LC2783CD8TR

LC2783 70V High Efficiency Synchronous Step-Down DC/DC Converter DESCRIPTION FEATURES LC2783 is a high efficiency, monolithic synchronous step-down DC/DC converter utilizing Jitter Function frequency, average current mode control architecture. Capable of delivering up to 3A continuous load with excellent line and load regulation. The device operates from an input voltage range of 7V to 70V and provides an adjustable output voltage from 3V to 40V.  In conclusion, LC2783 is a full function and high performance, high reliability buck DC-DC converter. PIN OUT & MARKING APPLICATIONS Distributed power systems Networking systems POE Industry application VFB EN GND VIN LC2783 XXXX YW               Internal high-side and external low-side MOSFET Max output current: 3A Adjustable output voltage, VFB=1V Constant voltage accurate: ±2% No external compensation needed Jitter function Efficiency: up to 94% Short circuit protection Thermal shutdown protection Under voltage lock-out Available in SOP-8 package SS LG BST SW SOP-8 LC2783: Product code XXXX: Lot No. YW: Date code (year & week) ORDERING INFORMATION Part No. Package Tape&Reel LC2783CD8TR SOP8 4000pcs/reel www.leadchip.com.cn 1 Your final power solution LC2783 TYPICAL APPLICATION 24.9K 8 10R 100K 4.7nF 4 SW 33uH BST 5 SS LG 6 5V Vout 4.7R GND 4.7uF EN 1uF 4.7R 2 1nF FB 470uF 7 1uF 100uF 1 Vin NMOS 3 VIN Figure 1 24.9K 8 10R 4.7nF SW 4 EN BST 5 SS LG 6 100k FB 33uH 5V Vout 1uF 4.7R NC 2 GND 4.7uF 7 1nF 4.7uF 100uF 1 Vin 470uF 3 VIN Figure 2 PIN DESCRIPTION Pin # Name 1 EN 2 3 4 5 6 GND VIN SW BST LG 7 SS 8 FB Description Enable input. Setting it to high level or Float may turn on the chip, while setting it to ground level will turn off the chip. Ground. Power supply input. Place a 1μF ceramic capacitor between VIN and GND as close as possible. Power switching output connect to external inductor. Connect a 1uF capacitor between BST and SW pin to supply current for the top switch driver. Driver of Low side NMOS, Connect to the gate of NMOS. Soft-start node. Connecting a 1nF capacitor to ground make the Buck converter output rise smoothly. Feedback voltage. www.leadchip.com.cn 2 Your final power solution LC2783 ABSOLUTE MAXIMUM RATING Parameter Value VIN to GND SW to GND BS to GND HG, LG, VFB,EN to GND Max operating junction temperature(TJ) Ambient temperature(TA) SOP-8 Package thermal resistance (JC) Storage temperature(TS) Lead temperature & time ESD (HBM) -0.3 to 75 V -0.3 to VIN VSW-0.3 to VSW+6 V -0.3 to 6 V 125C -40C – 85C 45C / W -40C – 150C 260C, 10S >2000V Note: Exceed these limits to damage to the device. Exposure to absolute maximum rating conditions may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN=12V, TA=25C, unless otherwise stated) Symbol Parameter Conditions Min Typ 7 Max Unit 70 V VIN Input voltage VUVLO UVLO voltage 6.2 V UVLO hysteresis 0.8 V ICCQ Quiescent current VFB = 1.1V, force driver off. 0.6 ISB Standby current No load, VIN=12V,VOUT=5V 0.6 mA IOUT=1A 50 mΩ High side RDSON Of Power MOS 0.98 1.02 mA VFB Feedback voltage FSW Switching frequency 150 KHz DMAX Maximum duty cycle 91 % IOUT=1A 1 2.5 V Minimum on-time 250 ns VENH EN high threshold 1.2 V VENL EN low threshold 0.7 V ILIMIT Secondary cycle-by-cycle current limit 7 A TSD Thermal shutdown temp 150 °C TSH Thermal shutdown hysteresis 30 °C www.leadchip.com.cn Minimum duty cycle, no CC 3 Your final power solution LC2783 BLOCK DIAGRAM VIN EN、Over Temp & UVLO EN VFB PWM Comp Error Amp SS Regulator Logic BOOT DRV SW ∑ OSC DRV LG GND TYPICAL PERFORMANCE CHARACTERISTICS (VOUT=5V) Temp vs. Iin Efficiency 1.0 100% 90% 0.9 0.8 70% Iin (mA) Effiiciency(%) 80% 60% VIN=12V VIN=24V VIN=30V VIN=48V VIN=60V 50% 40% 30% 0.0 0.5 1.0 1.5 2.0 Iout(A) 2.5 3.0 0.7 0.6 VIN=12V VIN=24V VIN=36V 0.5 -40 3.5 Switch Frequency vs. Temp -20 0 20 40 Temp (℃) 60 80 Supply Current vs. Input Voltage 165 1.3 160 1.2 150 Supply Current(mA) Frequency(KHz) 155 145 140 135 130 125 VIN=12V VIN=24V VIN=36V 120 115 -40 -20 0 20 www.leadchip.com.cn 40 60 80 Temp(℃）) 100 120 1.1 1.0 0.9 0.8 0.7 0.6 0.5 140 4 0 10 20 30 Vin(V) 40 50 60 Your final power solution LC2783 Short Circuit Short Circuit (Vin=12V, Freq=1.5Hz) (Vin=12V, Freq=23kHz) 670ms CH3: SW CH1: Vin, CH2: Vout, CH3: SW, CH4: Isw Power On Power Off (Vin=12V, Vout=5V, Iout=3A) (Vin=12V, Vout=5V, Iout=3A) CH1: Vin, CH2: Vout, CH3: SW, CH4: Isw CH1: Vin, CH2: Vout, CH3: SW, CH4: Isw Power On Power Off (Vin=24V, Vout=5V, Iout=3A) (Vin=24V, Vout=5V, Iout=3A) CH1: Vin, CH2: Vout, CH3: SW, CH4: Isw www.leadchip.com.cn CH1: Vin, CH2: Vout, CH3: SW, CH4: Isw 5 Your final power solution LC2783 DETAILED DESCRIPTION Input under voltage protection LC2783 provides an input voltage up to 70V and operates from an input voltage range of 7V to 70V. If VIN drops below 6.2V, the UVLO circuit inhibits switching. Once VIN rises above 7V, the UVLO clears, and the soft-start sequence activates. Soft-start LC2783 has an External soft-start circuitry to reduce supply inrush current during startup conditions. When the device exits under-voltage lockout (UVLO), shutdown mode, or restarts following a thermal-overload event, the soft-start circuitry slowly ramps up current available after 1ms. SS programming pin. Connect a capacitor from this pin to ground to program the soft start time. 𝑇𝑆𝑆 = 𝐶𝑆𝑆 × 1𝑉/2𝑢𝐴 Constant voltage output LC2783 presets the VFB voltage to 1V. The output voltage can be set by extra resistance. Short circuit protection When LC2783 enter short circuit protection, the system will enter hit-cup mode, and frequency drop to 23KHZ per cycle and stop switching for 670mS. Inductor selection Given the desired input and output voltages, the inductor value and operating frequency determine the ripple current: 𝑉𝑂𝑈𝑇 𝑉𝑂𝑈𝑇 ∆𝐼𝐿 = (1 − ) 𝑓×𝐿 𝑉𝐼𝑁(𝑀𝐴𝑋) Once the value for L is known, the type of inductor must be selected. Actual core loss is independent of core size for a fixed inductor increased inductance requires more turns of wire and therefore copper losses will increase. Copper losses also increase as frequency increases Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates ‘hard’, which means that inductance collapses abruptly when the peak design current is exceeded. This result in an abrupt increase in inductor ripple current and consequent output voltage ripple. Do not allow the core to saturate. www.leadchip.com.cn 6 Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or perm alloy materials are small and don’t radiate much energy, but generally cost more than powdered iron core inductors with similar characteristics. The choice of which style Lower ripple current reduces power losses in the inductor, ESR losses in the output capacitors and output voltage ripple. Highest efficiency operation is obtained at low frequency with small ripple current. However, achieving this requires a large inductor. There is a trade-off between component size, efficiency and operating frequency. A reasonable starting point is to choose a ripple current that is about 40% of IOUT(MAX). To guarantee that ripple current does not exceed a specified maximum, the inductance should be chosen according to: 𝑉𝑂𝑈𝑇 𝑉𝑂𝑈𝑇 L= (1 − ) 𝑓 × ∆𝐼𝐿(𝑀𝐴𝑋) 𝑉𝐼𝑁(𝑀𝐴𝑋) value, but is very dependent on the inductance selected. As the inductance or frequency increases, core losses decrease. Unfortunately, inductor to use mainly depends on the price versus size requirements and any radiated field/EMI requirements. New designs for surface mount inductors are available from Coil craft. Input capacitor (CIN) selection The input capacitance CIN is needed to filter the square wave current at the drain of the top power MOSFET. To prevent large voltage transients from occurring, a low ESR input capacitor sized for the maximum RMS current should be used. The maximum RMS current is given by: 𝐼𝑅𝑀𝑆 ≅ 𝐼𝑂𝑈𝑇(𝑀𝐴𝑋) × 𝑉𝑂𝑈𝑇 𝑉𝐼𝑁 ×√ −1 𝑉𝐼𝑁 𝑉𝑂𝑈𝑇 This formula has a maximum at VIN=2VOUT, where: 𝐼𝑅𝑀𝑆 ≅ 𝐼𝑂𝑈𝑇(𝑀𝐴𝑋) /2 This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life which makes it advisable to further derate the capacitor, or choose Your final power solution LC2783 a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. For low input voltage applications, sufficient bulk input capacitance is needed to minimize transient effects during output load changes. Output capacitor (COUT) selection The selection of COUT is determined by the effective series resistance (ESR) that is required to minimize voltage ripple and load step transients as well as the amount of bulk capacitance that is necessary to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response. The output ripple, △VOUT, is determined by: 1 ∆𝑉𝑂𝑈𝑇 < ∆𝐼𝐿 ( + 𝐸𝑆𝑅) 8𝑓 × 𝐶𝑂𝑈𝑇 The output ripple is highest at maximum input voltage since △IL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, special polymer, aluminum electrolytic, and ceramic capacitors are all available in surface mount packages. Special polymer capacitors are very low ESR but have lower capacitance density than other types. Tantalum capacitors have the highest capacitance density but it is important to only use types that have been surge tested for use in switching power supplies Aluminum electrolytic capacitors have significantly higher ESR, but can be used in cost-sensitive applications provided that consideration is given to ripple current ratings and long-term reliability. Ceramic capacitors have excellent low ESR characteristics and small footprints. Thermal shutdown The junction temperature of the IC is monitored internally. If the junction temperature exceeds the threshold value (typically 150°C), the converter shuts off. This is non-latch protection. There is about 30°C hysteresis. Once the junction temperature drops around 120°C, it initiates a Softstart. TYPICAL APPLICATION CIRCUITS 24.9K 8 10R 4 EN BST 5 SS LG 6 100K 4.7nF SW 33uH 5V Vout 4.7R GND 4.7uF 1uF 4.7R 2 1nF FB 470uF 7 1uF 100uF 1 Vin NMOS 3 VIN Figure3. 12V-70V VIN, 5V/3A www.leadchip.com.cn 7 Your final power solution LC2783 24.9K 8 10R 33uH EN BST 5 SS LG 6 9V Vout 1uF 4.7R 4.7R GND 4.7uF SW 200k 4.7nF 4 2 1nF FB 470uF 7 1uF 100uF 1 Vin NMOS 3 VIN Figure4. 12V-70V VIN, 9V/3A 24.9K 8 10R 270K 4.7nF 4 33uH EN BST 5 SS LG 6 12V Vout 1uF 4.7R 4.7R GND 4.7uF SW 2 1nF FB 470uF 7 1uF 100uF 1 Vin NMOS 3 VIN Figure5. 14V-70V VIN, 12V/3A www.leadchip.com.cn 8 Your final power solution LC2783 LAYOUT GUIDE PCB layout is very important to achieve stable operation. For best results, use the following guidelines and figures as reference. 1) Keep the connection between the input ground and GND pin as short and wide as possible. 2) Keep the connection between the input capacitor and VIN pin as short and wide as possible. 3) Use short and direct feedback connections. Place the feedback resistors and compensation components as close to the chip as possible. 4) Route SW away from sensitive analog areas such as FB. Top Layout Bottom Layout www.leadchip.com.cn 9 Your final power solution LC2783 PACKAGE OUTLINE Package SOP-8 Devices per reel 4000pcs Package specification： Unit: mm www.leadchip.com.cn 10 Your final power solution