VIPER28

Operation descriptions

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7.9

About CONT pin

Referring to the Figure 23, through the CONT PIN, the below features can be implemented:

1.

Current Limit set point

2.

Over-voltage protection on the converter output voltage

The Table9 on page21 referring to the Figure 23, lists the external resistance combinations

needed to activate one or plus of the CONT pin functions.

Figure 23. CONT pin configuration

7.10

Feed-back and overload protection (OLP)

The VIPER28 is a current mode converter: the feedback pin controls the PWM operation,

controls the burst mode and actives the overload protection of the device. Figure 24 on

page 23 and Figure 25 show the internal current mode structure.

typical values) the drain current is sensed and converted in voltage that is applied to the non

inverting pin of the PWM comparator.

This voltage is compared with the one on the feedback pin through a voltage divider on

cycle by cycle basis. When these two voltages are equal, the PWM logic orders the switch

In case of overload the feedback pin increases in reaction to this event and when it goes

comparator is disabled.

Table 9.

CONT pin configurations

Function / component

See Figure 6

No

No

OVP

≥ 80 KΩ

See Equation 4

Yes

See Figure 6

See Equation 4

Yes

Current Limit Comparator

To OVP Protection

Rov p

SOFT

START

CONT

Daux

Rlim

From SenseFET

Auxiliary

winding

To PWM Logic

OVP DETECTION

LOGIC

Curr. Lim.

BLOCK

OCP