AM-FM SWITCHING

AM-FM switching is achieved by applying a DC voltage at pin 13, to switch the internal reference.

TYPICAL DC VOLTAGE (refer to the test circuit)

Pins

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

Unit

AM

3

1.1

3

1.1

1.1

2.5

3

0.7

1.2

3

0

2.1

2.1

2.9

3

2.9

V

FM

3

0

3

0

0

2.4

3

0

0.9

3

0

3

3

2.7

2.7

2.7

V

APPLICATION SUGGESTION

Recommended values referred to the test circuit of Figure 1

Part

Number

Recommended

Value

Purpose

Smaller than

Recommended Value

Larger than

Recommended Value

C1

100

µF

AGC Bypass

Increase of the distortion at

low audio frequency

Increase of the AGC time

constant

C2 (1)

100nF

AM Input DC Cut

C3 (1)

10nF

FM Input DC Cut

C4

C5

20nF

20nF

FM Amplifier Bypass

Reduction of sensitivity

- bandwidth increase

- higher noise

C7

100nF

FM detector Decoupling

Danger of RF Irradiation

C8

100nF

Power Supply Bypass

Noise increase of the audio

output

C9

10

µF

AGC Bypass

Increase of the distortion at

low audio frequency

Increase of the AGC time

constant

C10 (1)

56pF

Tuning of the AM

Oscillator at 1455kHz

C11

10nF

50ms FM De-emphasis

C12

100nF

Output DC Decoupling

Low audio frequency cut

C13

220

µF

Power Supply Decoupling

Increase of the distortion at

low frequency

C16

2.7nF

AM Detector capacitor

Low suppression of the IF

frequency and harmonics

Increase of the audion

distortion

R1 (1)

68

Ω

FM Input Matching

R2 (1)

56

Ω

AM Input Matching

R3

330

Ω

Ceramic Filter Matching

R4

6.8k

Ω

FM Detector Coil Q Setting

Audio output decrease and

lower distortion

Audio output increase and

higher distortion

R5

560

Ω

FM Detector Load Resistor

Audio output decrease and

higher AMR

R6

13k

Ω

AM Detector Coil Q Setting

Lower IF Gain and Lower

AGC Range

Higher IF Gain and Lower

AGC Range

(1) Only for test circuit.

TDA7220

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