CDK1304 Cadeka Microcircuits LLC., CDK1304 Datasheet - Page 9

• Manufacturer Part Number: CDK1304
• Description: 10-bit, 25 Msps 135mw A/d Converter
• Manufacturer: Cadeka Microcircuits LLC.

Data Sheet
Typically, the top side voltage drop for V
equal:
and the bottom side voltage drop for V
equal:
Figure 5 shows an example of expected voltage drops for
©2008 CADEKA Microcircuits LLC
V
V
RHF
RLS
– V
– V
Figure 4. Ladder Force/Sense Circuit
Figure 5. Reference Ladder Circuit
RHS
RLF
= 2.25 % of (V
= 1.9 % of (V
RHF
RHF
– V
– V
RLF
RLF
RHF
RLS
) (typical)
) (typical)
to V
to V
RHS
RLF
will
will
a specific case. V
is tied to AGND. A 90mV drop is seen at V
and a 75mV increase is seen at V
Analog Input
V
V
with respect to the voltage reference. (See Voltage Refer-
ence section.)
The drive requirements for the analog inputs are very
minimal when compared to most other converters due to
the CDK1304 extremely low input capacitance of only 5pF
and very high input resistance of 50kΩ.
The analog input should be protected through a series
resistor and diode clamping circuit as shown in Figure 7.
Calibration
The CDK1304 uses an auto-calibration scheme to ensure
10-bit accuracy over time and temperature. Gain and off-
set errors are continually adjusted to 10-bit accuracy dur-
ing device operation. This process is completely transpar-
ent to the user.
Upon powerup, the CDK1304 begins its calibration al-
gorithm. In order to achieve the calibration accuracy
required, the offset and gain adjustment step size is a
fraction of a 10-bit LSB. Since the calibration algorithm
is an oversampling process, a minimum of 10,000 clock
cycles are required. This results in a minimum calibration
time upon powerup of 400μs (for a 25MHz clock). Once
calibrated, the CDK1304 remains calibrated over time and
temperature.
Since the calibration cycles are initiated on the rising edge
of the clock, the clock must be continuously applied for
the CDK1304 to remain in calibration.
IN
RLS
is the analog input. The input voltage range is from
Figure 6. Recommended Input Protection Circuit
to V
RHS
(typically 4.0V) and will scale proportionally
REF
of 4.0V is applied to V
RLS
(= 0.075V).
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RHS
RHF
(= 3.91V),
, and V
RLF
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