ETA3410 3MHz 2A High ŋ Step-Down Converter in DFN2x2-8L Package

Transcription

1 ŋ (%) ETA34 3MHz 2A High ŋ StepDown Converter in DFN2x28L Package DESCRIPTION The ETA34 is a highefficiency, DCtoDC stepdown switching regulator, capable of delivering up to 2A of output current. The devices operate from an input voltage range of 2.6V to 5.5V and provide output voltages from.6v to VIN, making the ETA34 ideal for low voltage power conversions. Running at a fixed frequency of 3MHz allows the use of small inductance value and low DCR inductors, thereby achieving higher efficiencies. Other external components, such as ceramic input and output caps, can also be small due to higher switching frequency, while maintaining exceptional low noise output voltages. Builtin EMI reduction circuitry makes this converter ideal power supply for RF applications. Internal softstart control circuitry reduces inrush current. Shortcircuit and thermaloverload protection improves design reliability. ETA34 is housed in a tiny DFN2x28L package FEATURES ŋ up to 96% Up to 2A Max Output Current 3MHz Frequency Internal Compensation Clock Dithering Tiny DFN2x28L Package APPLICATIONS USB ports/hubs Hot Swaps Cellphones Tablet PC Set Top Boxes ORDERING INFORMATION PART PACKAGE PIN TOP MARK ETA34D2I DFN2x28 CEYW Date Code Product Number TYPICAL APPLICATION V IN 2.6V to 5.5V μf AVIN MODE 8 PVIN AGND PGND 3 μh k 6k.8V/2A 3MHz StepDown Converter 2 4 V OUT.8V/2A 22pF μf Mode= V OUT =3.3V Vin=4V Vin=4.2V Proprietary Information DO NOT Distribute

2 ETA34 PIN CONFIGURATION ABSOLUTEMAXIMUM RATINGS (Note: Exceeding these limits may damage the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.) PGND AGND DFN2x PVIN AVIN MODE PVIN, AVIN,,,, MODE Voltage....3V to 6V to ground current...internally limited Maximum Power Dissipation.mW Operating Temperature Range... C to 85 C Storage Temperature Range. 55 C to 5 C ELECTRICAL CHACRACTERISTICS (VIN = 3.6V, unless otherwise specified. Typical values are at TA = 25oC.) PARAMETER CONDITIONS MIN TYP MAX UNITS Input Voltage Range V Input UVLO Rising, Hysteresis=mV 2. V Input Supply Current V =.65V,MODE=GND μa Input Shutdown Current. μa Feedback Voltage V IN =2.5 to 5.5V V Input Current. μa Output Voltage Range.6 V IN V Load Regulation.5 %/A Line Regulation V IN =2.7 to 5.5V.4 %/V Switching Frequency MHz NMOS Switch On Resistance I =ma 5 mω PMOS Switch On Resistance I =ma 8 mω PMOS Switch Current Limit A Leakage Current V OUT =5.5V,V = or 5.5V,= GND μa, MODE Input Current =MODE=GND μa,mode Input Low Voltage.4 V,MODE Input High Voltage.5 V Thermal Shutdown Rising, Hysteresis =5 C 6 C PIN DESCRIPTION PIN # NAME DESCRIPTION PGND Power Ground. Bypass with a μf ceramic capacitor to PVIN 2 Inductor Connection. Connect an inductor Between and the regulator output. 3 AGND Analog Ground, Connect to PGND 4 Feedback Input. Connect an external resistor divider from the output to and GND to set the output to a voltage between.6v and VIN 5 Enable pin for the IC. Drive this pin to high to enable the part, low to disable. Proprietary Information DO NOT Distribute 2

3 ŋ (%) V OUT normalized (%) V OUT normalized (%) ŋ (%) ŋ (%) ŋ (%) ETA34 PIN # NAME DESCRIPTION 6 MODE When forced high, the device operates in fixed frequency PWM mode. When forced low, it enables the Power Save Mode with automatic transition from PFM mode to fixed frequency PWM mode. This pin must be terminated. 7 AVIN Analog Power. Short externally to PVIN 8 PVIN Supply Voltage. Bypass with a μf ceramic capacitor to PGND TYPICAL CHARACTERISTICS (Typical values are at TA = 25 O C unless otherwise specified.) Mode= V OUT =.2V Mode= V OUT =.8V Mode= V OUT =3.3V Vin=4V Vin=4.2V Mode=VIN V OUT =.8V V OUT Accuracy Vs I OUT V OUT =.8V I OUT (A) V OUT Accuracy Vs V IN IOUT=mA V OUT =.8V IOUT=5mA V IN (V) Proprietary Information DO NOT Distribute 3

4 ETA34 TYPICAL CHARACTERISTICS (Typical values are at TA = 25 O C unless otherwise specified.) ITCHING WAVEFORMS Light Load ma Mode=VIN ITCHING WAVEFORMS Light Load ma Mode=GND ITCHING WAVEFORMS Medium Load.5A I I I 5nS/Div 5nS/Div 5nS/Div Load Transient =.2V.2A to.a Load Transient =.8V.2A to.5a ShortCircuit Recovery I I I μs/div μs/div 5μS/Div StartUp Waveform No Load StartUp Waveform IOUT=A Shutdown Waveform IOUT=A I I I 5μS/Div μs/div μs/div Proprietary Information DO NOT Distribute 4

5 ETA34 FUNCTION DESCRIPTION The ETA34 high efficiency switching regulator is a small, simple, DCtoDC stepdown converter capable of delivering up to 2A of output current. The device operates in pulsewidth modulation (PWM) at 3MHz from a 2.6V to 5.5V input voltage and provides an output voltage from.6v to VIN, making the ETA34 ideal for onboard postregulation applications. An internal synchronous rectifier improves efficiency and eliminates the typical Schottky freewheeling diode. Using the on resistance of the internal highside MOSFET to sense switching currents eliminates currentsense resistors, further improving efficiency and cost. Loop Operation ETA34 uses a PWM currentmode control scheme. An openloop comparator compares the integrated voltagefeedback signal against the sum of the amplified currentsense signal and the slope compensation ramp. At each rising edge of the internal clock, the internal highside MOSFET turns on until the PWM comparator terminates the on cycle. During this ontime, current ramps up through the inductor, sourcing current to the output and storing energy in the inductor. The current mode feedback system regulates the peak inductor current as a function of the output voltage error signal. During the off cycle, the internal highside Pchannel MOSFET turns off, and the internal lowside Nchannel MOSFET turns on. The inductor releases the stored energy as its current ramps down while still providing current to the output. Current Sense An internal currentsense amplifier senses the current through the highside MOSFET during on time and produces a proportional current signal, which is used to sum with the slope compensation signal. The summed signal then is compared with the error amplifier output by the PWM comparator to terminate the on cycle. Current Limit There is a cyclebycycle current limit on the highside MOSFET. When the current flowing out of exceeds this limit, the highside MOSFET turns off and the synchronous rectifier turns on. ETA34 utilizes a frequency foldback mode to prevent overheating during shortcircuit output conditions. The device enters frequency foldback mode when the voltage drops below mv, limiting the current to I PEAK and reducing power dissipation. Normal operation resumes upon removal of the shortcircuit condition. Softstart ETA34 has a internal softstart circuitry to reduce supply inrush current during startup conditions. When the device exits undervoltage lockout (UVLO), shutdown mode, or restarts following a thermaloverload event, the l softstart circuitry slowly ramps up current available at. UVLO and Thermal Shutdown If PVIN/AVIN drops below.9v, the UVLO circuit inhibits switching. Once PVIN/AVIN rises above 2.V, the UVLO clears, and the softstart sequence activates. Thermaloverload protection limits total power dissipation in the device. When the junction temperature exceeds TJ= 6 C, a thermal sensor forces the device into shutdown, allowing the die to cool. The thermal sensor turns the device on again after the junction temperature cools by 5 C, resulting in a pulsed output during continuous overload conditions. Following a thermalshutdown condition, the softstart sequence begins. Design Procedure Setting Output Voltages Output voltages are set by external resistors. The threshold is.6v. R TOP = R BOTTOM x [(V OUT /.6) ] Inductor Selection The peaktopeak ripple is limited to % of the maximum output current. This places the peak current far enough from the minimum overcurrent trip level to ensure reliable operation while providing enough current ripples for the current mode converter to operate stably. In this case, for 2A maximum output current, the maximum inductor ripple current is 667 ma. The inductor size is estimated as following equation: L IDEAL =(V IN(MAX) V OUT )/I RIPPLE *D MIN *(/F OSC ) Therefore, for V OUT =.8V, The inductor values is calculated to be L =.6μH. Proprietary Information DO NOT Distribute 5

6 ETA34 Chose μh For V OUT =.2V, The inductor values is calculated to be L =.469μH. Chose.47μH The resulting ripple is I RIPPLE =(V IN(MAX) V OUT )/L ACTUAL *D MIN *(/F OSC ) When, V OUT =.8V, I RIPPLE = 3mA V OUT =.2V, I RIPPLE = 665mA Output Capacitor Selection For most applications a nominal μf or 22μF capacitor is suitable. The ETA34 internal compensation is designed for a fixed corner frequency that is equal to FC= = 5Khz 2 π COUT L For example, for V OUT =.8V, L=μH, C OUT =μf, for V OUT =.2V, L=.47μH, C OUT =22μF The output capacitor keeps output ripple small and ensures controlloop stability. The output capacitor must also have low impedance at the switching frequency. Ceramic, polymer, and tantalum capacitors are suitable, with ceramic exhibiting the lowest ESR and highfrequency impedance. Output ripple with a ceramic output capacitor is approximately as follows: V RIPPLE = IL (PEAK) [ / (2π x f OSC x C OUT )] If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows: V RIPPLE(ESR) = IL (PEAK) x ESR Input Capacitor Selection The input capacitor in a DCtoDC converter reduces current peaks drawn from the battery or other input power source and reduces switching noise in the controller. The impedance of the input capacitor at the switching frequency should be less than that of the input source so highfrequency switching currents do not pass through the input source. The output capacitor keeps output ripple small and ensures controlloop stability. BLOCK DIAGRAM MODE.6V Ref UVLO & Thermal shutdown ISense IN EA Comp Network Σ PWM Logic AntiShootThrough Driver 3MHz OSC Slope Comp Vcomp GND Proprietary Information DO NOT Distribute 6

7 ETA34 TYPICAL APPLICATION V IN 2.6V to 5.5V PCB LAYOUT 4 IN μf μH K V OUT.2V/2A 22pF 22μF GND 2 K.2V/2A 3MHz StepDown Converter PACKAGE OUTLINE DFN2X28L PACKAGE OUTLINE AND DIMSIONS Proprietary Information DO NOT Distribute 7