Ordering number : ENA0587A LA5744MP Monolithic Linear IC Separately-Excited Step-Down Switching Regulator (Variable Type) http://onsemi.com Overview The LA5744MP is a separately-excited step-down switching regulator (variable type). Functions • High efficiency. • Time-base generator (300kHz) incorporated. • Current limiter incorporated. • Thermal shutdown circuit incorporated. • Soft start circuit incorporated. Specifications Maximum Ratings at Ta = 25°C Parameter Input voltage Maximum output current SW pin application reverse voltage Allowable power dissipation Symbol Conditions Ratings Unit VIN 30 IO max 3 A VSW -1 V Pd max Mounted on a circuit board.* V 3.9 W Operating temperature Topr -30 to +125 °C Storage temperature Tstg -40 to +150 °C * Specified circuit board : 76.1×114.3×1.6mm3 : Copper foil ratio 60% FR4 Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability. Recommended Operating Conditions at Ta = 25°C Parameter Input voltage range Symbol VIN Semiconductor Components Industries, LLC, 2013 August, 2013 Conditions Ratings Unit 4.5 to 28 V 31407 MS PC / 11707 MS PC 20060929-S00007 No.A0587-1/5 LA5744MP Electrical Characteristics at Ta = 25°C, VO = 5V Parameter Symbol Ratings Conditions min Reference voltage Efficiency Switching frequency VOS VIN = 15V, IO = 1.0A η VIN = 15V, IO = 1.0A f typ 1.20 Unit max 1.23 1.26 83 300 360 kHz Line regulation ΔVOLINE VIN = 8 to 20V, IO = 1.0A 40 100 mV Load regulation ΔVOLOAD VIN = 20V, IO = 0.5 to 1.5A 10 30 ΔVO/ΔTa Output voltage temperature VIN = 15V, IO = 1.0A 240 V % ±0.5 Designed target value. * mV mV/°C coefficient Ripple attenuation factor RREJ Current limiter operating voltage IS Thermal shutdown operating f = 100 to 120Hz 45 VIN = 15V dB 3.1 A TSD Designed target value. * 165 °C ΔTSD Designed target value. * 15 °C temperature Thermal shutdown Hysteresis width * Design target value : No measurement made. Package Dimensions unit : mm (typ) 3275 Pd max - Ta 4.5 1.5 9.9 1.3 4.5 (8.8) 1.2 10.0 (1.6) 0.9 1.7 0.2 0.4 1 5 2.7 SANYO : SMP5 Allowable power dissipation, Pd max - W 4.5 Specified sbstrate: 76.1×114.3×1.6mm3 Copper foil ratio 60% FR4 4.0 3.90 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -30 -20 0 20 40 60 80 100 Ambient temperature, Ta - °C 120 140 160 MSG06072 Pin Assignment (1) VIN (2) SWOUT (3) GND (4) VOS (5) SS No.A0587-2/5 LA5744MP Block Diagram VIN 1 2 SWOUT Constant current circuit Reg. OCP Reset OSC Drive Comp. TSD 4 VOS Amp. ON/OFF Comp. 0.4V VREF 5 3 SS GND Application Circuit Example L1 22μH VIN SWOUT LA5744MP C2 390μF D1 SBD C1 470μF /50V VOS SS GND R2 R1 C3 1μF Notes : 1. C3 is for the soft start function. Delete C3 and keep the SS pin open when the soft start function is not necessary. 2. In some cases, the output may not turn on if power is applied when a load is connected. If this is a problem, increase the value of the inductor. No.A0587-3/5 LA5744MP Protection Circuit Functional Descriptions 1. Overcurrent protection function The overcurrent protection function detects, on a cycle-by-cycle basis, the output transistor current and turns off that output transistor current if it exceeds 3.1A. Limit current Inductor current SWOUT voltage 2. Short circuit protection function This IC prevents the current from increasing when the outputs are shorted by setting the switching frequency to 30kHz if the VOS pin voltage falls below 0.8V. Note 3 : If the soft start function is not used, the IC will start up with the overcurrent protection function operating. At this time, the switching frequency will be cut in half. This means that the switching frequency will be 15kHz at startup. Note 4 : Since the switching frequency becomes 30kHz when the VOS pin voltage falls under 0.8V, the current capacity is reduced. If a load is applied with the VOS pin voltage over 0.8V, the inductance value operates at 22μH. If a load is to be applied when this voltage is under 0.8V, the inductance value must be increased. Description of Functional Settings 1. Calculation equation to set the output voltage This IC controls the switching output so that the VOS pin voltage becomes 1.23V (typ). The equation to set the output voltage is as follows : R2 VO = 1+ × 1.23V(typ) R1 The VOS pin has the inrush current of 1μA (typ). Therefore, the error becomes larger when R1 and R2 resistance values are large. 2. Startup Delay Function The output voltage rises when the internal voltage reaches 0.4V (typical). Until that point, a capacitor is charged from an internal 10μA (typical) constant-current supply. The startup delay time can be calculated as shown below Example : Assume a 1μF capacitor is used. Td = C × V 1μF × 0.4 = = 40 ms i 10μA No.A0587-4/5 LA5744MP Timing Chart VIN voltage 30kHz 300kHz SWOUT voltage 1.23V 0.8V VOS voltage 0V Td ON Semiconductor and the ON logo are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent-Marking.pdf. SCILLC reserves the right to make changes without further notice to any products herein. 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