LTC2933
28
2933fa
For more information www.linear.com/LTC2933
Typical applicaTions
Seven-Power Supply Monitor
Figure 7 in the Typical Applications section illustrates
how to use the LTC2933 auxiliary comparators to expand
power supply monitoring to seven channels. The system is
powered by a 12V source, which is also monitored. The 9V
rail can be monitored, in addition to the six input channels
(12V, 5V, 3.3V, 2.5V, 1.8V and 24V), using an external
resistive divider which feeds the OV and UV tap voltages
to the auxiliary comparators on inputs GPI1 and GPI2.
Since the auxiliary comparators’ thresholds are fixed at
0.5V ±10mV, to monitor a 9V ±10% power supply, the
following equations apply:
+
R1+R2+R3
=
0.9 • 9V
R3
R1+R2+R3
=
0.49V
1.1• 9V
For R3 = 8.87k, the equations yield: R2 = 2.4k and R1 =
168k.
The GPI1 comparator monitors the UV limit and is pro-
grammed for negative polarity. The GPI2 comparator moni-
tors the OV limit and is programmed for positive polarity.
A second resistive divider is used to divide the
24V
rail
voltage down to 1.08V, in order to use the low leakage,
low range of the V5 channel.
