LTC2912 Linear Technology, LTC2912 Datasheet - Page 7

• Manufacturer Part Number: LTC2912
• Description: Single UV/OV Voltage Monitor
• Manufacturer: Linear Technology

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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 confi gured to monitor a posi-
tive voltage V
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
ing voltage, I
resistive divider, V
and V
1. Choose R
Figure 1. 3-Resistor Positive UV/OV Monitoring Confi guration
R
overvoltage monitor.
R
A
A
UV
is chosen to set the desired trip point for the
= 0 5 . •
is the desired undervoltage trip point.
V
n
R
R
R
I
n
C
B
A
A
V
n
n
is the desired nominal current through the
to obtain the desired OV trip point
using the 3-resistor circuit confi guration
V
V
LTC2912
VH
VL
OV
OV
n
+
–
is the desired overvoltage trip point
0.5V
n
is the desired nominal operat-
–
+
–
+
UV
OV
2912 F01
(1)
2. Choose R
Once R
point for the undervoltage monitor.
3. Choose R
Once R
If any of the variables V
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 cur-
rent in the resistive divider is 10μA.
1. Find R
2. Find R
3. Determine R
R
R
R
R
R
B
C
B
C
A
= 0 5 . •
=
=
=
=
A
A
10
10
and R
V
A
10
B
0 5
I
is known, R
0 5
n
n
5
I
.
.
to set the OV trip point of the monitor.
to set the UV trip point of the monitor.
n
µA
V
µA
µA
B
V
C
–
V
V
to complete the design
Figure 2. Typical Supply Monitor
to obtain the desired UV trip point
R
B
•
C
•
–
5V ±10%
A
V
are known, R
4 5
5 5
to complete the design.
V
45 3
UV
5
–
V1
5
n
.
.
V
V
R
R
442k
R
10.2k
R
45.3k
.
V
V
C
B
A
–
B
B
k
n
–
R
≈
is chosen to set the desired trip
, I
−
A
45 3
45 3
n
10 2
, V
VH1
VL1
.
.
.
UV
LTC2912-1
k
C
k
k
GND
V
V
≅
5V
is determined by:
or V
CC
CC
≈
10 2
2912 F02
442
OV
UV
OV
.
k
k
change, then each
LTC2912
7
2912fa
(2)
(3)