Datasheet

SDA
SCL
A0
A1
IN0
ADC128D818
GND
V+
IN1
VREF
IN5-
LM4140
+
+
0.1 PF
(optional)
Positive
Pseudo-
Differential
Input Voltage
Positive
Single-Ended
Input Voltage
R1
R2
VS1
INT
Microcontroller
R
GPO1
GPO2
GPO3
GPO4
RA_top
RA_bottom
R R
1 PF
1 PF
0.1 PF
IN4+
R3
R4
VS2
VIN2
IN2
IN3
IN7+
IN6-
R
TRACE
RA_top
RA_bottom
ADC128D818
www.ti.com SNAS483E –FEBRUARY 2010–REVISED MARCH 2013
Figure 35. Temperature Response Structure
(Assuming the interrupt output pin, INT, is reset before the next temperature reading)
EXAMPLE APPLICATIONS
General Voltage Monitoring
Figure 36. Typical Analog Input Application
A typical application for ADC128D818 is voltage monitoring. In this application, the inputs would most often be
connected to linear power supplies of 2.5V, 3.3V, ±5V and ±12V inputs. These inputs should be attenuated with
external resistors to any desired value within the input range. The attenuation is done with resistors R1 and R2
for the positive single-ended voltage, and R3 and R4 for the positive pseudo-differential voltage.
A typical single-ended application might select the input voltage divider to provide 1.9V at the analog input of the
ADC128D818. This is sufficiently high for good resolution of the voltage, yet leaves headroom for upward
excursions from the supply of about 25%. To simplify the process of resistor selection, set the value of R2 first.
Select a value for R2 between 10 kOhm and 100 kOhm. This is low enough to avoid errors due to input leakage
currents yet high enough to protect both the inputs under and overdrive conditions as well as minimize loading of
the source. Finally, calculate R1 to provide a 1.9V input using simple voltage divider derived formula:
R1 = [(VS1 - VIN2) / VIN2 ] x R2 (7)
Care should be taken to bypass V+ with decoupling 0.1 µF ceramic capacitor and 1 µF tantalum capacitor. If
using the external reference option, VREF should be connected to a voltage reference, such as the LM4140, and
should also be decoupled to the ground plane by a 0.1 µF ceramic capacitor and a 1 µF tantalum capacitor. For
both supplies, the 0.1 µF capacitor should be located as close as possible to the ADC128D818.
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