L9305A datasheet(4/6 Pages) STMICROELECTRONICS

4 / 6 page

APPLICATION INFORMATIONS (refer to application circuit)

D1 and D2 diodes are required only for reverse po-

larity protection.

If VS may be higher than VZS a resistor RS is neces-

sary to limit the zener current IZS. In order to deter-

mine RS value the following equations can be used :

VS MAX –VD1 –VZS min

< IZS MAX

2) VS min –VD1 –RS –ISON MAX >VST min

where from Tamb =25

°C:

-VSMAX and VSmin are the maximum and minimum

values of power supply voltage

-VD1 is the forward diode D1 voltage drop

-VZS min =20 V

-IZS MAX = 30 mA for d.c. mode and IZS MAX =80 mA

for pulsed mode (see Absolute maximum ratings)

-ISOM MAX =30 mA

-VST min = 3.5 V

If no RS value can satisfy the system 1), 2) a more

powerfull external zener DZ = 18 V is required.

Then 1) becomes :

VS MAX –VD1 –18

<IDZ MAX

where IDZ MAX is the maximum allowed DZ current.

VA voltage cannot be higher than 20 V otherwise

output overvoltage protection may be activated.

Morever VA must be less than 16 V if short circuit

protection is required.

DZ2 = 22 to 24 V is a mandatory for output 7 protec-

tion if VS may be higher than 26 V.

MOUNTING INSTRUCTION

The L9305A is assembled in a new plastic package,

the Powerdip, in which 8 pins (from 9 to 16) are at-

tached to the frame and remover the heat produced

by the chip.

Figure 2 and 3 show two ways of heatsinking. In the

first case, a PC board copper area is used as a

heatsink I = 65 mm. While in the second case, the

device is soldered to an external heatsink. In both

examples, the thermal resistance junction-ambient

is 35

°C/W.

Figure 2 : Example of Heatsink Using PC Board

Copper (I = 65 mm).

Figure 3 : Example of an External Heatsink.

L9305A

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