L5983TR STMicroelectronics, L5983TR Datasheet - Page 11

• Manufacturer Part Number: L5983TR
• Description: IC REG SW 1.5A STEPDOWN 8-VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5983TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 18 V
• Current - Output: 1.5A
• Frequency - Switching: 250kHz ~ 1MHz
• Voltage - Input: 2.9 ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-VFQFN, 8-VFQFPN
• Power - Output: 1.5W
• For Use With: 497-6386 - BOARD EVAL FOR L5983
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6860-2; L5983TR

L5983
4.2
Soft-start
The soft-start is essential to assure correct and safe startup of the step-down converter. It
avoids inrush current surge and makes the output voltage increase 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, 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 7.
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 R1 and R2 is the resistor
Doc ID 13005 Rev 7
SR
OUT
SS
=
TIME
SR
Figure
VREF
=
32 64
-----------------
Fsw
7). The soft-start staircase consists of 64
⋅
⋅
⎛
⎝
1
+
R1
------- -
R2
⎞
⎠
TIME
is 8 ms.
Functional description
REF
) of the error
11/43