16% loss in efficiency for a 800mA, 1.8V output. Input Capacitor Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for the input of the step-down converter. To estimate the required input capacitor size, determine the acceptable input ripple level (V PP) and solve for C IN. The calculated value varies with input voltage and is a maximum when V IN is double the output voltage. VO VIN CIN = VO VIN VPP IO VO VIN VO VIN CIN(MIN) = 1 VPP IO
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Always examine the ceramic capacitor DC voltage coef- ficient characteristics when selecting the proper value. For example, the capacitance of a 10μF, 6.3V, X5R ceram- ic capacitor with 5.0V DC applied is actually about 6 μF. The maximum input capacitor RMS current is: VO VIN VO VIN The input capacitor RMS ripple current varies with the input and output voltage and will always be less than or equal to half of the total DC load current. VO VIN VO VIN for VIN = 2 · VO: IO RMS(MAX)I 2= The term VO VIN VO VIN appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when V O is twice V IN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at 50% duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2504. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. A laboratory test set-up typically consists of two long wires running from the bench power supply to the evalu- ation board input voltage pins. The inductance of these wires, along with the low-ESR ceramic input capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage dur- ing load transients. Errors in the loop phase and gain measurements can also result. Since the inductance of a short PCB trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. In applications where the input power source lead induc- tance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or alu- minum electrolytic should be placed in parallel with the low ESR, ESL bypass ceramic. This dampens the high Q network and stabilizes the system. Confi guration Output Voltage Inductor 0.9V Adjustable With External Feedback 1V, 1.2V 1.5 μH 1.5V, 1.8V 2.2 μH 2.5V, 3.3V 3.3 μH Table 1: Inductor Values. Output Capacitor The output capacitor limits the output ripple and pro- vides holdup during large load transitions. A 4.7 μF to 10μF X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL charac- teristics necessary for low output ripple. The output voltage droop due to a load transient is dom- inated by the capacitance of the ceramic output capacitor. During a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. Within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. The relationship of the output volt- age droop during the three switching cycles to the output capacitance can be estimated by: COUT = 3 · ΔILOAD VDROOP · FS Once the average inductor current increases to the DC load level, the output voltage recovers. The above equa- tion establishes a limit on the minimum value for the output capacitor with respect to load transients. The internal voltage loop compensation also limits the minimum output capacitor value to 4.7μF. This is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. Increased output capac- itance will reduce the crossover frequency with greater phase margin. Adjustable Output Resistor Selection The output voltage on the step-down converter is pro- grammed with external resistors R2 and R6. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the mini- mum suggested value for R6 is 59kΩ. Although a larger value will further reduce quiescent current, it will also
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET increase the impedance of the feedback node, making it more sensitive to external noise and interference. Table 2 summarizes the resistor values for various output volt- ages with R6 set to either 59k Ω for good noise immu- nity or 221kΩ for reduced no load input current. With enhanced transient response for extreme pulsed load application, an external feed-forward capacitor (C1 in Fig.3) can be added. VOUT (V) R6 = 59kΩ R2 (kΩ) R6 = 221kΩ R2 (kΩ) 0.9* 0 0 1.0 6.65 24.3 1.1 13.3 48.7 1.2 19.6 73.2 1.3 26.1 97.6 1.4 32.4 124 1.5 39.2 147 1.8 59.0 221 1.85 61.9 232 2.0 71.5 274 2.5 105 392 2.8 124 464 3.0 137 511 3.3 158 590 Table 2: Step-Down Converter Resistor Values for Various Output Voltages. Thermal Calculations There are three types of losses associated with the AAT2504 step-down converter: switching losses, con- duction losses, and quiescent current losses. Conduction losses are associated with the R DS(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 con- duction mode (CCM), a simplified form of the LDO losses is given by: PTOTAL IO 2 · (RDSON(HS) · VO + RDSON(LS) · [VIN - VO]) VIN + (tsw · F · IO + IQ) · VIN IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down con- verter switching losses. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: PTOTAL = IO 2 · RDSON(HS) + IQ · VIN Since RDS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be inves- tigated over the complete input voltage range. Given the total losses, the maximum junction tempera- ture can be derived from the θ JA for the QFN34-20 pack- age which is 50°C/W. TJ(MAX) = PTOTAL · ΘJA + TAMB LDO Linear Regulator Input Capacitor A 1μF or larger capacitor is typically recommended for CIN in most applications. A C IN capacitor is not required for basic LDO regulator operation; however, if the AAT2504 is physically located more than three centime- ters from an input power source, a C IN capacitor will be needed for stable operation. C IN should be located as closely to the device VLDO pins as practically possible. C IN 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 C IN. There is no specific capacitor ESR requirement for CIN; however, ceramic capacitors are rec- ommended for C IN due to their inherent capability over tantalum capacitors to withstand input current surges from low impedance sources such as batteries in portable devices. Output Capacitor For proper load voltage regulation and operational sta- bility, a capacitor is required between pins OUTA, OUTB, and GND. The C OUT capacitor connection to the LDO regulator ground pin should be made as direct as practi- cally possible for maximum device performance. The AAT2504 has been specifically designed to function with very low ESR ceramic capacitors. For best performance, ceramic capacitors are recommended. * For the 0.9V output, R6 is open.
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Typical output capacitor values for maximum output cur- rent conditions range from 1μF to 10μF. Applications utilizing the exceptionally low output noise and optimum power supply ripple rejection characteris- tics of the AAT2504 should use 2.2μF or greater for C OUT. If desired, C OUT may be increased without limit. In low output current applications where output load is less than 10mA, the minimum value for C OUT can be as low as 0.47μF. Capacitor Characteristics Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT2504. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counter- parts. A ceramic capacitor typically has very low ESR, is lower cost, has a smaller PCB footprint, and is non- polarized. Line and load transient response of the LDO regulator is improved by using low ESR ceramic capaci- tors. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. Equivalent Series Resistance ESR is a very important characteristic to consider when selecting a capacitor. ESR is the internal series resistance associated with a capacitor that includes lead resistance, internal connections, size and area, material composi- tion, and ambient temperature. Typically, capacitor ESR is measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or alumi- num electrolytic capacitors. Ceramic Capacitor Materials Ceramic capacitors less than 0.1 μF are typically made from NPO or C0G materials. NPO and C0G materials generally have tight tolerance and are very stable over temperature. Larger capacitor values are usually com- posed of X7R, X5R, Z5U, or Y5V dielectric materials. NPO and C0G material types are not recommended for use with LDO regulators since the capacitor tolerance can vary more than ±50% over the operating temperature range of the device. A 2.2 μF Y5V capacitor could be reduced to 1μF over temperature; this could cause prob- lems for circuit operation. X7R and X5R dielectrics are much more desirable. The temperature tolerance of X7R dielectric is better than ±15%. Capacitor area is anoth- er contributor to ESR. Capacitors which are physically large in size will have a lower ESR when compared to a smaller sized capacitor of an equivalent material and capacitance value. These larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size. Consult capacitor vendor datasheets carefully when selecting capacitors for LDO regulators. Adjustable Output Resistor Selection The output voltage on the linear regulator is programmed with external resistors: R4 and R7 for LDOA and R5 and R8 for LDOB. Table 3 summarizes the resistor values for various output voltages with R4 and R5 set to either 59kΩ for good noise immunity or 221k Ω for reduced no load input current. LDO VOUT (V) R7, R8 = 59kΩ R4, R5 (kΩ) R7, R8 = 221kΩ R4, R5 (kΩ) 0.6* 0 0 0.8 19.6 75 0.9 29.4 113 1.0 39.2 150 1.1 49.9 187 1.2 59.0 221 1.3 68.1 261 1.4 78.7 301 1.5 88.7 332 1.8 118 442 1.85 124 464 2.0 137 523 2.5 187 715 3.3 267 1000 Table 3: LDO Linear Regulators Resistor Values for Various Output Voltages. POK Output LDOA of the AAT2504 features an integrated Power OK comparator which can be used as an error flag. The POK open drain output goes low when output voltage is 10% (typ) below its nominal regulation voltage. Additionally, any time LDOA is in shutdown, the POK output is pulled low. Connect a pull-up resistor from POK to OUTA. *For the 0.6V output, R7 and R8 are open.
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Enable Function The AAT2504 features an LDO regulator enable/disable function. Each LDO has its own dedicated enable pin. These pins (ENA, ENB) are active high and are compatible with CMOS logic. To assure the LDO regulators will switch on, ENA/B must be greater than 1.4V. The LDO regulators will shut down when the voltage on the ENA/B pins falls below 0.6V. In shutdown, the LDO regulators will con- sume less than 1.0μA of current. If the enable function is not needed in a specific application, it may be tied to V IN to keep the LDO regulator in a continuously on state. Thermal Protection Each of the two LDOs of the AAT2504 has an internal ther- mal protection circuit which will turn on when the device die temperature exceeds 140°C. The LDO regulator out- puts will remain in a shutdown state until the internal die temperature falls back below the 125°C trip point. No-Load Stability The LDOs in the AAT2504 are designed to maintain out- put voltage regulation and stability under operational no-load conditions. This is an important characteristic for applications where the output current may drop to zero. Reverse Output-to-Input Voltage Conditions and Protection Under normal operating conditions, a parasitic diode exists between the output and input of the LDO regula- tor. The input voltage should always remain greater than the output load voltage maintaining a reverse bias on the internal parasitic diode. Conditions where V OUT might exceed VIN should be avoided since this would forward bias the internal parasitic diode and allow excessive cur- rent flow into the V OUT pin, possibly damaging the LDO regulator. In applications where there is a possibility of V OUT exceeding VIN for brief amounts of time during nor- mal operation, the use of a larger value C IN capacitor is highly recommended. A larger value of C IN with respect to COUT will effect a slower C IN decay rate during shut- down, thus preventing VOUT from exceeding VIN. In appli- cations where there is a greater danger of V OUT exceed- ing VIN for extended periods of time, it is recommended to place a Schottky diode across V IN to VOUT (connecting the cathode to V IN and anode to V OUT). The Schottky diode forward voltage should be less than 0.45V. Thermal Considerations and High Output Current Applications The LDOs of the AAT2504 are designed to deliver con- tinuous output load currents of 300mA each under nor- mal operation. This is desirable for circuit applications where there might be a brief high in-rush current during a power-on event. The limiting characteristic for the maximum output load current safe operating area is essentially package power dissipation and the internal preset thermal limit of the device. In order to obtain high operating currents, care- ful device layout and circuit operating conditions need to be taken into account. The following discussions will assume the LDO regulator is mounted on a printed circuit board utilizing the mini- mum recommended footprint as stated in the layout con- siderations section of this document. At any given ambi- ent temperature (T A), the maximum package power dis- sipation can be determined by the following equation: PD(MAX) = TJ(MAX) - TA θJA Constants for the AAT2504 are T J(MAX) (the maximum junction temperature for the device, which is 125°C) and θ JA = 50°C/W (the package thermal resistance). Typically, maximum conditions are calculated at the maximum operating temperature of T A = 85°C and under normal ambient conditions where T A = 25°C. Given T A = 85°C, the maximum package power dissipation is 800mW. At TA = 25°C, the maximum package power dissipation is 2W. The maximum continuous output current for the AAT2504 is a function of the package power dissipation and the input-to-output voltage drop across the LDO regulator. To determine the maximum output current for a given output voltage, refer to the following equation. This cal- culation accounts for the total power dissipation of the LDO regulator, including that caused by ground current. PD(MAX) = [(VIN - VOUTA)IOUTA + (VIN · IGND)] + [(VIN - VOUTB)IOUTB + (VIN · IGND)]
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Layout The suggested PCB layout for the AAT2504 is shown in Figures 1 and 2. The following guidelines should be used to help ensure a proper layout. 1. The input capacitors (C4, C7, C8, and C9) should connect as closely as possible to VIN, VLDOA, VLDOB, VP, and PGND. 2. The output capacitor (C5, and C6) of the LDOs con- nect as closely as possible to OUT. C2 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. Do not make the node small by using a narrow trace. The trace should be kept wide, direct, and short. 3. The feedback trace should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high-current load trace will degrade DC load regulation. Feedback resistors should be placed as closely as possible to VOUT to minimize the length of the high impedance feedback trace. If possible, they should also be placed away from the LX (switching node) and inductor to improve noise immunity. 4. The resistance of the trace from the load return to the 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. Ensure all ground pins are tied to the ground plane. No pins should be left floating. For maximum power dissipation, it is recommended that the exposed pad (EP) must be soldered to a good conductive PCB ground plane layer to further increase local heat dissipation.
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Manufacturer Part Number Value ( μF) Voltage Rating Temp. Co. Case Size Murata GRM219R60J106KE19 10 6.3 X5R 0805 Murata GRM188R60J475KE19 4.7 6.3 X5R 0603 Murata GRM188R61A225KE34 2.2 10 X5R 0603 Murata GRM188R61A105KA61 1.0 10 X5R 0603 Murata GRM185R60J105KE26 1.0 6.3 X5R 0603 Table 4: Surface Mount Capacitors. Manufacturer Part Number Inductance (μH) Saturated Rated Current (mA) DCR (m Ω) Size (mm) LxWxH Type Sumida CDRH2D14-1R5 1.5 1800 63 3.2x3.2x1.55 Shielded Sumida CDRH2D14-2R2 2.2 1500 94 3.2x3.2x1.55 Shielded Sumida CDRH2D14-3R3 3.3 1200 125 3.2x3.2x1.55 Shielded Coiltronics SD3812-1R5 1.5 1580 78 4.0x4.0x1.2 Shielded Coiltronics SD3812-2R2 2.2 1320 111 4.0x4.0x1.2 Shielded Coiltronics SD3812-3R3 3.3 1100 159 4.0x4.0x1.2 Shielded Taiyo Yuden NR3010-1R5 1.5 1200 80 3.0x3.0x1.0 Shielded Taiyo Yuden NR3010-2R2 2.2 1100 95 3.0x3.0x1.0 Shielded Taiyo Yuden NR3010-3R3 3.3 870 140 3.0x3.0x1.0 Shielded Table 5: Suggested Inductors and Suppliers.
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET
Ordering Information
Marking1 Part Number (Tape and Reel)2Channel 1 Channel 2 Channel 3 QFN34-20 0.9V 0.6V 0.6V XWXYY AAT2504IZL-BAA-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 (0.6V) A 0.9 B 1.2 E 1.5 G 1.8 I 1.9 Y 2.5 N 2.6 O 2.7 P 2.8 Q 2.85 R 2.9 S 3.0 T 3.3 W 4.2 C 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET AAT2504178 Adjustable 3-Channel RegulatorSystemPower TM PRODUCT DATASHEET Advanced Analogic Technologies, Inc.
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Package Information
4.00 ± 0.05 3.00 ± 0.05 0.075 ± 0.075 0.40 ± 0.10 0.24 ± 0.06 0.50 ± 0.05 0.214 ± 0.0360.025 ± 0.025 0.925 ± 0.125 7.5° ± 7.5° Top View Bottom View Side View Detail "B" Detail "A" Option A: C0.30 (4x) max Chamfered corner Option B: R0.30 (4x) max Round corner Pin 1 indicator (optional) Detail "A" Index Area (D/2 x E/2) Detail "B" 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.