U4256BM-R Datasheet, PDF (7/19 Pages) ATMEL Corporation – Frequency Synthesizer for Radio Tuning

U4256BM-R
DAC 1, 2 in AM Mode
(Pin 3 and Pin 4)
In AM mode the DAC input voltage V_(PDO) is internal connected to 3 V. The gains of
DAC1 and DAC2 have a range of 0.46 × 3 V to 3.03 × 3 V. V_(PDO) is the PLL tuning volt-
age output. This range is divided into 256 steps. So one step is approximately
(3.03 - 0.46) × 3 V/255 = 0.01007 × 3 V. The gain of DAC1 can be controlled by the Bits
36 to 43 (G-2⁰ to G-2⁷) and the gain of DAC2 by the Bits 0 to 7 (G-2⁰ to G-2⁷) as
following:
Gain DAC1
Decimal
Approximately B43 B42 B41 B40 B39 B38 B37 B36
Gain
Gain DAC2
Decimal
Approximately B7 B6 B5 B4 B3 B2 B1 B0
Gain
0.4607 × 3 V
0
0
0
0
0
0
0
0
0
0.4710 × 3 V
0
0
0
0
0
0
0
1
1
0.4812 × 3 V
0
0
0
0
0
0
1
0
2
0.4915 × 3 V
0
0
0
0
0
0
1
1
3
...
...
...
...
...
...
...
...
...
...
1.0029 × 3 V
0
0
1
1
0
1
0
1
53
...
...
...
...
...
...
...
...
...
...
3.0097 × 3 V
1
1
1
1
1
1
0
1
253
3.0196 × 3 V
1
1
1
1
1
1
1
0
254
3.0296 × 3 V
1
1
1
1
1
1
1
1
255
Offset = 31 (intermediate position)
Remark: V_(PDO) is 3 V in AM mode.
The offset of DAC1 and DAC2 has a range of +1.46 V to -1.49 V. This range is divided
into 64 steps. So one step is approximately 2.95 V/ 63 = 46.8 mV. The offset DAC1 can
be controlled by the Bits 44 to 49 (O-2⁰ to O-2⁵) and the offset of DAC2 by the Bits 8 to
13 (O-2⁰ to O-2⁵) as following:
Offset DAC1
Decimal
Approximately B49
B48
B47
B46
B45
B44
Gain
Offset DAC2
Approximately B13
B12
B11
B10
B9
Decimal
B8
Gain
1.4606 V
0
0
0
0
0
0
0
1.4138 V
0
0
0
0
0
1
1
1.3665 V
0
0
0
0
1
0
2
1.3196 V
0
0
0
0
1
1
3
...
...
...
...
...
...
...
...
-0.0079 V
0
1
1
1
1
1
31
...
...
...
...
...
...
...
...
-1.3975 V
1
1
1
1
0
1
61
-1.4447 V
1
1
1
1
1
0
62
-1.4917 V
1
1
1
1
1
1
63
Gain = 53 (intermediate position)
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4562C–AUDR–08/04