Ordering number : ENA0742 LA5774 Monolithic Linear IC Separately-excited Step-down Switching Regulator (Variable Type) http://onsemi.com Overview The LA5774 is a Separately-excited step-down switching regulator (variable type). Functions Low-ESR capacitor with increased reliability applicable as the output smoothing capacitor. High efficiency. Four external parts. Time-base generator (160kHz) incorporated. Current limiter incorporated. Thermal shutdown circuit incorporated. Soft start circuit incorporated. Specifications Absolute Maximum Ratings at Ta = 25C Parameter Symbol Maximum Input voltage VIN max Maximum Output current SW pin application reverse voltage Allowable power dissipation Conditions Ratings Unit 30 V IO max 3 A VSW -1 V 1.75 W Pd max1 No heat sink Pd max2 Infinite heat sink 7.5 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 = 25C Parameter Input voltage range Symbol VIN Semiconductor Components Industries, LLC, 2013 August, 2013 Conditions Ratings Unit 4.5 to 28 V 31407 MS PC B8-9090 No.A0742-1/5 LA5774 Electrical Characteristics at Ta 25C, VO = 3.3V Ratings Parameter Symbol Conditions Unit min Reference voltage VOS VIN = 15V, IO = 1.0A VIN = 15V, IO = 1.0A f VIN = 15V, IO = 1.0A Efficiency Switching frequency typ 1.235 max 1.26 1.285 V 78 160 192 kHz Line regulation VOLINE VIN = 8 to 20V, IO = 1A 40 100 mV Load regulation VOLOAD VIN = 15V, IO = 0.5 to 1.5A 10 30 VO/Ta Output voltage temperature 128 % mV 0.5 Designed target value. * mV/C coefficient Ripple attenuation factor RREJ Current limiter operating voltage f = 100 to 120Hz IS Thermal shutdown operating 45 VIN = 15V dB 3.1 A TSD Designed target value. * 165 C TSD Designed target value. * 15 C temperature Thermal shutdown Hysteresis width * Design target value: No measurement made. Package Dimensions unit : mm (typ) 3079C Pd max -- Ta 10.4MAX 10.0 4.5 2.7 2.7 0.9 5 1 0.8 (1.6) 17.8 21.3 23.0 15.0 1.3 (8.8) 3.6 Allowable power dissipation, Pd max -- W 10.0 1.7 0.45 4.5 8.0 7.5 100×100×1.5mm3 6.0 5.6 50×50×1.5mm3 4.0 3.3 2.0 1.75 Al heat sink mounting torque 39N⋅cm silicone grease applied 30×30×1.5mm3 No heat sink 0 -30 -20 8.4 Infinite heat sink θjc=5°C 0 20 40 60 80 100 Ambient temperature, Ta -- °C 120 140 160 MSG07021 220-5H Pin Assignment (1) VIN (2) SWOUT (3) GND (4) VOS (5) SS No.A0742-2/5 LA5774 Block Diagram VIN 1 2 SWOUT Reg. OCP Reset OSC Drive Comp. THD 4 VOS Amp. VREF 5 3 SS GND Application Circuit Example L1 68μH VIN SWOUT LA5774 C2 390μF D1 SBD C1 470μF /50V VOS SS GND R2 R1 C3 1μF Notes: C3 is for the soft start function. Delete C3 and keep the SS pin open when the soft start function is not necessary. No.A0742-3/5 LA5774 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 1A (typ). Therefore, the error becomes larger when R1 and R2 resistance values are large. 2. Start delay function The SS pin has the internally-connected 22A (typ) constant-current supply. When the voltage of SS pin exceeds the threshold voltage, the regulator starts operation. As the threshold voltage is 0.62V (typ), the start delay time can be calculated as follows: ex. For setting at 1F Td = C × V 1μF × 0.62 = = 28.2 ms i 22μA 3. Soft start function The internal PWM waveform has the voltage value as shown in the right. If down-conversion from the voltage of VIN = 15 V to VIN = 3.3V is to be made, for example, the PWM-ON duty has the value as shown below. 1.5V 0.62V PWM wave VOUT PWMduty = V − Vsat + VF = 23 % IN (Note that calculation is made with Vsat = 1V and VF = 0.2V) The output voltage of error amplifier, which is 3.3 V, is the value with PWM = 23%, as calculated in the above equation, so that this voltage is determined as follows: Ver = (VPWM) PWMduty + VPWML = 0.88V 0.23 + 0.62V = 0.82V (VPWM is the PWM amplitude value or 0.88V(typ) while VPWML is the lower limit voltage of PWM waveform or 0.62V(typ)) SS pin and error amplifier output voltages are designed to prefer the lower voltages, so that VOUT will reach the designed regulation voltage in timing when the SS pin voltage exceeds the error amplifier output. Therefore, the soft start time is calculated as follows: Tss = C × ΔVPWM × PWMduty C × 0.88 × PWMduty = 22μA i For the set conditions of C = 1F and PWMduty = 23%: Tss = 1μF × 0.88V × 0.23 = 9.2ms 22μA No.A0742-4/5 LA5774 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. 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. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PS No.A0742-5/5