AD8555 Analog Devices, AD8555 Datasheet - Page 22

• Manufacturer Part Number: AD8555
• Description: Zero-Drift, Single-Supply, Sensor Signal Amplifier with Digitally Programmable Gain and Offset
• Manufacturer: Analog Devices

AD8555
Table 13. Examples of DAT_SUM
Second Stage Gain Code
000
000
000
000
000
001
001
111
VA0 to VA2 is the 3-bit control signal for the second stage gain,
VB0 to VB6 is the 7-bit control signal for the first stage gain,
and VC0 to VC7 is the 8-bit control signal for the output offset.
PFUSE is the signal from the parity fuse, and MFUSE is the
signal from the master fuse.
The function of the 2-input AND gate (cell and2) is to ignore
the output of the parity circuit (signal PAR_SUM) when the
master fuse has not been blown. PARITY_ERROR is set to 0
when MFUSE = 0. In the simulation mode, for example, parity
check is disabled. After the master fuse has been blown, i.e.,
after the AD8555 has been programmed, the output from the
parity circuit (signal PAR_SUM) is fed to PARITY_ERROR.
VB0
VB1
VB2
VB3
VB4
VB5
VB6
VC0
VC1
VC2
VC3
VC4
VC5
VC6
VC7
VA0
VA1
VA2
IN01
IN02
IN03
IN04
IN05
IN06
IN07
IN08
IN09
IN10
IN11
IN12
IN13
IN14
IN15
IN16
IN17
IN18
First Stage Gain Code
000 0000
000 0000
000 0000
000 0001
100 0001
000 0000
000 0001
111 1111
EOR18
OUT
Figure 52. Functional Circuit of AD8555 Parity Check
I0
PFUSE
DOT_SUM
Rev. 0 | Page 22 of 28
IN1
IN2
Output Offset Code
0000 0000
1000 0000
1000 0001
0000 0000
0000 0000
0000 0000
1000 0000
1111 1111
EOR2
OUT
I1
When PARITY_ERROR is 0, the AD8555 behaves as a pro-
grammed amplifier. When PARITY_ERROR is 1, a parity error
has been detected, and VOUT is connected to VSS.
The 18-bit data signal (VA0 to VA2, VB0 to VB6, and VC0 to
VC7) is fed to an 18-input exclusive-OR gate (Cell EOR18). The
output of Cell EOR18 is the signal DAT_SUM. DAT_SUM = 0 if
there is an even number of 1s in the 18-bit word; DAT_SUM =
1 if there is an odd number of 1s in the 18-bit word. Examples
are given in Table 13.
MFUSE
PAR_SUM
IN1
IN2
AND2
OUT
I2
Number of Bits with 1
0
1
2
1
2
1
3
18
PARITY_ERROR
DAT_SUM
0
1
0
1
0
1
1
0