STEF4S datasheet(10/22 Pages) STMICROELECTRONICS

10 / 22 page

Typical characteristics

STEF4S

10/22

DocID025259 Rev 2

The capacitance to be added to CSS pin can be also estimated by using the following

theoretical formula:

Equation 1

The above value is not valid if CSS is not connected. CSS is expressed in Farad and the time

in seconds.

A ceramic low leakage capacitor is suggested for this purpose. The formula is meant as a

theoretical support to choose the CSS capacitor and it does not take into account the

capacitor tolerance, temperature and process variations.

Figure 4. Startup time

5.3

UVLO and voltage clamp selection

The device can be used either on the 3.3 V or on the 5 V lines. The operating mode can be

selected through the VCP pin.

If this pin is set at high level (VCP > 2 V) the operating mode is 5 V. In this mode the UVLO

threshold is 3.6 V typical, the clamping voltage is set to 5.7 V.

If the VCP pin is pulled to low level (VCP < 0.4 V), the operating mode is 3.3 V. In this mode

the UVLO threshold is 2.3 V typical, the clamping voltage is set to 3.8 V.

5.4

Enable pin

The EN pin is used to turn on/off the device. The device is disabled when the EN pin voltage

is lower than 0.4 V, enabled if the EN pin voltage is higher than 2 V.

4.35

10 6

–

Tss

STEF4S 数据表(PDF) 10 Page - STMicroelectronics