Datasheet

I+ = [(0.0168)(b)(I
+
_VOLTAGE)] + [(4.932)(10
-3
)(a)(I
+
_TEMP)]
+ [1 ± (4.932)(10
-3
)(a) ± 0.0168(b)](I
+
_SHUTDOWN)
|
4095d
|
D
OUT
'V
IN
(VREF - 3VREF)
1V
2V
3200d
|
|
|
|
1600d
2(2
12
)
|
|
|
ADC128D818
www.ti.com SNAS483E –FEBRUARY 2010–REVISED MARCH 2013
For the above equation, ΔVIN = INx - GND, where 0 ≤ x ≤ 7, for the single-ended configuration, and ΔVIN = (IN+
- IN-) for the pseudo-differential configuration. In theory, ΔVIN can be of any value between 0V and (VREF-
3LSb/2). Any ΔVIN value outside of this range will produce a digital output code of 0 or 4095. Figure 26 shows a
theoretical plot of D
OUT
vs. ΔVIN and some sample D
OUT
calculation using the equation above.
Figure 26. D
OUT
vs ΔVIN for a 12-bit ADC assuming VREF = 2.56V.
POWER MANAGEMENT
To understand the average supply current (I+), the conversion rates must be introduced. ADC128D818 has three
types of conversion rates: Continuous Conversion Mode, Low Power Conversion Mode, and One Shot Mode. In
the Low Power Conversion Mode, the device converts all of the enabled channels then enters shutdown mode;
this process takes approximately 728 ms to complete. (More information on the conversion rate will be discussed
in the Conversion Rate Register — Address 07h and One-Shot Register — Address 09h sections).
Each type of conversion produces a different average supply current. The supply current for a voltage conversion
will be referred to as I+_VOLTAGE, a temperature conversion as I+_TEMP, and the shutdown mode as
I+_SHUTDOWN. These values can be obtained from Typical Performance Characteristics plots.
In general, I+ is the average supply current while ADC128D818 is operating in the Low Power Conversion Mode
with all of the available channels enabled. Its plot can be seen in the Typical Performance Characteristics section
and its equation is shown below.
where
• "a" is the number of local temperature available.
• "b" is the number of ENABLED voltage channel. (2)
Each mode of operation has a different "a" and "b" values. The following table shows the value for "a" and the
maximum value for "b" for each mode.
Table 4. "a" and "b" Values
a b (Max)
Mode 0 1 7
Mode 1 0 8
Mode 2 1 4
Mode 3 1 6
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