A7425 AITSEMI | Alldatasheet
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AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 1 - DESCRIPTION FEATURES A7425 is a wide input voltage, high efficiency current mode Synchronous step -down DC/DC converter. A7425 provides up to 2.5A output current at 500kHz switching frequency. A7425 integrates a 130mΩ high side and an 80 mΩ low side MOSFET to achieve high conversion efficiency up to 96%. The current mode control architecture supports fast transient response and simple compensation circuit. Protection features include cycle -by-cycle current limit, thermal shutdown, and short circuit protection. The A7425 is available in SOP8 package.
ORDERING INFORMATION
SPQ: 4,000pcs/Reel A7425M8R A7425M8VR Note V: Halogen free Package R: Tape & Reel AiT provides all RoHS products Up to 40V Input Surge Voltage Continuous Operating Input Voltage up to 36V Up to 2.5A Output Current 500kHz Switching Frequency Up to 96% Efficiency Stable with Low -ESR Ceramic Output Capacitors Resistor Programmable High -Side MOS FET Peak Current Limit from 1.0A to 3.5A ±2% Feedback Voltage Accuracy Power Saving Mode reduc es the quiescent current to 0.9mA Advanced Feature Set Integrated Soft-Start of Thermal Shutdown Cycle-by-Cycle Current Limit protection Available in SOP8 package APPLICATION Distributed Power Systems Notebook Computers Broadband Communications Flat Panel TVs and Monitors Vehicle Electronics TYPICAL APPLICATION
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 2 - PIN DESCRIPTION Top View Pin # Symbol Function 1 SW Power Switching Output to External Inductor. 2 BS High Side Bias Pin. This provides power to the internal high-side MOSFET gate driver. Connect a 100nF capacitor from BS pin to SW pin. 3 EN Enable Input. EN is pulled up to 5V with a 2MΩ resistance, and contains a precise 2V logic threshold. Drive this pin to a logic-high or leave unconnected to enable the IC. Drive to a logic-low to disable the IC and enter shutdown mode.
4 GND
Ground. Connect this pin to a large PCB copper area for best heat dissipation. Return FB, COMP, and ISET to this GND, and connect this GND to power GND at a single point for best noise immunity. 5 FB Feedback Input. The voltage at this pin is regulated to 0.8V. Connect to the resistor divider between output and GND to set the output voltage. 6 COMP Error Amplifier Output. This pin is used to compensate the converter.
7 ISET
Output Current Setting Pin. Connect a resistor from ISET to GND to program the output current limit. 8 IN Power Supply Input. Bypass this pin with a suitable large ceramic capacitor to GND, placed as close to the IC as possible.
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 3 - ABSOLUTE MAXIMUM RATINGS Input Supply Voltage -0.3V ~ 42V SW Voltage -0.3V ~ 42V Boost Voltage -0.3V ~ (VSW + 5.5V) EN Pin -0.3V ~ 6V FB COMP ISET Pin -0.3V ~ 5.5V Junction Temperature Internal Limited Storage Temperature -55°C ~ 150°C Lead Temperature (Soldering 10 sec.) 260°C Class 2 Ratings per ESDA/JEDEC JS-001-2014 Human Body Model ±4kV Operating Ratings Operating Temperature -40°C ~ 85°C Max Junction Temperature -40°C ~ 125°C Package Thermal Resistance RθJA, SOP8 90°C/W RθJC, SOP8 45°C/W 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 A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 4 -
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25℃, unless otherwise noted. Parameter Symbol Conditions Min. Typ. Max. Unit Input Supply Voltage Input Voltage VIN 4.75 - 36 V Input UVLO UVLO Threshold VUVLO VIN Rising 3.9 4.1 4.3 V Hysteresis VUVLOHYS VIN Falling - 250 - mV Input Supply Current Operation Current IVIN IOUT=0mA - 0.9 - mA Quiescent Current IQ VFB=1V - 0.8 1 mA Shutdown Supply Current ISHUTDOWN EN=0V - 6 10 μA ENABLE Enable Threshold (High) VEN_HIGH 2 - - V Enable Hysteresis VEN_HYS - - 0.4 V Enable Internal Pull Up IEN 5.3 6 10 μA Iset Characteristics ISET Voltage VISET 0.98 1.005 1.02 V ISET to IOUT DC Current Gain GISET RISET=62kΩ - 20,000 - A/A High-Side MOSFET Current Limit ILIM_HS RISET=62kΩ - 4 - A Error Amplifier Output Sink Current ISINK VFB=0.7V - 150 - μA Output Source Current ISOURCE VFB=0.9V - 50 - μA Open Loop Gain GVO - 4,000 - V/V Feedback Pin Feedback Voltage VFB 788 800 812 mV Feedback Current IFB - 0.1 50 nA Frequency Switching Frequency fSW_0.8V VFB=0.8V 450 500 550 kHz Hiccup Waiting Time tFSW_0V VFB=0V - 200 - ms Maximum Duty Cycle DMAX fSW=500kHz - 90 - %
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 5 - Parameter Symbol Conditions Min. Typ. Max. Unit MOSFET High-Side MOSFET On ResistanceNOTE1 RDS(ON_H) - 130 - mΩ Low-Side MOSFET On ResistanceNOTE1 RDS(ON_L) - 80 - mΩ High-Side MOSFET Leakage Current IHIGH_LEAK VSW = 0V - - 1 μA Low-Side MOSFET Leakage Current ILOW_LEAK VSW = VIN - - 1 μA Soft-start Soft-Start TimeNOTE1 tSS - 1.5 - ms Thermal Shutdown Thermal Shutdown ThresholdNOTE1 TSDN - 160 - °C Thermal Shutdown Hysteresis TSDN_HYS - 25 - °C NOTE1: Guaranteed by design.
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 6 - TYPICAL PERFORMANCE CHARACTERISTICS 1. Efficiency vs. Output Current 2. Efficiency vs. Output Current 3. Reference Voltage vs. Input Voltage 4. Reference vs. Temperature 5. Output Voltage vs. Output Current 6. Switching Frequency vs. Input Voltage
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 7 - 7. Switching Frequency vs. Temperature 8. Current Limit vs. Temperature 9. Load Transient Response 10. Load Transient Response 11. Load Transient Response 12. Load Transient Response
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 8 - 13. Switching 14. Switching 15. Efficiency vs. IOUT @ VOUT=5V
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 9 - TYPICAL APPLICATION CIRCUIT Low cost Application Circuit SUGGESTED COMPONENT VALUES VOUT (V) R6(kΩ) R4(kΩ) R2(kΩ) L1(μH) C3(nF) C5(μF) C6(μF) 12 270 19.6 10 6.8 4.7 22 22 9 200 19.6 10 6.8 4.7 22 22 5 62 11.8 10 6.8 4.7 22 22 3.3 62 20 4.3 4.7 4.7 22 22
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 10 - BLOCK DIAGRAM
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 11 - DETAILED INFORMATION Operation As seen in Functional Block Diagram, the A7425 is a peak current mode pulse width modulation (PWM) converter. The converter operates as follows: A switching cycle starts when the rising edge of the Oscillator clock output causes the High -Side Power Switch to turn on and the Low-Side Power Switch to turn off. With the SW side of the inductor now connected to IN, the inductor current ramps up to store energy in the magnetic field. The inductor current level is measured by the Current Sense Amplifier and added to the Oscillator ramp signal. If t he resulting summation is higher than the COMP voltage, the output of the PWM Comparator goes high. When this happens or when Oscillator clock output goes low, the High -Side Power Switch turns off. At this point, the SW side of the inductor swings to groun d through the internal Low Side Power Switch, causing the inductor current to decrease and magnetic energy to be transferred to output. This state continues until the cycle starts again. The High-Side Power Switch is driven by logic using BS as the positiv e rail. This pin is charged to V SW + 5V when the Low-Side Power Switch turns on. The Oscillator normally switches at 500 kHz. However, if FB voltage is lower than 0.4 V, A7425 will go into short circuit of auto-restart mode with very low power. Power Saving Mode Operation At very light loads, the A7425 will enter Power Saving Mode. In this mode, the regulator automatically skips switching cycles with internal control loop, and its quiescent current is reduced to 0.9mA. Enable Pin The A7425 has an enable input EN for turning the IC on or off. The EN pin contains a precision 2V comparator with 200mV hysteresis and a 2MΩ pull-up resistance. The comparator can be used with a resistor divider from VIN to program a startup voltage higher than the normal UVLO val ue. It can be used with a resistor divider from V OUT to disable charging of a deeply discharged battery, or it can be used with a resistor divider containing a thermistor to provide a temperature -dependent shutoff protection for over temperature battery. The thermistor should be thermally coupled to the battery pack for this usage. If left floating, the EN pin w ill be pulled up to roughly 5V by the internal 2 MΩ pull-up resistance. It can be driven from standard logic signals greater than 2V, or driven with open -drain logic to provide digital on/off control. Thermal Shutdown The A7425 disables switching when its j unction temperature exceeds 160 °C and resumes when th e temperature has dropped by 25°C.
peak-to-peak ripple current being 30% of the maximum load current.
1 ILPK-PK
ILIM is the internal current limit, which is typically 4A, as shown in Electrical Characteristics Table. voltage bias Diode can be a low cost one such as 1N4148 or BAT54. Figure 3. External High Voltage Bias Diode This diode is also recommended for high duty cycle operation and high output voltage applications.
during switching, its ESR also affects efficiency. ceramic capacitor is placed right next to the IC. parallel. For tantalum or electrolytic capacitors, choose a capacitor with less than 50mΩ ESR. Figure 4. Stability Compensation
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 15 - CCOMP2 is needed only for high ESR output capacitor. The feedback loop of the IC is s tabilized by the components at th e COMP pin, as shown in Figure 4. The DC loop gain of the system is determined by the following equation: AVDC = COMPVEA OUT GAI 0.8V The dominant pole P1 is due to CCOMP: fP1 = COMPVEA EA CA2 G The second pole P2 is the output pole: fP2 = OUTOUT OUT CV2 I The first zero Z1 is due to RCOMP and CCOMP: fZ1 = COMPCOMPCR2 And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used): fP3 = 2COMPCOMPCR2 The following steps should be used to compensate the IC: STEP 1. Set the cross over frequency at 1/10 of the switching frequency via RCOMP: RCOMP = 0.8Vx G10G fCV2 COMPEA SWOUTOUT (Ω) STEP 2. Set the zero fZ1 at 1/4 of the cross over frequency. The equation for CCOMP is: CCOMP = COMP2 Rf SW (F) STEP 3. If the output capacitor’s ESR is high enough to cause a zero at lower than 4 times the cross over frequency, an additional compensation capacitor CCOMP2 is required. The condition for using CCOMP2 is: RESRCOUT ≥ OUTSWCf 2 (Ω) And the proper value for CCOMP2 is: COMP2 = COMP ESRCOUTOUT R RC Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, a small value CCOMP2 such as 100pF may improve stability against PCB layout parasitic effects.
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 17 -
PACKAGE INFORMATION
Dimension in SOP8 (Unit: mm) Symbol Millimeters Inches Min Max Min Max A 1.400 1.700 0.055 0.067 A1 0.050 0.150 0.002 0.006 A2 1.350 1.550 0.053 0.061 b 0.330 0.510 0.013 0.020 c 0.170 0.250 0.007 0.010 D 4.700 5.100 0.185 0.200 E 3.800 4.000 0.150 0.157 E1 5.800 6.200 0.228 0.244 e 1.270 BSC 0.050 BSC L 0.400 1.270 0.016 0.050 L1 1.040 REF 0.041 REF θ 0° 8° 0° 8°
AiT Semiconductor Inc. www.ait-ic.com A7425 DC-DC CONVER TER B UCK (STEP-DOWN) 40V , 2.5A, 500kHz SYNCHRONOUS REV1.1 - MAR 2019 RELEASED, SEP 2019 UPDATED - - 18 - 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 adv ises 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 warr anted 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 de ath, personal injury, or server 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 t o customer product design or application support. AiT warrants the performance of its products of the specifications applicable at the time of sale.