ST1S14 STMicroelectronics, ST1S14 Datasheet - Page 9

• Manufacturer Part Number: ST1S14
• Description: Up to 3 A step down switching regulator
• Manufacturer: STMicroelectronics

ST1S14
4.1
4.2
4.3
Power supply and voltage reference
The internal regulator circuit consists of a start-up circuit, an internal voltage pre-regulator,
the bandgap voltage reference and the bias block that provides current to all the blocks. The
starter supplies the start-up current to the entire device when the input voltage goes high
and the device is enabled (inhibit pin connected to ground). The pre-regulator block supplies
the bandgap cell with a pre-regulated voltage that has a very low supply voltage noise
sensitivity.
Voltages monitor
An internal block continuously senses the V
good, the regulator begins operating. There is also a hysteresis on the V
Figure 4.
Soft Start
The startup phase minimizes the inrush current and decreases the stress of the power
components at the power up. The startup takes place when V
threshold.
As shown in
Phase 1: [V
Phase 2: [VFB>300 mV & n
Phase 3: [VFB>300 mV & n
The output capacitor is charged with a typical peak inductor current equal to 1.45 A and
the nominal f
A internal counter determines phase 2 time (see
The reference of the error amplifier is ramped in 44 steps (one step every 64 clks).
A low pass filter smooths each step to minimize output discontinuity. Considering the
typical 850 kHz switching frequency, the phase two duration is 3.3 msec
The reference of the embedded error amplifier is connected to the nominal reference
voltage (1.222 typical) derived from the internal bandgap generator. The soft start
phase ends at this time.
FB
Internal circuit
Figure
<300 mV]
SW
5, the soft start event is composed of three main phases:
is divided by 5
COUNT
COUNT
Doc ID 17977 Rev 1
<2816 clks]
=2816 clks]
cc
, V
ref
and V
Figure
bg
. If the monitored voltages are
5).
IN
crosses the selected UVLO
Functional description
CC
(UVLO).
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