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Ordering number : ENA0742
Monolithic Linear IC
LA5774
Overview
Separately-excited Step-down
Switching Regulator (Variable Type)
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 Maximum Input voltage Maximum Output current SW pin application reverse voltage Allowable power dissipation Symbol VIN max IO max VSW Pd max1 Pd max2 Operating temperature Storage temperature Topr Tstg No heat sink Infinite heat sink Conditions Ratings 30 3 -1 1.75 7.5 -30 to +125 -40 to +150 Unit V A V W W C C
Recommended Operating Conditions at Ta = 25C
Parameter Input voltage range Symbol VIN Conditions Ratings 4.5 to 28 Unit V
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31407 MS PC B8-9090 No.A0742-1/5
LA5774
Electrical Characteristics at Ta = 25C, VO = 3.3V
Parameter Reference voltage Efficiency Switching frequency Line regulation Load regulation Output voltage temperature coefficient Ripple attenuation factor Current limiter operating voltage Thermal shutdown operating temperature Thermal shutdown Hysteresis width * Design target value: No measurement made. TSD Designed target value. * 15 C RREJ IS TSD f = 100 to 120Hz VIN = 15V Designed target value. * 3.1 165 45 dB A C Symbol VOS f VOLINE VOLOAD VO/Ta Conditions min VIN = 15V, IO = 1.0A VIN = 15V, IO = 1.0A VIN = 15V, IO = 1.0A VIN = 8 to 20V, IO = 1A VIN = 15V, IO = 0.5 to 1.5A Designed target value. * 128 1.235 Ratings typ 1.26 78 160 40 10 0.5 192 100 30 max 1.285 V % kHz mV mV mV/C Unit
Package Dimensions
unit : mm (typ) 3079C
10.0
Pd max -- Ta
3.6
2.7
10.4max 10.0
4.5 1.3
Allowable power dissipation, Pd max -- W
8.0 7.5
100x100x1.5mm3
Infinite heat sink jc=5C
15.0
6.0 5.6
50x50x1.5mm3 Al heat sink mounting torque 39Ncm silicone grease applied
40 60 80 100 120 140 160 MSG07021
(8.8)
17.8 21.3 23.0
4.0 3.3 2.0 1.75
30x30x1.5mm3 No heat sink
0.9
2.7
1
5 0.8 0.45 4.5 8.4
(1.6)
1.7
0 -30 -20
0
20
Ambient temperature, Ta -- C
SANYO : 220-5H
Pin Assignment
(1) VIN (2) SWOUT (3) GND (4) VOS (5) SS
No.A0742-2/5
LA5774
Block Diagram
VIN 1 Reg. OCP
2 SWOUT
OSC
Reset
Drive
Comp.
THD 4 VOS VREF
Amp.
5 SS
3 GND
Application Circuit Example
L1 68H
VIN
SWOUT
LA5774
C1 470F /50V D1 SBD C2 390F
VOS SS
C3 1F
GND
R2 R1
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+ x 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 x V 1F x 0.62 = = 28.2 ms i 22A
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.
VOUT PWMduty = V - Vsat + VF = 23 % IN
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 3.3 V, is the value with PWM = 23%, as calculated in the above equation, so that this voltage is determined as follows: Ver = (VPWM) x PWMduty + VPWML = 0.88V x 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 x VPWM x PWMduty C x 0.88 x PWMduty = 22A i
For the set conditions of C = 1F and PWMduty = 23%:
Tss = 1F x 0.88V x 0.23 = 9.2ms 22A
No.A0742-4/5
LA5774
Timing Chart
VIN
SWOUT
VOUT
Td
Tss
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This catalog provides information as of March, 2007. Specifications and information herein are subject to change without notice. PS No.A0742-5/5

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