PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator General Description Features The AAT2500B is a three-channel regulator consisting of a step-down converter with an input voltage range of 2.7V to 5.5V plus two low dropout (LDO) linear regulators. • VIN Range: 2.7V to 5.5V • 800mA Buck Converter • Linear Regulators ▪ LDOA: 500mA ▪ LDOB: 150mA • Adjustable Output Voltage • Low Dropout Voltage • High Output Accuracy: ±1.5% • High Efficiency Step-Down Converter • 85μA (Typical) of Total IQ • Independent Enable Pins • Integrated Power MOSFETs • 2MHz Switching Frequency • Over-Temperature and Current Limit Protection • QFN34-20 Package • -40°C to +85°C Temperature Range The step-down converter delivers up to 800mA of output current, while consuming 30μA of typical no load quiescent current. The switching frequency is 2MHz, minimizing the size of external components. The two LDOs (LDOA/LDOB) have independent inputs and are capable of delivering up to 500mA and 150mA respectively. A Power-OK (POK) function provides an open drain output signal when LDOA is within regulation. Both LDOs feature low quiescent current and a low dropout voltage. The output voltages for both LDOs are adjustable to as low as 0.6V. The linear regulators have independent Enable pins. The AAT2500B is available in a Pb-free 3x4mm QFN34-20 package and is rated over the -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 L LX VOUT (Buck) AAT2500B FB VIN VIN R1 OUTA R1A 100kΩ VLDOA VLDOB VP SYNC POK EN 2500B.2008.03.1.0 C OUT POK FBA OUTB OUTB R1B FBB ENA ENB OUTA R2B R2A 2.2μF R2 2.2μF PGND AGND www.analogictech.com 1 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Pin Descriptions Pin # Symbol 1 FBB 2 ENA 3 ENB 4 SYNC 5 FB 6 7 AGND PGND 8, 9 LX 10 VP 11, 12 13 N/C VIN 14 EN 15 POK 16 FBA 17 18 19 20 EP OUTA VLDOA VLDOB OUTB Function Feedback input pin for LDOB. This pin is connected to OUTB. It is used to see the output of LDOB to regulate to the desired value via an external resistor divider. For fixed versions, short FBB to OUTB. Enable pin for LDOA. When connected low, LDOA is disabled and consumes less than 1μA of current. When connected high, normal operation. Enable pin for LDOB. When connected low, LDOB is disabled and consumes less than 1μA of current. When connected high, normal operation. Oscillator synchronization pin for the step-down converter. The internal oscillator is disabled and the stepdown converter can be synchronized to an external clock applied to this pin. Feedback input pin for the step-down converter. This pin is connected to the converter output. It is used to see the output of the converter to regulate to the desired value via an external resistor divider. Ground connection pin. Main power ground return pin for the step-down converter. Connect to the output and input capacitor return. Connect inductor to this pin. Switching node internally connected to the drain of both high- and low-side MOSFETs. Bias supply. Supply power for the internal circuitry. Connect to input power via low pass filter with decoupling to AGND. Not connected. Input supply voltage for the converter. Must be closely decoupled. Enable for the step-down converter. A logic low disables the converter and it consumes less than 1μA of current. A logic high enables normal operation. Power-OK pin with open drain output. It is pulled low when the OUTA pin is outside the regulation window of ±10%. Place a pull-up resistor between POK and OUTA. Feedback input pin for LDOA. This pin is connected to OUTA. It is used to see the output of LDOA to regulate to the desired value via an external resistor divider. For fixed versions, short FBA to OUTA. LDOA output pin; should be closely decoupled with a low-ESR ceramic capacitor. Input voltage pin for linear regulator A; should be closely decoupled. Input voltage pin for linear regulator B; should be closely decoupled. LDOB output pin; should be closely decoupled with a low-ESR ceramic capacitor. Exposed paddle; connect to ground directly beneath the package. Pin Configuration QFN34-20 (Top View) OUTA VLDOA VLDOB OUTB 17 18 19 20 FBB ENA ENB SYNC FB AGND 1 16 2 15 3 14 4 13 5 12 6 11 FBA POK EN VIN N/C N/C 9 10 8 7 VP LX LX PGND 2 www.analogictech.com 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Absolute Maximum Ratings1 Symbol VP, VIN, VLDO VLX VFB VEN TJ TLEAD Description Input Voltage and Bias Power to GND LX to GND FB to GND EN and EN_LDO to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units 6.0 -0.3 to VP + 0.3 -0.3 to VP + 0.3 -0.3 to 6.0 -40 to 150 300 V V V V °C °C Value Units 2.0 50 W °C/W Thermal Information Symbol PD θJA Description Maximum Power Dissipation (TA = 25°C) Thermal Resistance2 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. 2500B.2008.03.1.0 www.analogictech.com 3 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Electrical Characteristics1 VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C. Symbol Description Conditions Bias Power Supply IQ Quiescent Current ISHDN Shutdown Current UVLO Min ENA = ENB = EN = VIN; ILOAD = 0 ENA = ENB = EN = GND VIN Rising Hysteresis VIN Falling Under-Voltage Lockout Voltage LDOA, LDOB Input Voltage VLDO VOUT VFB VDOA VDOB ΔVOUT/ VOUT*ΔVIN VEN(L) VEN(H) ISHT TSD THYS LDOA VPOK Output Voltage Tolerance IOUT = 1mA to IOUT(MAX) Feedback Voltage Dropout Voltage2, 3 Dropout Voltage2, 3 IOUT = 500mA IOUT = 150mA Line Regulation4 VIN = VOUT + 1 to 5.0V Enable Threshold Low Enable Threshold High Shutdown Current Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis VIN = 5V Power-OK Trip Threshold VOUT Rising, TA = 25°C VPOKHYS Power-OK Hysteresis VPOK(LO) IPOK Power-OK Output Voltage Low Power-OK Output Leakage Current TA = 25°C TA = -40°C to +85°C Typ Max Units 80 145 1.0 2.6 μA μA V mV V 5.5 1.5 2.5 0.607 500 150 V % V mV mV 0.09 %/V 0.6 V V μA °C °C 250 2.0 1.8 -1.5 -2.5 0.593 0.6 1.5 1.0 140 15 82 94 98 1.0 ISINK = 1mA VPOK <5.5V, VOUT in Regulation 0.4 1.0 % of VOUT % of VOUT V μA 1. The AAT2500B 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. 2. VDO is defined as VIN - VOUT when VOUT is 98% of nominal. 3. For VOUT < 2.1V, VDO = 1.8 - VOUT. 4. CIN = 10μF. 4 www.analogictech.com 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Electrical Characteristics (continued)1 VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C. Symbol Step-Down VIN VOUT VOUT VFB ISHDN ILX_LEAK IFB ILIM RDS(ON)H RDS(ON)L ΔVOUT/VOUT ΔVOUT/ VOUT*ΔVIN FOSC TSD THYS VEN(L) VEN(H) IEN Description Conditions Converter; IOUT = 800mA Input Voltage Output Voltage Tolerance VOUT Programmable Range Feedback Threshold Voltage Shutdown Current LX Leakage Current Feedback Leakage Current Limit High Side Switch On Resistance Low Side Switch On Resistance Load Regulation IOUT = 0 to 800mA; VIN = 2.7V to 5.5V Min 2.7 -3.0 0.9 0.891 Typ Max Units 5.5 3.0 VIN 0.909 1.0 1.0 0.2 1.2 280 160 0.5 V % V V μA μA μA A mΩ mΩ % 0.2 %/V 0.9 EN = GND VIN = 5.5, VLX = 0 - VIN VFB = 1.0V ILOAD = 0 to 800mA Line Regulation Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High EN Input Leakage 1.6 2.0 140 15 2.4 0.6 VEN = 5V, VIN = 5V 1.4 -1.0 1.0 MHz °C °C V V μA 1. The AAT2500B 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. 2500B.2008.03.1.0 www.analogictech.com 5 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Typical Characteristics–Step-Down Converter Step-Down Converter Efficiency vs. Output Current Output Voltage Error vs. Temperature (VOUT = 1.8V) (VIN = 3.6V; VOUT = 2.5V) 0.4 90 0.3 Efficiency (%) 80 70 60 VIN = 5.5V VIN = 4.2V 50 40 VIN = 3.6V 30 20 PWM/Light Load Mode VIN = 2.7V 10 Output Error (%) 100 Forced PWM Mode 1 10 0.2 0.1 0.0 -0.1 800mA 100mA -0.2 -0.3 -0.4 0 0.1 100 -0.5 -40 1000 -15 Output Current (mA) 60 85 (VOUT = 2.5V; Forced PWM) 0.2 0.4 VIN = 3V 0.1 Output Voltage Error (%) Output Voltage Error (%) 35 Step-Down Converter Line Regulation (VOUT = 2.5V; Forced PWM) VIN = 3.6V 0.0 -0.1 VIN = 4.2V -0.2 VIN = 5.5V -0.3 0.3 50mA 1mA 0.2 100mA 0.1 0.0 600mA -0.1 800mA -0.2 0.1 1 10 100 1000 2.8 3.1 Output Current (mA) 3.7 4.0 4.3 4.6 4.9 5.2 Step-Down Converter Output Ripple Step-Down Converter Load Transient (VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA) (VIN = 3.6V; IOUT = 300mA to 650mA) 1.79 1.0 0.8 0.6 0.4 0.2 2.2 Output Voltage (top) (V) 1.80 IINDUCTOR 5.5 2.0 VOUT 1.8 1.6 Time (200ns/div) I OUT 0.9 IL 0.6 0.3 0.0 Load and Inductor Current (bottom) (A) VOUT Inductor Current (bottom) (A) 1.81 3.4 Input Voltage (V) 1.82 Output Voltage (top) (V) 10 Temperature (°C) Step-Down Converter Load Regulation 6 400mA 600mA Time (20µs/div) www.analogictech.com 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Typical Characteristics–Step-Down Converter (continued) Step-Down Converter Line Transient No Load Quiescent Current vs. Input Voltage (VOUT = 1.8V; IOUT = 800mA; VIN = 3.6V-4.2V) (Step-Down Converter Enabled; Both LDOs Enabled) 4.0 3.5 0.02 0.00 -0.02 160 Quiescent Current (µA) Input Voltage (top) (V) 4.5 Output Voltage (AC Coupled) (bottom) (V) 5.0 140 120 85°C 100 25°C 80 60 -40°C 40 20 0 2.7 3.1 3.5 3.9 Time (20µs/div) Switching Frequency (MHz) Quiescent Current (µA) 110 100 90 85°C 70 25°C 50 40 -40°C 30 20 2.7 3.1 3.5 3.9 4.3 4.7 5.1 (VIN = 3.6V; VOUT = 1.2V) 600mA 2.00 800mA 400mA 1.95 1.90 1.85 1.80 1.75 5.5 -40 -15 10 35 60 Step-Down Converter Turn-Off (VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA) (VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA) 0 VOUT 0V 1.5 1.0 0.5 IL 0.0 4 Enable (top) (V) VOUT (middle) (V) 1.8V 6 Time (50µs/div) 2500B.2008.03.1.0 EN 2 0 VOUT 1.8V IL 1.0 0V 0.5 0.0 Inductor Current (bottom) (A) EN Inductor Current (bottom) (A) 6 2 85 Temperature (ºC) Step-Down Converter Soft Start 4 5.5 2.05 Input Voltage (V) Enable (top) (V) VOUT (middle) (V) 5.1 Step-Down Converter Switching Frequency vs. Temperature (Step-Down Converter Enabled; Both LDOs Disabled) 60 4.7 Input Voltage (V) No Load Quiescent Current vs. Input Voltage 80 4.3 Time (100µs/div) www.analogictech.com 7 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Typical Characteristics–Step-Down Converter (continued) High Side Switch On Resistance vs. Input Voltage Low Side Switch On Resistance vs. Input Voltage 400 350 120°C 380 100°C RDS(ON)L (mΩ Ω) RDS(ON)H (mΩ Ω) 300 85°C 360 340 320 300 280 260 25°C 250 200 150 25°C 100 240 220 50 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) 8 120°C 100°C 85°C 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) www.analogictech.com 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Typical Characteristics–LDO Regulator LDO Load Regulation LDO Load Regulation (VOUT = 1.8V) (VOUT = 1.2V) 1.2 Output Voltage Error (%) Output Voltage Error (%) 2.0 1.6 1.2 VIN = 3.3V 0.8 VIN = 2.7V 0.4 0.0 -0.4 -0.8 VIN = 3.6V -1.2 VIN = 4.2V VIN = 5.5V -1.6 VIN = 4.2V 0.9 VIN = 3.6V 0.6 0.3 0.0 -0.3 VIN = 2.7V -0.6 1 10 100 0.1 1000 1 Output Current (mA) 100 LDO Line Regulation (VOUT = 2.7V) (VOUT = 2.7V) 2.0 VIN = 5.5V 0.9 1.6 VIN = 4.2V VIN = 3.6V 0.6 0.3 0.0 -0.3 1000 Output Current (mA) VIN = 3.0V -0.6 VIN = 3.3V -0.9 Output Voltage (V) Output Voltage Error (%) 10 LDO Load Regulation 1.2 400mA 1.2 500mA 0.8 0.4 0.0 200mA 100mA -0.4 300mA -0.8 -1.2 -1.6 -2.0 3.0 -1.2 0.1 1 10 100 1000 3.5 Output Current (mA) 4.0 4.5 5.0 5.5 Input Voltage (V) Output Voltage vs. Input Voltage LDO Output Voltage Variation vs. Temperature (VOUT = 2.7V) (VOUT = 2.7V) 0.1 Output Voltage Error (%) 3.0 2.9 Output Voltage (V) VIN = 3.3V -0.9 -1.2 -2.0 0.1 2.8 VIN = 5.0V 100mA 2.7 500mA 400mA 300mA 200mA 2.6 2.5 2.4 2.3 2.2 2.7 2.9 3.1 3.3 3.5 3.7 0.0 -0.2 -0.3 150mA -0.4 -0.5 -0.6 -0.7 -0.8 -40 Input Voltage (V) 2500B.2008.03.1.0 500mA -0.1 -15 10 35 60 85 Temperature (°C) www.analogictech.com 9 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Typical Characteristics–LDO Regulator (continued) Dropout Voltage vs. Temperature LDO Load Transient (VOUT = 2.7V) (VOUT = 1.8V; IOUT = 500mA) Output Voltage (AC coupled) (top) (mV) Dropout Voltage (mV) 350 300 250 500mA 200 150 300mA 100 50 150mA 0 -40 50 0 -50 0.6 0.4 0.2 0.0 -15 10 35 60 85 Temperature (°C) Time (50µs/div) LDO Load Transient LDO Line Transient (VOUT = 1.8V; IOUT = 150mA) (VOUT = 1.8V; IOUT = 500mA) -20 0.3 0.2 0.1 0.0 Output Voltage (AC coupled) (top) (mV) 0 100 Time (50µs/div) 50 0 -50 4.5 4.0 3.5 3.0 Input Voltage (bottom) (V) 20 Output Current (bottom) (A) 40 Output Voltage (AC coupled) (top) (mV) Output Current (bottom) (A) 100 400 Time (50µs/div) LDO Line Transient (VOUT = 1.8V; IOUT = 150mA) Output Voltage (AC coupled) (top) (mV) 50 0 -50 4.5 4.0 3.5 3.0 Input Voltage (bottom) (V) 100 Time (50µs/div) 10 www.analogictech.com 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Functional Block Diagram FB VP VIN See Note Voltage Reference DH Err. Amp. SYNC LX Logic Control Logic EN DL PGND OUTA VLDOA Over-Current Protection ENB ENA FBA Err. Amp. VLDOB Err. Amp. Over-Current Protection Voltage Reference 91% VREF See Note POK OUTB See Note FBB AGND Note: For adjustable version, the internal feedback divider is omitted and the FB pin is tied directly to the internal error amplifier. Functional Description Switch-Mode Step-Down Converter The AAT2500B 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, minimizing the size of the inductor. The converter requires only three external components (CIN, COUT, and L). LDOA can deliver 500mA. LDOA can deliver 150mA. Each regulator has independent input voltage and enable pins and operates wth ceramic capacitors. The switching regulator is a monolithic step-down converter operating with input voltage range of 2.7V to 5.5V. Power devices are sized for 800mA current capability while maintaining over 90% efficiency at full load. It consumes 30μA of typical no load quiescent current, making it also ideal for light load applications. The oscillator operates at 2MHz, minimizing the cost and size of external components. 2500B.2008.03.1.0 A logic low on the EN pin shuts the converter down and makes it consume less than 1μA of current. www.analogictech.com 11 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator 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 limited. As load impedance decreases and the output voltage falls closer to zero, more power is internally dissipated, raising the device temperature. Thermal protection completely 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 LDOA sources 500mA and LDOB sources 150mA of current. For added flexibility, both regulators have independent input voltages 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 short-circuit and thermal protection 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 AAT2500B is in shutdown mode. Under-Voltage Lockout Internal bias of all circuits is controlled via the VIN pin. Under-voltage lockout guarantees sufficient VIN 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 hysteresis. Once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. Applications Information Step-Down Converter Inductor Selection The step-down converter uses peak current mode control 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 AAT2500B stepdown converter is 0.51A/μsec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 2.2μH inductor. m= 0.75 ⋅ VO 0.75 ⋅ 1.5V A = = 0.51 L 2.2μH μsec 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 saturation 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 2.2μH 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 (VPP) and solve for CIN. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. CIN = V ⎞ VO ⎛ · 1- O VIN ⎝ VIN ⎠ ⎛ VPP ⎞ - ESR · FS ⎝ IO ⎠ VO ⎛ V ⎞ 1 · 1 - O = for VIN = 2 · VO VIN ⎝ VIN ⎠ 4 CIN(MIN) = 12 www.analogictech.com 1 ⎛ VPP ⎞ - ESR · 4 · FS ⎝ IO ⎠ 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10μF, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6μF. The maximum input capacitor RMS current is: IRMS = IO · VO ⎛ V ⎞ · 1- O VIN ⎝ 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 ⎛ V ⎞ · 1- O = VIN ⎝ VIN ⎠ D · (1 - D) = 0.52 = 1 2 for VIN = 2 · VO: IRMS(MAX) = VO IO 2 ⎛ V ⎞ · 1- O The term VIN ⎝ VIN ⎠ appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when VO is twice VIN. 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 AAT2500B. 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 evaluation 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 during 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. 2500B.2008.03.1.0 In applications where the input power source lead inductance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or aluminum electrolytic should be placed in parallel with the low ESR, ESL bypass ceramic. This dampens the high Q network and stabilizes the system. Configuration Output Voltage Inductor 0.9V Adjustable With External Feedback 1V, 1.2V 1.5V, 1.8V 2.5V, 3.3V 1.5μH 2.2μH 3.3μH Table 1: Inductor Values. Output Capacitor The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7μF 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 characteristics necessary for low output ripple. The output voltage droop due to a load transient is dominated 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 voltage 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 equation 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 capacitance will reduce the crossover frequency with greater phase margin. www.analogictech.com 13 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Adjustable Output Resistor Selection The output voltage on the step-down converter is programmed with external resistors R2 and R6. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for R6 is 59kΩ. Although a larger value will further reduce quiescent current, it will also 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 voltages with R6 set to either 59kΩ for good noise immunity 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* 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 2.8 3.0 3.3 0 6.65 13.3 19.6 26.1 32.4 39.2 59.0 61.9 71.5 105 124 137 158 0 24.3 48.7 73.2 97.6 124 147 221 232 274 392 464 511 590 Table 2: Step-Down Converter Resistor Values for Various Output Voltages. Thermal Calculations There are three types of losses associated with the AAT2500B 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 LDO losses is given by: PTOTAL = IO2 · (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 converter switching losses. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: PTOTAL = IO2 · RDSON(HS) + IQ · 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 QFN34-20 package 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 CIN capacitor is not required for basic LDO regulator operation; however, if the AAT2500B 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 closely to the device VLDO pins as practically 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, 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. * For the 0.9V output, R6 is open. 14 www.analogictech.com 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Output Capacitor For proper load voltage regulation and operational stability, a capacitor is required between pins OUTA, OUTB, and GND. The COUT capacitor connection to the LDO regulator ground pin should be made as direct as practically possible for maximum device performance. The AAT2500B 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 AAT2500B 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. generally have tight tolerance and are very stable over temperature. Larger capacitor values are usually composed 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 2.2μF Y5V capacitor could be reduced to 1μF over temperature; this could cause problems for circuit operation. X7R and X5R dielectrics are much more desirable. The temperature tolerance of X7R dielectric is better than ±15%. Capacitor area is another 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 Capacitor Characteristics Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT2500B. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lower cost, has a smaller PCB footprint, and is nonpolarized. Line and load transient response of the LDO regulator is improved by using low ESR ceramic capacitors. 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 composition, and ambient temperature. Typically, capacitor ESR is measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors. Ceramic Capacitor Materials Ceramic capacitors less than 0.1μF are typically made from NPO or C0G materials. NPO and C0G materials 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 221kΩ for reduced no load input current. LDO VOUT (V) R7, R8 = 59kΩ R4, R5 (kΩ) R7, R8 = 221kΩ R4, R5 (kΩ) 0.6* 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 0 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 0 75 113 150 187 221 261 301 332 442 464 523 715 1000 Table 3: LDO Linear Regulators Resistor Values for Various Output Voltages. * For the 0.6V output, R7 and R8 are open. 2500B.2008.03.1.0 www.analogictech.com 15 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator POK Output LDOA of the AAT2500B 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. to COUT will effect a slower CIN decay rate during shutdown, thus preventing VOUT from exceeding VIN. In applications where there is a greater danger of VOUT exceeding VIN for extended periods of time, it is recommended to place a Schottky diode across VIN to VOUT (connecting the cathode to VIN and anode to VOUT). The Schottky diode forward voltage should be less than 0.45V. Thermal Considerations and High Output Current Applications Enable Function The AAT2500B 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 consume less than 1.0μA of current. 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. Thermal Protection Each of the two LDOs of the AAT2500B has an internal thermal protection circuit which will turn on when the device die temperature exceeds 140°C. The LDO regulator outputs will remain in a shutdown state until the internal die temperature falls back below the 125°C trip point. The LDOs of the AAT2500B are designed to deliver continuous output load currents of 300mA each under normal 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, careful 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 minimum recommended footprint as stated in the layout considerations section of this document. At any given ambient temperature (TA), the maximum package power dissipation can be determined by the following equation: No-Load Stability The LDOs in the AAT2500B are 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. 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 highly recommended. A larger value of CIN with respect 16 PD(MAX) = TJ(MAX) - TA θJA Constants for the AAT2500B are TJ(MAX) (the maximum junction temperature for the device, which is 125°C) and θJA = 50°C/W (the package thermal resistance). Typically, maximum conditions are calculated at the maximum operating temperature of TA = 85°C and under normal ambient conditions where TA = 25°C. Given TA = 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 AAT2500B 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 calculation 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)] www.analogictech.com 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Layout 3. The suggested PCB layout for the AAT2500B is shown in Figures 1 and 2. The following guidelines should be used to help ensure a proper layout. 1. 2. The input capacitors (C4, C7, C8, and C9) should connect as closely as possible to VIN, VLDOA, VLDOB, VP, and PGND. The output capacitor (C5, and C6) of the LDOs connect 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. Figure 1: AAT2500B Evaluation Board Top Side Layout. 2500B.2008.03.1.0 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. 5. 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. Figure 2: AAT2500B Evaluation Board Bottom Side Layout. www.analogictech.com 17 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator SYNC U1 R10 100k VIN FB 5 MODE/SYNC 4 R1 AAT2500B FB LX 9 LX LX VOUT_BUCK L1 VIN 13 MODE/SYNC LX VIN OUTA Buckout 8 CDRH2D14 17 OUTA C2 10μF 100 3 2 1 C4 0.1μF VLDOA 18 VLDOA POK R3 15 100k C8 1μF VINA 3 2 1 VINB VLDOB 19 C9 1μF VLDOB FBA 16 FBA 20 OUTB 1 FBB C3 R2 C1 100pF .01μF R4 OUTA VP 10 VP OUTB EN FBB OUTB EN EN 14 1 2 3 ENB ENB 3 1 2 3 ENA 2 ENA R12 (open) ENB PGND ENA AGND R5 7 R7 59.0k R8 59.0k C6 2.2μF R6 59.0k C5 2.2μF 6 GND C7 10μF EP 1 2 3 GND GND POK POK GND VOUT_BUCK (V) 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 2.8 3.0 3.3 R2 (kΩ) 0 6.65 13.3 19.6 26.1 32.4 39.2 59 61.9 71.5 105 124 137 158 L1 (μH) 1.5 1.5 1.5 1.5 1.5 1.5 2.2 2.2 2.2 2.2 3.3 3.3 3.3 3.3 VOUT_LDO (V) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3 R4, R5 (kΩ) 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267 U1 AAT2500B QFN34-20 L1 Sumida CDRH2D14 or Coltronics SD3812 C2, C7 10μF, 6.3V, X5R, 0805 GRM219R60J106KE19 C5, C6 2.2μF, 10V, X5R, 0603 GRM188R61A225KE34 C8, C9 1μF, 6.3V, X5R, 0603 GRM185R60J105KE26 Figure 3: AAT2500B Evaluation Board Schematic. 18 www.analogictech.com 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Manufacturer Part Number Value (μF) Voltage Rating Temp. Co. Case Size Murata Murata Murata Murata Murata GRM219R60J106KE19 GRM188R60J475KE19 GRM188R61A225KE34 GRM188R61A105KA61 GRM185R60J105KE26 10 4.7 2.2 1.0 1.0 6.3 6.3 10 10 6.3 X5R X5R X5R X5R X5R 0805 0603 0603 0603 0603 Table 4: Surface Mount Capacitors. Manufacturer Part Number Inductance (μH) Saturated Rated Current (mA) DCR (mΩ) Size (mm) LxWxH Type Sumida Sumida Sumida Coiltronics Coiltronics Coiltronics Taiyo Yuden Taiyo Yuden Taiyo Yuden CDRH2D14-1R5 CDRH2D14-2R2 CDRH2D14-3R3 SD3812-1R5 SD3812-2R2 SD3812-3R3 NR3010-1R5 NR3010-2R2 NR3010-3R3 1.5 2.2 3.3 1.5 2.2 3.3 1.5 2.2 3.3 1800 1500 1200 1580 1320 1100 1200 1100 870 63 94 125 78 111 159 80 95 140 3.2x3.2x1.55 3.2x3.2x1.55 3.2x3.2x1.55 4.0x4.0x1.2 4.0x4.0x1.2 4.0x4.0x1.2 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Table 5: Suggested Inductors and Suppliers. 2500B.2008.03.1.0 www.analogictech.com 19 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Ordering Information Voltage Package Channel 1 Channel 2 Channel 3 Marking1 Part Number (Tape and Reel)2 QFN34-20 Adj. (0.9V) Adj. (0.6V) Adj. (0.6V) YUXYY AAT2500BIZL-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 Adjustable (0.6V) 0.9 1.2 1.5 1.8 1.9 2.5 2.6 2.7 2.8 2.85 2.9 3.0 3.3 4.2 Code A B E G I Y N O P Q R S T W C 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 20 www.analogictech.com 2500B.2008.03.1.0 PRODUCT DATASHEET AAT2500B SystemPowerTM Adjustable 3-Channel Regulator Package Information1 QFN34-20 Index Area (D/2 x E/2) Detail "A" Detail "B" 4.00 ± 0.05 0.925 ± 0.125 7.5° ± 7.5° 0.025 ± 0.025 0.214 ± 0.036 Side View 3.00 ± 0.05 Top View Bottom View 0.40 ± 0.10 0.075 ± 0.075 Option B: R0.30 (4x) max Round corner 0.50 ± 0.05 Option A: C0.30 (4x) max Chamfered corner 0.24 ± 0.06 Pin 1 indicator (optional) Detail "A" 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. 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. 2500B.2008.03.1.0 www.analogictech.com 21