VIPER20B datasheet(14/17 Pages) STMICROELECTRONICS

14 / 17 page

schematic to be adapted depending the specific

needs. If the proposed schematic is used, the

pulse duration must be kept at a low value (500ns

is sufficient) for minimizing consumption. The

optocoupler must be able to provide 20mA

through the optotransistor.

PRIMARY PEAK CURRENT LIMITATION

The primary IDPEAK current and, as resulting

effect, the output power can be limited using the

simple circuit shown in figure 18. The circuit

based on Q1, R1 and R2 clamps the voltage on

the COMP pin in order to limit the primary peak

current of the device to a value:

IDPEAK

VCOMP

− 0.5

HID

where:

VCOMP

= 0.6 x

+ R2

The suggested value for R1+R2 is in the range of

220K

Ω.

OVER-TEMPERATURE PROTECTION:

Over-temperature protection is based on chip

temperature sensing. The minimum junction

temperature at which over-temperature cut-out

occurs is 140

oC while the typical value is 160oC.

The device is automatically restarted when the

junction temperature decreases to the restart

temperature threshold that is typically 34

oC below

the shutdown value (see figure 6).

Figure 16: Slope Compensation

13V

OSC

COMP

SOURCE

DRAIN

VDD

VIPer

FC00462

13V

OSC

COMP

SOURCE

DRAIN

VDD

VIPer

F C00452

Figure 15: Typical Compensation Network

13V

OSC

COMP SOURCE

DRAIN

VDD

VIPer

10 k

Ω

FC00 472

Figure 17:External Clock Synchronization

Figure 18:Current Limitation Circuit Example

13V

OSC

COMP SOURCE

DRAIN

VDD

VIPer

FC 00 482

VIPer20B / VIPer20BSP

14/17

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