7/16

L6598

Figure 4. Soft Start and frequency shifting block

to a transconductance amplifier, as shown in fig. 4. Thus this voltage signal is converted in a growing current

start is equal to:

[1]

where

[2]

[3]

[4]

Since the second term of eq.1 is equal to zero, we have:

[5]

[6]

Css

Ifmin

Ifstart

Iss

gm

OSC

Iosc

I

osc

I

fmin

I

fstart

g

()

–

()

+

I

fmin

I

fstart

g

C

ss

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

t

–





+

==

I

fmin

R

fmin

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

I

fsart

,

R

fstart

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

V

REF

,

2V

==

=

()

+

1

R

fm in

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

1

R

fst art

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

+





==

I

()

I

fm in

V

REF

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

==

I

fst art

g

C

ss

-------------- T

SS

–

0T

SS

→

C

g

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

==

I

SS

I

fstart

K

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

T

SS

→

C

g

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

T

SS

→

C

ss

g

-----------

T

SS

k

–

→

==

=