Application information

AN1882

18/30

Doc ID 10209 Rev 4

5.1.4

As it is shown in the

Section 3.2 the system stability can be studied with the loop transfer

function given by the

Equation 3Equation 3. If the output capacitor is a ceramic type the zero

due to the ESR generally will be out of the system bandwidth, so the stability of the system

will be ensured by the cancellation between the pole due to the output capacitor and the

Equation 15

Equation 16

The higher is the bandwidth, the faster will be the transient response but the bandwidth (and

poles as mentioned in the

Section 3.2. The zero due to the compensation network must be

Equation 17

ESR zero is in the system bandwidth and it can be used to stabilize the system so the zero

function).

5.2

Losses and efficiency

There are losses affecting the efficiency of the application. Some of these losses are related

to the device and others are related to the external components. The most important losses

are listed below.

5.2.1

Conduction losses

These losses are basically due to the not negligible resistances of the internal switches and

the external inductor. Usually the current ripple across the inductor is negligible and so to

estimate the conduction losses of the inductor, the average output current can be

considered. The conduction losses of the switches depend also on the duty cycle of the

losses are:

G

LOOP s

()

g

sC

2

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

=

R

1

2

πf

g

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

=

C

3

5

2

πf

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

500pF

=

=