A7121A AITSEMI | Alldatasheet
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AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 1 - DESCRIPTION FEATURES The A7121A is a high efficiency synchronous step- down DC -DC converter. Its input voltage range is from 2.7V to 6V and provides an adjustable regulated output voltage from 0.6V to 3.4V while delivering up to 2A of output current. The current mode architecture of A7121A operation with internal compensation allows the transient response to be optimized over a wide range of loads and output capacitors. The very low supply current with no load is 60uA and even drops to <1uA in shutdown. The 2.7V to 6.0V input voltage range makes the A7121A ideally designed for single Li -Ion, two to four AA battery - powered applications. It’s 100% duty cycle provides low dropout operation to extend battery life in portable systems. The PWM pulse skipping mode of A7121A, 1MHz internal switching frequency, allows very small inductors and capacitors and provides very low output ripple voltage for noise sensitive applications. The A7121A is available in SOT-25 and SOT -26 packages.
ORDERING INFORMATION
SPQ: 3,000pcs/Reel E5 A7121AE5R A7121AE5VR SOT-26 SPQ: 3,000pcs/Reel E6 A7121AE6R A7121AE6VR Note V: Halogen free Package R: Tape & Reel AiT provides all RoHS products High Efficiency: Up to 97% Vin Range from 2.7V to 6V Output Voltage as Low as 0.6V, VREF=0.6V 1MHz Constant Switching Frequency 2.0A Output Current at VIN=3V Quiescent Current: 60μA (input < 4.2V) Slope Compensated Current Mode Control for Excellent Line and Load Transient Response Robust protection features, OCP, SCP, TSD 100% Duty Cycle in Dropout Shutdown Current <1uA Internal Soft start Circuitry Available in SOT-25 and SOT-26 packages APPLICATION Set Top Box, Cable Modem, xDSL Platforms LCD TV Power Supply & Metering Platforms General Purpose Point of Load (POL) Portable Instruments, Notebook Computer Battery Powered Equipment Wireless Access Point Router Microprocessors and DSP Core Supplies Digital Still and Video Cameras TYPICAL APPLICATION Figure 1. Typical Application Circuit
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 2 - PIN DESCRIPTION Top View Top View Pin # Symbol Function SOT-25 SOT-26 1 1 EN Regulator Enable control input. Drive EN above 1.1V to turn on the part. Drive EN below 0.6V to turn it off. In shutdown, all functions are disabled drawing <1μA supply current. Do not leave EN floating. 2 2 GND Ground 3 3 LX Power Switch Output. It is the Switch note connection to inductor. This pin connects to the drains of the internal P -CH and N -CH MOSFET switches. 4 4 VIN Power supply input pin. Must be closely decoupled to GND with a 22μF or greater ceramic capacitor. - 5 PG Power Good Indicator. This pin is an open drain logic output. Connect PG to an external pull-up resistor and get a high level output. PG is pulled to ground when the output voltage is less than 91.5% of the target output voltage. Let PG float or connect to ground when don’t use PG function. 5 6 FB Feedback Input Pin. Connect FB to the center point of the external resistor divider. The feedback threshold voltage is 0.6V.
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 3 - ABSOLUTE MAXIMUM RATINGS VIN, Input Supply Voltage -0.3V ~ +7V EN, FB VFB Voltages -0.3V ~ VIN+0.3V SW Voltages -0.3V ~ VIN+0.3V ESD Ratings Human Body Model ±4 kV θJA, SOT-25, SOT-26 220°C/W θJC, SOT-25, SOT-26 55°C/W Operating Temperature Range -40°C ~ 85°C Junction Temperature NOTE2 Internal Limit Storage Temperature Range -65°C ~ 150°C Lead Temperature (Soldering, 10s) +260°C Stress beyond above listed “Absolute Maximum Ratings” may lead permanent damage to the device. These are stress ratings only and operations of the device at these or any other conditions beyond those indicated in the operational sections of the specifications are not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 4 - ELECTRICAL CHARACTERISTICSNOTE3 VIN =VEN= 3.6V, TA = 25°C, unless otherwise noted. Parameter Conditions Min. Typ. Max. Unit Input Voltage Range 2.7 6.0 V Input DC Supply Current Active Mode Shutdown Mode VFB=0.5V or VOUT=90% VFB=0V, VIN=4.2V 0.1 300 μA μA Regulated Feedback Voltage TA = +25°C 0.5880 0.6000 0.6120 V 0°C ≤ TA ≤ 85°C 0.5865 0.6000 0.6135 V -40°C ≤ TA ≤ 85°C 0.5820 0.6000 0.6180 V Feedback Input Bias Current VFB = 0.65V ±30 nA Reference Voltage Line Regulation VIN = 2.7V to 5.5V, IOUT=300mA 0.5 0.60 %/V Output Voltage Line Regulation VIN = 2.7V to 5.5V IOUT=300mA 0.5 0.60 %/V Output Voltage Load Regulation IOUT=300 to 2000mA 0.25 %/A Peak Inductor Current VIN=3V, VFB=0.5V or VOUT=90%, Duty Cycle <35% 4.5 A Oscillator Frequency VFB=0.6V or VOUT=100% 0.8 1.0 1.2 MHz RDS(ON) of P-CH MOSFET ILX = 300mA 110 mΩ RDS(ON) of N-CH MOSFET ILX = -300mA 80 mΩ LX Leakage VEN = 0V, VLX = 0V or 5V, VIN = 5V ±0.01 ±1 μA Soft start 1 ms UVLO VIN Rising 2.3 2.5 2.7 V VIN Falling 2 2.2 2.4 V EN Threshold Low -40°C ≤ TA ≤ 85°C 0.6 V EN Threshold High 1.1 V EN Leakage Current ±0.01 ±1 μA Thermal Shutdown NOTE 4 155 ℃ PG Measured at FB pin with respect to VREF 85 91.5 % NOTE 1: Thermal Resistance is specified with approximately 1 square of 1 oz copper. NOTE 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: A7121A: TJ = TA + (PD)x(220°C/W) NOTE 3: Specifications over the temperature range are guaranteed by design and characterization. NOTE 4: Guaranteed by design and characterization only.
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 5 - TYPICAL OPERATING CHARACTERISTICS Test Figure 1 above unless otherwise specified VOUT Ripple 3. VIN=3.6V,VOUT=1.8V,IOUT=0 4. VIN=3.6V,VOUT=1.8V,IOUT=2.0A Load Transient 5. VIN=5V,VOUT=1.2V,IOUT=0.5-1.5A 6. VIN=5V,VOUT=1.2V,IOUT=0.5-2A
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 6 - Soft-start 7. VIN=3.6V,VOUT=1.8V,IOUT=0 8. VIN=3.6V,VOUT=1.8V,IOUT=2A 9. Efficiency vs. IOUT @VOUT=1.8V
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 7 - BLOCK DIAGRAM
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 8 - DETAILED INFORMATION Operation A7121A is a monolithic switching mode Step-Down DC-DC converter. It utilizes internal MOSFETs to achieve high efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a fixed switching frequency, and uses the slope compensated current mode architecture. This Step -Down DC- Current Mode PWM Control Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for excellent load and line responses and protection of the internal main switch (P- CH MOSFET) and synchronous rectifier (N-CH MOSFET). During normal operation, the internal P- CH MOSFET is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. The current comparator, I COMP, limits the peak inductor current . When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indicated by the current reversal comparator, IZERO, or the beginning of the next clock cycle. Idle Mode Operation At very light loads, the A7121A automatically enters pulse skipping Mode. In the pulse skipping Mode, the inductor current may reach zero or reverse on each pulse. The PWM control loop will automatically skip pulses to maintain output regulation. The bottom MOSFET is turned off by the current reversal comparator, IZERO, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator. Power Good Output (PG) PGOOD is an open-drain type output and requires a pull up resistor. PGOOD is actively held low in soft-start, standby, and shutdown. It is released when the output voltage rises above 91.5% of nominal regulation point. The PGOOD signal goes low if the output is turned off or falls below 91.5% of nominal regulation point. Dropout Operation When the input voltage decreases toward the value of the output voltage, the A7121A allows the main switch to remain on for more than one switching cycle and increases the duty cycle NOTE5 until it reaches 100%. The output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. At low
Where tON is the main switch on time and f OSC is the oscillator frequency (1MHz). oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty cycle decreases. A7121A. These items are also illustrated graphically in Figure 2.
- The power traces, including the GND trace, the LX trac e and the V IN trace should be kept short, direct
- The VFB pin should be connected directly to the feedback resistor. The resistive divider R1/R2 must be
connected between the (+) plate of C3 and ground.
- Connect the (+) plate of C1 to the V IN pin as closely as possible. This capacitor provides the AC current
- Keep the switching node, LX, away from the sensitive VFB node.
- Keep the (-) plates of C1 and C3 as close as possible.
Figure 2. A7121A Suggested Layout
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 10 -
Application Information
Setting the Output Voltage Figure 1 above shows the basic application circuit with A7121A. The external resistor sets the output voltage according to the following equation: VOUT = 0.6V X R1 R21 R1=150kΩ for all outputs; R2= 100kΩ for V OUT=1.0V, R2=150kΩ for V OUT =1.2V, R2=300kΩ for V OUT =1.8V, R2=475kΩ for V OUT =2.5V, R2=604kΩ for V OUT =3.0V, and R2=680kΩ for V OUT =3.3V. (Use 1% tolerance resistor) Inductor Selection For most designs, the A7121A operates with inductors of 1μH to 4.7μH. Low inductance values are physically smaller but require faster switching, which results in some efficiency loss. The inductor value can be derived from the following equation: L = OSC L IN OUTIN OUT fx x ΔIV )V(Vx V WhereΔIL is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high ripple currents. Choose inductor ripple current approximately 35% of the maximum load current 2000mA, or ΔIL=700mA. For output voltages above 2 .0V, when light-load efficiency is important, the minimum recommended inductor is 2.2μH. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the 50mΩ to 150mΩ range. For higher efficiency at heavy loads (above 5 00mA), or minimal load regulation (but some transient overshoot), the resistance should be kept below 100mΩ. The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Table 1 lists some typical surface mount inductors that meet target applications for the A7121A. Brand P/N L(μH) DCR(Ω) IRATED(A) ISAT(A) Size(L*W*H), (mm) Table 1 Recommended Inductors
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 11 - Input Capacitor Selection The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input capacitor impedance at the switching frequency shall be less than input source impedance to prevent high frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. A 22μF ceramic capacitor for most applications is sufficient. Output Capacitor Selection The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The output capacitor must have low impedance at the switching frequ ency. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current. The output ripp le ΔVOUT is determined by: ΔVOUT ≤ VOUT x (VIN-VOUT) VIN x fOSC x L x (ESR+ 1 8 x fOSC x C3) VOUT R1(kΩ) R2(kΩ) L1(μH) C2(pF) C1(μF) C3(μF) 3.3V 150 680 2.2 22 22 22 3.0V 150 604 2.2 22 22 22 2.5V 150 475 2.2 22 22 22 1.8V 150 300 2.2 22 22 22 1.2V 150 150 2.2 22 22 22 1.0V 150 100 2.2 22 22 22 Table 2 Recommended Component Values for Figure 1 Typical Application Circuit
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 12 -
PACKAGE INFORMATION
Dimension in SOT-25 (Unit: mm) Symbol Millimeters Inches Min Max Min Max A 1.050 1.250 0.041 0.049 A1 0.000 0.100 0.000 0.004 A2 1.050 1.150 0.041 0.045 b 0.300 0.500 0.012 0.020 c 0.100 0.200 0.004 0.008 D 2.820 3.020 0.111 0.119 E 1.500 1.700 0.059 0.067 E1 2.650 2.950 0.104 0.116 e 0.950 BSC 0.037 BSC e1 1.800 2.000 0.071 0.079 L 0.300 0.600 0.012 0.024 θ 0° 8° 0° 8°
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 13 - Dimension in SOT-26 (Unit: mm) Symbol Millimeters Inches Min Max Min Max A 1.050 1.250 0.041 0.049 A1 0.000 0.100 0.000 0.004 A2 1.050 1.150 0.041 0.045 b 0.300 0.500 0.012 0.020 c 0.100 0.200 0.004 0.008 D 2.820 3.020 0.111 0.119 E 1.500 1.700 0.059 0.067 E1 2.650 2.950 0.104 0.116 e 0.950 BSC 0.037 BSC e1 1.800 2.000 0.071 0.079 L 0.300 0.600 0.012 0.024 θ 0° 8° 0° 8°
AiT Semiconductor Inc. www.ait-ic.com A7121A DC-DC CONVERTER BUCK (STEP-DOWN) 1MHz, 2.0A, 6V SYNCHRONOUS REV1.4 - JUL 2013 RELEASED, MAY 2020 UPDATED - - 14 - IMPORTANT NOTICE AiT Semiconductor Inc. (AiT) reserves the right to make changes to any its product, specifications, to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. AiT Semiconductor Inc. 's integrated circuit products are not designed, intended, authorized, or warranted to be suitable for use in life support applications, devices or systems or other critical applications. Use of AiT products in such applications is understood to be fully at the risk of the customer. As used herein may involve potential risks of death, pe rsonal injury, or server e property, or environmental damage. In order to minimize risks associated with the customer's applications, the customer should provide adequate design and operating safeguards. AiT Semiconductor Inc. assumes to no liability to customer product design or application support. AiT warrants the performance of its products of the specifications applicable at the time of sale.