LTC2910 データシートの表示（PDF） - Linear Technology
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LTC2910 Datasheet PDF : 16 Pages
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LTC2910
APPLICATIONS INFORMATION
Voltage Monitoring
The LTC2910 is a low power octal voltage monitoring
circuit with eight individual undervoltage monitor inputs.
A timeout period that holds a reset after all faults have
cleared is adjustable using an external capacitor and is
disabled, by tying TMR to VCC.
Each voltage monitor is compared to a fixed 0.5V reference
for detecting undervoltage conditions. When configured
to monitor a positive voltage Vm, the application is con-
nected as shown in Figure 1. For negative inputs Vm is
connected as shown in Figure 2. RA is now connected to
the REF pin and RB remains connected to the monitored
voltage Vm.
Using the configurations in Figures 1 and 2, a UV condi-
tion will result when the magnitude of the voltage at Vm
is less than its designed threshold.
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 configured for
negative supply monitoring, a reset condition occurs when
the supply voltage is less negative than the configured
threshold.
The three-state input pin SEL is connected to GND, VCC, or
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.
Vm
RB
Vn
–
+
RA
–+ 0.5V
LTC2910
UVn
2910 F01
Figure 1. Positive UV Monitoring Configuration
Table 1. Voltage Polarity Programming (VRT = 0.5V Typical)
SEL
V7 INPUT
V8 INPUT
VCC
Open
GND
Positive
V7 < VRT → UV
Positive
V7 < VRT → UV
Negative
V7 > VRT → UV
Positive
V8 < VRT → UV
Negative
V8 > VRT → UV
Negative
V8 > VRT → UV
2-Step Design Procedure
The following 2-step design procedure allows selecting
appropriate resistances to obtain the desired UV trip point
for the positive voltage monitor circuit in Figure 1 and the
negative voltage monitor circuit in Figure 2.
For positive supply monitoring, Vm is the desired nominal
operating voltage, Im is the desired nominal current through
the resistive divider, and VUV is the desired undervoltage
trip point.
For negative supply monitoring, to compensate for the 1V
reference, 1V must be subtracted from Vm and VUV before
using each in the following equations.
1. Choose RA to obtain the desired UV trip point
RA is chosen to set the desired trip point for the
undervoltage monitor.
RA
=
0.5V
Im
•
Vm
VUV
(1)
LTC2910
REF
1V
RA
Vn
–
+
UVn
RB
–+ 0.5V
Vm
2910 F02
Figure 2. Negative UV Monitoring Configuration
2910fb
8
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