Ordering number : ENA1438B LA5756 Monolithic Linear IC Separately-excited Step-down Switching Regulator (Variable Type) http://onsemi.com Overview The LA5756 is a separately-excited step-down switching regulator (variable type). Features • Output smoothing condenser can use a Low ESR condenser for the reliability improvement • High efficiency • Four external parts • Time-base generator (80kHz) incorporated • Current limiter incorporated • Thermal shutdown circuit incorporated • Soft start circuit incorporated Specifications Maximum Ratings at Ta = 25°C Parameter Symbol Conditions Ratings Unit Input voltage VIN max 34 V Output current IO max 3.5 A SW pin application reverse VSW Allowable power dissipation Pd max1 Infinite heat sink. -1 V 7.5 W Pd max2 No heat sink. 1.75 W Operating temperature Topr -30 to +125 °C Storage temperature Tstg -40 to +150 °C 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 32 V 62409 SY 20090611-S00001 / 41509 MS / 40809 MS 20090326-S00003 No.A1438-1/4 LA5756 Electrical Characteristics at Ta = 25°C, VO = 3.3V Parameter Symbol Ratings Conditions min Reference voltage VOS Efficiency η typ 1.235 Unit max 1.26 1.285 V 78 Switching frequency f VIN = 15V, IO = 1.0A Line regulation ΔVOLINE VIN= 8 to 20V, IO=1.0A 60 Load regulation ΔVOLOAD VIN = 15V, IO = 0.5 to 1.5A Output voltage temperature coefficient ΔVO/ΔTa Designed target value* Ripple attenuation factor RREJ f = 100 to 120Hz Current limiter operating voltage IS VIN = 15V Thermal shutdown operating temperature TSD Thermal shutdown hysteresis width ΔTSD % 80 100 kHz 40 100 mV 10 30 mV ±0.5 mV/°C 45 dB Designed target value* 165 °C Designed target value* 15 °C 4.2 A * Designed target value: No measurement made. Package Dimensions unit : mm (typ) 3376 Pd max -- Ta 4.5 1.3 21.3 15.5 (8.8) 15.0 10.4 MAX 10.0 2.7 3.6 0.9 1 2 5 0.4 0.8 3.15 (1.6) 1.7 7.05 Allowable power dissipation, Pd max -- W 10.0 8.0 7.5 100×100×1.5mm3 6.0 5.6 50×50×1.5mm3 4.0 3.3 2.0 1.75 Infinite heat sink θjc=5°C Al heat sink mounting torque 39N⋅cm silicone grease applied 30×30×1.5mm3 No heat sink 0 -30 -20 0 20 40 60 80 100 Ambient temperature, Ta -- °C 120 140 160 MSG07021 SANYO : 220-5HMDB Pin Assignment (1)VIN (2)SWOUT (3)GND (4)VOS (5)SS No.A1438-2/4 LA5756 Block Diagram VIN 1 2 SWOUT Constnt Current Circuit OCP Reg. RESET OSC DRIVE Comp. TSD 4 VOS Amp. ON/OFF Comp. 0.4V VREF 5 SS 3 GND Application Circuit Example L1 VIN SWOUT LA5756 C2 D1 C1 VOS SS GND R2 R1 C3 Notes: C3 is for the soft start function. Delete C3 and keep the SS pin open when the soft function is not necessary. 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 1.26V (typ). The equation to set the output voltage is as follows: R2 VO = 1+ × 1.26V(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. No.A1438-3/4 LA5756 2. Start delay function The SS pin has the internally-connected 10μA (typ) constant-current supply. When the voltage of SS pin exceeds the threshold voltage, the regulator starts operation. As the threshold is 0.62V(typ), the start delay time can be calculated as follows: ex. For setting at 1μF Td = C × V 1μ × 0.4 = = 40 msec 10μ i Timing Chart VIN SWOUT VOUT Td Tss 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. 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This literature is subject to all applicable copyright laws and is not for resale in any manner. PS No.A1438-4/4