AN3011 datasheet(31/37 Pages) STMICROELECTRONICS

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AN3011

Efficiency

Doc ID 16043 Rev 1

31/37

Except for the no-load condition, the variation with load and line is very low ([6.731 V; 6.786

V],

ΔV

OUT_OVP = 55 mV less then 1% of variation); including the values in the no-load

condition ([6.731 V; 7.035 V],

ΔV

OUT_OVP = 304 mV less then 5% of variation).

Considering a 10% precision of the OVP threshold in the CONT pin ([2.7 V; 3.3 V]), using as

ROVP and RLIM 1% precision resistances and with a turn ratio between the secondary and

auxiliary windings which has a precision of 5%, and considering a large production, it is

possible to fix the output overvoltage at 25% over the nominal output voltage, making sure

that the OVP protection is not erroneously activated.

It is possible to not implement this protection, if it is not necessary, by not mounting the D2

diode and the R14 resistor. Therefore if OVP protection is not required, the total number of

components can be reduced.

3.6

Brown-out protection

Brown-out protection is basically an unlatched device shutdown function with a typical use

of sensing mains undervoltage or the main unplug. The VIPer27 has a dedicated pin (BR,

pin 5) for this function, which must be connected to the DC HV bus. If protection is not

required, it can be disabled by connecting the pin to ground. In the converter presented

here, brown-out protection is implemented but can be disabled by changing the J7 jumper

setting (see schematic in Figure 2). The settings of the J7 jumper are shown in Figure 34

and 35. The converter's shutdown is accomplished by means of an internal comparator,

internally referenced to 450 mV (typ, VBRth), which disables the PWM if the voltage applied

at the BR pin is below the internal reference (as shown in Figure 36). PWM operation is re-

enabled as the BR pin voltage is more than 450 mV plus 50 mV of voltage hysteresis that

ensures noise immunity. The brown-out comparator is also provided with current hysteresis.

An internal 10 µA current generator is ON as long as the voltage applied at the brown-out

pin is below 450 mV and OFF if the voltage exceeds 450 mV plus the voltage hysteresis.

230

7.029

6.735

6.760

6.752

265

7.035

6.786

6.765

6.762

Table 21.

Overvoltage protection activation level test results (continued)

VOUT_OVP (V)

VIN

(VRMS)

Load

No-load

25% of load

Half-load (1.1 A)

Full-load

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