MT91610AQ Zarlink Semiconductor, MT91610AQ Datasheet - Page 4

• Manufacturer Part Number: MT91610AQ
• Description: Description = Short Loop Subscriber Line Interface Circuit (SLIC) With 2-4 Wire Conversion, Programmable Line Impedance, Ringing Amplification And On-hook Transmission For Did ;; Package Type = Qsop ;; No. Of Pins = 36
• Manufacturer: Zarlink Semiconductor

MT91610
Impedance Programming
The MT91610 allows the designer to set the device’s
impedance across TIP and RING, (Z
network balance impedance, (Z
external low cost components.
The impedance (Z
network balance, (Z
4.)
The
calculated once the 2W - 4W gain has been set.
Line Impedance
For
impedance of the line, (Z
impedance across TIP and RING, (Z
match. Therefore:
Z
The relationship between Z
that set Z
Z
where kZ
The value of k can be set by the designer to be any
value between 500 and 2000. R4 and R5 should be
greater than 100k
Network Balance Impedance
The network balance impedance, (Z
transhybrid loss performance for the circuit. The
transhybrid loss of the circuit depends on both the 4 -
2 Wire gain and the 2 - 4 Wire gain.
The method of setting the values for R6 (or Z6... it
can be a complex impedance) is given as below:
R6 = R7 * (R9 / R10) * 2.2446689 * ( Z
Please note that in the case of Z
(the THL compromized case) R6 is a complex
impedance. In the general case of Z
Z
resistor.
4
o
o
NB
= Z
/ ( Ra+Rb) = kZ
(the THL optimised case), R6 is just a single
optimum
TR
network
Ra = Rb
o
TR
= R5
is given by the formula:
balance
performance,
o
TR
NB
/ R4
) is set by R4, R5, while the
), is set by R6, R8, (see Figure
impedance
o
o
), and the device’s
and the components
NB
the
o
), separately with
not equal to Z
NB
NB
o
characteristic
), will set the
TR
should
matched to
/ Z
), should
TR
NB
), and
+ Z
be
NB
o
)
Loop Supervision
The Loop Supervision circuit monitors the state of
the phone line and when the phone goes “Off Hook"
the SHK pin goes high to indicate this state. This pin
reverts to a low state when the phone goes back "On
Hook" or if the loop resistance is too high (>2.3K )
When loop disconnect dialling is being used, SHK
pulses to logic 0 indicate the digits being dialled.
This output should be debounced.
Constant Current Control & Voltage
Fold Over Mode
The SLIC employs a feedback circuit to supply a
constant feed current to the line. This design is
accomplished by sensing the sum of the voltages
across the feed resistors, Ra and Rb, and comparing
it to the input reference voltage, Vref, that
determines the constant current feed current.
By using a resistive divider network, (Figure 3), it is
possible to generate the required voltage to set the
loop current, I
using the following formula:
I
where,
From Figure 3 with Ra = Rb = 100
For I
For I
For I
LOOP
LOOP
LOOP
LOOP
= [V
** See Figure 6
G = R2 / (R1 + R2)
I
R1= 200K
R2
**k
(Ra +Rb)
LOOP
= 20mA, R2 = 72.73 K
= 25mA, R2 = 100 K
= 30mA, R2 = 133.33 K
DD
Figure 3 - Loop Setting
* G] * 3
LOOP
is in Ampere.
. This voltage can be calculated
C2
0.47uF
Preliminary Information
R1
200K
+5V
6
V
MT91610
REF