Datasheet

Drift=
V V-
REFMAX REFMIN
V TempRange´
REFNOM
x10 (ppm)
6
V =
HYST
|V V |-
PRE POST
V
NOM
´ 10 (ppm)
6
ADS1259
www.ti.com SBAS424D –JUNE 2009– REVISED AUGUST 2011
Reference Drift External Reference
The ADS1259 internal reference is designed for To select the ADS1259 for external reference
minimal drift error, which is defined as the change in operation, set the EXTREF register bit = 1 (default). If
reference voltage over temperature. The drift is desired, the internal reference can continue to
calculated using the box method, as described by provide a +2.5V reference output via the REFOUT
Equation 2. and AVSS pins. In this case, set the RBIAS register
bit = 1 to power the internal reference. If the internal
reference is activated, an external 1μF capacitor from
REFOUT to AVSS is required.
Where: For external reference applications, place a 1μF
(minimum) capacitor close to the VREFP and VREFN
V
REFMAX
, V
REFMIN
, and V
REFNOM
are the maximum,
pins.
minimum, and nominal reference output voltages,
respectively, over the specified temperature
Because the ADS1259 measures the signal inputs
range. (2)
(AINP and AINN) against the reference inputs
(VREFP and VREFN), reference noise and drift may
The ADS1259 internal reference features a maximum
degrade overall system performance. In ratiometric
drift coefficient of 5ppm/°C over 0°C to +85°C
measurement applications, reference noise and drift
operating range and 12ppm/°C over –40°C to +105°C
have a cancelling effect. In absolute measurement
operating range.
applications, reference noise and drift directly effect
the conversion results.
Thermal Hysteresis
Thermal hysteresis of the internal reference is defined
Voltage Reference Inputs (VREFP, VREFN)
as the change in voltage after operating the device at
ESD diodes protect the reference inputs. To keep
+25°C, cycling the device through the specified
these diodes from turning on, make sure the voltages
temperature range, and returning to +25°C. It can be
on the reference pins do not go below AVSS by more
expressed as Equation 3.
than 300mV, and likewise do not exceed AVDD by
more than 300mV.
The absolute maximum reference input range is:
AVSS – 300mV < (VREFP or VREFN) < AVDD + 300mV(4)
Where:
Note that the valid operating range of the reference
V
HYST
= thermal hysteresis (in units of ppm).
inputs are shown in the Electrical Characteristics
V
NOM
= nominal reference voltage (+2.5V).
table.
V
PRE
= reference voltage measured at +25°C
pretemperature cycling.
V
POST
= reference voltage measured after the
device has been cycled from +25°C through the
temperature range of 0°C and +85°C and
returned to +25°C. (3)
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