参数资料
型号: LA5744MP
元件分类: 稳压器
英文描述: 3.1 A SWITCHING REGULATOR, 360 kHz SWITCHING FREQ-MAX, PSSO5
封装: SMP-5
文件页数: 4/5页
文件大小: 73K
代理商: LA5744MP
LA5744MP
No.A0587-4/5
Protection Circuit Functional Descriptions
1. Overcurrent protection function
The overcurrent protection function detects, on a cycle-by-cycle basis, the output transistor current and turns off that
output transistor current if it exceeds 3.1A.
2. Short circuit protection function
This IC prevents the current from increasing when the outputs are shorted by setting the switching frequency to 30kHz
if the VOS pin voltage falls below 0.8V.
Note 3 : If the soft start function is not used, the IC will start up with the overcurrent protection function operating. At this
time, the switching frequency will be cut in half. This means that the switching frequency will be 15kHz at
startup.
Note 4 : Since the switching frequency becomes 30kHz when the VOS pin voltage falls under 0.8V, the current capacity is
reduced. If a load is applied with the VOS pin voltage over 0.8V, the inductance value operates at 22H. If a load
is to be applied when this voltage is under 0.8V, the inductance value must be increased.
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 1.23V (typ).
The equation to set the output voltage is as follows :
The VOS pin has the inrush current of 1A (typ). Therefore, the error becomes larger when R1 and R2 resistance
values are large.
2. Startup Delay Function
The output voltage rises when the internal voltage reaches 0.4V (typical). Until that point, a capacitor is charged from
an internal 10
A (typical) constant-current supply. The startup delay time can be calculated as shown below
Example : Assume a 1
F capacitor is used.
VO = 1+
× 1.23V(typ)
R2
R1
Td =
=
= 40 ms
C
× V
i
1
F × 0.4
10
A
Limit current
Inductor current
SWOUT voltage
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