Datasheet

Data Sheet ADM12914
Rev. D | Page 9 of 16
THEORY OF OPERATION
VOLTAGE SUPERVISION
The ADM12914 supervises up to four voltage rails for under-
voltage and overvoltage conditions. Two pins, VHx and VLx,
are assigned to monitor each rail, one for overvoltage detection
and the other for undervoltage detection. Each pin is connected
to the input of an internal voltage comparator, and its voltage
level is internally compared with a 0.5 V voltage reference with
very high threshold accuracy of ±0.8%. The device is specified over
the extended operating temperature range from −40°C to +125°C.
The output of each of the internal undervoltage comparators is
tied to a common
UV
output pin. Likewise, the outputs of the
internal overvoltage comparators are tied to a common
OV
output pin.
VH1
1.8V
VL1
VH2
VL2
VH3
VL3
VH4
VL4
SEL
TIMER
UV
OV
LATCH/DIS
REF
GND
V
CC
ADM12914
2.5V
3.3V
5V
SYSTEM
PSU
08265-003
Figure 16. Typical Applications Diagram
POLARITY CONFIGURATION
The ADM12914 is capable of monitoring supply voltages of
both positive and negative polarities. The SEL pin is a three-
state pin that determines the polarity of Input 3 and Input 4. As
summarized in Table 5, the SEL pin is connected to either GND
or V
CC
, or is not connected.
When an input is configured to monitor a positive voltage, using
the three resistor scheme that is shown in Figure 17, VHx is
connected to the high-side tap of the resistor divider and VLx
is connected to the low-side tap of the resistor divider.
Conversely, when an input is configured to monitor a negative
voltage, UVx and OVx are swapped internally. The negative
voltage for monitoring is then connected as shown in Figure 18.
VHx remains connected to the high-side tap and VLx remains
connected to the low-side tap. Within this configuration, an
undervoltage condition occurs when the monitored voltage is less
negative than the programmed threshold, and an overvoltage
condition occurs when the monitored voltage is more negative
than the programmed threshold.
Table 5. Polarity Configuration
Input 3 Input 4
SEL Pin Polarity UV Condition OV Condition Polarity UV Condition OV Condition
Connected to V
CC
Positive VH3 < 0.5 V VL3 > 0.5 V Positive VH4 < 0.5 V VL4 > 0.5 V
Left Unconnected Positive VH3 < 0.5 V VL3 > 0.5 V Negative VL4 > 0.5 V VH4 < 0.5 V
Connected to GND
Negative
VL3 > 0.5 V
VH3 < 0.5 V
Negative
VL4 > 0.5 V
VH4 < 0.5 V