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8.3.5.3 Output Data Format

The output data can be configured to two's complement (default) or offset binary formatting using SPI register

writes (register 0x8F and 0x92). Table 8-7 provides an overview for minimum and maximum output codes for the

two formatting options. The actual output resolution is set by the output bit mapper.

Table 8-7. Overview of minimum and maximum output codes vs output resolution for different formatting

Two's Complement (default)

Offset Binary

RESOLUTION (BIT)

VIN,MAX

0x1FFF

0x7FFF

0x3FFF

0xFFFF

0x0000

0x2000

0x8000

VIN,MIN

0x2000

0x8000

0x0000

8.3.5.4 Output Formatter

The digital output interface utilizes a flexible output bit mapper as shown in Figure 8-39. The bit mapper takes

the 14-bit output directly from the ADC or from digital filter block and reformats it to a resolution of 14, 16, 18 or

20-bit. With parallel output format the maximum output resolution supported is 14-bit. With serial CMOS output

the output serialization factor gets adjusted accordingly for 2-, 1- and 1/2-wire interface mode. When using a

higher resolution output in non-decimation mode, the 2 LSBs are set to 0. The maximum output data rate can

not be exceeded independently of output resolution and serialization factor.

NCO

14-Bit

Output

14-Bit ADC

CMOS

Interface

Output Bit

Mapping

14 Bit

16 Bit

18 Bit

20 Bit

Figure 8-39. Interface output bit mapper

Table 8-8 provides an overview for the resulting serialization factor depending on output resolution and output

modes. Note that the DCLKIN frequency needs to be adjusted accordingly as well. Changing the output

resolution to 16-bit, 2-wire mode for example would result in DCLKIN = FS * 4 instead of * 3.5.

The output bit mapper can be used for bypass and decimation filter.

Table 8-8. Serialization factor vs output resolution for different output modes

OUTPUT

RESOLUTION

Interface

SERIALIZATION

FCLK

DCLKIN

DCLK

D0/D1

14-bit (default)

2-Wire

FS/2

FS* 3.5

FS* 7

1-Wire

14x

FS* 7

FS* 14

½-Wire

28x

FS* 14

FS* 28

16-bit

2-Wire

FS/2

FS* 4

FS* 8

1-Wire

16x

FS* 8

FS* 16

½-Wire

32x

FS* 16

FS* 32

18-bit

2-Wire

FS/2

FS* 4.5

FS* 9

1-Wire

18x

FS* 9

FS* 18

½-Wire

36x

FS* 18

FS* 36

20-bit

2-Wire

10x

FS/2

FS* 5

FS* 10

1-Wire

20x

FS* 10

FS* 20

½-Wire

40x

FS* 20

FS* 40

The programming sequence to change the output interface and/or resolution from default settings is shown in

Section 8.3.5.5.

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ADC3643

SBAS886 – OCTOBER 2020

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