Analog Input Range/Coding Format
The reference voltage directly defines the input
voltage range in both the unipolar and bipolar
configurations. In the unipolar configuration
(BP/UP low), the first code transition occurs
0.5 LSB above AGND, and the final code transi-
tion occurs 1.5 LSB’s below VREF. Coding is in
straight binary format. In the bipolar configura-
tion (BP/UP high), the first code transition occurs
0.5 LSB above -VREF and the last transition oc-
curs 1.5 LSB’s below +VREF. Coding is in an
offset-binary format. Positive full scale gives a
digital output of all ones, and negative full scale
gives a digital output of all zeros.
The BP/UP mode pin may be switched after cali-
bration without having to recalibrate the
converter. However, the BP/UP mode should be
changed during the previous conversion cycle,
that is, between HOLD falling and EOC falling.
If BP/UP is changed at any other time, one
dummy conversion cycle must be allowed for
proper acquisition of the input.
Grounding and Power Supply Decoupling
The CS5012A/14/16 use the analog ground con-
nection, AGND, only as a reference voltage. No
dc power currents flow through the AGND con-
nection, and it is completely independent of
DGND. However, any noise riding on the AGND
input relative to the system’s analog ground will
induce conversion errors. Therefore, both the ana-
log input and reference voltage should be referred
to the AGND pin, which should be used as the
entire system’s analog ground reference point.
The digital and analog supplies to the
CS5012A/14/16 are pinned out separately to
minimize coupling between the analog and digital
sections of the chip. All four supplies should be
decoupled to their respective grounds using
0.1
µ
F ceramic capacitors. If significant low-fre-
quency noise is present on the supplies, 1
µ
F
tantalum capacitors are recommended in parallel
with the 0.1
µ
F capacitors.
The positive digital power supply of the
CS5012A/14/16 must never exceed the positive
analog supply by more than a diode drop or the
device could experience permanent damage. If
the two supplies are derived from separate
sources, care must be taken that the analog sup-
ply comes up first at power-up. The system
connection diagram in Figure 36 shows a decou-
pling scheme which allows the CS5012A/14/16
to be powered from a single set of
±
5V rails.
As with any high-precision A/D converter, the
CS5012A/14/16 require careful attention to
grounding and layout arrangements. However, no
unique layout issues must be addressed to prop-
erly apply the device. The CDB5012/14/16
evaluation board is available for the
CS5012A/14/16, which avoids the need to de-
sign, build, and debug a high-precision PC board
to initially characterize the part. The board comes
with a socketed CS5012A/14/16, and can be
quickly reconfigured to simulate any combination
of sampling, calibration, CLKIN, and analog in-
put range conditions.
CS5012A, CS5014, CS5016
2-28 DS14F6
