參數(shù)資料
型號(hào): L5980TR
廠商: 意法半導(dǎo)體
英文描述: 0.7A step-down switching regulator
中文描述: 0.7A的降壓開關(guān)穩(wěn)壓器
文件頁(yè)數(shù): 10/37頁(yè)
文件大?。?/td> 959K
代理商: L5980TR
Functional description
L5980
10/37
4.2
Soft-start
The soft-start is essential to assure correct and safe start up of the step-down converter. It
avoids inrush current surge and makes the output voltage increases monothonically.
The soft -start is performed by a staircase ramp on the non-inverting input (V
REF
) of the
Error Amplifier. So the output voltage slew rate is:
Equation 1
where SR
VREF
is the slew rate of the non-inverting input and R1, R2 is the resistor divider to
regulate the output voltage (see
Figure 7
). The soft-start stair case consists of 64 steps of
9.5mV each one, from 0V to 0.6V. The time base of one step is of 32 clock cycles. So the
soft start time and then the output voltage slew rate depend on the switching frequency.
Figure 7.
Soft start scheme.
Soft start time results:
Equation 2
For example with a switching frequency of 250kHz the SS
TIME
is 8ms.
SR
OUT
SR
VREF
1
R2
-------
+
=
SS
TIME
Fsw
-----------------
=
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