TMI3280

TMI3280 600KHz, 18V，2A Synchronous Step-Down Converter FEATURES                High Efficiency: Up to 95% 600KHz Frequency Operation 2.0A Output Current Up to 96% duty 3.5V to 18V Input Voltage Range 0.6V Reference Constant on time(COT) Mode Control for Excellent Line and Load Transient Response Integrated internal compensation Stable with Low ESR Ceramic Output Capacitors Over Current Protection with Hiccup-Mode Input overvoltage protection(OVP) Thermal Shutdown Inrush Current Limit and Soft Start Available in SOT23-6 Package -40°C to +85°C Temperature Range GENERAL DESCRIPTION The TMI3280 is a fully integrated, high– efficiency 2.0A synchronous rectified step-down converter. The TMI3280 operates at high efficiency over a wide output current load range. This TMI3280 adopts the instant PWM architecture to achieve fast transient responses for high step down applications and high efficiency at light loads. The TMI3280 requires a minimum number of readily available standard external components and is available in a 6-pin SOT23 ROHS compliant package. APPLICATIONS      Distributed Power Systems Digital Set Top Boxes Flat Panel Television and Monitors Notebook computer Wireless and DSL Modems TYPICAL APPILCATION Figure 1. Basic Application Circuit TMI and SUNTO are the brands of TOLL microelectronic TMI3280 V1.2 2016.11 www.toll-semi.com www.suntosemi.com 1 TMI3280 ABSOLUTE MAXIMUM RATINGS (Note 1) Parameter Value Unit Input Supply Voltage ,EN -0.3~23 V LX Voltages -0.3~23 V FB Voltage -0.3~6 V BS Voltage -0.3~25 V Storage Temperature Range -65~150 °C Junction Temperture(Note2) 155 °C Power Dissipation 600 mW Lead Temperature(Soldering,10s) 260 °C PIN CONFIGURATION SOT23-6 Top Mark: S4CXXX (S4C: Device Code, XXX: Inside Code) Part Number Package Top mark Quantity/ Reel TMI3280 SOT23-6 S4CXXX 3000 www.toll-semi.com www.suntosemi.com 2 TMIandSUNTOarethebrandsofTOLLmicroelectronic. TMI3280 V1.2 2016.11 TMI3280 PIN FUNCTIONS Pin Name Function 1 BS 2 GND 3 FB 4 EN 5 IN Power supply Pin 6 LX Switching Pin Bootstrap. A capacitor connected between LX and BST pins is required to form a floating supply across the high-side switch driver. Ground Adjustable version feedback input. Connect FB to the center point of the external resistor divider. Drive this pin to a logic-high to enable the IC. Drive to a logic-low to disable the IC and enter micro-power shutdown mode. ESD RATING Items Description Value Unit VESD Human Body Model for all pins ±2000 V JEDEC specification JS-001 RECOMMENDED OPERATING CONDITIONS Items Description Voltage Range IN 3.5 18 V TA Operating Temperature Range -40 85 °C TMI and SUNTO are the brands of TOLL microelectronic TMI3280 V1.2 2016.11 Min Max Unit www.toll-semi.com www.suntosemi.com 3 TMI3280 ELECTRICAL CHARACTERISTICS (Note 3) ( VIN=12V ,VOUT=5V , TA = 25°C, unless otherwise noted.) Parameter Conditions Input Voltage Range OVP Min Typ 3.5 Threshold Max Unit 18 V 19 UVLO Threshold V 3.0 V Supply Current in Operation VEN=2.0V, VFB=1.1V 0.4 Supply Current in Shutdown VEN =0 or EN = GND 1 Regulated Feedback Voltage TA = 25°C,3.5V≤VIN ≤18V 0.588 0.6 0.6 mA uA 0.612 V High-Side Switch On-Resistance 120 mΩ Low-Side Switch On-Resistance 80 mΩ High-Side Switch Leakage Current VEN=0V, VLX=0V Upper Switch Current Limit Minimum Duty Cycle Oscillation Frequency 0 10 2.5 uA A 600 KHz 96 % Minimum On-Time 60 nS Thermal Shutdown 160 ℃ Maximum Duty Cycle VFB=0.6V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD) x (250°C/W). Note 3: 100% production test at +25°C. Specifications over the temperature range are guaranteed by design and characterization. Note 4: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency www.toll-semi.com www.suntosemi.com 4 TMIandSUNTOarethebrandsofTOLLmicroelectronic. TMI3280 V1.2 2016.11 TMI3280 FUNCTIONAL DESCRIPTION Internal Regulator The TMI3280 is a current mode step down DC/DC converter that provides excellent transient response with no extra external compensation components. This device contains an internal, low resistance, high voltage power MOSFET, and operates at a high 600K operating frequency to ensure a compact, high efficiency design with excellent AC and DC performance. Error Amplifier The error amplifier compares the FB pin voltage with the internal FB reference (VFB) and outputs a current proportional to the difference between the two. This output current is then used to charge or discharge the internal compensation network to form the COMP voltage, which is used to control the power MOSFET current. The optimized internal compensation network minimizes the external component counts and simplifies the control loop design. Internal Soft-Start The soft-start is implemented to prevent the converter output voltage from overshooting during startup. When the chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 0.6V. When it is lower than the internal reference (REF), SS overrides REF so the error amplifier uses SS as the reference. When SS is higher than REF, REF regains control. The SS time is internally fixed to 1ms. Over-Current-Protection and Hiccup The TMI3280 has cycle-by-cycle over current limit when the inductor current peak value exceeds the set current limit threshold. Meanwhile, output voltage starts to drop until FB is below the Under-Voltage (UV) threshold, typically 30% below the reference. Once a UV is triggered, the TMI3280 enters hiccup mode to periodically restart the part. This protection mode is especially useful when the output is dead-short to ground. The average short circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator. The TMI3280 exits the hiccup mode once the over current condition is removed. Startup and Shutdown If both VIN and EN are higher than their appropriate thresholds, the chip starts. The reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator provides stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low and thermal shutdown. In the shutdown procedure, the signaling path is first blocked to avoid any fault triggering. The COMP voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown command. TMI and SUNTO are the brands of TOLL microelectronic TMI3280 V1.2 2016.11 www.toll-semi.com www.suntosemi.com 5 TMI3280 FUNCTIONAL BLOCK DIAGRAM Figure 2. TMI3280 Block Diagram APPLICATION INFORMATION Setting the Output Voltage The external resistor divider is used to set the output voltage (see Typical Application on page 1). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor. Choose R1 to be around 51kΩ for optimal transient response. R2 is then given by: R2  R1 Vout / VFB  1 Vout R1(KΩ) 5.1V 3.3V 1.8V 1.55V 1.25V 1.20V 1.05V www.toll-semi.com www.suntosemi.com 6 51 51 51 51 51 51 33 R2(KΩ) 6.8 11.3 25.5 33 47 51 47 TMIandSUNTOarethebrandsofTOLLmicroelectronic. TMI3280 V1.2 2016.11 TMI3280 Selecting the Inductor A 4.7μH to 22μH inductor with a DC current rating of at least 25% percent higher than the maximum load current is recommended for most applications. For highest efficiency, the inductor DC resistance should be less than 15mΩ. For most designs, the inductance value can be derived from the following equation. L Vout  (Vin  Vout ) Vin  I L  f OSC Where ΔIL is the inductor ripple current. Choose inductor ripple current to be approximately 30% if the maximum load current, 2A. The maximum inductor peak current is: I L ( MAX )  I LOAD  IL 2 Under light load conditions below 100mA, larger inductance is recommended for improved efficiency. Setting the Output Capacitor The output capacitor (C2) is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by: VOUT  VOUT  VOUT  1   1   RESR  fS  L  VIN   8 fS C2  Where L is the inductor value and RESR is the equivalent series resistance (ESR) value of the output capacitor. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the output voltage ripple can be estimated by: VOUT   VOUT VOUT  1  2 8 fS  L C2  VIN  In the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: VOUT  VOUT  VOUT  1   RESR fS  L  VIN  The characteristics of the output capacitor also affect the stability of the regulation system. The TMI3280 can be optimized for a wide range of capacitance and ESR values. PCB Layout Guide PCB layout is very important to achieve stable operation. It is highly recommended to duplicate EVB layout for optimum performance. If change is necessary, please follow these guidelines and take Figure 4 for reference. TMI and SUNTO are the brands of TOLL microelectronic TMI3280 V1.2 2016.11 www.toll-semi.com www.suntosemi.com 7 TMI3280 1) Keep the path of switching current short and minimize the loop area formed by Input capacitor, high-side MOSFET and low-side MOSFET. 2) Bypass ceramic capacitors are suggested to be put close to the Vin Pin. 3) Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. 4) VOUT, LX away from sensitive analog areas such as FB. 5) Connect IN, LX, and especially GND respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. www.toll-semi.com www.suntosemi.com 8 TMIandSUNTOarethebrandsofTOLLmicroelectronic. TMI3280 V1.2 2016.11 TMI3280 PACKAGE INFORMATION SOT23-6 TMI and SUNTO are the brands of TOLL microelectronic TMI3280 V1.2 2016.11 www.toll-semi.com www.suntosemi.com 9