Datasheet

VDD
GND
AIN0
VDD
GND
AIN1
VDD
GND
AIN2
VDD
GND
AIN3
AIN
P
AIN
N
GND
ADS1115
t
SAMPLE
ON
OFF
S
1
S
2
OFF
ON
ADS1113
ADS1114
ADS1115
SBAS444B –MAY 2009–REVISED OCTOBER 2009 www.ti.com
MULTIPLEXER If it is possible that the voltages on the input pins may
violate these conditions, external Schottky clamp
The ADS1115 contains an input multiplexer, as
diodes and/or series resistors may be required to limit
shown in Figure 24. Either four single-ended or two
the input current to safe values (see the Absolute
differential signals can be measured. Additionally,
Maximum Ratings table).
AIN0 and AIN1 may be measured differentially to
AIN3. The multiplexer is configured by three bits in Also, overdriving one unused input on the ADS1115
the Config register. When single-ended signals are may affect conversions taking place on other input
measured, the negative input of the ADC is internally pins. If overdrive on unused inputs is possible, again
connected to GND by a switch within the multiplexer. it is recommended to clamp the signal with external
Schottky diodes.
ANALOG INPUTS
The ADS1113/4/5 use a switched-capacitor input
stage where capacitors are continuously charged and
then discharged to measure the voltage between
AIN
P
and AIN
N
. The capacitors used are small, and to
external circuitry the average loading appears
resistive. This structure is shown in Figure 26. The
resistance is set by the capacitor values and the rate
at which they are switched. Figure 25 shows the
on/off setting of the switches illustrated in Figure 26.
During the sampling phase, S
1
switches are closed.
This event charges C
A1
to AIN
P
, C
A2
to AIN
N
, and C
B
to (AIN
P
– AIN
N
). During the discharge phase, S
1
is
first opened and then S
2
is closed. Both C
A1
and C
A2
then discharge to approximately 0.7V and C
B
discharges to 0V. This charging draws a very small
transient current from the source driving the
Figure 24. ADS1115 MUX
ADS1113/4/5 analog inputs. The average value of
this current can be used to calculate the effective
The ADS1113 and ADS1114 do not have a
impedance (R
eff
) where R
eff
= V
IN
/I
AVERAGE
.
multiplexer. Either one differential or one
single-ended signal may be measured with these
devices. For single-ended measurements, connect
the AIN1 pin to GND. Note that in subsequent
sections of this data sheet, AIN
P
refers to AIN0 and
AIN
N
refers to AIN1 for the ADS1113 and ADS1114.
When measuring single-ended inputs it is important to
note that the negative range of the output codes are
not used. These codes are for measuring negative
Figure 25. S
1
and S
2
Switch Timing for Figure 26
differential signals such as (AIN
P
– AIN
N
) < 0. ESD
diodes to VDD and GND protect the inputs on all
three devices (ADS1113, ADS1114, and ADS1115).
To prevent the ESD diodes from turning on, the
absolute voltage on any input must stay within the
following range:
GND – 0.3V < AINx < VDD + 0.3V
12 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): ADS1113 ADS1114 ADS1115