Ordering number : ENA1439 LA5757TP Monolithic Linear IC Separately-excited Step-down Switching Regulator (Variable Type) http://onsemi.com Overview The LA5757TP 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 (300kHz) 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 1.5 A SW pin application reverse VSW Allowable power dissipation Pd max -1 V 1.1 W Operating temperature Storage temperature Topr -30 to +125 °C Tstg -40 to +150 °C Mounted on a specified board* * Specified board: 114.3mm × 76.1mm × 1.6mm, glass epoxy board. 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 40809 MS 20090326-S00004 No.A1439-1/6 LA5757TP Electrical Characteristics at Ta = 25°C, VO = 5V Parameter Symbol Ratings Conditions min Reference voltage VOS Efficiency η Unit typ 1.230 max 1.255 1.280 V 83 Switching frequency f VIN = 15V, IO = 1.0A Line regulation ΔVOLINE VIN= 8 to 20V, IO=1.0A 240 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 % 300 360 kHz 40 100 mV 10 30 ±0.5 mV mV/°C 45 dB Designed target value* 165 °C Designed target value* 15 °C 1.6 A * Designed target value: No measurement made. Package Dimensions unit : mm (typ) 3332 Pd max -- Ta 6.5 2.3 1.5 5.0 2.5 1.2 0.8 (5.5) 7.0 0.5 0.2 0.6 (0.65) 1.3 1 2 0.5 0.5 1.2 Allowable power dissipation, Pd max -- W 1.4 1.2 1.1 Specified board: 114.3×76.1×1.6mm3 glass epoxy board. With specified board 1 0.8 0.6 0.4 0 --30--20 5 0.22 0.2 0 20 40 60 80 100 120 140 Ambient temperature, Ta -- °C SANYO : TP5HFA Pin Assignment (1)VIN (2)SWOUT (3)GND (4)VOS (5)SS No.A1439-2/6 LA5757TP Block Diagram VIN 1 2 SWOUT Constnt Current Circuit OCP Reg. RESET OSC DRIVE Comp. TSD 2 VOS Amp. ON/OFF Comp. 0.4V VREF 5 SS 3 GND Application Circuit Example L1 VIN SWOUT LA5757TP 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 1.255V (typ). The equation to set the output voltage is as follows: R2 VO = 1+ × 1.255V(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.A1439-3/6 LA5757TP 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 × 0.62 = = 28.2 msec 22μ i 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 = 15V to 3.3V output to be made, for example, the PWM-ON duty has the value as shown below. VOUT + VF PWMduty = = 25% VIN - Vsat + VF 1.5V 0.62V PWM wave (Note that calculation is made with Vsat = 1V and VF = 0.2V) The output voltage of error amplifier, which is 3.3V, is the value with PWM = 25%, as calculated in the above equation, so that this voltage is determined as follows: Ver = (ΔVPWM) × PWMduty + VPWML = 0.88V × 0.25 + 0.62V = 0.84V (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 strt time is calculated as follows: Tss = C × ΔVPWM × PWMduty C × 0.88 × PWMduty = 22μA i For the set conditions of C = 1μF and PWMduty = 25%: Tss = 1μ × 0.88V × 0.25 = 10msec 22μA No.A1439-4/6 LA5757TP Timing Chart VIN SWOUT VOUT Tss Td Overcurrent protection characteristic 8 6 85 Efficiency -- % Output voltage, VO -- V 7 Efficiency -- VIN 90 VIN = 12V VO = 5V CIN = 1000μF COUT = 470μF L = 68μH 5 4 3 IO = 0.5 A 80 1.5A 1.0A 75 70 2 65 1 0 0 0.4 0.8 1.2 1.6 60 2.0 0 10 Load current, IL -- A VOsat -- ISW 30 40 30 40 ISTB -- VIN 250 1.4 Standby current, ISTB -- μA Output saturation voltage, VOsat -- V 1.6 20 Input voltage, VIN -- V 1.2 1.0 0.8 0.6 0.4 200 150 100 50 0.2 0 0 0.25 0.5 0.75 1.0 Switch current, ISW -- A 1.25 1.5 0 0 10 20 Input voltage, VIN -- V No.A1439-5/6 LA5757TP LR -- IL 1.0 INR -- VIN 2.5 Input regulation, INR -- % Load regulation, LR -- % 2.0 0.5 0 -0.5 1.5 1.0 0.5 0 -1.0 0 0.25 0.5 0.75 1.0 Load current, IL -- A 1.25 1.5 -0.5 0 5 10 15 20 25 30 Input voltage, VIN -- V ON Semiconductor and the ON logo are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). 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