LTC2914 Linear Technology, LTC2914 Datasheet - Page 8

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

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APPLICATIO S I FOR ATIO
LTC2914
Voltage Monitoring
The LTC2914 is a low power quad voltage monitoring cir-
cuit with four undervoltage and four overvoltage inputs. A
timeout period that holds OV or UV asserted after all faults
have cleared is adjustable using an external capacitor and
is externally disabled.
Each voltage monitor has two inputs (VHn and VLn) for
detecting undervoltage and overvoltage conditions. When
confi gured to monitor a positive voltage V
3-resistor circuit confi guration shown in Figure 1, V Hn is
connected to the high-side tap of the resistive divider and
VLn is connected to the low-side tap of the resistive divider.
If an input is confi gured as a negative voltage monitor, the
outputs UV
is then connected as shown in Figure 2. Note, VHn is still
connected to the high-side tap and VLn is still connected
to the low-side tap.
Polarity Selection
The three-state polarity-select pin (SEL) selects one of three
possible polarity combinations for the input thresholds,
as described in Table 1. When an input is confi gured for
negative supply monitoring, VHn is confi gured to trigger an
overvoltage condition and VLn is confi gured to trigger an
undervoltage condition. With this confi guration, an OV con-
dition occurs when the supply voltage is more negative than
the confi gured threshold and a UV condition occurs when
the voltage is less negative than the confi gured threshold.
8
Figure 1. 3-Resistor Positive UV/OV Monitoring Confi guration
V
n
R
R
R
n
C
B
A
and OV
VHn
VLn
LTC2914
U
n
+
–
in Figure 1 are swapped internally. V
0.5V
U
–
+
–
+
W
UV
OV
n
2914 F01
n
n
U
using the
n
The three-state input pin SEL is connected to GND, V
left unconnected during normal operation. When the pin
is left unconnected, the maximum leakage allowed from
the pin is ±10µA to ensure it remains in the open state.
Table 1 shows the three possible selections of polarity
based on the SEL pin connection.
Table 1. Voltage Polarity Programming (V
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 positive voltage monitor circuit in Figure 1
and the negative voltage monitor circuit in Figure 2.
Figure 2. 3-Resistor Negative UV/OV Monitoring Confi guration
Open
GND
SEL
V
CC
V
n
R
R
R
A
B
C
VH3 < V
VL3 > V
VH3 < V
VL3 > V
VH3 < V
VL3 > V
LTC2914
REF
VHn
VLn
V3 INPUT
Negative
Positive
Positive
+
–
UOT
UOT
UOT
UOT
UOT
UOT
0.5V
→ OV
→ OV
→ UV
→ UV
→ UV
→ OV
–
+
–
+
+
–
UOT
+
–
VH4 < V
VH4 < V
VH4 < V
VL4 > V
VL4 > V
VL4 > V
1V
= 0.5V Typical)
V4 INPUT
Negative
Negative
Positive
OV
UV
UOT
UOT
UOT
2914 F02
UOT
UOT
UOT
n
n
→ UV
→ OV
→ OV
→ UV
→ OV
→ UV
CC
2914f
or