AN3115

Component selection guidelines

Doc ID 16830 Rev 3

17/28

The selection of the TVS diode must be based on the maximum peak power dissipation that

the diode is capable of supporting.

Select the TVS diode which is capable of supporting the required Ipp (A) value indicated in

Table 8

.

2.5

DC-DC output capacitors (C3, C4, C6) and ferrite bead

An electrolytic low cost capacitor is needed on the DC-DC converter output stage (C3 in

Figure 6

). Moreover, two ceramic capacitors are recommended to reduce the high

frequency switching noise. The switching noise is due to the voltage spikes of the fast

switching action of the output switch, and to the parasitic inductance of the output

capacitors. To minimize these voltage spikes, special low-inductance ceramic capacitors

can be used, and their lead lengths must be kept short and as close as possible to the IC

pins (C4 and C6 in Figure 9). In case of high switching noise, it is possible to increase the

C6 capacitor up to 4.7 µF, 2.2 µF is a good compromise to reduce the switching noise.

Figure 8.

Example of LNBTVS diode connection

D2

VoRX

EXTM

LNBH23L

C10

VoTX

C15

R9

D3

1N4007

D6

LNBTVSx -22xx

IF Connector

Lseries >13nH

D2

C10

R9

D2

VoRX

EXTM

LNBH23L

C10

VoTX

C15

R9

D3

1N4007

D6

LNBTVSx -22xx

IF Connector

Lseries >13nH

D2

C10

R9

Table 8.

Recommended LNBTVS

Vendor

Part number

Ipp (A)

8/20 µs

STMicroelectronics

LNBTVS4-220S

23.1

334

LNBTVS4-221S

23.1

334

LNBTVS4-222S

23.1

334

LNBTVS6-221S

23.1

500