AN628 APPLICATION NOTE

14/35

The voltage open loop gain contains two poles in the origin, then stability problem can arise. Connecting the

sured.

Pin 14. VFEED (Error amplifier input). This pin (see fig. 16), connected to the boosted output voltage through a

To be considered that the R1, togheter with the feedback network(see pin 13 description) define the E/A gain.

The R1/Rr ratio affects the load regulation (lower output current increases the output voltage) with the following

relation:

The R1 and R2 will be chosen in the high precision class:

Pin 15. P-UVLO (Programmable supply undervoltage threshold). An internal divider (between pin 19, pin 15 and

ground) and an internal comparator with a threshold voltage of 1.28V fixes the default turn-on and turn-off 15.5V

supply threshold, is useful know (see fig. 17), the typical resistor value, useful to design the external divider, are:

R1 = 394k, R2 = 88k and R3 = 58k. Anyway, in fig. 17a/b a diagram with threshold values and a table, useful

For DISABLE function see Appendix B.

G

pw

P

O

X

CO

⋅

V

O

V

ea

∆

⋅

--------------------------

G

pw

⇒

P

O

V

O

V

ea

∆

⋅

--------------------------

1

sC

O

⋅

---------------

⋅

==

f

c

P

O

V

O

V

ea

∆

2

π C

O

⋅⋅

⋅

--------------------------------------------------







1

2

π R1 C

r

⋅⋅

------------------------------





⋅

=

R

r

2.75

2

π f

c

C

r

⋅⋅

--------------------------

≤

R1

R2

--------

V

O

5.1V

------------

1

–

=

V

Omax

∆

V

ea

∆

R1

⋅

R

r

--------------------------

=