MAS9191A datasheet(18/36 Pages) MAS

18 / 36 page

DA9191A.000

July 31, 1997

FUNCTIONS

The signal is fed to the SC-type audio expander with

expansion ratio 1:2. The expander can also be

bypassed with switch S5. The switch is controlled

with bit S5 in register 03HEX. After switch S5 the

signal goes to the EXPOUT output pin. An external

capacitor is used to connect the signal to the

RAUDIN input and to filter F6. Filter F6 is a 4th order

SC-type lowpass filter. The gain at 1kHz is 0dB. After

filtering the signal and the external accessory input

EINR can be summed with switch S8. The control bit

for the switch is in register 03HEX. The summed signal

is amplified with GC2, which has a -15dB...+15dB

gain with 16 steps. The gain is controlled with bits

0..3 in register 03HEX. The amplified signal can be

summed with SIDETONE. The side tone can be

switched on with S9, which has a control bit in

Amp with feedback signal SIDEFB. The gain of the

Op Amp is controlled by external components.

COMPIN is normally used as an input for the side

tone amplifier circuit.

Filter F7 is a second order low pass filter. The cutoff

frequency is 20kHz and the gain at 1kHz is 0dB.

After filtering the signal can be connected to three

amplifiers with switches M1, S10 and S11. The

control bits are located in registers 02HEX and 03HEX.

A4 is the earphone amplifier, which is a single input

differential output amplifier.

Amplifier A5 is for

external accessories and is capable of driving a

capacitive load. The load capacitance is 1nF and the

block has a 4.82dB gain. The third amplifier A3 is a

buzzer driver. It drives the signal to the power

transistor, which drives the buzzer. The buzzer

represents a high inductive load of 1.2mH/25ohm.

The block stabilizes the current flow through the

external buzzer which depends on the current gain

factor of the external bipolar transistor. The emitter

resistor of the transistor must be 6.8 ohms. Three

current values (peak values) can be chosen with

switch M1:10mA, 66mA and 160mA. The tolerance

of the external resistor will directly affect the buzzer

current. The RX audio block can be set into power

down mode together with the TX audio block. The

AUDIOP bit in

purpose. The blocks are in power down mode after a

reset.

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