AN1707 datasheet(4/5 Pages) STMICROELECTRONICS

4 / 5 page

AN1707

UVLO Start Up

4/5

UVLO START UP

The UVLO startup feature requires an off-line

voltage, together with a resistor, to be connected

to the Vcc pin, as shown in

Figure 1 on page 1.

The Vcc waveform at startup is shown in

Figure 7.

You should study the charging and discharging

time of the C1 capacitor time in order to choose

the optimum value of C1 for your application. The

C1 value should insure a sufficient discharge

delay time to avoid reaching the UVLOL voltage

value (8.2 V) which would turn off the circuit

before the first current pulses arrive.

Fig. 6: VSUP and VCAP dynamic behavior

Fig. 7: UVLO Start Up and Ivsup

C1 and C2 charging time

C1 and C2 dicharging time

Vcc = 13V RMS (DC)

C1 and C2 charging time

C1 and C2 dicharging time

Vcc = 13V RMS (DC)

Ivsup

on Vcap

UVLOH = 14.1V

UVLOL = 8.2V

VCC

Vtpron = 13.15V

Vtproff = 12.85V

Choise of C1 for the

minimum margin

in order to guarantee

the circuit ON state

Ivsup

on Vcap

UVLOH = 14.1V

UVLOL = 8.2V

VCC

Vtpron = 13.15V

Vtproff = 12.85V

Choise of C1 for the

minimum margin

in order to guarantee

the circuit ON state

Ivsup

on Vcap

UVLOH = 14.1V

UVLOL = 8.2V

VCC

Vtpron = 13.15V

Vtproff = 12.85V

Choise of C1 for the

minimum margin

in order to guarantee

the circuit ON state

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