The LA5774 is a Separately-excited step-down switching regulator (variable type).
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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
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
Conditions
Ratings
4.5 to 28
Unit
V
Semiconductor Components Industries, LLC, 2013
August, 2013
31407 MS PC B8-9090 No.A0742-1/5
LA5774
Electrical Characteristics
at Ta
½
25C, VO = 3.3V
Ratings
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
V
OLINE
V
OLOAD
V
O/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
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
100×100×1.5mm
3
Infinite heat sink
θjc=5°C
6.0
5.6
50×50×1.5mm
3
Al heat
sink
mounting
torque
39N⋅cm
silicone
grease
applied
40
60
80
100
120
140
160
MSG07021
15.0
(8.8)
17.8
21.3
23.0
4.0
3.3
2.0
1.75
30×30×1.5mm
3
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
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
68μH
VIN
SWOUT
LA5774
C1
470μF
/50V
D1
SBD
C2
390μF
VOS
SS
C3
1μF
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+
×
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.
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)
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
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