External components list for L3235

To set the SLIC into operation the following parameters have to be defined:

- The AC SLIC impedance at line terminals ”Zs” to which the return loss measurements is referred. It can

be real (typ. 600

Ω) or complex.

- The equivalent AC impedance of the line ”Zl” used for evaluation of the trans-hybrid loss performance

(2/4 wire conversion). It is usually a complex impedance.

- The value of the two protection resistors Rp in series with the line termination.

Once, the above parameters are defined, it is possible to calculate all the external components using the

following table. The typical values has been obtained supposing: Zs = 600

Ω; Zl = 600Ω;Rp = 50Ω

Name

Suggested Value

Function

Formula

39K

Ω

390nF

Delay Time

On-hook Off-hook

(1)

39K

Ω

390nF

Delay Time

GK Detector

51K

Ω

Bias Set

8.4K

Ω to 33KΩ

Ext. Current Limit. Progr.

564

− 3mA

CR

4.7

µF

6.3 V 30%

Negative Battery

Filter

1

2

50

Protection Resistors

Ω (2)

1M

Ω 20%

Termination Resistor

100

µF

6.3V 20%

DC/AC current feedback splitting

1

2

2500

Ω 1%

12500

Ω 1%

2W AC Impedance programmation

220pF 20%

AC Feedback compensation

f1 = 300KHz

1

2

12500

Ω 1%

Slic Impedance Balancing Net.

2500

Ω 1%

RAS = 25

ZB

Line impedance Balancing Net.

⋅ Zl

220pF 20%

⋅

4.7

µF 30%

DC Decoupling Tx Output

1

6.28

D1, D2

1N4007

Line Rectifier

Text

(3)

External Transistor

100nF

±5V supply filter

100nF/100V

Notes:

1) For proper operation Cf should be selected in order to verify the following conditions:

A) cf > 150nF

B)

Ω.

3) ex: BD140; MJE172; MJE350.... (SOT32 or SOT82 package available also for surface mount). For low power application (reduced battery

voltage) BCP53 (SOT223 surface mount package) can be used. Depending on application enviroment an heatsink could be necessary.

L3234 - L3235

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