A5975AD datasheet(42/50 Pages) STMICROELECTRONICS

42 / 50 page

Application information

A5975AD

42/50

Doc ID 018761 Rev 1

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 m

Ω) 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 shows the type III compensation network stabilizing the system with ceramic

capacitors at the output (the optimum components value depends on the application). This

configuration introduces two zeroes and a low frequency pole in the designed bandwidth

and so guarantees a proper phase margin.

Figure 31.

MLCC compensation network circuit

Z ESR

π ESR C

OUT

⋅⋅

⋅

------------------------------------------------

bandwidth

Z ESR

10 f

⋅

A5975AD Fiches technique(PDF) 42 Page - STMicroelectronics