SL1062A datasheet(3/9 Pages) SLS

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SL1062A

System Logic

Semiconductor

SLS

Vref

internally

generated

temperature

compensated reference voltage of 3.7 V and R9 is an

external resistor connected between SLPE and VEE.

In normal use the value of R9 would be 20

Ω.

Changing the value of R9 will also affect microphone

gain, DTMF gain, gain control characteristics,

sidetone level, maximum output swing on LN and the

DC characteristics (especially at the lower voltages).

Under

normal

conditions,

when

ISLPE>>ICC + 0.5 mA + Ip, the static behaviour of the

circuit is that of a 3.7 V regulator diode with an

internal resistance equal to that of R9. In the audio

frequency range the dynamic impedance is largely

determined by R1. Fig.2 shows the equivalent

impedance of the circuit.

Leq = C3 x R9 x RP

RP = 16.2 K

Ω

Figure 2. Equivalent impedance circuit

At line currents below 9mA the internal reference

voltage is automatically adjusted to a lower value

(typically 1.6 V at 1 mA) This means that more sets

can be operated in parallel with DC line voltages

(excluding the polarity guard) down to an absolute

minimum voltage of 1.6 V.

At line currents below 9 mA the circuit has limited

sending and receiving levels. The internal reference

voltage can be adjusted by means of an external

resistor (RVA). This resistor when connected between

LN and REG will decrease the internal reference

voltage and when connected between REG and SLPE

will increase the internal reference voltage.

Microphone inputs MIC+ and MIC- and gain pins

GAS1 and GAS2

The circuit has symmetrical microphone inputs. Its

input impedance is 64 K

Ω (2 x32 KΩ) and its voltage

gain is typically 52 dB (when R7 = 68 K

Ω, see

Figure 3).

Dynamic,

magnetic,

piezo-electric

electret (with built-in FET source followers) can be

used.

The gain of the microphone amplifier can be adjusted

between 44 dB and 52 dB to suit the sensitivity of

the transducer in use. The gain is proportional to the

value of R7 which is connected between GAS1 and

GAS2.

Stability is ensured by two external capacitors, C6

connected between GAS1 and SLPE and C8

connected between GAS1 and VEE. The value of C6

is 100 pF but this may be increased to obtain a first-

order low-pass filter. The value of C8 is 10 limes the

value of C6. The cut-off frequency corresponds to

the time constant R7 x C6.

Input MUTE

When MUTE is LOW or open circuit, the DTMF

input is enabled and the microphone and receiving

amplifier inputs are inhibited. The reverse is true

when MUTE is HIGH, MUTE switching causes only

negligible clicking on the line and earpiece output. If

the number of parallel sets in use causes a drop in

line current to below 6 mA the DTMF amplifier

becomes active independent to the DC level applied

to the MUTE input.

Dial-tone multi-frequency input DTMF

When the DTMF input is enabled dialling tones may

be sent on to the line. The voltage gain from DTMF

to LN is typically 25.5 dB (when R7 = 68 K

Ω) and

varies with R7 in the same way as the microphone

gain. The signalling tones can be heard in the

earpiece at a low level (confidence tone).

Receiving amplifier IR, QR and GAR

The receiving amplifier has one input (IR) and a non-

inverting output (QR). The IR to QR gain is typically

31 dB (when R4 = 100 K

Ω). It can be adjusted

between 20 and 31 dB to match the sensitivity of the

transducer in use. The gain is set with the value of

R4 which is connected between GAR and QR. The

overall receive gain, between LN and QR, is

calculated by subtracting the anti-sidetone netwo rk

attenuation (32 dB) from the amplifier gain. Two

external capacitors, C4 and C7, ensure stability. C4 is

normally 100 pF and C7 is 10 times the value of C4.

The value of C4 may be increased to obtain a first-

order low-pass filter. The cut-off frequency will

depend on the time constant R4 x C4.

The output voltage of the receiving amplifier is

specified for continuous-wave drive. The maximum

output

voltage

will

higher

under

speech

conditions where the peak to RMS ratio is higher.

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