TMI3281

TMI3281 1MHz, 18V，2A Synchronous Step-Down Converter FEATURES               GENERAL DESCRIPTION The TMI3281 is a fully integrated, high– efficiency 2.0A synchronous rectified step-down converter. The TMI3281 operates at high efficiency over a wide output current load range. The TMI3281 has force PWM operation mode and low EMI for light load The TMI3281 requires a minimum number of readily available standard external components and is available in a 6-pin SOT23 ROHS compliant package. High Efficiency: Up to 95%@5V 1MHz Frequency Operation 2.0A Output Current No Schottky Diode Required 3.5V to 18V Input Voltage Range 0.6V Reference Slope Compensated Current 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 over voltage protection(OVP) Thermal Shutdown Inrush Current Limit and Soft Start Available in SOT23-6 Package APPLICATIONS Distributed Power Systems Digital Set Top Boxes Flat Panel Television and Monitors Notebook computer Wireless and DSL Modems      TYPICAL APPILCATION C1 1 VIN 5 BS VIN LX 6 L1 VOUT CIN 22μ F R1 4 ON / OFF EN FB 3 COUT GND R2 2 22μ F Figure 1. Basic Application Circuit TMI and SUNTO are the brands of TOLL microelectronic TMI3281 V1.0 2017.11 www.toll-semi.com www.suntosemi.com 1 TMI3281 ABSOLUTE MAXIMUM RATINGS (Note 1) Parameter Value Unit Input Supply Voltage ,EN -0.3~23 V LX Voltages -0.3~23 V FB Voltage -0.3~25 V BS Voltage -0.6~25 V Storage Temperature Range -65~150 °C Junction Temperature(Note2) 160 °C Power Dissipation 600 mW Lead Temperature(Soldering,10s) 260 °C Over operating free-air temperature range (unless otherwise noted) PACKAGE/ORDER INFORMATION SOT23-6 Top Mark: T36XXX (T36: Device Code, XXX: Inside Code) www.toll-semi.com 2 Part Number Package Top mark Quantity/ Reel TMI3281 SOT23-6 T36XXX 3000 www.suntosemi.com TMI and SUNTO are the brands of TOLL microelectronic. TMI3281 V1.0 2017.11 TMI3281 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 pin 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. Don’t floating this pin. 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 TMI3281 V1.0 2017.11 Min www.toll-semi.com Max Unit www.suntosemi.com 3 TMI3281 ELECTRICAL CHARACTERISTICS (Note 3) ( VIN=12V ,VOUT=5V , TA = 25°C, unless otherwise noted.) Parameter Test Conditions Input Voltage Range Min Typ 3.5 OVP Threshold Max Unit 18 V 19 UVLO Threshold V 3.0 Supply Current in Shutdown VEN =0 Regulated Feedback Voltage TA = 25°C,3.5V≤VIN ≤18V V 2 0.588 0.6 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 1 MHz 92 % Minimum On-Time 100 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 4 www.suntosemi.com TMI and SUNTO are the brands of TOLL microelectronic. TMI3281 V1.0 2017.11 TMI3281 OPERATION Internal Regulator The TMI3281 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 1MHz 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. Over-Current-Protection and Hiccup The TMI3281 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 TMI3281 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 TMI3281 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 TMI3281 V1.0 2017.11 www.toll-semi.com www.suntosemi.com 5 TMI3281 FUNCTIONAL BLOCK DIAGRAM Figure 2. TMI3281 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 www.toll-semi.com 6 www.suntosemi.com Vout R1(KΩ) R2(KΩ) 5.1V 3.3V 1.8V 1.55V 1.25V 1.20V 1.05V 51 51 51 51 51 51 33 6.8 11.3 25.5 33 47 51 47 TMI and SUNTO are the brands of TOLL microelectronic. TMI3281 V1.0 2017.11 TMI3281 Inductor Selection 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  fOSC 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  I L 2 Under light load conditions below 100mA, larger inductance is recommended for improved efficiency. Output Capacitor Selection The output capacitor (Cout) 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   f S  L  VIN   8  f S  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  f S  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 f S  L  VIN  The characteristics of the output capacitor also affect the stability of the regulation system. The TMI3281 can be optimized for a wide range of capacitance and ESR values. Layout Consideration 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 for reference. TMI and SUNTO are the brands of TOLL microelectronic TMI3281 V1.0 2017.11 www.toll-semi.com www.suntosemi.com 7 TMI3281 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 IN 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 8 www.suntosemi.com TMI and SUNTO are the brands of TOLL microelectronic. TMI3281 V1.0 2017.11 TMI3281 PACKAGE INFORMATION SOT23-6 Note: 1) All dimensions are in millimeters. 2) Package length does not include mold flash, protrusion or gate burr. 3) Package width does not include interlead flash or protrusion. 4) Lead popularity (bottom of leads after forming) shall be 0.10 millimeters max. 5) Pin 1 is lower left pin when reading top mark from left to right. TMI and SUNTO are the brands of TOLL microelectronic TMI3281 V1.0 2017.11 www.toll-semi.com www.suntosemi.com 9