Datasheet

3072(C0 h)0
Code
ExternalReference(V)=
3072(C0 h)0
Code
TotalAnalogSupplyVoltage(V)=
30720(7800h)
Code
DeviceGain(V/V)=
Temp Sensor Coefficient
Temp Reading( V) 168,000 V-m m
Temperature ( C) =°
+ 25°C
ADS1158
SBAS429D –JUNE 2008– REVISED MARCH 2011 www.ti.com
Reference Reading (REF)
INTERNAL SYSTEM READINGS
In this configuration, the external reference is
Analog Power-Supply Reading (VCC)
connected to the analog input and an internal
reference is connected to the reference of the ADC.
The analog power-supply voltage of the ADS1158
The data from this register indicate the magnitude of
can be monitored by reading the VCC register. The
the external reference voltage.
supply voltage is routed internal to the ADS1158 and
is measured and scaled using an internal reference.
The scale factor of Equation 7 converts the code
The supply readback channel outputs the difference
value to external reference voltage:
between AVDD and AVSS (AVDD – AVSS), for both
single and dual configurations. Note that it is required
to disable chopping (CHOP = 0) before taking this
(7)
reading.
This readback function can be used to check for
The scale factor of Equation 5 converts the code
missing or an out-of-range reference. If the reference
value to volts:
input pins are floating (not connected), internal
biasing pulls them to the AVSS supply. This pull
causes the output code to tend toward '0'. Bypass
(5)
capacitors connected to the external reference pins
may slow the response of the pins when open. When
When the power supply falls below the minimum
reading this register immediately after power-on,
specified operating voltage, the full operation of the
verify that the reference has settled to ensure an
ADS1158 cannot be ensured. Note that when the
accurate reading. Note that it is required to disable
total analog supply voltage falls to below
chopping (CHOP = 0) before taking this reading.
approximately 4.3V, the returned data are set to zero.
The SUPPLY bit in the status byte is then set. The bit
Temperature Reading (TEMP)
clears when the total supply voltage rises
approximately 50mV higher than the lower trip point.
The ADS1158 contains an on-chip temperature
sensor. This sensor uses two internal diodes with one
The digital supply (DVDD) may be monitored by
diode having a current density of 16x of the other.
looping-back the supply voltage to an input channel.
The difference in current densities of the diodes
A resistor divider may be required for bipolar supply
yields a difference voltage that is proportional to
operation to reduce the DVDD level to within the
absolute temperature.
range of the analog supply.
As a result of the low thermal resistance of the
Gain Reading (GAIN)
package to the printed circuit board (PCB), the
internal device temperature tracks the PCB
In this configuration, the external reference is
temperature closely. Note also that self-heating of the
connected both to the analog input and to the
ADS1158 causes a higher reading than the
reference input of the ADC. The data from this
temperature of the surrounding PCB. Note that it is
register indicate the gain of the device.
required to disable chopping (CHOP = 0) before
The following scale factor (Equation 6) converts the
taking this reading.
code value to device gain:
The scale factor of Equation 8 converts the
temperature reading to °C. Before using the equation,
(6)
the temperature reading code must first be scaled to
microvolts.
To correct the device gain error, the user software
can divide each converter data value by the device
gain. Note that this corrects only for gain errors
originating within the ADC; system gain errors that
(8)
occur because of an external gain stage error or
because of reference errors are not compensated.
Where Temp Sensor Coeff = 563μV/°C (if the
Note that it is also required to disable chopping
ADS1158 and test PCB temperatures are forced
(CHOP = 0) before taking this reading.
together), or 394μV/°C if only the ADS1158
temperature is forced and the test PCB is in free
air.
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