VIPER17LN データシートの表示（PDF） - STMicroelectronics

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VIPER17LN

Off-line high voltage converters

STMicroelectronics 

VIPER17

Operation descriptions

7.9

About CONT pin

Referring to the Figure 27, 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 Table 9 on page 21 referring to the Figure 27, lists the external resistance combinations

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

Figure 27. CONT pin configuration

Daux

Rov p

CONT

Auxiliary

winding

Rlim

SOFT

START

OVP DETECTION

LOGIC

Curr. Lim.

BLOCK

Current LOimCPit Comparator

To PWM Logic

From SenseFET

To OVP Protection

7.10

Table 9. CONT pin configurations

Function / component

IDlim reduction

OVP

RLIM (1)

See Figure 8

≥ 80 KΩ

IDlim reduction + OVP

1. RLIM have to be fixed before RFF and ROVP

See Figure 8

ROVP

No

See Equation 4

See Equation 4

DAUX

No

Yes

Yes

Feed-back and over load protection (OLP)

The VIPER17 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 28 on

page 23 and Figure 29 show the internal current mode structure.

With the feedback pin voltage between VFBbm and VFBlin, (respectively 0.5 V and 3.3 V,

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

off of the power MOSFET. The drain current is always limited to IDLIM value.

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

higher than VFBlin the drain current is limited or to the default IDLIM value or the one imposed

21/33

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