ADS8556 Datasheet, PDF (28/47 Pages) Texas Instruments – 16-14-12-Bit Six-Channel Simultaneous Sampling ANALOG-TO-DIGITAL CONVERTERS

ADS8556, ADS8557, ADS8558
SBAS404D – OCTOBER 2006 – REVISED FEBRUARY 2016
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CONVST_A
CONVST_B
CONVST_C
BUSY
(C20 = C21 = 0)
SEL_A = SEL_B = 1, SEL_C = 0
FS
48 SCLKs
SDO_A
CHA0 CHA1 CHC0
SDO_B
SEL_A = 1, SEL_B = SEL_C = 0
FS
CHB0 CHB1 CHC1
96 SCLKs
SDO_A
CHA0 CHA1 CHB0 CHB1 CHC0 CHC1
Figure 37. Serial Interface: Data Output with One or Two Active SDOs
7.3.2.4 Output Data Format
The data output format of the ADS855x is binary twos complement, as shown in Table 3.
For the ADS8557, which delivers 14-bit conversion results, the leading two bits of the 16-bit frame are '0' in the
serial interface mode. In parallel interface mode, the output pins DB[15:14] are held low.
Respectively, when the ADS8558 outputs 12 bits of data, the first four bits of a serial 16-bit frame are zeros, in
parallel interface mode the output pins DB[15:12] are held low.
DESCRIPTION
Positive full-scale
Midscale + 0.5LSB
Midscale – 0.5LSB
Negative full-scale
INPUT VOLTAGE VALUE
4 V_REF or 2 V_REF
V_REF / (2 × resolution)
–V_REF / (2 × resolution)
–4 V_REF or –2 V_REF
Table 3. Output Data Format
BINARY CODE (HEXADECIMAL CODE)
ADS8556
ADS8557
ADS8558
0111 1111 1111 1111 (7FFF)
0001 1111 1111 1111 (1FFF)
0000 0111 1111 1111 (7FF)
0000 0000 0000 0000 (0000)
0000 0000 0000 0000 (0000)
0000 0000 0000 0000 (0000)
1111 1111 1111 1111 (FFFF)
0011 1111 1111 1111 (3FFF)
0000 1111 1111 1111 (FFF)
1000 0000 0000 0000 (8000)
0010 0000 0000 0000 (2000)
0000 1000 0000 0000 (800)
7.4 Device Functional Modes
7.4.1 Hardware Mode
With the HW/SW input (pin 62) set low, the device functions are controlled via the pins and, optionally, control
register bits C[22:18], C[15:13], and C[9:0].
Generally, the device can be used in hardware mode and switched into software mode to initialize or adjust the
control register settings (for example, the internal reference DAC) and switched back to hardware mode
thereafter.
7.4.2 Software Mode
When the HW/SW input is set high, the device operates in software mode with functionality set only by the
control register bits (corresponding pin settings are ignored).
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