TEA7092 datasheet(51/57 Pages) STMICROELECTRONICS

51 / 57 page

RL1

SRL

SW1

Figure 67

VI - RINGER FEATURES (continued)

VI.3 - Ring Frequency Generator

The ring frequency values which can be generated

are those given Page 45 of this application note.

On the Table given at Page 45, only the frequency

values for n > 15 are given, the frequency values

from n = 1 (1000000) to n = 15 (1001111) are also

accessible, if it is neccessary to generate a fre-

quency higher than 1645Hz.

VI.4 - Output Power Optimization

The power available on Pin LSOUT (Pin 44) de-

pends on :

- The country requires :

• Minimum input ac level in test conditions.

• Ring impedance.

Taking in account these main requests the power

on Pin LSOUT (Pin 44) is optimized through the

resistor R40 connected on Pin RCO (Pin 41).

- The yield of the switch mode power supply.

The principal parameters which influence the

yield are :

• D7 VBE value.

• T1 VCEsat and base current values (the maxi-

mum IC PEAK value is 100mA).

• L1 serial resistor value.

• Current consumption on Pin VZP (Pin 38) and

on Pin RSU (Pin 40).

• Bias current consumption on Pin VLS

This paragraph gives information on :

- The switch mode power supply concept.

- The switch mode power supply yield.

- The ring output power optimization on Pin LSOUT

(Pin 44).

VI.4.1 - Switch Mode Power Supply Concept

After the ring bridge, the switch mode power supply

concept is represented in Figure 67.

Input voltage equivalent to VRING1

VE1

Input voltage after the switch SW1

Mean input current

Output voltage at Pin VLS (Pin 1)

Mean output current

Voltage across D7 when it is in

forward mode

IE0

Primary bias current

IS0

Secondary bias current

RL1

Resistive part of the coil L1

Switch SW1

- VCEsat of T1 PNP

-IB1, T1 base current

-tD, T1 desaturation time

-VE1 =VE -VCEsat(T1)

Figure 68 gives the voltage,VE1, the current in the

coil, ISELF, the current in D7, IDIODE and the current

in the switch SW1 given by C6, ICAPA.

The value of the maximum current in the coil is fixed

by tON and tOFF depends on RL. When RL de-

creases, tON increases. The coil value should be

calculated so that the current in the coil reaches the

zero value with the minimum charge.

IMax.

= tON

⋅

VE1

− VLS

(1)

L is the value of the coil L1.

The ratio between tON and tOFF is :

tON

tOFF

+ VLS

VE1

− VLS

(2)

The output current IS is :

IMax.

⋅

tON

+ tOFF

(3)

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