VIPER28LD datasheet(24/32 Pages) STMICROELECTRONICS

24 / 32 page

Operation descriptions

VIPER28

24/32

Doc ID 15028 Rev 5

7.12

Extra power management function (EPT)

Some applications need an extra power for a limited time window during which the converter

regulation has to be guaranteed. The extra power management function allows to design a

converter that can satisfy this request and is provided by the EPT pin, see

Table 8 on

page 8.

This function requires the use of a capacitor on EPT pin (CEPT) that is charged or

discharged by means of a 5 µA current cycle by cycle. When the drain current raises over

85% of Idlim value, see IDLIM_EPT (Table 8 on page 7), the current generator charges CEPT

while when the drain current is below IDLIM_EPT discharges the capacitor. If CEPT ‘s voltage

reaches the VEPT threshold (typical, 4 V), the converter is shut down.

After the converter shut down, the VDD voltage will drop below the VDD(ON) start up

threshold (typ. 14.5 V) and according to the auto restart operation

(see

Section 7.5 on page 17) the VDD pin voltage have to fall below the VDD(RESTART)

threshold (typical, 4.5 V) in order to charge again the VDD capacitor. Moreover the PWM

operation is enabled again only when the voltage on EPT pin, drop below the VEPT(RESTART)

(typical, 0.6 V). The low CEPT discharge current in combination with its low restart threshold,

ensures safe operations and avoids overheating in case of repeated overload events. The

value of CEPT has to be selected in order to prevent the device overheating. The EPT pin

can be connected to GND if the function is not used.

VIPER28LD 数据表(PDF) 24 Page - STMicroelectronics