DocID023949 Rev 2

11/19

AN4209

General design procedure

2

General design procedure

This section presents general design guidelines. Figure 8 shows a simplified schematic

where an STRVS device is inserted between the noisy source and the vulnerable device to

protect it against repetitive transient surges.

Figure 8. Basic STRVS protection circuit

2.1

Key Rules

To ensure that absolute ratings are not exceeded, designers have to evaluate the worst

case conditions in the application to select the suitable device. The three criteria shown in

Table 2 are required:

2.2

Transil selection process

This proposed methodology is based on a systematic approach to match the general case

study. The device selection uses a recursive process. Steps are described below:

Noisy

source

t

Device

under

test

Protection

Table 2. Basic design criteria

Criteria

Application conditions

Device parameter

1

Be invisible under operating voltage

(standby). Leakage current should

have no effect on normal circuit

performance

Maximum operating

voltage,

Stand-off voltage

2

Protect device against repetitive

electrical overstress by instantly

clamping spike voltages to a

nondestructive level.

Voltage protection,

Clamping voltage

3

Maintain the junction temperature

within specifications to guarantee a

high reliability. This point must be

obeyed in transient and steady state

working mode.

Repetitive current,

Power dissipation,