LTC2914 Linear Technology, LTC2914 Datasheet - Page 9

• Manufacturer Part Number: LTC2914
• Description: Quad UV/OV Positive/Negative Voltage Monitor
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
For positive supply monitoring, V
operating voltage, I
the resistive divider, V
point and V
For negative supply monitoring, to compensate for the 1V
reference, 1V must be subtracted from V
before using each in the following equations.
1. Choose R
2. Choose R
3. Choose R
If any of the variables V
step must be recalculated.
Positive Voltage Monitor Example
A positive voltage monitor application is shown in Figure 3.
The monitored voltage is a 5V ±10% supply. Nominal cur-
rent in the resistive divider is 10µA.
R
overvoltage monitor.
Once R
point for the undervoltage monitor.
Once R
R
R
R
A
B
C
A
= 0 5 . •
=
is chosen to set the desired trip point for the
= 0 5 . •
V
I
A
A
n
n
I
I
n
n
UV
is known, R
and R
V
A
B
C
–
V
Figure 3. Positive Supply Monitor
to Complete the Design
R
to obtain the desired OV trip point
to obtain the desired UV trip point
is the desired undervoltage trip point.
5V ±10%
A
V
V
V
V
UV
B
OV
–
V1
n
n
n
U
are known, R
is the desired nominal current through
R
R
442k
R
10.2k
R
45.3k
C
B
A
–
B
OV
n
R
B
, I
A
is chosen to set the desired trip
n
U
is the desired overvoltage trip
, V
VH1
VL1
UV
LTC2914
GND
V
V
5V
or V
CC
CC
C
n
2914 F03
is determined by:
is the desired nominal
SEL
W
OV
UV
OV
change, then each
n
, V
OV
U
and V
(1)
(2)
(3)
UV
1. Find R
2. Find R
3. Determine R
Negative Voltage Monitor Example
A negative voltage monitor application is shown in Figure 4.
The monitored voltage is a –5V ±10% supply. Nominal
current in the resistive divider is 10µA. For the negative
case, 1V is subtracted from V
1. Find R
2. Find R
3. Determine R
R
R
R
R
R
R
B
C
B
C
A
A
=
=
=
=
=
=
10
10
10
A
10
B
0 5
A
10
B
0 5
–
0 5
0 5
5
.
.
5
.
.
10
to set the OV trip point of the monitor.
to set the UV trip point of the monitor.
to set the OV trip point of the monitor.
to set the UV trip point of the monitor.
µA
µA
V
µA
µA
µA
V
V
V
V
V
Figure 4. Negative Supply Monitor
µA
–
–5V ±10%
•
C
•
C
•
–
• –
1
V
4 5
4 5
5 5
to complete the design.
to complete the design.
– .
V3
45 3
5
5
5
.
.
.
5 5
V
V
−
R
46.4k
R
8.45k
R
549k
V
5
.
A
B
C
V
V
V
V
–
46 4
V
k
–
–
≈
–
1
−
–
.
V
1
45 3
1
45 3
V
10 2
V
1
k
REF
VH3
VL3
V
.
−
−
.
.
LTC2914
k
n
≈
8 45
46 4
k
GND
k
V
, V
V
5V
.
≅
CC
CC
46 4
≈
.
2914 F04
10 2
OV
SEL
442
.
k
k
OV
UV
.
and V
≅
≈
k
k
549
8 45
k
LTC2914
.
UV
k
k
.
9
2914f