Datasheet

ADS1100
12
SBAS239B
www.ti.com
APPLICATIONS INFORMATION
The sections that follow give example circuits and tips for
using the ADS1100 in various situations.
An evaluation board, the ADS1100EVM, is available. This
small, simple board connects to an RS-232 serial port on
almost any PC. The supplied software simulates a digital
voltmeter, and also displays raw output codes in hex and
decimal. All features of the ADS1100 can be controlled from
the main window. For more information, contact TI or your
local TI representative, or visit the Texas Instruments website
at http://www.ti.com/.
BASIC CONNECTIONS
For many applications, connecting the ADS1100 is extremely
simple. A basic connection diagram for the ADS1100 is
shown in Figure 4.
The fully differential voltage input of the ADS1100 is ideal for
connection to differential sources with moderately low source
impedance, such as bridge sensors and thermistors. Al-
though the ADS1100 can read bipolar differential signals, it
cannot accept negative voltages on either input. It may be
helpful to think of the ADS1100 positive voltage input as non-
inverting, and of the negative input as inverting.
When the ADS1100 is converting, it draws current in short
spikes. The 0.1µF bypass capacitor supplies the momentary
bursts of extra current needed from the supply.
The ADS1100 interfaces directly to standard mode, fast
mode, and high-speed mode I
2
C controllers. Any
microcontroller’s I
2
C peripheral, including master-only and
non-multiiple-master I
2
C peripherals, will work with the
ADS1100. The ADS1100 does not perform clock-stretching
(i.e., it never pulls the clock line low), so it is not necessary
to provide for this unless other devices are on the same I
2
C
bus.
Pull-up resistors are necessary on both the SDA and SCL
lines because I
2
C bus drivers are open-drain. The size of
these resistors depends on the bus operating speed and
capacitance of the bus lines. Higher-value resistors consume
less power, but increase the transition times on the bus,
limiting the bus speed. Lower-value resistors allow higher
speed at the expense of higher power consumption. Long
bus lines have higher capacitance and require smaller pull-
up resistors to compensate. The resistors should not be too
small; if they are, the bus drivers may not be able to pull the
bus lines low.
CONNECTING MULTIPLE DEVICES
Connecting multiple ADS1100s to a single bus is almost
trivial. The ADS1100 is available in eight different ver-
sions, each of which has a different I
2
C address. An
example showing three ADS1100s connected on a single
bus is shown in Figure 5. Up to eight ADS1100s (provided
their addresses are different) can be connected to a single
bus.
Note that only one set of pull-up resistors is needed per bus.
You might find that you need to lower the pull-up resistor
values slightly to compensate for the additional bus capaci-
tance presented by multiple devices and increased line
length.
1
2
3
6
5
4
V
IN+
GND
4.7µF (typ.)
SCL
V
IN–
V
DD
V
DD
V
DD
Positive Input
(0V to 5V)
Negative Input
(0V to 5V)
SDA
SDA
SCL
ADS1100
Microcontroller or
Microprocessor
with I
2
C Port
I
2
C Pull-Up Resistors
1kΩ to 10kΩ (typ.)
FIGURE 4. Typical Connections of the ADS1100.