5

U4256BM-R

4562C–AUDR–08/04

Function of DAC1, 2 in

FM and AM Mode

(Pin 3 and Pin 4)

For automatic tuner alignment, the DAC1 and DAC2 of the U4256BM-R can be con-

trolled by setting gain of VPDO and offset values. The following figure shows the

principle of the operation. In FM Mode the gain is in the range of 0.69

× V

V

nected to the varicaps of the preselection filters. For alignment, offset and gain is set for

having the best tuner tracking.

Figure 6. Principle Operation for Alignment

The DAC mode can be controlled by setting the Bit 34 as following:

If Bit 34 = 1 (AM Mode), the DAC1, DAC2 can be used as standard DAC converters.

The internal voltage of 3 V is connected to the gain- and offset-input of DAC1 and DAC2

(only in AM Mode). The gain is in the range of 0.46

× 3 V to 3.03 × 3 V. The offset range

is +1.46 V to -1.49 V.

Figure 7. Internal Components at DAC1,2 Output

DAC Mode

B34

FM

0

AM

1

PDO (FM)

Offset

DAC1,2

+/-

Gain

Vref (AM)

(3 V)

Bit 34

VS

DAC1,2