Datasheet

ADS7830
www.ti.com SBAS302C –DECEMBER 2003–REVISED OCTOBER 2012
READING WITH REFERENCE ON/OFF then the settling time must be reconsidered after
PD1 is set to logic ‘1’. In other words, whenever
The internal reference defaults to off when the
the internal reference is turned on after it has
ADS7830 power is on. To turn the internal reference
been turned off, the settling time must be long
on or off, see Table 1. If the reference (internal or
enough to get 8-bit accuracy conversion.
external) is constantly turned on and off, a proper
3. When the internal reference is off, it is not turned
amount of settling time must be added before a
on until both the first Command Byte with PD1 =
normal conversion cycle can be started. The exact
‘1’ is sent and then a STOP condition or repeated
amount of settling time needed varies depending on
START condition is issued. (The actual turn-on
the configuration.
time occurs once the STOP or repeated START
See Figure 17 for an example of the proper internal
condition is issued.) Any Command Byte with
reference turn-on sequence before issuing the typical
PD1 = ‘1’ issued after the internal reference is
read sequences required for the F/S mode when an
turned on serves only to keep the internal
internal reference is used.
reference on. Otherwise, the internal reference
would be turned off by any Command Byte with
When using an internal reference, there are three
PD1 = ‘0’.
things that must be done:
The example in Figure 17 can be generalized for a
1. In order to use the internal reference, the PD1 bit
HS mode conversion cycle by simply swapping the
of Command Byte must always be set to logic ‘1’
timing of the conversion cycle.
for each sample conversion that is issued by the
sequence, as shown in Figure 15.
If using an external reference, PD1 must be set to ‘0’,
2. In order to achieve 8-bit accuracy conversion
and the external reference must be settled. The
when using the internal reference, the internal
typical sequence in Figure 15 or Figure 16 can then
reference settling time must be considered, as
be used.
shown in the Internal V
REF
vs Turn-On Time
Typical Characteristic plot. If the PD1 bit has
been set to logic ‘0’ while using the ADS7830,
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