ST1S14 STMicroelectronics, ST1S14 Datasheet - Page 21

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

ST1S14
7.1.2
Table 8.
In case the selected capacitor is ceramic (so neglecting the ESR contribution), the input
voltage ripple can be calculated as:
Equation 20
Output capacitor
The output capacitor is very important to meet the output voltage ripple requirement.
Using a small inductor value is useful to reduce the size of the choke but it increases the
current ripple. So, to reduce the output voltage ripple, a low ESR capacitor is required.
Nevertheless, the ESR of the output capacitor introduces a zero in the open loop gain,
which helps to increase the phase margin of the system. If the zero goes to a very high
frequency, its effect is negligible.
TAIYO YUDEN
Ceramic capacitors:
If available for the required value and voltage rating, these capacitors usually have a
higher RMS current rating for a given physical dimension (due to very low ESR).
The drawback is the considerably high cost.
Tantalum capacitors:
Small tantalum capacitors with very low ESR are becoming more available. However,
they can occasionally burn if subjected to very high current during charge.
Therefore, it is suggested to avoid this type of capacitor for the input filter of the device
as they could be stressed by an high surge current when connected to the power
supply.
Manufacturer
Ceramic capacitors
Ceramic capacitors and very low ESR capacitors that introduce a zero outside the
designed bandwidth (f
should be avoided. A leading network across the upper resistor of the voltage divider is
useful to increase the phase margin and compensate the system (see
Voltage
voltage because the singularities becomes more split.
High ESR capacitors
The “high ESR capacitor” definition stands for a capacitor having an ESR value able to
introduce a zero into the designed system bandwidth, which can be, as a general rule,
up to f
MURATA
SW
List of ceramic capacitors for the ST1S14
divider). The effectiveness of the leading network increases at high output
/5 at maximum. Tantalum or electrolytic capacitors belongs to this group.
V
GRM42-2 X7R 475K 50
IN PP
UMK325BJ106MM-T
Z
=1/(2*pi*ESR*C
Doc ID 17977 Rev 1
=
Series
-----------------------
C
IN
I
O
⋅
f
SW
⋅
OUT
⎛
⎝
1
–
, see
D
--- -
η
⎞ D
⎠
Capacitor value (µ)
⋅
Chapter 6: Closing the
+
D
--- -
η
⋅
4.7
10
(
1 D
–
)
Application information
Rated voltage (V)
Chapter 6.3:
loop) in general
50
50
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