Datasheet MC33215B, MC33215FB Datasheet (Motorola)

Device

Operating

Temperature Range

Package



ORDERING INFORMATION

MC33215FB
MC33215B

T

A

= –20° to +70°C

TQFP–52

SDIP–42

B SUFFIX

PLASTIC PACKAGE

CASE 858
(SDIP–42)

Order this document by MC33215/D

FB SUFFIX

PLASTIC PACKAGE

CASE 848B

(TQFP–52)

52

1

42

1

1

MOTOROLA ANALOG IC DEVICE DATA

 

   
 

The MC33215 is developed for use in fully electronic telephone sets with
speakerphone functions. The circuit performs the ac and dc line termination,
2–4 wire conversion, line length AGC and DTMF transmission. The
speakerphone part includes a half duplex controller with signal and noise
monitoring, base microphone and loudspeaker amplifiers and an efficient
supply. The circuit is designed to operate at low line currents down to 4.0 mA
enabling parallel operation with a classical telephone set.

• Highly Integrated Cost Effective Solution

• Straightforward AC and DC Parameter Adjustments

• Efficient Supply for Loudspeaker Amplifier and Peripherals

• Stabilized Supply Point for Handset Microphone

• Stabilized Supply Point for Base Microphone

• Loudspeaker Amplifier can be Powered and Used Separately

• Smooth Switch–Over from Handset to Speakerphone Operation

• Adjustable Switching Depth for Handsfree Operation

Simplified Application

This device contains 2782 active transistors.

Attenuator

DTMF

Attenuator

Duplex

Controller

Line

Driver

Current
Splitter

1:10

Handset

Microphone

Base

Microphone

V

CC

or

External Supply

Base Loudspeaker

Auxiliary Input

Handset Earpiece

Receive Signal

Telephone
Line

V

CC

Supply

DC Slope

Line Current

DC Offset

AC
Impedance

R

x

LS

BM

HM

MF

This document contains information on a new product. Specifications and information herein
are subject to change without notice.

 Motorola, Inc. 1997 Rev 0

MC33215

2

MOTOROLA ANALOG IC DEVICE DATA

FEATURES

Line Driver and Supply

• AC and DC Termination of Telephone Line

• Adjustable Set Impedance for Real and Complex

Termination

• Efficient Supply Point for Loudspeaker Amplifier and

Peripherals

• Two Stabilized Supply Points for Handset and Base

Microphones

• Separate Supply Arrangement for Handset and

Speakerphone Operation

Handset Operation

• Transmit and Receive Amplifiers

• Differential Microphone Inputs

• Sidetone Cancellation Network

• Line Length AGC

• Microphone and Earpiece Mute

• Separate Input for DTMF and Auxiliary Signals

• Parallel Operation Down to 4.0 mA of Line Current

Speakerphone Operation

• Handsfree Operation via Loudspeaker and Base
Microphone

• Integrated Microphone and Loudspeaker Amplifiers

• Differential Microphone Inputs

• Loudspeaker Amplifier can be Powered and Used

Separately from the Rest of the Circuit

• Integrated Switches for Smooth Switch–Over from
Handset to Speakerphone Operation

• Signal and Background Noise Monitoring in Both
Channels

• Adjustable Switching Depth for Handsfree Operation

•



Switch–Over

   

• Dial Tone Detector in the Receive Channel

TQFP–52

Figure 1. Pin Connections

1
2
3
4
5
6
7
8

9
10
11
12
13
14
15
16
17
18
19
20
21

42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22

1
2
3
4
5
6
7

8

9
10
11
12
13

14 15 16 17 18 19 20 21 22 23 24 25 26

39
38
37
36
35
34
33

32
31
30
29
28
27

52 51 50 49 48 47 46 45 44 43 42 41 40

SLB
REG
SLP
MFI
HM1
HM2

BM2
BM1
V

DD

TSA
TSE
TBN
MUT

LSF

BVO

PPL

LSI

VOL

SWD

REF

AGC

Gnd

RLS
RSA
RSE
RBN

SLB
REG

SLP
MFI
HM1
HM2
BM2

BM1
V

DD

TSA
TSE
TBN

MUT

V

CC

VLN
VHF
VMC

SPS
PRS

SWT
LSM

LSF

BVO

PPL

LSI

VOL

SWD

REF

AGC

Gnd

RLS

RSA
RSE
RBN

RXI

GRX
RXO
RXS

PGD

LSO

VLS
LSB

(Top View)

(Top View)

N/C

N/C

N/C

N/C

SPS

PRS

SWT

LSM

N/C

RXS

RXO

GRX

RXI

N/C

N/C

N/C

N/C

VMC

VHF

VLN

CC

N/C

PGD

LSO

VLS

LSB

V

SDIP–42

MC33215

3

MOTOROLA ANALOG IC DEVICE DATA

MAXIMUM RATINGS

Rating Min Max Unit

Peak Voltage at VLN –0.5 12 V
Maximum Loop Current – 160 mA
Voltage at VLS (if Powered Separately) –0.5 12 V
Voltage at VHF (if Externally Applied) –0.5 5.5 V
Voltage at SPS, MUT, PRS, LSM –0.5 7.5 V
Maximum Junction Temperature – 150 °C
Storage Temperature Range –65 150 °C

NOTE: ESD data available upon request.

RECOMMENDED OPERATING CONDITIONS

Characteristic Min Max Unit

Biasing Voltage at VLN 2.4 10 V
Loop Current 4.0 130 mA
Voltage at VLS 2.4 8.0 V
Voltage at VHF (if Externally Applied) 2.4 5.0 V
Voltage at SPS, MUT, PRS, LSM 0 5.0 V
Operating Ambient Temperature Range –20 70 °C

ELECTRICAL CHARACTERISTICS (All parameters are specified at T = 25°C, I

line

= 18 mA, VLS = 2.9 V, f = 1000 Hz,

PRS

= high, MUT = high, SPS = low, LSM = high, test figure in Figure 17 with S1 in position 1, unless otherwise stated.)

Characteristic

Min Typ Max Unit

DC LINE VOLTAGE

Line Voltage V

line

ÁÁÁÁ

V

Parallel Operation, I

line

= 4.0 mA – 2.4 –

I

line

= 20 mA

3.9

4.2

4.5

I

line

= 70 mA

4.8

ÁÁÁÁ

5.2

5.6

SUPPLY POINT V

DD

Internal Current Consumption from V

DD

–

ÁÁÁÁ

1.2

1.5

mA

VDD = 2.5 V

SUPPLY POINT VMC

DC Voltage at VMC (= VMC0)

1.6

ÁÁÁÁ

1.75

1.9

V

Current Available from VMC

1.0

ÁÁÁÁ

–

–

mA

VMC = VMC0 – 200 mV

SUPPLY POINT VHF

DC Voltage at VHF (= VHF0)

2.6

ÁÁÁÁ

2.8

3.0

V

Internal Current Consumption from VHF

–

ÁÁÁÁ

1.4

2.0

mA

VHF = VHF0 + 100 mV

Current Available from VHF

2.0

ÁÁÁÁ

–

–

mA

VHF = VHF0 – 300 mV

SUPPLY POINT V

CC

Current Available from V

CC

13

ÁÁÁÁ

15

–

mA

VCC = 2.4 V , I

line

= 20 mA

ÁÁÁÁ

DC Voltage Drop Between VLN and V

CC

–

ÁÁÁÁ

1.0

1.5

V

I

line

= 20 mA

ÁÁÁÁ

SUPPLY INPUT VLS

Internal Current Consumption from VLS

–

ÁÁÁÁ

1.0

1.5

mA

MC33215

4

MOTOROLA ANALOG IC DEVICE DATA

ELECTRICAL CHARACTERISTICS

(continued) (All parameters are specified at T = 25°C, I

line

= 18 mA, VLS = 2.9 V, f = 1000 Hz,

PRS

= high, MUT = high, SPS = low, LSM = high, test figure in Figure 17 with S1 in position 1, unless otherwise stated.)

Characteristic UnitMaxTypMin

LOGIC INPUTS

Logic Low Level Pins PRS, MUT, SPS, LSM – – 0.4 V
Logic High Level Pins PRS, MUT, SPS, LSM 2.0 – 5.0 V
Internal Pull Up Pins PRS, MUT, LSM – 100 – kΩ
Internal Pull Down Pin SPS

–

ÁÁÁÁ

100

–

kΩ

Tx CHANNEL, HANDSET MICROPHONE AMPLIFIER

Voltage Gain from VHM to V

line

46

ÁÁÁÁ

47

48

dB

VHM = 1.5 mVrms

Gain Reduction in Mute Condition

60

ÁÁÁÁ

–

–

dB

MUT = Low or PRS = Low or SPS = High

Input Impedance at HM1 and HM2

14

ÁÁÁÁ

18

22

kΩ

Common Mode Rejection Ratio

–

ÁÁÁÁ

50

–

dB

Total Harmonic Distortion at VLN

–

ÁÁÁÁ

–

2.0

%

VHM = 4.5 mVrms

Psophometrically Weighted Noise Level at V

line

–

ÁÁÁÁ

–72

–

dBmp

HM1 and HM2 Shorted with 200 Ω

Tx CHANNEL, BASE MICROPHONE AMPLIFIER (SPS = HIGH, Tx MODE FORCED)

Voltage Gain from VBM to V

line

53

ÁÁÁÁ

55.5

58

dB

VBM = 0.5 mVrms

БББББББББББББББББББ

Input Impedance at BM1 and BM2

ÁÁÁ

14

ÁÁÁÁ

ÁÁÁ18ÁÁ22ÁÁ

kΩ

БББББББББББББББББББ

Common Mode Rejection Ratio

ÁÁÁ

–

ÁÁÁÁ

ÁÁÁ50ÁÁ–ÁÁ

dB

Total Harmonic Distortion at VLN

–

ÁÁÁÁ

–

2.0

%

VBM = 1.5 mV

Psophometrically Weighted Noise Level at V

line

–

ÁÁÁÁ

–62

–

dBmp

BM1 and BM2 Shorted with 200 Ω

Gain Reduction in Mute Condition

60

–

–

dB

MUT = Low or PRS = Low or SPS = Low

Tx CHANNEL, DTMF AMPLIFIER (MUT = LOW OR PRS = LOW)

Voltage Gain from VMF to V

line

34

ÁÁÁÁ

35

36

dB

VMF = 7.5 mVrms

Input Impedance at MFI

14

ÁÁÁÁ

18

22

kΩ

Gain Reduction in Mute Condition

60

ÁÁÁÁ

–

–

dB

MUT = High or PRS = Low

Rx CHANNEL, EARPIECE AMPLIFIER

Voltage Gain from V

RXI

to V

EAR

(Note 1)

23

ÁÁÁÁ

24

25

dB

V

line

= 20 mVrms

Gain Reduction in Mute Condition

60

ÁÁÁÁ

–

–

dB

MUT = Low or SPS = Low

Input Impedance at RXI

24

ÁÁÁÁ

30

36

kΩ

Psophometrically Weighted Noise Level at V

EAR

–

ÁÁÁÁ

130

–

µVrms

RXI Shorted to Gnd via 10 µF

Confidence Level During DTMF Dialing

10

ÁÁÁÁ

15

20

mVrms

VMF = 7.5 mVrms, MUT = Low

Output Swing Capability into 150 Ω

680

ÁÁÁÁ

–

–

mVpp

THD ≤2%

Output Swing Capability into 450 Ω

1800

ÁÁÁÁ

–

–

mVpp

THD ≤2%, R

RXO

= 360 kΩ

NOTE: 1.Corresponding to –0.6 dB gain from the line to output RXO in the typical application.

MC33215

5

MOTOROLA ANALOG IC DEVICE DATA

ELECTRICAL CHARACTERISTICS (continued) (All parameters are specified at T = 25°C, I

line

= 18 mA, VLS = 2.9 V, f = 1000 Hz,

PRS

= high, MUT = high, SPS = low, LSM = high, test figure in Figure 17 with S1 in position 1, unless otherwise stated.)

Characteristic UnitMaxTypMin

Rx CHANNEL, LOUDSPEAKER PRE–AMPLIFIER (SPS = HIGH, Rx MODE FORCED)

Voltage Gain from V

RXI

to V

RLS

(Note 2)

21

ÁÁÁÁ

24

27

dB

V

line

= 20 mVrms

Gain Reduction in Mute Condition

60

ÁÁÁÁ

–

–

dB

SPS = Low or MUT = Low

Rx CHANNEL, LOUDSPEAKER AMPLIFIER

Voltage Gain from V

LSI

to V

LSP

25

ÁÁÁÁ

26

27

dB

V

LSI

= 10 mVrms

БББББББББББББББББББ

Attenuation at Delta R

VOL

= 47 kΩ

ÁÁÁ

–

ÁÁÁÁ

ÁÁÁ32ÁÁ–ÁÁ

dB

Psophometrically Weighted Noise Level at V

LSP

–

ÁÁÁÁ

1.2

–

mVrms

RXI Shorted to Gnd via 10 µF

Confidence Level During DTMF Dialing

150

ÁÁÁÁ

200

250

mVrms

VMF = 7.5 mVrms MUT = Low

Available Peak Current from LSO

110

ÁÁÁÁ

–

–

mApeak

Output Capability into 25 Ω

1.8

–

–

Vpp

THD ≤2%, V

LSI

= 55 mVrms

Output Capability into 25 Ω

2.7

ÁÁÁÁ

–

–

Vpp

THD ≤2%, V

LS

= 5.0 V, V

LSI

= 90 mVrms

Gain Reduction in Mute Condition

60

ÁÁÁÁ

–

–

dB

LSM = Low

Rx CHANNEL PEAK–TO–PEAK LIMITER

Peak–to–Peak Limiter Attack Time

–

ÁÁÁÁ

–

5.0

ms

V

LSI

Jumps from 40 mVrms to 120 mVrms

Peak–to–Peak Limiter Release Time

–

ÁÁÁÁ

300

–

ms

V

LSI

Jumps from 120 mVrms to 40 mVrms

THD at 10 dB Overdrive

–

ÁÁÁÁ

–

7.0

%

V

LSI

= 120 mVrms

Peak–to–Peak Limiter Disable Threshold at PPL

–

ÁÁÁÁ

–

0.1

V

AUTOMATIC GAIN CONTROL

Gain Reduction in Transmit and Receive Channel with Respect to I

line

= 18 mA

4.5

ÁÁÁÁ

6.0

7.5

dB

I

line

= 70 mA

БББББББББББББББББББ

Á

Gain Variation in Transmit and Receive Channel with Respect to I

line

=18 mA with

AGC Disabled (AGC to VDD)

ÁÁÁ

Á

–

ÁÁÁÁ

ÁÁÁ

Á

–

ÁÁ

Á

1.5

ÁÁ

Á

dB

Highest Line Current for Maximum Gain

–

20

–

mA

Lowest Line Current for Minimum Gain

–

50

–

mA

BALANCE RETURN LOSS

Balance Return Loss with Respect to 600 Ω

20

–

–

dB

SIDETONE

Voltage Gain from VHM to V

EAR

–

–

28

dB

S1 in Position 2

LOGARITHMIC AMPLIFIERS AND ENVELOPE DETECTORS

Voltage Gain from RXI to RSA

18

20

22

dB

V

RXI

= 15 mVrms

Voltage Gain from BMI to TSA

17.5

18.5

19.5

dB

VBM = 0.5 mVrms

Dynamic Range of Logarithmic Compression from TSA to TSE and RSA to RSE

40

–

–

dB

I

TSA

and I

RSA

from 2.5 µA to 250 µA

Envelope Tracking Between TSE and RSE and Between TBN and RBN

–

±3.0

–

dB

Maximum Source Current from TSE or RSE

0.3

0.4

0.5

µA

NOTE: 2.Corresponding to –0.6 dB gain from the line to output RLS in the typical application.

MC33215

6

MOTOROLA ANALOG IC DEVICE DATA

ELECTRICAL CHARACTERISTICS

(continued) (All parameters are specified at T = 25°C, I

line

= 18 mA, VLS = 2.9 V, f = 1000 Hz,

PRS

= high, MUT = high, SPS = low, LSM = high, test figure in Figure 17 with S1 in position 1, unless otherwise stated.)

Characteristic UnitMaxTypMin

LOGARITHMIC AMPLIFIERS AND ENVELOPE DETECTORS

Maximum Sink Current into TSE or RSE

100

–

–

µA

Maximum Sink Current into TBN and RBN

0.7

1.0

1.3

µA

Maximum Source Current from TBN or RBN

100

–

–

µA

Dial Tone Detector Threshold at V

line

–

20

–

mVrms

Speech Noise Threshold Both Channels

–

4.5

–

dB

ATTENUATOR CONTROL

Switching Depth

46

50

54

dB

Adjustable Range for Switching Depth

24

–

60

dB

Gain Variation in Idle Mode for Both Channels

–

25

–

dB

Current Sourced from SWT

7.0

10

13

µA

Tx Mode

Current Sunk into SWT

7.0

10

13

µA

Rx Mode

PIN FUNCTION DESCRIPTION

Pin

SDIP–42 TQFP–52

Name Description

1

47

V

CC

Supply Output for Loudspeaker Amplifier and Peripherals

2

48

VLN

Line Connection Input

3

49

VHF

Supply Output for Speakerphone Section and Base Microphone

4

50

VMC

Supply Output for Handset Microphone

–

51

N/C

Not Connected

–

52

N/C

Not Connected

5

1

SLB

SLP Buffered Output

6

2

REG

Regulation of Line Voltage Adjustment

7

3

SLP

DC Slope Adjustment

8

4

MFI

DTMF Input

9

5

HM1

Handset Microphone Input 1

10

6

HM2

Handset Microphone Input 2

11

7

BM2

Base Microphone Input 2

12

8

BM1

Base Microphone Input 1

13

9

V

DD

Supply Input for Speech Part

14

10

TSA

Transmit Sensitivity Adjustment

15

11

TSE

Transmit Signal Envelope Timing Adjustment

16

12

TBN

Transmit Background Noise Envelope Timing Adjustment

17 13 MUT Transmit and Receive Mute Input

–

14

N/C

Not Connected

–

15

N/C

Not Connected

18

16

SPS

Speakerphone Select Input
19 17 PRS Privacy Switch Input
20

18

SWT

Switch–Over Timing Adjustment
21 19 LSM Loudspeaker Mute Input

MC33215

7

MOTOROLA ANALOG IC DEVICE DATA

PIN FUNCTION DESCRIPTION (continued)

Pin

DescriptionName

SDIP–42 DescriptionNameTQFP–52

–

20

N/C

Not Connected
22

21

RXS

Receive Amplifier Stability
23

22

RXO

Receive Amplifier Output
24

23

GRX

Earpiece Amplifier Feedback Input
25

24

RXI

Receive Amplifier Input

–

25

N/C

Not Connected

–

26

N/C

Not Connected
26

27

RBN

Receive Background Noise Envelope Timing Adjustment
27

28

RSE

Receive Signal Envelope Timing Adjustment
28

29

RSA

Receive Sensitivity Adjustment
29

30

RLS

Receive Output for Loudspeaker Amplifier
30

31

Gnd

Small Signal Ground
31

32

AGC

Line Length AGC Adjustment
32

33

REF

Reference Current Set
33

34

SWD

Switching Depth Adjustment for Handsfree
34

35

VOL

Volume Control Adjustment
35

36

LSI

Loudspeaker Amplifier Input
36

37

PPL

Peak–to–Peak Limiter Timing Adjustment
37

38

BVO

Bias Voltage for Loudspeaker Amplifier Output
38

39

LSF

Loudspeaker Amplifier Feedback Input

–

40

N/C

Not Connected

–

41

N/C

Not Connected
39

42

LSB

Loudspeaker Amplifier Bootstrap Output
40

43

VLS

Supply Input for Loudspeaker Amplifier
41

44

LSO

Loudspeaker Amplifier Output
42

45

PGD

Power Ground

–

46

N/C

Not Connected

MC33215

8

MOTOROLA ANALOG IC DEVICE DATA

DESCRIPTION OF THE CIRCUIT

Based on the typical application circuit as given in
Figure 18, the MC33215 will be described in three parts: line
driver and supplies, handset operation, and handsfree
operation. The data used refer to typical data of the
characteristics.

LINE DRIVER AND SUPPLIES

The line driver and supply part performs the ac and dc
telephone line termination and provides the necessary
supply points.

AC Set Impedance

The ac set impedance of the telephone as created by the
line driver and its external components can be approximated
with the equivalent circuit shown in Figure 2.

Figure 2. Equivalent of the AC impedance

Inductor+R

REG1xCREG

x

R

SLP
11

Slope

+

R

SLP
11

xǒ1

)

R

REG1

R

REG2

Ǔ

C

VLN

10 n

C

VDD

100

µ

Z

VDD

620

Z

bal

R

SLB

2.2 k

R

REG

∞

R

REG1

360 k

C

REG

220 n

Slope

Inductor

With the component values of the typical application, the
inductor calculates as 1.6 H. Therefore, in the audio range of
300 Hz to 3400 Hz, the set impedance is mainly determined
by Z

VDD

. As a demonstration, the impedance matching or

Balance Return Loss BRL is shown in Figure 3.

100

40

BRL (dB)

f, FREQUENCY (Hz)

Figure 3. Balance Return Loss

35
30
25
20
15
10

5.0
0

1000 10000

The influence of the frequency dependent parasitic
components is seen for the lower frequencies (Inductor) and
the higher frequencies (C

VLN

) by a decreasing BRL value.

DC Set Impedance

The line current flowing towards the MC33215 application
is partly consumed by the circuitry connected to V

DD

while

the rest flows into Pin VLN. At Pin VLN, the current is split up

into a small part for biasing the internal line drive transistor
and into a large part for supplying the speakerphone. The
ratio between these two currents is fixed to 1:10. The dc set
impedance or dc setting of the telephone as created by the
line driver and its external components can be approximated
with the equivalent of a zener voltage plus a series resistor
according to:

V

zener

+

0.2 x

ǒ

1

)

R

REG1

R

REG2

Ǔ

)ǒ10 µAxR

REG1

Ǔ

ILN+I

line–IVDD

R

slope

+

R

SLP
11

xǒ1

)

R

REG1

R

REG2

Ǔ

With:

VLN+V

zener

)

ǒ

ILN x R

slope

Ǔ

If R

REG2

is not mounted, the term between the brackets

becomes equal to 1.

With the values shown in the typical application and under

the assumption that I

VDD

= 1.0 mA, the above formulas can

be simplified to:

VLN+3.8 V

)

ǒ

ǒ

I

line

–1.0mAǓx20

Ǔ

^

3.8 V

)ǒI

line

x20

Ǔ

In the typical application this leads to a line voltage of 4.2 V
at 20 mA of line current with a slope of 20 Ω. Adding a 1.5 V
voltage drop for the diode bridge and the interruptor, the dc
voltage at tip–ring will equal 5.7 V.

If the dc mask is to be adapted to a country specific
requirement, this can be done by adjusting the resistors
R

REG1

and R

REG2

, as a result, the zener voltage and the

slope are varied. It is not advised to change the resistor R

SLP

since this changes many parameters. The influence of R

REG1

and R

REG2

is shown in Figure 4.

Figure 4. Influence of R

REG1

and R

REG2

on the DC Mask

0

12

VLN (V)

I

line

(mA)

10

8.0

6.0

4.0

2.0

0

20 40 60 80 100

.

R

REG1

= 470 k

R

REG2

= 220 k

R

REG1

= 365 k

R

REG2

= 220 k

R

REG1

= 470 k

R

REG2

= Infinite

R

REG1

= 365 k

R

REG2

= Infinite

As can be seen in Figure 4, for low line currents below
10 mA, the given dc mask relations are no longer valid. This
is the result of an automatic decrease of the current drawn

MC33215

9

MOTOROLA ANALOG IC DEVICE DATA

from Pin REG by the internal circuit (the 10 µA term in the
formulas). This built–in feature drops the line voltage and
therefore enables parallel operation.

The voltage over the line driver has to be limited to 12 V to
protect the device. A zener of 11 V at VLN is therefore the
maximum advised.

V

DD

Supply

The internal circuitry for the line driver and handset
interface is powered via VDD. This pin may also be used to
power peripherals like a dialer or microcontroller. The voltage
at V

DD

is not internally regulated and is a direct result of the

line voltage setting and the current consumption at V

DD

internally (I

VDD

) and externally (I

PER

). It follows that:

VDD+

VLN –

ǒ

I

VDD

)

I

PER

Ǔ

xR

set

For correct operation, it must be ensured that VDD is
biased at 1.8 V higher than SLP. This translates to a
maximum allowable voltage drop across Z

VDD

of

V

zener

– 1.8 V. In the typical application, this results in a
maximum allowable current consumption by the peripherals
of 2.0 mA.

VMC Supply

At VMC, a stabilized voltage of 1.75 V is available for
powering the handset microphone. Due to this stabilized
supply, microphones with a low supply rejection can be used
which reduces system costs. In order to support the parallel
operation of the telephone set, the voltage at VMC will be
maintained even at very low line currents down to 4.0 mA.

Under normal supply conditions of line currents of 20 mA
and above, the supply VMC is able to deliver a guaranteed
minimum of 1.0 mA. However, for lower line currents, the
supply capability of VMC will decrease.

Figure 5. VMC Under Different Microphone Loads

0

1.8

VMC (V)

I

VMC

(mA)

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1.0

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

I

line

= 4.0 mA

2.7 k VMC–VHF

I

line

= 20 mA

I

line

= 4.0 mA

If, during parallel operation, a high current is required from
VMC, a 2.7 k resistor between VMC and VHF can be applied.
In Figure 5, the VMC voltage under different microphone
currents, is shown.

VHF Supply

VHF is a stabilized supply which powers the internal
duplex controller part of the MC33215, and which is also
meant to power the base microphone or other peripherals.
The base microphone however, can also be connected to
VMC, which is preferred in case of microphones with a poor
supply rejection. Another possibility is to create an additional
filter at VHF, like is shown in the typical application. The
supply capability of VHF is guaranteed as 2.0 mA for line
currents of 20 mA and greater.

Since in parallel operation not enough line current is
available to power a loudspeaker and thus having a
speakerphone working, the current internally supplied to VHF
is cut around 10 mA of line current to save current for the
handset operated part. A small hysteresis is built in to avoid
system oscillations.

When the current to VHF is cut, the voltage at VHF will
drop rapidly due to the internal consumption of 1.4 mA and
the consumption of the peripherals. When VHF drops below

2.0 V, the device internally switches to the handset mode,
neglecting the state of the speakerphone select Pin SPS.

In case an application contains a battery pack or if it is
mains supplied, speakerphone operation becomes possible
under all line current conditions. In order to avoid switch–over
to handset operation below the 10 mA, VHF has to be
supplied by this additional power source and preferably kept
above 2.4 V.

V

CC

Supply

At V

CC

the major part of the line current is available for
powering the loudspeaker amplifier and peripheral circuitry.
This supply pin should be looked at as a current source since
the voltage on V

CC

is not stabilized and depends on the
instantaneous line voltage and the current to and consumed
from V

CC

.

The maximum portion of the line current which is available

at V

CC

is given by the following relation:

I

VCC

+

ǒ

10
11

xǒI

line–IVDD

Ǔ

Ǔ

–I

VMC

–I

VHF

This formula is valid when the voltage drop from VLN to

V

CC

is sufficient for the current splitter to conduct all this

current to V

CC

. When the drop is not sufficient, the current
source saturates and the surplus of current is conducted to
the power ground PGD to avoid distortion in the line driver. In
fact, when no current is drawn from V

CC

, the voltage at V

CC

will increase until the current splitter is in balance. In Figure 6
this behavior is depicted.

MC33215

10

MOTOROLA ANALOG IC DEVICE DATA

A. Maximum Available Current at V

CC

Figure 6. Available Current at V

CC

0

100

I

line

(mA)

0

3.5

CC

VLN–V (V)

I

line

(mA)

90
80
70
60
50
40
30
20
10

0

20 40 60 80 100

3.0

2.5

2.0

1.5

1.0

0.5
0

20 40 60 80 100

B. Voltage Drop to V

CC

I

VCC/lline

(%)

I

VCC(max) (mA)

VCC to VLS

I

VCC

at 98% of

I

VCC(max)

I

VCC

at 50% of

I

VCC(max)

VCC Open

mA AND %

For instance, at a line current of 20 mA a maximum of

15 mA of current is available at V

CC

. If all this current is

taken, V

CC

will be 1.7 V below VLN. When not all this current

is drawn from V

CC

, but for instance only 1.0 mA for biasing of

the loudspeaker amplifier, the voltage at V

CC

will be 1.2 V
below VLN. Although the measurements for Figure 6 are
done with R

REG1

= 365 k, the results are also globally valid

for other dc settings.

As can be seen from Figure 6, the voltage at V

CC

is limited
by the voltage at VLN minus 1.0 V. This means that the
voltage at V

CC

is limited by the external zener at VLN. If it is

necessary to limit the voltage at V

CC

in order to protect

peripheral circuits, a zener from V

CC

to Gnd can be added. If

the supply of the loudspeaker VLS is also connected to V

CC

,

it is advisable that V

CC

does not exceed 8.0 V.

The high efficiency of the V

CC

power supply contributes
to a high loudspeaker output power at moderate line
currents. More details on this can be found in the handsfree
operation paragraph.

HANDSET OPERATION

During handset operation, the MC33215 performs the
basic telephone functions for the handset microphone and
earpiece. It also enables DTMF transmission.

Handset Microphone Amplifier

The handset microphone is to be capacitively connected
to the circuit via the differential input HM1 and HM2. The
microphone signal is amplified by the HMIC amplifier and
modulates the line current by the injection of the signal into
the line driver. This transfer from the microphone inputs to the
line current is given as 15/(R

SLP

/11), which makes a total

transmit voltage gain A

HM

from the handset microphone

inputs to the line of:

AHM+

V

line

V

HM

+

15

R

SLP

ń

11

x

Z

line

xZ

set

Z

line

)

Z

set

With the typical application and Z

line

= 600 Ω the transmit

gain calculates as 47 dB.

In case an electret microphone is used, it can be supplied
from the stabilized microphone supply point VMC of 1.75 V
properly biased with resistors R

HM1

and R

HM2

. This allows
the setmaker to use an electret microphone with poor supply
rejection to reduce total system costs. Since the transmit gain
A

HM

is fixed by the advised R

SLP

= 220 Ω and the constraints

of set impedance and line impedance, the transmit gain is set

by adjusting the sensitivity of the handset microphone by
adjusting the resistors R

HM1

and R

HM2

. It is not advised to
adjust the gain by including series resistors towards the Pins
HM1 and HM2.

A high pass filter is introduced by the coupling capacitors

C

HM1

and C

HM2

in combination with the input impedance. A
low pass filter can be created by putting capacitors in parallel
with the resistors R

HM1

and R

HM2

.

The transmit noise is measured as –72 dBmp with the
handset microphone inputs loaded with a capacitively
coupled 200 Ω. In a real life application, the inputs will be
loaded with a microphone powered by VMC. Although VMC
is a stablized supply voltage, it will contain some noise which
can be coupled to the handset microphone inputs, especially
when a microphone with a poor supply rejection is used. An
additional RC filter on VMC can improve the noise figure, see
also the base microphone section.

Handset Earpiece Amplifier

The handset earpiece is to be capacitively connected to
the RXO output. Here, the receive signal is available which is
amplified from the line via the sidetone network and the R

x

and EAR amplifiers. The sidetone network attenuates the
receive signal from the line via the resistor divider composed
of R

SLB

and Z

bal

, see also the sidetone section. The

attenuation in the typical application by this network equals

24.6 dB. Then the signal from the sidetone network is
pre–amplified by the amplifier R

x

with a typical gain of 6.0 dB.
This amplifier also performs the AGC and MUTE functions,
see the related paragraphs. Finally, the signal is amplified by
the noninverting voltage amplifier EAR. The overall receive
gain A

RX

from the line to the earpiece output then follows as:

ARX+

V

RXO

V

line

+

ASTxA

RXI

xǒ1

)

R

RXO

R

GRX

Ǔ

With: AST = Attenuation of the Sidetone Network

A

RXI

= Gain of the Pre–Amplifier R

x

For the typical application an overall gain from the line to

the earpiece is close to 0 dB.

The receive gain can be adjusted by adjusting the resistor

ratio R

RXO

over R

GRX

. However, R

RXO

also sets the

confidence tone level during dialing which leaves R

GRX

to be
chosen freely. A high pass filter is introduced by the coupling
capacitor C

RXI

together with the input impedance of the input

MC33215

11

MOTOROLA ANALOG IC DEVICE DATA

RXI. A second high pass filtering is introduced by the
combination of C

GRX

and R

GRX

. A low pass filter is created

by C

RXO

and R

RXO

. The coupling capacitor at the output
RXO is not used for setting a high pass filter but merely for dc
decoupling.

In combination with dynamic ear capsules, the EAR
amplifier can become unstable due to the highly inductive
characteristic of some of the capsules. To regain stability, a
100 nF capacitor can be connected from RXS to Gnd in
those cases. An additional 10 nF at the RXI input, as shown
in the typical application, improves the noise figure of the
receiver stage.

Sidetone Cancellation

The line driver and the receiver amplifier of the MC33215
are tied up in a bridge configuration as depicted in Figure 7.
This bridge configuration performs the so–called hybrid
function which, in the ideal case, prevents transmitted signals
from entering the receive channel.

Figure 7. Sidetone Bridge

VHMx15

R

SLP

ń

11

VLN

Z

line

//Z

set

SLP

R

SLP

/11

Gnd

Z

bal

R

SLB

Gnd

RXI
Receive

Transmit

As can be seen from Figure 7 by inspection, the receiver
will not pick up any transmit signal when the bridge is in
balance, that is to say when:

Z

bal

R

SLB

+

Z

line

ńń

Z

set

R

SLP

ń

11

The sidetone suppression is normally measured in an
acoustic way. The signal at the earpiece when applying a
signal on the microphone is compared with the signal at the
earpiece when applying a signal on the line. The suppression
takes into account the transmit and receive gains set. In fact
the sidetone suppression can be given as a purely electrical
parameter given by the properties of the sidetone bridge
itself. For the MC33215, this so–called electrical sidetone
suppression A

STE

can be given as:

A

STE

+

1–

Z

bal

R

SLB

x

R

SLP

ń

11

Z

line

ńń

Z

set

Values of –12 dB or better, thus A

STE

< 0.25, can easily be

reached in this way.

Automatic Gain Control

To obtain more or less constant signal levels for transmit
and receive regardless of the telephone line length, both the
transmit and receive gain can be varied as a function of line
current when the AGC feature is used. The gain reduction as
a function of line current, and thus line length, is depicted in
Figure 8.

0

0

AGC (dB)

I

line

(mA)

Figure 8. Automatic Gain Control

–1.0

–2.0

–3.0

–4.0

–5.0

–6.0

10 20 30 40 50 60 70

R

AGC

= 20 k

R

AGC

= 30 k

For small line currents, and thus long lines, no gain
reduction is applied and thus the transmit and receive gains
are at their maximum. For line currents higher than I

start

, the

gain is gradually reduced until a line current I

stop

is reached.
This should be the equivalent of a very short line, and the
gain reduction equals 6.0 dB. For higher line currents the
gain is not reduced further. For the start and stop currents the
following relations are valid:

I

stop

+

1

R

SLP

ń

11

I

start

+

1

R

SLP

ń

11

–

20 µ xR

AGC

R

SLP

ń

11

For the typical application, where R

AGC

= 30 kΩ, the gain

will start to be reduced at I

start

= 20 mA while reaching 6.0 dB

of gain reduction at I

stop

= 50 mA. When AGC is connected to

V

DD

, the AGC function is disabled leading to no gain
reduction for any line current. This is also sometimes called
PABX mode.

The automatic gain control takes effect in the HMIC and R

x

amplifiers as well as in the BMIC amplifier. In this way the
AGC is also active in speakerphone mode, see the handsfree
operation paragraph.

Privacy and DTMF Mode

During handset operation a privacy and a DTMF mode can

be entered according the logic Table 1.

Table 1. Logic Table for Handset Mode

Logic Inputs

Amplifiers

SPS MUT PRS

Mode

HMIC BMIC DTMF R

x

RX

att

EAR

0

1

1

Handset Normal

On

Off

Off

On

Off

On

0

1

0

Handset Privacy

Off

Off

On

On

Off

On

0

0

X

Handset DTMF

Off

Off

On

Off

Off

On

MC33215

12

MOTOROLA ANALOG IC DEVICE DATA

Table 2. Logic Table for Handsfree Mode

Logic Inputs

Amplifiers

SPS MUT PRS

Mode

HMIC BMIC DTMF R

x

RX

att

EAR

1

1

1

Handsfree Normal

Off

On

Off

On

On

Off

1

1

0

Handsfree Privacy

Off

Off

On

On

On

Off

1

0

X

Handsfree DTMF

Off

Off

On

Off

On

Off

By applying a logic 0 to Pin MUT, the DTMF mode is
entered where the DTMF amplifier is enabled and where the
R

x

amplifier is muted. A DTMF signal can be sent to the line

via the MFI input for which the gain A

DTMF

is given as:

A

DTMF

+

V

line

V

MFI

+

3.75

R

SLP

ń

11

x

Z

line

xZ

set

Z

line

)

Z

set

In the typical application, the gain equals 35 dB. The
DTMF gain can be controlled by a resistor divider at the input
MFI as shown in the typical application. The signal has to be
capacitively coupled to the input via C

MFI

which creates a
high pass filter with the input impedance. The line length
AGC has no effect on the DTMF gains.

The signal applied to the MFI input is made audible at the
earpiece output for confidence tone. The signal is internally
applied to the GRX pin where it is amplified via the EAR
amplifier which is used as a current to voltage amplifier. The
gain is therefore proportional to the feedback resistor R

RXO

.

For R

RXO

= 180 kΩ the gain equals 6.0 dB. The confidence
tone is also audible at the loudspeaker output when the
loudspeaker amplifier is activated, see speakerphone
operation.

By applying a logic 0 to Pin PRS

, the MC33215 enters
privacy mode. In this mode, both handset and handsfree
microphone amplifiers are muted while the DTMF amplifier is
enabled. Through the MFI input, a signal, for example music
on hold, can be sent to the line. In the same way, the MFI
input can also be used to couple in signals from, for instance,
an answering machine.

HANDSFREE OPERATION

Handsfree operation, including DTMF and Privacy modes,
can be performed by making Pin SPS high according T able 2.
The handset amplifiers will be switched off while the base
amplifiers will be activated. The MC33215 performs all the
necessary functions, such as signal monitoring and
switch–over, under supervision of the duplex controller.

With the MC33215 also a group listening–in application
can be built. For more information on this subject please refer
to application note AN1574.

Base Microphone Amplifier

The base microphone can be capacitively connected to
the circuit via the differential input BM1 and BM2. The setup
is identical to the one for the handset microphone amplifier.
The total transmit voltage gain A

BM

from the base

microphone inputs to the line is:

ABM+

V

line

V

BM

+

37.5

R

SLP

ń

11

x

Z

line

xZ

set

Z

line

)

Z

set

With the typical application and Z

line

= 600 Ω the transmit

gain calculates as 55 dB.

The electret base microphone can be supplied directly
from VHF but it is advised to use an additional RC filter to
obtain a stable supply point, as shown in the typical
application. The microphone can also be supplied by VMC.
The transmit gain is set by adjusting the sensitivity of the
base microphone by adjusting the resistors R

BM1

and R

BM2

.
It is not advised to adjust the gain by including series
resistors towards the Pins BM1 and BM2.

A high pass filter is introduced by the coupling capacitors

C

BM1

and C

BM2

in combination with the input impedance. A
low pass filter can be created by putting capacitors in parallel
with the resistors R

BM1

and R

BM2

.

Loudspeaker Amplifier

The loudspeaker amplifier of the MC33215 has three major
benefits over most of the existing speakerphone loudspeaker
amplifiers: it can be supplied and used in a telephone line
powered application but also stand alone, it has an all NPN
bootstrap output stage which provides maximum output
swing under any supply condition, and it includes a
peak–to–peak limiter to limit the distortion at the output.

The loudspeaker amplifier is powered at Pin VLS. In
telephone line powered applications, this pin should be
connected to V

CC

where most of the line current is available,

see the V

CC

supply paragraph. In an application where an
external power supply is used, VLS and thus the loudspeaker
amplifier can be powered separately from the rest of the
circuit. The amplifier is grounded to PGD, which is the circuits
power ground shared by both the loudspeaker amplifier and
the current splitter of the V

CC

supply. Half the supply voltage
of VLS is at BVO, filtered with a capacitor to VLS. This
voltage is used as the reference for the output amplifier.

The receive signal present at RLS can be capacitively

coupled to LSI via the resistor R

LSI

. The overall gain from

RLS to LSO follows as:

ALS+

V

LSO

V

RLS

+

–

R

LSF

R

LSI

x4.0

In the typical application this leads to a loudspeaker gain

A

LS

of 26 dB. The above formula follows from the fact that the
overall amplifier architecture from RLS to LSO can be looked
at as an inverting voltage amplifier with an internal current
gain from LSI to LSF of 4. The input LSI is a signal current
summing node which allows other signals to be applied here.

MC33215

13

MOTOROLA ANALOG IC DEVICE DATA

Figure 9. Loudspeaker Output Stage

VLS

Loudspeaker

C

LSO

LSB

LSO

PGD

T2

T1

1.5 VLS
VLS

0.5 VLS

VLS

0.5 VLS
0

0.5 VLS
0

–0.5 VLS

VLS

Figure 10. Loudspeaker Amplifier Output Power with External Supply

2.0

140

P

LSP

(mW)

VLS (V)

2.0

300

R

LSP

= 25

Ω

R

LSP

= 50

Ω

R

LSP

= 25

Ω

R

LSP

= 50

Ω

P

LSP

(mW)

VLS (V)

120

250

100

200

80

150

60

100

20

50

0

0

3.0

4.0 3.0

5.0 4.0

6.0 5.0

7.0 6.08.0

7.0

8.0

40

A. Peak–to–Peak Limiter Active B. Peak–to–Peak Limiter Disabled

The total gain from the telephone line to the loudspeaker
output includes, besides the loudspeaker amplifier gain, also
the attenuation of the sidetone network and the internal gain
from RXI to RLS. When in receive mode, see under duplex
controller, the gain from RXI to RLS is maximum and equals
24 dB at maximum volume setting. The attenuation of the
sidetone network in the typical application equals 24.6 dB
which makes an overall gain from line to loudspeaker of

25.4 dB. Due to the influence of the line length AGC on the R

x

amplifier, the gain will be reduced for higher line currents.

The output stage of the MC33215 is a modified all NPN
bootstrap stage which ensures maximum output swing under
all supply conditions. The major advantage of this type of
output stage over a standard rail–to–rail output is the higher
stability. The principle of the bootstrap output stage is
explained with the aid of Figure 9.

The output LSO is biased at half the supply VLS while the
filtering of the loudspeaker with the big capacitor C

LSO

requires that LSB is biased at VLS. In fact, because of the
filtering, LSB is kept at VLS/2 above the LSO output even if
LSO contains an ac signal. This allows the output transistor

T2 to be supplied for output signals with positive excursions
up to VLS without distorting the output signal. The resulting
ac signal over the loudspeaker will equal the signal at LSO.
As an indication of the high performance of this type of
amplifier, in Figure 10, the output power of the loudspeaker
amplifier as a function of supply voltage is depicted for 25 Ω
and 50 Ω loads with both the peak–to–peak limiter active and
disabled. As can be seen, in case the peak–to–peak limiter is
disabled, the output power is roughly increased with 6.0 dB,
this at the cost of increased distortion levels up to 30%.

In a telephone line powered application, the loudspeaker
amplifier output power is limited not only by the supply
voltage but also by the telephone line current. This means
that in telephones the use of 25 Ω or 50 Ω speakers is
preferred over the use of the cheaper 8.0 Ω types. Figure 11
gives the output power into the loudspeaker for a line
powered application and two different dc settings with the
peak–to–peak limiter active. In case the peak–to–peak limiter
is disabled the output power will be increased for the higher
line currents up to 6.0 dB.

MC33215

14

MOTOROLA ANALOG IC DEVICE DATA

0

100

P

LSP

(mW)

I

line

(mA)

R

REG1

= 365 k

R

REG2

= 220 k

R

LSP

= 25

Ω

Figure 11. Loudspeaker Amplifier Output

Power when Line Powered

R

REG1

= 365 k

R

REG2

= 220 k

R

LSP

= 50

Ω

R

REG1

= 365 k

R

REG2

= Infinite

R

LSP

= 50

Ω

R

REG1

= 365 k

R

REG2

= Infinite

R

LSP

= 25

Ω

20 40 60 80 100

90
80
70
60
50
40
30
20
10

0

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 C

PPL

capacitor. Figure 12 depicts the limiter’s attack

behavior with C

PPL

= 100 nF. The release time is given as

3 x C

PPL

x R

PPL

. In the typical application this leads to a

release time of 300 ms.

Figure 12. Peak–to–Peak Limiter Dynamic Behavior

0

0.5 V/DIV

t, TIME (ms)

V

LSO

V

PPL

V

in

1.0

2.0

3.0 4.0

5.0

6.0

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 C

BVO

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

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.

0

0

dA

LSP

(dB)

V

VOL

(mV), dA

LSP

(dB)

Figure 13. Volume Reduction

100 200 300 400 500

–5.0

–10
–15

–20
–25

–35

–30

–40

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

VOL

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 R

LSF

only . At R

LSF

= 180 kΩ the gain

from MFI to LSO equals 28.5 dB.

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
A

LOOP(max)

. It follows:

A

LOOP(max)

= A

BMRX(max)

+ A

RXBM(max)

– A

SWD

(dB)

With: A

BMRX(max)

= Maximum gain from BM1 and BM2 to
RXI as a function of line length AGC and line
impedance matching

A

RXBM(max)

= Maximum gain from RXI to BM1 and
BM2 as a function of line length AGC and acoustic
coupling

MC33215

15

MOTOROLA ANALOG IC DEVICE DATA

A

SWD

= Switching depth as performed in the

attenuators

To avoid howling, the maximum possible loop gain should
be below 0 dB and preferably below –10 dB for comfort. In a
practical telephone design, both the A

BMRX(max)

and the

A

RXBM(max)

will be less than 20 dB thus a switching depth of
50 dB will give a loop gain of less than –10 dB. An optimized
sidetone network is of high importance for handsfree
operation. The better the network matches with the
telephone line the less local feedback and the smaller the
switching range can be.

The amount of gain reduction A

SWD

obtained by the

duplex controller is set via resistor R

SWD

according:

A

SWD

+

20log

ǒ

3.6 x R

SWD

R

REF

Ǔ

2

(dB)

In the typical application the gain reduction will be 50 dB.

To compare the transmit and receive signals with each
other, they have to be monitored. This is done by making a
signal envelope and a background noise envelope via the
C

TSE

, C

TBN

capacitors for the transmit channel and via the

C

RSE

, C

RBN

capacitors for the receive channel. In Figure 14,
a schematic behavior of the envelopes is depicted which is
equal for both transmit and receive.

The voltage signal at the input is first transferred to a
current via the sensitivity adjust network. Then this current is
led through a diode which gives a logarithmic compression in
voltage. It is this voltage from which the signal envelope is
created by means of asymmetric charge and discharge of the
signal envelope capacitor. The noise envelope voltage then
follows in a similar way. Based on the envelope levels, the
MC33215 will switch to transmit, receive or idle mode
following Table 3. The fact that in receive mode the signal on
the base microphone is greater than it is in case of transmit

mode, due to the coupling of the high loudspeaker signal, is
automatically taken into account.

In the table, two particulars can be found. At first, the set
will go to idle mode if the signals are not at least 4.5 dB
greater then the noise floor, which calculates as a 13 mV
voltage difference in envelopes. This avoids continuous
switching over between the modes under slight variations of
the background noise due to, for instance, typing on a
keyboard. Second, a dial tone detector threshold is
implemented to avoid that the set goes to idle mode in
presence of a continuous strong receive signal like a dial
tone. The dial tone detector threshold is proportional to the
R

RSA

resistor. In the typical application with R

RSA

= 3.3 kΩ,
the threshold is at 1.26 mVrms at the input RXI or 20 mVrms
at the line. Line length AGC is of influence on the dial tone
detector threshold, increasing the level depending on the line
current with a maximum of 6.0 dB.

In order to perform a correct comparison between the
signal strengths, the sensitivity of the envelope detectors can
be adjusted via the resistors connected to TSA and RSA.
Based on the above, and on the fact that there is an effective
gain of 20 dB in the transmit monitor, it can be derived that for
stable operation the following two relations are valid:

20log

ǒ

R

TSA

Ǔ

t

20logǒR

RSA

Ǔ

–A

BMRX(max)

)

20 (dB)

20logǒR

TSA

Ǔ

u

20logǒR

RSA

Ǔ

–A

RXBM(max)

–ASW)

20 (dB)

By measuring the gains and choosing the R

RSA

, the limits

for R

TSA

follow. The choice for the sensitivity resistors is not
completely free. The logarithmic compressors and the
amplifier stages have a certain range of operation and, on the
receive side, the choice for R

RSA

is given by the desired dial
tone detector threshold. Figure 15 indicates the available
dynamic range for the selected value of the sensitivity
resistors.

Figure 14. Signal and Noise Envelopes

Microphone
Input Signal

1.8 V

Internal

TSA

R

TSA

C

TSA

TSE

C

TSE

C

TBN

TBN

VHF

VHF

MC33215

16

MOTOROLA ANALOG IC DEVICE DATA

Table 3. Logic Table for Switch–Over

TSE > RSE TSE > TBN + 13 mV RSE > V

DDT

RSE > RBN + 13 mV Mode

1

1

X

X

Transmit

1

0

X

X

Idle

0

X

1

X

Receive

0

X

0

1

Receive

0

X

0

0

Idle

The resistors for the sensitivity setting have to be coupled
capacitively to the pins for dc decoupling, and also to create
a high pass filter to suppress low frequent background noises
like footsteps and 50 Hz.

The switch–over timing is performed by charging and
discharging the C

SWT

capacitor. The switch–over from
transmit to receive or vice versa is fast, on the order of
milliseconds, and is proportional to the value of C

SWT

. The
switch–over to idle mode is slow, in the order of a few
seconds, and is proportional to the product of the values of
R

SWT

and C

SWT

. Figure 16 depicts a typical switch–over

behavior when applying transmit and receive stimuli.

The electrical characteristics and the behavior of the
MC33215 are not the only factor in designing a handsfree
speakerphone. During the design the acoustics have to be
taken into account from the beginning. The choice of the
transducers and the design of the cabinet are of great
influence on the speakerphone performance. Also, to
achieve a proper handsfree operation, the fine tuning of the
components around the duplex controller have to be done
with the final choice of the cabinet and the transducers.

Figure 15. Compression Range of the Signal Monitors

100

100.0E–3

V

RXI

(Vrms)

R

RSA

(Ω)

100

100.0E–3

R

TSA

(Ω)

A. Receive Monitor B. Transmit Monitor

Upper Limit of
Compression

Lower Limit of
Compression

Upper Limit of
Compression

Lower Limit of
Compression

V

BM1

(Vrms)

1000 100010000 10000100000 100000

10.0E–3

10.0E–3

1.0E–3

1.0E–3

100.0E–6

10.0E–6 100.0E–6

Dial Tone
Threshold

Figure 16. Switch–Over Behavior

Receive

Transmit

SWT

VMC – 0.5

VMC + 0.5

MC33215

17

MOTOROLA ANALOG IC DEVICE DATA

V

LSP

Figure 17. Test Circuit

Supply

Supply

1:10

V

DD

V

HM

V

BM

VHF

VLS

V

V

V

V

HM1

HM2

BM1

BM2

TSA

TSE

TBN

AGC

REF

SWD

VOL

RLS

BVO
VLS

LSB

LSO

PGD

LSF

T

x

Log–Amp

and
Envelope
Detectors

Analog
Control

Block

Peak

Limiter

Attenuator

Control

T

x

Attenuator

R

x

Attenuator

R

x

EAR

LSP

BMIC

HMIC

V

DD

VLN

V

RLS

Gnd

VMC

VHF

V

CC

SLB

SLP

MFI

SPS

MUT

PRS

LSM

SWT

RBN

RSE
RSA

RXI

RXO

GRX

RXSLSIPPL

R

x

Log–Amp

and Envelope

Detectors

Logic

Control

Block

DTMF

Driver

1x

MHM
MBM

MDF
MRX
MRA

M

EAR

AGC

AGC

AGC

MRA

MHM

MBM

MDF

M

EAR

AGC

REG

MRX

R

REG

360 k

I

line

Vac

V

line

Z

bal

33 k

R

SLB

2.2 k

Z

VDD

620

600

0.2 V

C

REG

220 n

C

VDD

100

µ

C

HM1

33 n

C

HM2

33 n

C

BM1

33 n

C

BM2

33 n

C

TSA

470 n

C

TSE

330 n

C

TBN

4.7

µ

R

TSA

2.2 k

R

AGC

30 k

R

REF

20 k

R

SWD

100 k

R

VOL

47 k

C

BVO

220 n

C

LSO

47

µ

R

LSO

180 k

25

C

LSI

47 n

R

LSI

36 k

V

LSI

R

GRX

24 k

R

RXO

180 k

C

GRX

47 n

V

EAR

V

RXI

C

EAR

10

µ

VHF

C

RXS

100 n

V

MF

V

SPS

V

MUT

V

PRS

V

LSM

V

SWT

C

RXI

47 n

R

RSA

3.3 k

C

RSA

470 n

C

RSE

330 n

C

RBN

4.7

µ

C

MF1

47 n

R

SLP

220

C

VCC

470

µ

C

VHF

47

µ

C

VMC

10

µ

R

PPL

1.0 M

C

PPL

100 n

MC33215

S1

2
1

MC33215

18

MOTOROLA ANALOG IC DEVICE DATA

Figure 18. Typical Application

Supply

Supply

1:10

V

DD

VHF

HM1

HM2

BM1

BM2

TSA

TSE

TBN

AGC

REF

SWD

VOL

RLS

BVO

VLS

LSB
LSO

PGD

LSF

T

x

Log–Amp

and Envelope

Detectors

Analog

Control

Block

Peak Limiter

Attenuator

Control

R

x

Attenuator

R

x

EAR

LSP

BMIC

HMIC

V

DD

VLNGnd

VMC

VHF

V

CC

SLB

SLP

MFI

SPS

MUT

PRS

LSM

SWT

RBN

RSE

RSA

RXI

RXO

GRX

RXSLSIPPL

Rx Log–Amp

and Envelope

Detectors

Logic Control

Block

DTMF

Driver

1x

MHM
MBM

MDF
MRX
MRA

M

EAR

AGC

AGC

AGC

MRA

MHM

MBM

MDF

M

EAR

AGC

REG

MRX

R

REG1

365 k

Z

bal

33 k

R

SLB

2.2 k

Z

VDD

620

0.2 V

C

REG

220 n

C

VDD

100

µ

C

HM1

33 n

C

HM2

33 n

C

BM1

33 n

C

BM2

33 n

C

TSA

1.0 µF
C

TSE

330 n

C

TBN

4.7

µ

R

TSA

470

R

AGC

30 k

R

REF

20 k

R

SWD

100 k

R

VOL

50 k

C

BVO

220 n

C

LSO

47

µ

R

LSO

180 k

R

GRX

24 k

R

RXO

180 k

C

GRX

47 n

150

Ω

C

EAR

10

µ

VHF

C

RXS

100 n

C

RXI

33 n

R

RSA

3.3 k

C

RSA

470 n

C

RSE

330 n

C

RBN

4.7

µ

C

MF1

47 n

R

SLP

220

C

VCC

470

µ

C

VHF

47

µ

C

VMC

10

µ

R

PPL

1.0 M

C

PPL

100 n

MC33215

VMC

VHF

V

CC

25

Ω

C

RLS

33 n

R

HM1

1.0 k

R

BM2

1.0 k

R

HM2

1.0 k

Dialer or

Microcontroller

T

x

Attenuator

Speakerphone

Button

Privacy

Button

Ring

Tip

T2

T1

Z1
10 V

V

DD

Hook
Switch

1
4
7
*

2

5
8
0

3
6
9
#

R

BM1

1.0 k

C

SWT

100 n

1.0 k

10

µ

F

R

SWT

2.2 M

VMC

0.01

R

LSI

36 k

R

REG2

10 n

MC33215

19

MOTOROLA ANALOG IC DEVICE DATA

FB SUFFIX

PLASTIC PACKAGE

CASE 848B–04

(TQFP–52)

ISSUE C

OUTLINE DIMENSIONS

NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.

2. CONTROLLING DIMENSION: MILLIMETER.

3. DATUM PLANE –H– IS LOCATED AT BOTTOM OF
LEAD AND IS COINCIDENT WITH THE LEAD WHERE
THE LEAD EXITS THE PLASTIC BODY AT THE
BOTTOM OF THE PARTING LINE.

4. DATUMS –A–, –B– AND –D– TO BE DETERMINED AT
DATUM PLANE –H–.

5. DIMENSIONS S AND V TO BE DETERMINED AT
SEATING PLANE –C–.

6. DIMENSIONS A AND B DO NOT INCLUDE MOLD
PROTRUSION. ALLOWABLE PROTRUSION IS 0.25
(0.010) PER SIDE. DIMENSIONS A AND B DO
INCLUDE MOLD MISMATCH AND ARE DETERMINED
AT DATUM PLANE –H–.

7. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR PROTRUSION
SHALL BE 0.08 (0.003) TOTAL IN EXCESS OF THE D
DIMENSION AT MAXIMUM MA TERIAL CONDITION.
DAMBAR CANNOT BE LOCATED ON THE LOWER
RADIUS OR THE FOOT.

DETAIL A

L

39

40

26

27

1

52

14

13

L

–A–

B

V

S

A–B

M

0.20 (0.008) D

S

H

A–B0.05 (0.002)

S

A–B

M

0.20 (0.008) D

S

C

–D–

B

V

–B–

S

A–B

M

0.20 (0.008) D

S

H

A–B0.05 (0.002)

S

A–B

M

0.20 (0.008) D

S

C

–H–

0.10 (0.004)

–C–

SEATING
PLANE

DATUM
PLANE

M

G

H

E

C

M

_

_

DETAIL C

U

_

Q

_

X

W

K

T

R

DETAIL C

DIM MIN MAX MIN MAX

INCHESMILLIMETERS

A 9.90 10.10 0.390 0.398
B 9.90 10.10 0.390 0.398
C 2.10 2.45 0.083 0.096
D 0.22 0.38 0.009 0.015
E 2.00 2.10 0.079 0.083
F 0.22 0.33 0.009 0.013
G 0.65 BSC 0.026 BSC
H ––– 0.25 ––– 0.010

J 0.13 0.23 0.005 0.009
K 0.65 0.95 0.026 0.037
L 7.80 REF 0.307 REF
M 5 10 5 10
N 0.13 0.17 0.005 0.007
Q 0 7 0 7
R 0.13 0.30 0.005 0.012
S 12.95 13.45 0.510 0.530

T 0.13 ––– 0.005 –––
U 0 ––– 0 –––
V 12.95 13.45 0.510 0.530

W 0.35 0.45 0.014 0.018

X 1.6 REF 0.063 REF

____
____

__

B

B

DETAIL A

–A–, –B–, –D–

JN

D

F

BASE METAL

SECTION B–B

S

A–B

M

0.02 (0.008) D

S

C

MC33215

20

MOTOROLA ANALOG IC DEVICE DATA

B SUFFIX

PLASTIC PACKAGE

CASE 858–01

(SDIP–42)

ISSUE O

OUTLINE DIMENSIONS

–A–

121

42 22

–B–

SEATING
PLANE

–T–

S

A

M

0.25 (0.010) T

S

B

M

0.25 (0.010) T

L

H

M

J

42 PL

D 42 PL

F

G

N

K

C

NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.

2. CONTROLLING DIMENSION: INCH.

3. DIMENSION L TO CENTER OF LEAD WHEN
FORMED PARALLEL.

4. DIMENSIONS A AND B DO NOT INCLUDE MOLD
FLASH. MAXIMUM MOLD FLASH 0.25 (0.010).

DIM MIN MAX MIN MAX

MILLIMETERSINCHES

A 1.435 1.465 36.45 37.21
B 0.540 0.560 13.72 14.22
C 0.155 0.200 3.94 5.08
D 0.014 0.022 0.36 0.56
F 0.032 0.046 0.81 1.17
G 0.070 BSC 1.778 BSC
H 0.300 BSC 7.62 BSC
J 0.008 0.015 0.20 0.38
K 0.115 0.135 2.92 3.43
L 0.600 BSC 15.24 BSC
M 0 15 0 15
N 0.020 0.040 0.51 1.02

____

Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty , representation or guarantee regarding
the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and
specifically disclaims any and all liability, including without limitation consequential or incidental damages. “T ypical” parameters which may be provided in Motorola
data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals”
must be validated for each customer application by customer’s technical experts. Motorola does not convey any license under its patent rights nor the rights of
others. Motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other
applications intended to support or sustain life, or for any other application in which the failure of the Motorola product could create a situation where personal injury
or death may occur. Should Buyer purchase or use Motorola products for any such unintended or unauthorized application, Buyer shall indemnify and hold Motorola
and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees
arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that
Motorola was negligent regarding the design or manufacture of the part. Motorola and are registered trademarks of Motorola, Inc. Motorola, Inc. is an Equal
Opportunity/Affirmative Action Employer.

Mfax is a trademark of Motorola, Inc.

How to reach us:
USA/EUROPE/Locations Not Listed: Motorola Literature Distribution; JAPAN: Nippon Motorola Ltd.; Tatsumi–SPD–JLDC, 6F Seibu–Butsuryu–Center,

P.O. Box 5405, Denver, Colorado 80217. 303–675–2140 or 1–800–441–2447 3–14–2 Tatsumi Koto–Ku, T okyo 135, Japan. 81–3–3521–8315
Mfax: [e-mail] – TOUCHTONE 602–244–6609 ASIA/PACIFIC: Motorola Semiconductors H.K. Ltd.; 8B Tai Ping Industrial Park,

– US & Canada ONLY 1–800–774–1848 51 Ting Kok Road, T ai Po, N.T., Hong Kong. 852–26629298

INTERNET: http://www.mot.com/SPS/

MC33215/D

◊