AAT2785IRN-AAA-T1

DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter General Description Features The AAT2785 is a 3-channel 1.8MHz step-down converter for applications where power efficiency and solution size are critical. The input voltage range is 2.7V to 5.5V and the outputs are adjustable from 0.6V to VIN. • VIN Range: 2.7 to 5.5V • Output Voltage Range: 0.6V to VIN • Output Current: ▪ Channel 3: 1.5A ▪ Channel 1: 600mA ▪ Channel 2: 600mA • Low Noise Light Load Mode • Low Ripple PWM Mode • Highly Efficient Step-Down Converters • Low RDS(ON) Integrated Power Switches • 100% Duty Cycle • 1.8MHz Switching Frequency • Internal Soft Start • Fast 150μs Turn-On Time • Over-Temperature Protection • Current Limit Protection • TDFN34-16 Package • -40°C to 85°C Temperature Range The AAT2785 incorporates a unique low noise architecture which reduces ripple and spectral noise. Channel 3 delivers up to 1.5A output current and channels 1 and 2 deliver up to 600mA each. The AAT2785 uses a high switching frequency to minimize the size of external components. The AAT2785 requires a minimum of external components to realize a high efficiency triple-output buck converter minimizing solution cost and PCB footprint. Each of the 3 regulators has an independent enable pin, adjustable output voltage and operates with low no load quiescent current, providing high efficiency over the entire load range. The AAT2785 is available in a Pb-free 16 pin TDFN34 package, and is rated over the -40°C to +85°C operating temperature range. Applications • • • • • • • • • Typical Application Cellular and Smart Phones Digital Cameras Handheld Instruments Mass Storage Systems Microprocessor / DSP Core / IO Power PDAs and Handheld Computers Portable Media Players USB Devices Wireless LAN L1 4.7μH VOUT1: 3.3V, 600mA LX1 IN R1 133k AAT2785 FB1 VIN: 2.7V–5.5V L2 4.7μH VP1_2 EN1 LX2 EN2 R4 29.4k LX3 EN3 FB3 C2 10μF GND C4 4.7μF PGND L3 1.5μH VP3 C3 4.7μF R3 133k FB2 C1 10μF VOUT2: 3.3V, 600mA R2 29.4k PGND VOUT3: 1.2V, 1.5A R5 59.0k R6 59.0k C5 10μF Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 1 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Pin Descriptions Pin # Symbol 1 PGND2 2 FB2 3 4 5 6 7 EN1 EN2 AGND IN EN3 8 FB3 9 10 11 PGND3 LX3 VP3 12 FB1 13 14 15 16 PGND1 LX1 VP1_2 LX2 EP EP Function Power ground return pin 2. Connect to the output and input capacitor return. Feedback input pin for channel 2. Connect an external resistor divider to this pin to program the output voltage to the desired value. Enable pin for channel 1. Active high. Enable pin for channel 2. Active high. Signal ground. Input supply pin for device. Supplies bias for the internal circuitry. Enable pin for channel 3. Active high. Feedback input pin for channel 3. Connect an external resistor divider to this pin to program the output voltage to the desired value. Power ground return pin 3. Connect to the output and input capacitor return. Power switching node for channel 3. Output switching node connects to the output inductor. Input power supply pin for channel 3. Must be closely decoupled. Feedback input pin for channel 1. Connect an external resistor divider to this pin to program the output voltage to the desired value. Power ground return pin 1. Connect to the output and input capacitor return. Power switching node for channel 1 and 2. Output switching node connects to the output inductor. Input power supply pin for channels 1 and 2. Must be closely decoupled. Power switching node for channel 2. Output switching node connects to the output inductor. Exposed pad. Connect to ground directly under the device. Use properly sized vias for thermal coupling to the ground plane. See section on PCB layout guidelines. Pin Configuration TDFN34-16 (Top View) PGND2 FB2 EN1 EN2 AGND IN EN3 FB3 2 1 16 2 15 3 14 4 13 5 12 6 11 7 10 8 9 LX2 VP1_2 LX1 PGND1 FB1 VP3 LX3 PGND3 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Absolute Maximum Ratings1 Symbol VIN, VP VLX VFB VEN TJ TLEAD Description Input Voltages to AGND/PGND LX1, LX2, LX3 to AGND/PGND FB1, FB2, FB3 to AGND/PGND EN1, EN2, EN3 to AGND/PGND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units 6.0 -0.3 to VIN + 0.3 -0.3 to VIN + 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 JA Description Maximum Power Dissipation2 Thermal Resistance3 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Mounted on an FR4 board. 3. Derate 20mW/°C above 25°C ambient temperature. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 3 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Electrical Characteristics1 VIN = VP = 3.6V; TA = -40°C to 85°C, unless noted otherwise. Typical values are at TA = 25°C. Symbol Description VIN Input Voltage VOUT Output Voltage Tolerance VOUT IQ1,2 IQ3 ISHDN Output Voltage Range Quiescent Current Channels 1, 2 Quiescent Current Channel 3 Shutdown Current LX Reverse Leakage Current LX Leakage Current Feedback Leakage P-Channel Current Limit P-Channel Current Limit High Side Switch On-Resistance Low Side Switch On-Resistance High Side Switch On-Resistance Low Side Switch On-Resistance Load Regulation Line Regulation Oscillator Frequency Channels 1,2 Oscillator Frequency Channel 3 Start-Up Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Enable Input Current ILX_LEAK ILX_LEAK IFB ILIM1,2 ILIM3 RDS(ON)H1,2 RDS(ON)L1,2 RDS(ON)H3 RDS(ON)L3 ΔVLOADREG ΔVLINEREG FOSC1,2 FOSC3 TS TSD THYS VIL VIH IEN Conditions IOUT3 = 0 to 1.5A; IOUT1,2 = 0 to 600mA; VIN = 2.7 to 5.5V Min Typ Max Units 2.7 5.5 V -3.0 3.0 % VIN 100 90 1.0 1.0 1.0 0.2 V μA μA μA μA μA μA A A mΩ mΩ mΩ mΩ % % MHz MHz μs °C °C V V μA 0.6 Per Channel, No Load No Load VEN1 = VEN2 = VEN3 = GND VIN Open, VLX = 5.5V; VEN = 0V VIN = 5.5V, VLX = 0 to VIN VFB = 1.0V 50 45 1.8 3.8 400 400 150 120 0.8 0.5 1.8 1.8 150 140 15 ILOAD1,2 = 0 to 600 mA; ILOAD3 = 0 to 1.5A VIN = 2.7 to 5.5V From Enable to Output Regulation 0.6 VIN = VEN = 5.5V 1.4 -1.0 1.0 1. The AAT2785 is guaranteed to meet performance specifications over the –40°C to +85°C operating temperature range, and is assured by design, characterization and correlation with statistical process controls. 4 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Efficiency vs. Output Current Load Regulation (Channel 1, 2; VOUT = 3.3V) (Channel 1, 2; VOUT = 3.3V) 105 3 95 2 85 75 65 55 45 VIN = 3.6V VIN = 4.2V VIN = 5V 35 25 15 0.1 1 10 100 Output Error (%) Efficiency (%) Typical Characteristics 1 0 -1 -2 VIN = 5V VIN = 4.2V VIN = 3.6V -3 -4 -5 1000 0.1 1 Efficiency vs. Output Current Load Regulation (Channel 3; VOUT = 1.2V) (Channel 3; VOUT = 1.2V) 100 1 90 0.8 80 0.6 70 60 50 40 30 VIN = 4.2V VIN = 3.6V VIN = 2.7V 20 10 0 0.1 1 10 100 1000 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0.1 10000 VIN = 4.2V VIN = 3.6V VIN = 2.7V 1 0.8 6 0.6 Output Error (%) Switching Frequency (%) 1 8 4 2 0 -2 -4 Channel 3 Channel 1, 2 2.3 2.8 3.3 3.8 4.3 Input Voltage (V) 4.8 100 1000 10000 Output Error vs. Temperature 10 -8 10 Output Current (mA) Switching Frequency vs. Input Voltage -6 1000 0.4 Output Current (mA) -10 100 Output Current (mA) Output Error (%) Efficiency (%) Output Current (mA) 10 5.3 5.8 0.4 0.2 0 -0.2 -0.4 -0.6 Channel 3 Channel 1, 2 -0.8 -1 -40 -15 10 35 60 85 Temperature (°C) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 5 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Quiescent Current vs. Input Voltage Quiescent Current vs. Input Voltage (Channel 1, 2; VOUT = 3.3V; No Load; Open Loop) (Channel 3; VOUT = 1.2V; No Load; Open Loop) 100 100 90 90 Supply Current (µA) Supply Current (µA) Typical Characteristics 80 70 60 50 40 30 85°C 25°C -40°C 20 10 0 3.2 3.5 3.8 4.1 4.4 4.7 5 5.3 80 70 60 50 40 30 85°C 25°C -40°C 20 10 0 5.6 2.6 2.9 3.2 Input Voltage (V) Switch On-Resistance (mΩ Ω) On-Resistance (mΩ Ω) 100°C 85°C 25°C 900 800 700 600 500 400 4.4 4.8 5.2 5.6 150 . 100°C 85°C 25°C 50 0 2.6 3.1 1.1 1 1 VIL (V) VIH (V) 1.1 0.9 0.8 4.6 5.1 5.6 5.1 0.9 0.8 85°C 25°C -40°C 0.7 6 4.1 VIL vs. Input Voltage 1.2 Input Voltage (V) 3.6 Input Voltage (V) 1.3 4.6 5.6 100 1.2 4.1 5.3 200 1.3 3.6 5 250 VIH vs. Input Voltage 3.1 4.7 300 Input Voltage (V) 0.6 2.6 4.4 (Channel 3; VOUT = 1.2V) 1000 4 4.1 P-Channel On-Resistance vs. Input Voltage (Channel 1, 2; VOUT = 3.3V) 3.6 3.8 Input Voltage (V) P-Channel On-Resistance vs. Input Voltage 300 3.2 3.5 85°C 25°C -40°C 0.7 5.6 0.6 2.6 3.1 3.6 4.1 4.6 Input Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 5.1 5.6 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Typical Characteristics Line Regulation Line Regulation (Channel 1, 2; VOUT = 3.3V) (Channel 3; VOUT = 1.2V) 1 0.5 0.4 0.3 Accuracy (%) Accuracy (%) 0.5 0 -0.5 IOUT = 10mA IOUT = 150mA IOUT = 300mA IOUT = 600mA -1 -1.5 3.5 4 4.5 5 5.5 0.1 0 -0.1 IOUT = 10mA IOUT = 100mA IOUT = 1000mA IOUT = 1500mA -0.2 -0.3 -0.4 -2 3 0.2 -0.5 2.6 6 4.1 4.6 5.1 5.6 Soft Start Soft Start (Channel 1, 2; VIN = 5V; VOUT = 3.3V; IOUT = 300mA) (Channel 3; VIN = 5V; VOUT = 1.2V; IOUT = 1mA) 3 1 0 1 0.5 0 3 2 1 0 1 0.5 Inductor Current (bottom) (A) 2 4 Enable Voltage (top) (V) Output Voltage (middle) (V) 4 0 Time (40µs/div) Time (40µs/div) Soft Start Output Ripple (Channel 3; VIN = 5V; VOUT = 1.2V; IOUT = 1.5A) (Channel 1, 2; VOUT = 3.3V; VIN = 4.6V; IOUT = 1mA) 4 1 0 1.5 1 0.5 0 Time (40µs/div) 0 -0.01 0.2 0.1 Inductor Current (bottom) (A) 2 Output Voltage (top) (V) 0.01 3 Inductor Current (bottom) (A) Enable Voltage (top) (V) Output Voltage (middle) (V) 3.6 Input Voltage (V)) Inductor Current (bottom) (A) Enable Voltage (top) (V) Output Voltage (middle) (V) Input Voltage (V)) 3.1 0 Time (400ns/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 7 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Typical Characteristics Output Ripple Output Ripple (Channel 1, 2; VOUT = 3.3V; VIN = 4.6V; IOUT = 600mA) (Channel 3; VOUT = 1.2V; VIN = 4.6V; IOUT = 1.5A) 0.01 0.8 0.6 0.4 0.2 0 -0.01 2 1.5 1 0.5 0 0 Time (400ns/div) Time (400ns/div) Output Ripple Output Ripple (Channel 1, 2; VOUT = 3.3V; VIN = 3.6V; IOUT = 600mA) (Channel 3; VOUT = 1.2V; VIN = 3.6V; IOUT = 1.5A) 0.01 0.8 0.6 0.4 0.2 0 -0.01 2 1.5 1 0.5 0 0 Time (400ns/div) Time (400ns/div) Output Ripple Output Ripple (Channel 1, 2; VOUT = 3.3V; VIN = 5V; IOUT = 600mA) (Channel 3; VOUT = 1.2V; VIN = 5V; IOUT = 1.5A) 0.01 0.8 0.6 0.4 0.2 0 -0.01 2 1.5 1 0.5 0 Time (400ns/div) 0 Time (400ns/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 Inductor Current (bottom) (A) -0.01 Output Voltage (top) (V) 0.01 0 Inductor Current (bottom) (A) Output Voltage (top) (V) Inductor Current (bottom) (A) -0.01 Output Voltage (top) (V) 0 Inductor Current (bottom) (A) Output Voltage (top) (V) 0.01 8 Inductor Current (bottom) (A) -0.01 Output Voltage (top) (V) 0 Inductor Current (bottom) (A) Output Voltage (top) (V) 0.01 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Typical Characteristics Output Ripple Load Transient (Channel 3; VOUT = 1.2V; VIN = 4.2V; IOUT = 1mA) (Channel 1, 2; VIN = 3.6V; IOUT = 100mA to 600mA; VOUT = 3.3V) 0 -0.02 0.4 0.2 0 Output Voltage (top) (V) 0.2 0.02 Inductor Current (bottom) (A) Output Voltage (top) (V) Output Current (middle) (A) Inductor Current (bottom) (A) 0.04 0 -0.2 600mA 100mA 600mA 100mA Time (100µs/div) Time (200µs/div) Load Transient Load Transient (Channel 1, 2; VIN = 3.6V; IOUT = 1mA to 600mA; VOUT = 3.3V) (Channel 3; VIN = 5V; IOUT = 0.1A to 1.5A; VOUT = 1.2V) 600mA 1mA 600mA 1mA 0.1 Output Voltage (top) (V) Output Voltage (top) (V) -0.2 0 1.5A -0.1 100mA 1.5A 100mA Time (400µs/div) Time (200µs/div) Load Transient Line Transient (Channel 3; VIN = 5V; IOUT = 0.5A to 1.5A; VOUT = 1.2V) (Channel 1, 2; VIN = 4V to 5V; IOUT = 600mA; VOUT = 3.3V) 1.5A 500mA 1.5A 500mA Time (400µs/div) Input Voltage (top) (V) -0.1 6 5 4 0.2 0.1 0 -0.1 -0.2 Output Voltage (bottom) (V) 0 Output Current (middle) (A) Inductor Current (bottom) (A) 0.1 Output Voltage (top) (V) Output Current (middle) (A) Inductor Current (bottom) (A) 0 Output Current (middle) (A) Inductor Current (bottom) (A) 0.2 Time (1ms/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 9 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Typical Characteristics Line Transient (Channel 3; VIN = 3.6V to 4.2V; IOUT = 1.5A; VOUT = 1.2V) Input Voltage (top) (V) 5 4 3 0.04 0.02 0 -0.02 -0.04 Output Voltage (bottom) (V) 6 Time (1ms/div) 10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Functional Block Diagram VP3 Comp. FB3 Error Amp LX 3 Logic Control Logic EN3 PGND3 OT OSC VP1_2 Comp. FB2 Error Amp Logic LX2 Control Logic EN2 PGND2 AGND OSC IN Comp. FB1 Error Amp Logic Voltage Ref EN1 LX1 Control Logic PGND1 Functional Description The AAT2785 is a high performance power management IC comprised of 3 buck converters. Each channel has an independent input voltage and enable pin. Operating at a switching frequency of 1.8MHz, the converter requires a minimum of small external components, reducing the solution cost and PCB footprint. All converters operate with an input voltage range of 2.7V to 5.5V. The output voltage range is 0.6V to VIN and is adjustable with an external resistor divider. Channel 3 power devices are sized for 1.5A output current. Channels 1 and 2 power devices are sized for 600mA output current while maintaining over 85% efficiency at full load. Peak efficiency is above 95%. Light load efficiency is maintained at greater than 80% down to 85% of full load current. All channels have excellent transient response, load and line regulation. Transient response time is typically less than 20μs. Soft start limits the current surge seen at the input and eliminates output voltage overshoot. The enable inputs, when pulled low, force the respective converter into a low power non-switching state consuming less than 1μA of current. For overload conditions, the peak input current is limited. Also, thermal protection completely disables switching if internal dissipation becomes excessive, thus protecting the device from damage. The junction over-temperature threshold is 140°C with 15°C of hysteresis. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuits prior to activation. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 11 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Control Loop The AAT2785 is a peak current mode step-down converter. The current through the P-channel MOSFET (high side) is sensed for current loop control, as well as shortcircuit and overload protection. A fixed slope compensation signal 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. 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 reference voltage is internally set to program the converter output voltage greater than or equal to 0.6V. Soft Start/Enable Soft start limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the AAT2785 into a low-power, non-switching state. The total input current during shutdown is less than 1μA. Low Dropout Operation For conditions where the input voltage drops to the output voltage level, the converter duty cycle increases to 100%. As the converter approaches the 100% duty cycle, the minimum off time initially forces the high side in time to exceed the 1.8MHz clock cycle and reduce the effective switching frequency. Once the input drops below the level where the converter can regulate the output, the high side P-channel MOSFET is enabled continuously for 100% duty cycle. At 100% duty cycle the output voltage tracks the input voltage minus the I*R drop of the high side P-channel MOSFET. Current Limit and Over-Temperature Protection For overload conditions, the peak input current is limited. To minimize power dissipation and stresses under current limit and short-circuit conditions, switching is terminated after entering current limit for a series of pulses. Switching is terminated for seven consecutive clock cycles after a current limit has been sensed for a series of four consecutive clock cycles. Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature 12 threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault condition is removed, the output voltage automatically recovers. Under-Voltage Lockout Internal bias of all circuits is controlled via the VIN input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation. Component Selection Inductor Selection: Channels 1 and 2 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 adjustable and low voltage fixed versions of channels 1 and 2 is 0.6A/ μs. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.8V output and 2.2μH inductor. m= L= 0.75 ⋅ VO 0.75 ⋅ 1.8V A = = 0.6 L 2.2µH µs 0.75 ⋅ VO 0.75 ⋅ 3.3V = = 4.1µH m A 0.6 µs In this case a standard 4.7μH value is selected. Table 1 displays the suggested inductor values for channels 1 and 2. The 4.7μH CDRH2D11 series inductor selected from Sumida has a 170mΩ DCR and a 0.88A DC current rating. At full load the inductor DC loss is 15mW which corresponds to a 1.5% loss in efficiency for a 600mA, 3.3V output. Inductor Selection: Channel 3 The internal slope compensation for the adjustable and low voltage fixed versions of channel 3 is 0.75A/μs. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.8V output and 1.8μH inductor. m= 0.75 ⋅ VO 0.75 ⋅ 1.8V A = = 0.75 L 1.8µH µs Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter L= 0.75 ⋅ VO 0.75 ⋅ 1.2V = = 1.2µH m A 0.75 µs The inductor should be set equal to the output voltage numeric value in micro henries (μH). This guarantees that there is sufficient internal slope compensation. 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. For channel 3, the 1.5μH LQH32PN1R5NN0L series Murata inductor has a 68.4m worst case DCR and a 1.75A DC current rating. At full 1.5A load, the inductor DC loss is 154mW which gives less than 5% loss in efficiency for a 1.5A, 1.2V output. 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 · 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 ⎠ IRMS(MAX) = Configuration 0.6V adjustable with external resistive divider Output Voltage 0.6V2.0V 2.5V 3.3V Inductor Slope Compensation 2.2μH 3.3μH 4.7μH 0.6A/μs Table 1: AAT2785 Inductor Values. 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) = 1 ⎛ VPP ⎞ - ESR · 4 · FS ⎝ IO ⎠ 0.52 = 1 2 ⎛ V ⎞ · 1- O IO 2 The term V ⎝ V ⎠ appears in both the input voltage ripple and input capacitor RMS current equations and is at 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 AAT2785. 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. The proper placement of the input capacitor (C1) can be seen in the evaluation board layout in the Layout section of this datasheet (see Figure 2). 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. 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 IN Select a 10μF to 22μF X7R or X5R ceramic capacitor for the VP1_2 and VP3 inputs. 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. D · (1 - D) = for VIN = 2 · VO VO Input Capacitor VO ⎛ V ⎞ · 1- O VIN ⎝ VIN ⎠ IN Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 13 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter aluminum electrolytic should be placed in parallel with the low ESR/ESL bypass ceramic capacitor. This dampens the high Q network and stabilizes the system. Output Capacitor: Channels 1 and 2 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. Output Capacitor: Channel 3 The output capacitor limits the output ripple and provides holdup during large load transitions. A 10μF to 22μF 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. Adjustable Output Resistor Selection immunity, the minimum suggested value for R2 and R4 are 29.4 k, and R6 is 59k. 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 and Table 3 summarize the resistor values for various output voltages of channel 1, channel 2, and channel 3. VOUT (V) R2 = R4 = 29.4kΩ R1 = R3 (kΩ) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.9 2.0 2.5 3.0 3.3 10 15 20 25 29 34 39 44 59 61 69 93 118 132 Table 2: AAT2785 Resistor Values for Various Output Voltages of Channel 1 and Channel 2. R6 = 221kΩ VOUT (V) R6 = 59kΩ R5 (kΩ) 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.0 3.3 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 237 267 75 113 150 187 221 261 301 332 442 464 523 715 887 1000 R5 (kΩ) Table 3: AAT2785 Resistor Values for Various Output Voltages of Channel 3. The output voltage for each channel of the AAT2785 is programmed with external resistors R1, R2, R3, R4, R5, and R6. To limit the bias current required for the external feedback resistor string while maintaining good noise 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Thermal Calculations Layout There are three types of losses associated with the AAT2785 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 losses is given by: The suggested PCB layout for the AAT2785 is shown in Figures 2 and 3. The following guidelines should be used to help ensure a proper layout. PTOTAL = IO2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO]) VIN 1. 2. 3. + (tsw · FS · 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: 4. 5. PTOTAL = IO2 · RDSON(H) + 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 JA for the TDFN34-16 package, which is 50°C/W. 6. 7. The power input capacitors (C5 and C8) should be connected as closely as possible to VP1_2, VP3 and PGND1,2,3 as shown in Figure 2. Due to the pin placement of VP1_2 and VP3 for all converters, proper decoupling is not possible with just one input capacitor. C1 and R7 are optional low pass filter components for the IN supply pin for the device if additional noise decupling is required in a noisy system C2 and L1, C6 and L2, C10 and L3 should be connected as closely as possible. The connection of L1, 2, 3 to the LX1, 2, 3 pin should be as short as possible. The feedback trace or FB pin 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. The resistance of the trace from the load returns to PGND1, 2 and 3 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 to avoid unwanted noise coupling. For good thermal coupling, PCB vias are required from the pad for the TDFN paddle to the bottom ground plane. The via diameter should be 0.3mm to 0.33mm and positioned on a 1.2mm grid. TJ(MAX) = PTOTAL · ΘJA + TAMB Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 15 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter LX 3 LX 2 LX 1 1 1 1 Evaluation Board Schematic L2 Vi n 1 1 4.7μH R7 0 EN1 EN2 EN3 1 2 3 1 2 3 1 2 3 R3 133k AA T2785 C5 10μF 1 2 3 4 5 6 7 8 C4 10μF C1 10μF PGND2 FB2 EN1 EN2 GND VIN EN3 FB3 LX 2 VP1_2 LX 1 PGND1 FB1 VP3 LX3 PGND3 16 15 14 13 12 11 10 9 1 1.5uH C9 opt U1 R5 59K C6 4.7μF 1 4.7μH L3 C3 opt R1 133K C2 4.7μF VOUT3 C10 10μF VOUT1 R2 29.4K R6 59K 1 1 Figure 1: AAT2785 Evaluation Board Schematic. Evaluation Board Layout Figure 2: AAT2785 Evaluation Board Component Side Layout. 16 VOUT2 R4 29.4k L1 C8 10μF PGND C7 opt Figure 3: AAT2785 Evaluation Board Solder Side Layout. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 PGND DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Component Part Number Manufacturer U1 L1, L2 AAT2785 CDRX2D11 AATI Sumida L3 LQH32PN1R5NN0L Murata C1 C2, C6 C5, C8, C10 C9 R1, R3 R2, R4 R5, R6 R7 GMR219R61A475KE19 GMR21BR60J106KE19 Generic Murata Murata Generic Generic Generic Generic Generic Description 3-Channel Step-Down DC/DC Converter 4.7μH 0.88A 170m (3.2x3.2x1.2)mm Shielded 1.5μH series Murata inductor has a 68.4m worst case DCR and a 1.75A DC Optional 4.7μF 10V 0805 10μF 6.3V 0805 56pF 6.3V 0402 133K 0402 29.4K 0402 59K 0402 Optional Table 4: AAT2785 Evaluation Board Bill of Materials. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 17 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Design Example Specifications VO3 VO1 VO2 VIN FS TAMB 1.2V @ 3.3V @ 3.3V @ 2.7V to 1.8MHz 85°C 1.5A (adjustable using 0.6V version), pulsed load ΔILOAD = 1.5A 600mA (adjustable using 0.6V version), pulsed load ΔILOAD = 600mA 600mA (adjustable using 0.6V version), pulsed load ΔILOAD = 600mA 4.2V (3.6V nominal) Channel 3 Output Inductor L= 0.75 ⋅ VO 0.75 ⋅ 1.2V = = 1.2µH ; use 1.5μH. (see Table 4). m A 0.75 µs Select Murata LQH32PN1R5NN0L 1.5μH 1.75A DC current rating DCR = 68mΩ. ΔI3 = ⎛ VO3 ⎛ V ⎞ 1.5V 1.5V ⎞ 1 - O3 = ⋅ 1= 357mA L⋅F ⎝ VIN ⎠ 1.5µH ⋅ 1.8MHz ⎝ 4.2V ⎠ IPK3 = 1.5A + 0.357A = 1.9A PL3 = IO32 ⋅ DCR = 1.5A2 ⋅ 68mΩ = 153mW Channels 1 and 2 Output Inductors L1 = L2 = 0.75 ⋅ VO 0.75 ⋅ 3.3V = = 4.1µH; use 4.7μH. (see Table 4) m A 0.6 µs Select Sumida CDRH2D11 4.7μH 0.88A DC current rating DCR = 170mΩ. ΔI1 = ΔI2 = ⎛ VO1 ⎛ V ⎞ 3.3V 3.3V ⎞ 1 - O1 = ⋅ 1= 84mA L⋅F ⎝ VIN ⎠ 4.7µH ⋅ 1.8MHz ⎝ 4.2V ⎠ IPK1 = IPK2 = 0.6A + 0.084A = 0.7A PL1 = PL2 = IO12 ⋅ DCR = 0.62 ⋅ 170mΩ = 61.2mW 18 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Channel 3 Output Capacitor COUT3 = 3 · ΔILOAD1 3 · 1.5A = = 12.5µF; use 10 to 22µF 0.2V · 1.8MHz VDROOP · FS IRMS(MAX) = VOUT · (VIN(MAX) - VOUT) 1 1.2V · (4.2V - 1.2V) · = 92mA = L · FS · VIN(MAX) 2 · 3 1.5µH · 1.8MHz · 4.2V 2· 3 1 · PESR = ESR · IRMS2 = 5mΩ · 92mA2 = 0.04mW Channels 1 and 2 Output Capacitors COUT1 = COUT2 = IRMS(MAX) = 3 · ΔILOAD1 3 · 0.6A = = 5µF; use 5.6µF VDROOP · FS 0.2V · 1.8MHz VOUT1 · (VIN(MAX) - VOUT1) 1 3.3V · (4.2V - 3.3V) · = 24mA = L · FS · VIN(MAX) 2 · 3 4.7µH · 1.8MHz · 4.2V 2· 3 1 · PESR = ESR · IRMS2 = 5mΩ · 28.9mA2 = 2.9µW Channel 3 Input Capacitor Input Ripple VPP = 30mV CIN3 = ⎛ VPP ⎝ IO3 IRMS(MAX) = 1 1 = = 9.3µF; use 10µF ⎞ ⎛ 30mV ⎞ - 5mΩ · 4 · 1.8MHz - ESR · 4 · FS ⎠ ⎝ 1.5A ⎠ IO = 0.75A 2 PESR = ESR · IRMS2 = 5mΩ · (0.75A)2 = 3mW Channels 1 and 2 Input Capacitors Input Ripple VPP = 15mV CIN1 = CIN2 = IRMS(MAX) = ⎛ VPP ⎝ IO1 1 1 = = 7µF; use 10µF ⎞ ⎛ 15mV ⎞ - 5mΩ · 4 · 1.8MHz - ESR · 4 · FS ⎠ ⎝ 0.6A ⎠ IO = 0.3A 2 PESR = ESR · IRMS2 = 5mΩ · (0.3A)2 = 0.45mW Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 19 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter AAT2785 Losses Total loss can be estimated by calculating the dropout (VIN = VO) losses where the power MOSFETs' RDS(ON) will be at the maximum value. All values assume an 85°C ambient temperature and a 120°C junction temperature with the TDFN 50°C/W package. PLOSS = IO32 · RDS(ON)H3 +2 · (IO12 · RDS(ON)H1,2) = 1.5A2 · 120m +2 · (0.6A2 · 400m) = 0.558W TJ(MAX) = TAMB + JA · PLOSS = 85°C + 50°C · 0.558W = 113°C. Manufacturer Part Number Inductance (μH) Max DC Current (A) DCR (Ω) Size (mm) LxWxH Type Sumida Sumida Sumida Sumida Taiyo Yuden Taiyo Yuden Taiyo Yuden Taiyo Yuden CDRH2D11 CDRH2D11 CDRH2D11 CDRH2D11 CBC2518T CBC2518T CBC2518T CBC2016T 1.5 2.2 3.3 4.7 1.0 2.2 4.7 2.2 1.48 1.27 1.02 0.88 1.2 1.1 0.92 0.83 0.068 0.098 0.123 0.170 0.08 0.13 0.2 0.2 3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 2.5x1.8x1.8 2.5x1.8x1.8 2.5x1.8x1.8 2.0x1.6x1.6 Shielded Shielded Shielded Shielded Wire Wound Chip Wire Wound Chip Wire Wound Chip Wire Wound Chip Table 5: Typical Surface Mount Inductors. 20 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Ordering Information Voltage Package Channel 1 Channel 2 Channel 3 Marking1 Part Number (Tape and Reel)2 TDFN34-16 0.6 0.6 0.6 2NXYY AAT2785IRN-AAA-T1 Skyworks Green™ products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074. Legend Voltage Code Adjustable (0.6V) A 1. XYY = assembly and date code. 2. Sample stock is generally held on all part numbers listed in BOLD. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012 21 DATA SHEET AAT2785 Three-Channel Step-Down DC/DC Converter Package Information TDFN34-16 3.000 ± 0.050 1.600 ± 0.050 Detail "A" 3.300 ± 0.050 4.000 ± 0.050 Index Area 0.350 ± 0.100 Top View 0.230 ± 0.050 Bottom View C0.3 (4x) 0.050 ± 0.050 0.450 ± 0.050 0.850 MAX Pin 1 Indicator (optional) 0.229 ± 0.051 Side View Detail "A" 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. Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. 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Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. 22 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 202045A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 11, 2012