MT91610 Просмотр технического описания (PDF) - Mitel Networks

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MT91610

Analog Ringing SLIC

Mitel Networks 

Preliminary Information

MT91610

As +5V is used as the reference voltage to generate

the loop current, any noise on the +5V rail will

deteriorate the PSR (Power Supply Rejection)

parameter of the SLIC. It is therefore important to

decouple +5V to GND. A 0.1uF cap at Vref pin (pin6)

is recommended.

The MT91610 operating current mode is

recommended to be between 20mA and 30mA. The

device will automatically switch to voltage hold over

mode should an unexpected long loop situation

occur for a given programmed loop current. The

lowest operational current should be 16mA with

VBAT set at -48V. A typical Operating Current versus

Loop Resistance with VBAT at -48V is shown in

Figure 7.

UD & Line Drivers Overcurrent

Protection

The Line Drivers control the external Battery Feed

circuit which provide power to the line and allows bi-

directional audio transmission.

The loop supervision circuitry provides bias to the

line drivers to feed a constant current. Overcurrent

protection is done by the following steps:

(A) External bipolar transistors to limit the current of

the NPN drivers to 50mA (Figure 5).

(B) The local controller should monitor the

Unbalance Detection output (UD) for any extended

period of assertion (>5 seconds). In such case the

controller should power down the device by asserting

the PD pin, and polls the device every 5 seconds.

The UD output can be used to support GND START

LOOP in a PaBX operation.

Please note that this UD output should be

disregarded and masked out if RC pin is active (ie

set to +5V).

Powering Up / Down Sequence

AGND is always connected

Powering Up: +5V, -5V, VBAT

PD to +5V for 100ms; PD to 0V

Powering Down: VBAT, -5V, +5V

Balanced Ringing & Automatic Ring

Tripping

Balanced Ringing is applied to the line by setting the

RC to +5V (pin 25) and connecting ringing signal

(20Hz) to RV (pin 35) as shown in Figure 4. A

1.2Vrms input will give approximately about 60Vrms

output across Tip and Ring, sufficient for short loop

SLIC application. The SLIC is capable of detecting

an Off Hook condition during ringing by filtering out

the large A.C. component. A 0.47uF cap should be

connected to pin CP6 (pin 29) to form such filter.

This filter allows a true Off Hook condition to be

monitored at pin SHK (pin 33). When an Off Hook

condition is detected by the SLIC, it will remove the

20Hz AC ringing voltage and revert to constant

current mode. The local controller will, however, still

need to deselect RC (set it to 0V).

The MT91610 supports short burst of ringing

cadence. A deglitching input (CP7) is provided to

ensure that the SHK pin is glitch free during the

assertion and de-assertion of RC. A 33nF cap

should be connected at this pin to GND.

A positive voltage source is required to be

connected to the pin DCRI (Figure 5) for normal

Ringing generation. The SLIC can perform ringing

even with the DCRI input connected to 0V. However,

it does require the VBAT to be lower than -48V (ie at

-53V or lower) and the 20Hz AC input should be a

square wave at 2Vrms.

Line Reversal

The MT91610 can deliver Line Reversal, which is

required in operation such as ANI, by simply setting

LR (pin 7) to +5V. The device transmission

parameters will cease during the reversal. The LR

(pin 7) should be set to 0V for all normal loop

operations.

Power Down And Wake Up

The MT91610 should normally be powered down to

conserve energy by setting the PD pin to +5V. The

SHK pin will be asserted if the equipment side (2

wire) goes off hook. The local controller should then

restore power to the SLIC for normal operations by

setting the PD pin to 0V.

Please note that there will be a short break (about

80ms) in the assertion time of SHK due to the time

required for the loop to power up and loop current to

flow. The local controller should be able to mask out

this time fairly easily.

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