a5975d STMicroelectronics, a5975d Datasheet - Page 42

• Manufacturer Part Number: a5975d
• Description: Up To 3 A Step-down Switching Regulator For Automotive Applications
• Manufacturer: STMicroelectronics

Application information
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Equation 47
MLCCs (multiple layer ceramic capacitor) with values in the range of 10 µF-22 µF and rated
voltages in the range of 10 V-25 V are available today at relatively low cost from many
manufacturers.
These capacitors have very low ESR values (a few mΩ) and are therefore occasionally used
for the output filter in order to reduce the voltage ripple and the overall size of the
application.
However, the zero given by the output capacitor falls outside the designed bandwidth and so
the system becomes unstable with the standard compensation network.
Figure 31
capacitors at the output (the optimum components value depends on the application). This
configuration introduces two zeros and a low frequency pole in the designed bandwidth and
so guarantees a proper phase margin.
Figure 31. MLCC compensation network circuit
shows the type III compensation network stabilizing the system with ceramic
f
Z ESR
Doc ID 018760 Rev 1
=
----------------------------------------------- -
2 π ESR C
f
⋅
LC
⋅
<
f
Z ESR
1
⋅
<
OUT
10 f
⋅
<
LC
bandwidth
A5975D