The LA5771MP is a separately-excited step-down switching regulator (3.3V).
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Features
•
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
Input voltage
Output current
SW pin application reverse voltage
Allowable power dissipation
Operating temperature
Storage temperature
Symbol
VIN max
IO max
Vsw
Pd max
Topr
Tstg
Mounted on the specified board *
Conditions
Ratings
30
3
-1
3.9
-30 to +125
-40 to +150
Unit
V
A
V
W
°C
°C
* Mounted on a specified board: 114.3mm×76.1mm×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
VIN
Symbol
Conditions
Ratings
5.5 to 28
Unit
V
Semiconductor Components Industries, LLC, 2013
August, 2013
13107 MS IM B8-8794 No.8273-1/5
LA5771MP
Electrical Characteristics
at Ta = 25°C
Parameter
Output 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
VO
η
f
ΔVOLINE
ΔVOLOAD
ΔVO/ΔTa
RREJ
IS
TSD
ΔTSD
Symbol
Conditions
min
VIN=15V, IO=1.0A
VIN=15V, IO=1.0A
VIN=15V, IO=1.0A
VIN=8 to 20V, IO=1.0A
VIN=15V, IO=0.5 to 1.5A
Designeed target value*
F=100 to 120Hz
VIN=15V
Designed target value*
Designed target value*
3.1
165
15
128
3.17
Ratings
typ
3.30
79
160
25
10
±0.5
45
192
80
30
max
3.43
V
%
kHz
mV
mV
mV/°C
dB
A
°C
°C
Unit
* Designed target value: No measurement made.
Package Dimensions
unit : mm (typ)
3275
4.5
Pd max - Ta
Mounted on a specified board:
114.3mm×76.1mm×1.6mm,
Copper foil ratio 60% FR4
1.3
Allowable power dissipation, Pd max - W
1.2
10.0
4.5
4.0
3.90
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
-30
(8.8)
9.9
(1.6)
1.7
0.9
0.4
4.5
1
5
SANYO : SMP5
1.5
0.2
2.7
0
20
40
60
80
100
120
140
160
Ambient temperature, Ta -
°C
ILA07131
Pin Assignment
VIN
SWOUT
GND
VOS
SS
No.8273-2/5
LA5771MP
Block Diagram
VIN 1
+
-
2 SWOUT
Reg.
OCP
OSC
Reset
Drive
Comp.
TSD
4 VOS
Amp.
VREF
5 SS
3 GND
Application Circuit Example
L1
VIN
SWOUT
LA5771MP
C1
VOS
SS
GND
D1
C2
C1: 220μF/35V
C2: 1000μF/6.3V
C3: 1μF/50V
D1: SBD
L1: 68μH
C3
Notes: C3 is for the soft start function. Delete C3 and keep the SS pin open when the soft function is not necessary.
No.8273-3/5
LA5771MP
Description of Functional Settings
1.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 is 0.62V(typ), the start delay time can be calculated
as follows:
ex. For setting at 1μF
C
×
V 1
μΑ ×
0
.
62V
=
Td
=
=
28.2ms
i
22
μΑ
2.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 is to be made,
for example, the PWM-ON duty has the value as shown below.
1.5V
0.62V
PWM wave
PWMduty
=
VOUT
=
23%
VIN - Vsat
+
VF
(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=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 strt
time is calculated as follows:
Tss
=
C
× Δ
VPWM
×
PWMduty C
×
0
.
88V
×
PWMduty
=
i
22
μ
A
1
μΑ ×
0
.
88V
×
0
.23
=
9.2ms
22
μ
A
For the set conditions of C=1μF and PWMduty=23%:
Tss
=
No.8273-4/5
LA5771MP
Timing Chart
VIN
SWOUT
VOUT
Td
Tss
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