CS5012A, CS5014, CS5016
Microprocessor Independent Operation
connections. The CS5012A/14/16 internally buff-
er all analog inputs (AIN, VREF, and AGND) to
ease the demands placed on external circuitry.
However, accurate system operation still requires
careful attention to details at the design stage re-
garding source impedances as well as grounding
and decoupling schemes.
The CS5012A/14/16 can be operated in a stand-
alone mode independent of intelligent control. In
this mode, CS and RD are hard-wired low. This
permanently enables the 3-state output buffers
and allows transparent latch inputs (CAL and
INTRLV) to be active. A free-running condition
is established when BW is tied high, CAL is tied
low, and HOLD is continually strobed low or tied
to EOT. The CS5012A/14/16’s EOC output can
be used to externally latch the output data if de-
sired. With CS and RD hard-wired low, EOC will
strobe low for four CLKIN cycles after each con-
version. Data will be unstable up to 100 ns after
EOC falls, so it should be latched on the rising
edge of EOC.
Reference Considerations
An application note titled "Voltage References for
the CS501X Series of A/D Converters" is avail-
able for the CS5012A/14/16. In addition to
working through a reference circuit design exam-
ple, it offers several built-and-tested reference
circuits.
During conversion, each capacitor of the cali-
brated capacitor array is switched between VREF
and AGND in a manner determined by the suc-
cessive-approximation algorithm. The charging
and discharging of the array results in a current
load at the reference. The CS5012A/14/16 in-
clude an internal buffer amplifier to minimize the
external reference circuit’s drive requirement and
preserve the reference’s integrity. Whenever the
array is switched during conversion, the buffer is
used to pre-charge the array thereby providing
the bulk of the necessary charge. The appropriate
array capacitors are then switched to the unbuf-
fered VREF pin to avoid any errors due to offsets
and/or noise in the buffer.
+5V
Reset
INTRLV
BW
RST
EOC
Latching
Output
A0
D15
Sampling
Clock
HOLD
12-Bit
Data
Out
CS
CS5012A
CS5014
CS5016
RD
CAL
D4
Figure 8. Microprocessor-Independent Connections
Serial Output
All successive-approximation A/D converters de-
rive their digital output serially starting with the
MSB. The CS5012A/14/16 present each bit to the
SDATA pin four CLKIN cycles after it is derived
and can be latched using the serial clock output,
SCLK. Just subsequent to each bit decision
SCLK will fall and return high once the bit infor-
mation on SDATA has stabilized. Thus, the rising
edge of the SCLK output should be used to clock
the data from the CS5012A/14/16 (See Figure 9).
The external reference circuitry need only pro-
vide the residual charge required to fully charge
the array after pre-charging from the buffer. This
creates an ac current load as the CS5012A/14/16
sequence through conversions. The reference cir-
cuitry must have a low enough output impedance
to drive the requisite current without changing its
output voltage significantly. As the analog input
signal varies, the switching sequence of the inter-
nal capacitor array changes. The current load on
the external reference circuitry thus varies in re-
sponse with the analog input. Therefore, the
external reference must not exhibit significant
ANALOG CIRCUIT CONNECTIONS
Most popular successive-approximation A/D con-
verters generate dynamic loads at their analog
2-24
DS14F6
CIRRUS [ CIRRUS LOGIC ]
