MC33215 데이터 시트보기 (PDF) - Motorola => Freescale

부품명

상세내역

일치하는 목록

MC33215

Telephone Line Interface and Speakerphone Circuit

Motorola => Freescale 

Freescale SMeCm3i3c2o15nductor, Inc.

Figure 11. Loudspeaker Amplifier Output

Power when Line Powered

100

90

RREG1 = 365 k

RREG2 = 220 k

80

RLSP = 25 Ω

RREG1 = 365 k

70

RREG2 = 220 k

60

RREG1 = 365 k RLSP = 50 Ω

RREG2 = Infinite

50 RLSP = 25 Ω

40 RREG1 = 365 k

30

RREG2 = Infinite

RLSP = 50 Ω

20

10

0

0

20

40

60

80

100

Iline (mA)

loudspeaker amplifier is muted which is needed for correct

handset operation.

The volume of the loudspeaker signal can be varied via a

potentiometer at VOL. A fixed current of 10 µA is running

through the potentiometer and the resulting voltage at VOL

is a measure for the gain reduction. The relation between

the voltage at VOL and the obtained gain reduction is given

in Figure 13.

Figure 13. Volume Reduction

0

–5.0

–10

–15

–20

The quality of the audio output of the loudspeaker amplifier

is mainly determined by the distortion level. To keep high

quality under difficult supply conditions, the MC33215

incorporates a peak–to–peak limiter. The peak–to–peak

limiter will detect when the output stage gets close to its

maximum output swing and will then reduce the gain from LSI

to LSF. The attack and release of the limiter is regulated by

the CPPL capacitor. Figure 12 depicts the limiter’s attack

behavior with CPPL = 100 nF. The release time is given as

3 x CPPL x RPPL. In the typical application this leads to a

release time of 300 ms.

Figure 12. Peak–to–Peak Limiter Dynamic Behavior

–25

–30

–35

–40

0

100

200

300

400

500

VVOL (mV), dALSP (dB)

It can be seen from Figure 13 that a linear variation of

RVOL will give a logarithmic gain reduction which adapts

better to the human ear than a linear gain reduction.

During DTMF dialing, see Table 2, a confidence tone is

audible at the loudspeaker of which the level is proportional

to the feedback resistor RLSF only. At RLSF = 180 kΩ the gain

from MFI to LSO equals 28.5 dB.

VLSO

VPPL

Vin

0

1.0

2.0

3.0

4.0

5.0

6.0

t, TIME (ms)

Figure 12 clearly shows that due to the action of the

peak–to–peak limiter, the output swing and thus the output

power is reduced with respect to the maximum possible as

already indicated in Figure 10. The peak–to–peak limiter can

be disabled by connecting the PPL pin to ground.

On top of the peak–to–peak limiter, the MC33215

incorporates a supply limiter, which reduces the gain rapidly

when the supply voltage VLS drops too much. This will

avoid malfunctioning of the amplifier and unwanted

oscillations. The voltage drop is detected via the BVO input

and for that reason the CBVO has to be connected to VLS

and not to Gnd.

The amplifier can be activated by making Pin LSM high. In

the typical application this pin is connected to SPS, which

activates the loudspeaker amplifier automatically when the

speakerphone mode is entered. When LSM is made low, the

Half Duplex Controller

To avoid howling during speakerphone operation, a half

duplex controller is incorporated. By monitoring the signals in

both the transmit and receive channel the duplex controller

will reduce the gain in the channel containing the smallest

signal. A typical gain reduction will be between 40 dB and

52 dB depending on the setting, see below. In case of equal

signal levels or by detection of noise only, the circuit goes into

idle mode. In this mode the gain reduction in both channels is

halfway, leading to 20 dB to 26 dB of reduction.

In a speakerphone built around the MC33215, following

the signal path from base microphone to the line and via

sidetone, loudspeaker and acoustic coupling back to the

microphone, the loop gain can be expressed as a sum of the

gains of the different stages. However, since the transmit and

receive gains are dependent on AGC and the sidetone

suppression is dependent on matching with the different lines

we are mostly interested by the maximum possible loop gain

ALOOP(max). It follows:

ALOOP(max) = ABMRX(max) + ARXBM(max) – ASWD (dB)

With: ABMRX(max) = Maximum gain from BM1 and BM2 to

RXI as a function of line length AGC and line

impedance matching

ARXBM(max) = Maximum gain from RXI to BM1 and

BM2 as a function of line length AGC and acoustic

coupling

14

For More Information On This ProdMuOcTtO, ROLA ANALOG IC DEVICE DATA

Go to: www.freescale.com

Share Link: