L7986TA STMicroelectronics, L7986TA Datasheet - Page 11

• Manufacturer Part Number: L7986TA
• Description: 3A step-down switching regulator
• Manufacturer: STMicroelectronics

Specifications of L7986TA

• Low Dropout Operation: 100% duty cycle

L7986TA
5.2
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
Amplifier. So the output voltage slew rate is:
Equation 1
where SR
divider to regulate the output voltage (see
steps of 9.5 mV each one, from 0 V to 0.6 V. 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 6.
Soft-start time results:
Equation 2
For example with a switching frequency of 250 kHz the SS
VREF
Soft-start scheme.
is the slew rate of the non-inverting input, while R1and R2 is the resistor
Doc ID 022098 Rev 1
SR
OUT
SS
=
TIME
SR
Figure
VREF
=
32 64
-----------------
Fsw
6). The soft-start stair case consists of 64
⋅
⋅
⎛
⎝
1
+
R1
------- -
R2
⎞
⎠
TIME
is 8 ms.
Functional description
REF
) of the Error
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