Datasheet

Data Sheet ADM12914
Rev. D | Page 11 of 16
tolerances, must fit within a monitor region of just 0.024 V. The
ADM12914 device with 0.1% resistors can achieve this level of
accuracy.
1.05V
+5%
TOLERANCE
–5%
TOLERANCE
1.026V
1V CORE
VOLTAGE
0.974V
0.95V
UV
V
OLTAGE
TIME
2.4% RANGE FOR OV MONITORING
2.4% RANGE FOR UV MONITORING
+2.6% SUPPLY REGULATION
–2.6% SUPPLY REGULATION
t
UOTO
08265-006
Figure 19. Monitoring Accuracy Example
VOLTAGE MONITORING EXAMPLE
To illustrate how the ADM12914 device works in a real-world
application, consider the 1 V input example shown in Figure 19,
with the addition of a −5 V rail.
The first step is to choose the current flow through both voltage
divider circuits, for example, 5 μA.
For the 1 V ± 5% input, due to the specified ±2.6% regulation of
the supply, the UV and OV threshold should be set in the middle
of the undervoltage and overvoltage monitoring bands, respec-
tively; in this case, on the ±3.8% points of the supply, which are
0.962 V for the UV threshold and 1.038 V for OV threshold.
Input these values into Equation 1 to Equation 3 as follows:
kΩ5.96
)105)(038.1(
)1)(5.0(
6




Z
R (1)
Insert the value of R
Z
into Equation 2.
Ωk7.41kΩ5.96
)105)(962.0(
)1)(5.0(
6




Y
R
(2)
Then substitute the calculated values for R
Z
and R
Y
into
Equation 3.
kΩ5.96Ωk7.41kΩ5.96
105
1
6




X
R
(3)
This design approach meets the application specifications. As
described previously, the 1 V rail is specified with an input
requirement of ±5% and a supply tolerance of ±2.6%. This
effectively means the OV threshold of the monitoring device,
including all the tolerance factors, must fit within the 1.026 V
to 1.05 V range. Similarly, the UV threshold range must be
between 0.95 V and 0.974 V.
The four worst-case scenarios of minimum and maximum
undervoltage and overvoltage thresholds are calculated as follows:
Minimum overvoltage threshold











%)1.0(
%)1.0(%)1.0(
1%)8.05.0(
_
Z
YX
MINOV
R
RR
VV










)001.1)(500,96(
)999.0)(7410500,96(
1496.0
=1.029 V > 1.026 V
Maximum overvoltage threshold











%)1.0(
%)1.0(%)1.0(
1%)8.05.0(
_
Z
YX
MAXOV
R
RR
VV
= 1.047 V < 1.05 V
The maximum and minimum overvoltage threshold values
reside within the 1.026 V to 1.05 V range specified.
The minimum and maximum undervoltage thresholds are
calculated as follows:
Minimum undervoltage threshold











%)1.0(%)1.0(
%)1.0(
1%)8.0V5.0(
_
Z
Y
X
MINUV
RR
R
V
= 0.9557 V > 0.95 V
Maximum undervoltage threshold











%)1.0(%)1.0(
%)1.0(
1%)8.0V5.0(
_
Z
Y
X
MAXUV
RR
R
V
= 0.9729 V < 0.974 V
These values fit within the specified undervoltage monitoring
range. All four worst-case scenarios satisfy the tolerance
requirement; therefore, the design approach is valid.
ADM12914
VH1
V
CC
5V
1V RAIL
GND
VL1
VL3
VH3
REF
UV
SEL
OV
–
5V RAI
L
1.09MΩ
14.3kΩ
93.1kΩ
96.5kΩ
7.41kΩ
96.5kΩ
08265-007
Figure 20. Positive and Negative Supply Monitor Example