Ordering number : ENA0490 LA5774MP Monolithic Linear IC Separately-excited Step-down Switching Regulator (Variable Type) http://onsemi.com Overview The LA5774MP 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 = 25°C Parameter Symbol Maximum Input voltage VIN max 30 V IO max 3 A Maximum Output current SW pin application reverse voltage Conditions Ratings VSW Allowable power dissipation Pd max Mounted on a substrate.* Unit -1 V 3.9 W Operating temperature Topr -30 to +125 °C Storage temperature Tstg -40 to +150 °C 3 * Specified substrate : 76.1×114.3×1.6mm : 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 72606 MS PC B8-9089 No.A0490-1/5 LA5774MP Electrical Characteristics at Ta = 25°C, VO = 3.3V Parameter Symbol Ratings Conditions min Reference voltage Efficiency Switching frequency VOS VIN = 15V, IO = 1.0A η VIN = 15V, IO = 1.0A f Unit typ 1.235 max 1.26 1.285 V 78 VIN = 15V, IO = 1.0A 160 192 kHz Line regulation ΔVOLINE VIN = 8 to 20V, IO = 1A 40 100 mV Load regulation ΔVOLOAD VIN = 15V, IO = 0.5 to 1.5A 10 30 ΔVO/ΔTa Output voltage temperature 128 % ±0.5 Designed target value. * mV 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 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 Allowable power dissipation, Pd max - W 4.5 2.7 4.0 3.90 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -30 -20 SANYO : SMP5 Specified sbstrate: 76.1×114.3×1.6mm3 Copper foil ratio 60% FR4 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.A0490-2/5 LA5774MP 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 LA5774MP 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.A0490-3/5 LA5774MP 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. 2. Start delay function The SS pin has the internally-connected 22μA (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 1μF 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 = (ΔVPWM) × PWMduty + VPWML = 0.88V × 0.23 + 0.62V = 0.82V (ΔVPWM 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 = 1μF and PWMduty = 23%: Tss = 1μF × 0.88V × 0.23 = 9.2ms 22μA No.A0490-4/5 LA5774MP 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. 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