Description

The CXA1946CR is a serial control electronic

volume IC designed for use in audio systems.

Features

· Loudness

· Volume control (0dB to 87dB in 1dB step,

dB)

· Balance

· Tone control (15 steps, 2 bands, 16dB to +16dB)

· Fader

(2dB-step to 20dB, 25dB, 35dB, 45dB, 60dB,

dB)

· Input selector (4 channels)

· Gain can be set for each input channel (common for channels 3 and 4)

· Serial data control (DATA, CLK, CE)

· Single 8V power supply

· Zero-cross detection circuit (with timer)

· Power-off mute

· Volume control and tone control input/output pins are separate.

Absolute Maximum Ratings

· Supply voltage

· Operating temperature

Topr

40 to +85

°C

· Storage temperature

Tstg

65 to +150

°C

· Allowable power dissipation

LQFP

180

mW (Ta = 85°C)

Operating Conditions

Supply voltage

6 to 12

CXA1946CR

E97516A7Y

Electronic Volume

Sony reserves the right to change products and specifications without prior notice. This information does not convey any license by
any implication or otherwise under any patents or other right. Application circuits shown, if any, are typical examples illustrating the
operation of the devices. Sony cannot assume responsibility for any problems arising out of the use of these circuits.

48 pin LQFP (Plastic)

For the availability of this product, please contact the sales office.

CXA1946CR

Block Diagram and Pin Configuration

DHC1

I
N

CHC1

I
N

DHC2

I
N

CHC2

I
N

GAIN12

GAIN11

IN14

IN13

IN12

IN11

IN21

IN22

IN23

IN24

GAIN21

GAIN22

FNTO1

REO1

CLK

DGND

GND

VCT

DATA

TIMER

REO2

FNTO2

LOUD

VCTBUFF

SHIFT REGISTER

LATCH

100k

LATCH CONTROL

8dB STEP

VOLUME

1dB STEP

VOLUME

TONE

FADER

VOLUME

8dB STEP

VOLUME

1dB STEP

TONE

FADER

LOUD

I
N

ZCDET

CXA1946CR

· TONE BASS/TREBLE

Setting value

D20/D24

D21/D25

14
12
10
8
6
4
2
0

1
1
1
1
0
0
0
0

1
1
0
0
1
1
0
0

D22/D26

1
0
1
0
1
0
1
0

· FADER

Setting value

D28

D29

60
45
35
25
20
18
16
14
12
10
8
6
4
2
0

1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0

1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0

D30

1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0

D31

1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0

· BOOST/CUT

Setting value

D23/D27

BOOST
CUT

1
0

· FADER SELECT

· RESET

Reset is performed automatically when power is first supplied to the IC; there is no reset pin.
The following table shows the respective statuses of various settings after a reset has been performed.
However, from the time when power is first supplied until the first data transfer, keep CE high by pulling it up
to Vcc, etc.

Setting value

D32

Attenuation of front signal
Attenuation of rear signal

1
0

MODE

Setting value

INPUT
VRC1
VRF1
VRC2
VRF2
LOUD
TONE BASS
TONE TREBLE
FADER

7dB

7dB
OFF
0dB
0dB
0dB, REAR

CXA1946CR

Electrical Characteristics

(Unless otherwise specified, Vcc = 8V, Ta = 25°C)

Item

Symbol

Measurement conditions

Min.

Typ.

Max.

Unit

Current consumption

Total harmonic distortion

Output noise voltage

Maximum output voltage

Separation

Volume maximum attenuation

Low

High

Bass max. boost gain

Bass max. cut gain

Treble max. boost gain

Treble max. cut gain

Low

High

Input voltage range

Loudness

Input voltage

THD

Vom

ATTm

Glb

Glh

Gbb

Gbc

Gtb

Gtc

Vsl

Vsh

Vin

No signal

1kHz, 5dBm output

input shorted, A weight

1kHz

100Hz, VRC = 16dB

10kHz, VRC = 16dB

DATA, CLK, CE

IN11 to 14, IN21 to 24, VRIN1, VRIN2,
TIN1, TIN2, FDIN1, FDIN2

0.005

0.01

1.5

µVrms

dBm

CXA1946CR

Electrical Characteristics Measurement Circuit

FNTO1

REO1

CLK

DGND

GND

VCT

DATA

TIMER

REO2

FNTO2

10k

V24

I
N

CHC1

I
N

DHC1

I
N

CHC2

I
N

DHC2

GAIN12

GAIN11

IN14

IN13

IN12

IN11

IN21

IN22

IN23

IN24

GAIN21

GAIN22

0027µ

10µ

0022µ

047µ

10k

0.39µ

10µ

39µ

10µ

0027µ

10µ

10k

0022µ

047µ

10k

0.01µ

3 to 6V

10k

OFF

OP AMP

220p

VCT-50mV

V7
AC

10µ

S5-1

10µ

S5-2

V23

V22

V21

V11

V12

V13

V14

S14

10k

S13

10k

S12

10k

S11

10k

S21

10k

S22

10k

S23

10k

S24

CXA1946CR

Application Circuit 1

0.39µ

0.0027µ

10µ

0.39µ

10µ

0.0027µ

0.047µ

10µ

0.0022µ

33µ

0.01µ

10µ

0.047µ

10µ

0.0022µ

FNTO1

REO1

CLK

DGND

GND

VCT

DATA

TIMER

REO2

FNTO2

I
N

CHC1

I
N

DHC1

I
N

CHC2

I
N

DHC2

GAIN12

GAIN11

IN14

IN13

IN12

IN11

IN21

IN22

IN23

IN24

GAIN21

GAIN22

10µ

Application circuits shown are typical examples illustrating the operation of the devices. Sony cannot assume responsibility for
any problems arising out of the use of these circuits or for any infringement of third party patent and other right due to same.

CXA1946CR

Application Circuit 2

0.39µ

0027µ

10µ

0.39µ

0027µ

047µ

10µ

0.0022µ

33µ

0.01µ

047µ

10µ

0.0022µ

FNTO1

REO1

CLK

DGND

GND

VCT

DATA

TIMER

REO2

FNTO2

I
N

CHC1

I
N

DHC1

I
N

CHC2

I
N

DHC2

GAIN12

GAIN11

IN14

IN13

IN12

IN11

IN21

IN22

IN23

IN24

GAIN21

GAIN22

10µ

CXA1946CR

Description of Operation

The CXA1946CR is a serial control electronic volume IC designed for use in audio systems.
The internal circuit of the IC consists of the following blocks:

1. Input selector
2. Volume
3. Loudness
4. Tone control
5. Fader
6. VCT buffer
7. Serial data I/O
8. Zero-cross detector (with timer)
9. Power-off mute

The operation of each block and notes on their use are described below.
Note that when the circuits for channels 1 and 2 are identical, the suffix "X" is added to pin names and device
names in order to distinguish between the two channels.

1. Input selector

There are two channels (stereo), each with four systems of input pins; the input selector selects one of
those input systems.
The gain between the input pins and the output pin of the input selector can be set independently for each
input system, except the gain for inputs 3 and 4 is common.
Determine the gain for each system through the settings of the feedback circuit constants as shown in Figs.
1 and 2. When each input gain is set to

1, short INAOX and GAIN

1,GAIN

2,GAIN

34.

The input impedance is 50k

(typ.) for each input.

The output impedance for INAO1 and INAO2 is low impedance (roughly 0

). The gain is not affected by the

load impedance.

Fig. 1. Input Selector (1)

50k

INX4

50k

INX3

50k

INX2

50k

INX1

VCT

GAINX2

GAINX1

GAINX34

INAOX

CXA1946CR

Fig. 2. Input Selector (2)

2. Volume

The volume circuit consists of two sections, an 8dB/step section and a 1dB/step section, as shown in Fig. 3.
This circuit also serves as a balance control because the volume for channel 1 and channel 2 can be set
independently.
To mute the output signal, send

dB data.

The input impedance is 9.5k

(typ.) for VRIN1 and VRIN2.

The output impedance for VOUT1 and VOUT2 is low impedance (roughly 0

). The volume step width and

gain are not affected by the load impedance.

3. Loudness

The configuration of the loudness circuit is shown in Fig. 3. C

LDHCX

and C

LDLCX

are connected externally,

and the loudness frequency characteristics are determined by these constants. The relationships between
C

LDHCX

LDLCX

and the frequency characteristics are as follows:

1/f

= 2

LDLCX

1/f

= 2

LDHCX

The loudness characteristics are not affected by the load impedance of VOUT1 and VOUT2.
Loudness is turned on and off by serial data bit D5.

Fig. 3. Volume and Loudness

50k

INX4

50k

INX3

50k

INX2

50k

INX1

VCT

GAINX2

GAINX1

GAINX34

INAOX

VRINX (input impedance 9.5k

)

20k

Total 40k

LOUD

6.18k

25.7k

8.92k

4.98k

20k

LDHCX

0.0022µ

LDLCX

0.047µ

LDHCX

LDLCX

VOUTX

Loudness

Volume

OFF

Loudness frequency

characteristics

CXA1946CR

4. Tone control

The configuration of the tone control circuit is shown in Fig. 4. C

TCLCX2

and C

TCHCX

are connected

externally, and the tone control frequency characteristics can be changed by changing these constants.

The relationships between C

TCLCX2

TCHCX

and the frequency characteristics are as follows:

1/f

= 2

TCLCX2

//R

)

1/f

= 2

TCHCX

The maximum bass boost and cut can be made smaller than in the Application Circuit by connecting an

external resistance to the TCLCX1 pin in series, or else connecting an external resistance to C

TCLCX2

parallel. (See Fig. 5.) Furthermore, the maximum treble boost and cut can be made smaller than in the

Application Circuit by connecting an external resistance to C

TCHCX

in series. (See Fig. 6.) However, when

these methods are used, variations in the absolute value of the CXA1946C internal resistance (±20% max.)

and in the external resistance will cause variations in the tone control characteristics. Set these constants

after studying all considerations carefully. Note that when the method illustrated in the Application Circuit is

used, variations in the internal resistance of the CXA1946C have no effect on the tone control

characteristics.

The input impedance is 19k

(typ.) for TIN1 and TIN2.

The output impedance for TCO1 and TCO2 is low impedance (roughly 0

). The tone step width and gain

are not affected by the load impedance.

Fig. 4. Tone Control

TCOX

14.1k

12k

TCLCX1

TCLCX2

0.39µ

BASS

CUT

OFF

BOOST

14.1k

12k

10k

CUT

OFF

BOOST

TREBLE

TCHCX

0.0027µ

Tone control frequency

characteristics

input impedance

19k

TINX

CXA1946CR

Fig. 5. Method for Reducing Bass Boost/Cut

Fig. 6. Method for Reducing Treble Boost/Cut

5. Fader

The configuration of the fader circuit is shown in Fig. 7. The fader operates by specifying the amount of

attenuation for either the front or rear output signal and by specifying which output signal (front or rear) is to

be attenuated.

The input impedance is 24k

(typ.) for FDIN1 and FDIN2.

The output impedance for FNTO1, FNTO2, REO1, and REO2 is low impedance (roughly 0

). The gain and

fader step width are not affected by the load impedance.

Fig. 7. Fader

TCLCX1

TCLCX2

(B)

RexB

TCLCX1

TCLCX2

TINX

(A)

RexA

10k

TCHCX

RexC

FDINX (input impedance 24k

)

FNTOX

Center

ATT

Center

ATT

REOX

CXA1946CR

6. VCT buffer

The internal circuit for the VCT pin is shown in Fig. 8.

This circuit generates the electric potential for the center between Vcc and GND (Vcc/2). The IC internal

operation reference potential is equal to the output potential of VCT buffer. The impedance for the VCT pin

(Pin 17) is high since it is connected to a bypass capacitor. Add an external buffer when using the electric

potential of the VCT pin as the external reference potential for the CXA1946.

Fig. 8. VCT Buffer

7. Serial data I/O

The serial data has a 32-bit structure as indicated in the specifications. Data input is conducted using three
inputs: DATA, CLK, and CE. DATA is shifted in the CXA1946C internal shift register at the rising edge of
CLK. The data in the shift register is latched at the falling edge of CE. Refer to this specification for details
on the timing.
The CXA1946C does not have a reset (initialize) pin. The internal shift register and latch are reset
automatically when power is first supplied to the IC. To execute a reset at other times, send the data
(statuses after reset ) shown in the item "RESET" of this specification to the CXA1946C.

8. Zero-cross detector (with timer)

Using the zero-cross detector, the internal latch data is overwritten the first time the input signal becomes
roughly 0 after serial data is sent (after CE goes low). This operation reduces noise when overwriting data.
Although there are usually no problems when a normal audio signal is input, in rare cases there may be
nothing except a large-amplitude input signal of the high band, causing the slew rate to become abnormally
high; the zero-cross detection signal is not output in such a case because the zero-cross detector response
speed is too slow. Another rare situation would be that the zero-cross detection signal is output very
infrequently because the input signal frequency is extremely low. In these types of instances, it is
conceivable that the internal latch data will not be overwritten after data is sent, or that it will take much time
until the data is overwritten. Therefore, to an external observer it will appear that the data is not being
overwritten regardless of the fact that data is being sent.
As a countermeasure, the IC is designed to permit the internal latch data to be forcibly overwritten if the
zero-cross detection signal is not output within a certain waiting period after the data is sent (after CE goes
low). This function is called the "timer." If the zero-cross detection signal is output within a certain waiting
period, the internal latch data is overwritten in synchronization with the zero-cross of the input signal.
The waiting period mentioned above can be changed according to the value of the external capacitor
connected to the TIMER pin. When the value of the capacitor is 0.01µF, the waiting period is approximately
500µs.

9. Power-off mute

When Vcc goes below 5V, the output stage bias of the fader output pins FNTO1, FNTO2, REO1, and
REO2 is turned off and the pins go to high impedance. This operation prevents popping noises caused by
the output pin potential deviating from Vcc/2 when the power is turned off.

100k

VCT

10µ

CXA1946CR

Connections and Characteristics of Each Block

In the Application Circuit, the signal path goes from the input selector to the volume (+loudness) to the tone

control to the fader. The sequence of the blocks in the signal path can be changed because the I/O pins for

each block are independent of each other. For example, it is possible to switch the sequence of the volume

circuit and the tone control so that the signal path goes from the input selector to the tone control to the volume

(+loudness) to the fader. When this connection method is used, the noise voltage in the fader output can be

reduced in actual use because the noise and signal up to the tone control are attenuated by the volume.

However, because the maximum output amplitude of the tone control circuit is limited by the supply voltage,

care should be given to the setting of the input signal level.

Although blocks in the Application Circuit are linked either by coupling capacitors or by direct connection, it is

also possible to insert external circuits between blocks. In this case, the gain will change according to the input

impedance of the following block and the impedance of the external circuit. In addition, the input impedance of

each block can vary by ±20% due to the characteristics of the IC. Consequently, the overall gain also varies.

Give careful consideration to the effects of this variation when setting the constants. The step widths (control

characteristics) of the volume, tone control, and fader are not affected.

Timing Chart

CLK

DATA

0.5µs

1.0µs

0.5µs

+ 0.5µs

is the maximum value for the timer operation time)

4.0µs

D30

D31

D32

Invalid

Timer Waiting Period Setting Chart (Vcc = 6 to 12V, operating temperature = 35°C to 85°C)

TIMER pin

capacitance C

Waiting peroid

Min.

Typ.

Max.

C = 100pF

C = 0.001µF

C = 0.01µF

C = 0.1µF

C = 1µF

C = 10µF

3µs

30µs

300µs

3ms

30ms

300ms

5µs

50µs

500µs

5ms

50ms

500ms

9µs

90µs

900µs

9ms

90ms

900ms

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