Datasheet
LTC2912
8
2912fb
For more information www.linear.com/LTC2912
APPLICATIONS INFORMATION
Voltage Monitoring
The LTC2912 is a low power voltage monitoring circuit
with an undervoltage and an overvoltage input. A timeout
period that holds OV and UV asserted after a fault has
cleared is adjustable using an external capacitor and may
be externally disabled. When configured to monitor a posi
‑
tive voltage V
n
using the 3‑resistor circuit configuration
shown in Figure 1, VH will be connected to the high side
tap of the resistive divider and VL will be connected to the
low side tap of the resistive divider.
3-Step Design Procedure
The following 3‑step design procedure allows selecting
appropriate resistances to obtain the desired UV and OV
trip points for the voltage monitor circuit in Figure 1.
For supply monitoring, V
n
is the desired nominal operat‑
ing voltage, I
n
is the desired nominal current through the
resistive divider, V
OV
is the desired overvoltage trip point
and V
UV
is the desired undervoltage trip point.
1. Choose R
A
to obtain the desired OV trip point
R
A
is chosen to set the desired trip point for the over‑
voltage monitor.
R
A
=
0.5V
I
n
•
V
n
V
OV
(1)
2. Choose R
B
to obtain the desired UV trip point
Once R
A
is known, R
B
is chosen to set the desired trip
point for the undervoltage monitor.
R
B
=
0.5V
I
n
•
V
n
V
UV
– R
A
(2)
3. Choose R
C
to complete the design
Once R
A
and R
B
are known, R
C
is determined by:
R
C
=
V
n
I
n
– R
A
– R
B
(3)
If any of the variables V
n
, I
n
, V
UV
or V
OV
change, then each
step must be recalculated.
Voltage Monitor Example
A typical voltage monitor application is shown in Figure 2.
The monitored voltage is a 5V ±10% supply. Nominal
current in the resistive divider is 10µA.
1. Find R
A
to set the OV trip point of the monitor.
R
A
=
0.5V
10µA
•
5V
5.5V
≈ 45.3k
2. Find R
B
to set the UV trip point of the monitor.
R
B
=
0.5V
10µA
•
5V
4.5V
– 45.3k ≅ 10.2k
3. Determine R
C
to complete the design.
R
C
=
5V
10µA
– 45.3k − 10.2k ≈ 442k
Figure 1. 3-Resistor Positive UV/OV Monitoring Configuration
Figure 2. Typical Supply Monitor
–
+
–
+
+
–
0.5V
LTC2912
UV
VH
R
C
R
B
R
A
2912 F01
V
n
VL
OV
VH1
R
C
442k
R
B
10.2k
R
A
45.3k
V
CC
GND
LTC2912-1
VL1
2912 F02
OV
UV
V
CC
5V
V1
5V ±10%