Datasheet

Microcontroller
SDA
SCL
A0
A1
INT
IN0
ADC128D818
GND
V+
IN1
IN2
IN3
IN4+
VREF
IN5-
IN6
IN7
RB_top
LM4140
+
(optional)
+
0.1 PF
SHUTDOWN
DC-DC
10VIN
argining Voltage
V+
V+
R
TRACE
R
R
R
RB_bottom
1 PF
1 PF
0.1 PF
RB_top
RB_bottom
ADC128D818
SNAS483E –FEBRUARY 2010–REVISED MARCH 2013 www.ti.com
Since SDA, SCL, and INT are open-drain pins, they should have external pull-up resistors to ensure that the bus
is pulled high until a master device or slave device sinks enough current to pull the bus low. A typical pull-up
resistor, R, ranges from 1.1 kOhm to 10 kOhm. Refer to NXP's "I2C-Bus Specification and User Manual" for
more information on sizing R.
Because there are two tri-level address pins (A0 and A1), up to 9 devices can share the same I
2
C bus. A trick to
set these serial addresses utilizes four GPO (general purpose output) pins from the master device as shown in
the example diagram. A table showing how to program these GPO pins can be seen below.
Table 7. Setting Serial Bus Address using GPO
A1 A0 GPO1 GPO2 GPO3 GPO4
LOW LOW Z LOW Z LOW
LOW MID Z LOW HIGH LOW
LOW HIGH Z LOW HIGH Z
MID LOW HIGH LOW Z LOW
MID MID HIGH LOW HIGH LOW
MID HIGH HIGH LOW HIGH Z
HIGH LOW HIGH Z Z LOW
HIGH MID HIGH Z HIGH LOW
HIGH HIGH HIGH Z HIGH Z
Voltage Monitoring for Power Supplies
Figure 37. Power Supply Application
Figure 37 shows a more complete systems application using a DC/DC converter. Such configuration can be used
in a power supply application. The point to make with this example diagram is the Serial Bus Address
connections. The previous example shows A0 and A1 connected to four GPOs, but this example shows a
simpler A0 and A1 connection using two resistor dividers. This connection accomplishes the same goal as the
GPO connection, that is, it can set A0 and A1 high, low, or to midscale.
For example, to set A0 high, don't populate RB_bottom; to set A0 low, don't populate RB_top; and to set A0 to
midscale, leave RB_top and RB_bottom as is and set them equal to each other. A typical RB value ranges from
1 kOhm to 10 kOhm.
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