LTC2965
7
2965fb
For more information www.linear.com/LTC2965
operaTion
The LTC2965 is a micropower single channel voltage
monitor with a 100V maximum operating voltage. Its
channel is comprised of an internal high value resistive
divider and a comparator with a high voltage output. A
reference voltage is provided to allow the thresholds to be
set independently. This configuration has the advantage
of being able to monitor very high voltages with very little
current draw while threshold programming is done using
low value resistors at low voltages. Integration of a resis
-
tive divider for high voltage sensing makes the LTC2965
a compact and low power solution for generating voltage
status signals to a monitoring system.
A built-in buffered reference gives the monitor flexibil
-
ity to operate independently from a high voltage supply
without the
requirement of additional low voltage biasing.
The reference provides an accurate voltage from which
a resistive divider to ground configures the threshold
voltage for the internal comparator. In addition, the REF
pin can be used as a logic high voltage for the range and
polarity select pins.
The input voltage threshold at V
IN
is determined by the
voltage on the INH and INL pins which are scaled by the
internal resistive divider. The LTC2965 offers two range
settings to select from, 10x and 40x, using the RS pin.
Use Table 1 to determine the correct configuration for
a desired range setting. The polarity select pin, (PS),
configures the OUT pin to be inverting or noninverting
with respect to V
IN
allowing the part to be configured for
monitoring overvoltage and undervoltage conditions with
either polarity output.
Table 1.
V
IN
MONITOR RANGE RANGE SELECTION RS
3.5V to 24.5V 10x L
14V to 98V 40x H
The INH pin determines the high or rising edge threshold
for V
IN
. If the monitored voltage connected to V
IN
rises
to the scaled INH voltage then the OUT pin is pulled high
assuming PS is ground. Likewise, the INL pin determines
the low or falling edge threshold for V
IN
in each channel.
If V
IN
falls to the scaled INL voltage then the OUT pin is
pulled low assuming PS is ground. The amount of hys-
teresis referred to V
IN
is the difference in voltage between
INH and INL scaled according to the RS pin configura-
tion. INH and INL have an allowable voltage range, V
CM
.
Figure 1 shows the allowable monitor voltage at V
IN
for
each range as a function of comparator reference input
voltage (INL/INH).
Typically, an external resistive divider biased from REF is
used to generate the INH and INL pin voltages. A built-in
hysteresis feature requiring only two resistors can be
enabled on either the V
IN
rising edge by grounding INH
or on the falling edge by grounding INL. For example, it
is appropriate to ground INH to activate rising edge hys
-
teresis if an accurate falling voltage threshold is required
for undervoltage detection. Conversely, it is appropriate
to ground INL for falling edge built-in hysteresis if an ac
-
curate overvoltage threshold is required. Do not ground
both INH and INL. Oscillation occurs if V
INL
> V
INH
unless
INH built-in hysteresis is enabled.
The high voltage OUT pins have the capability to be pulled
up to a user defined voltage as high as 100V with an
external resistor. The LTC2965 also includes an internal
500k pull-up resistor to an internal voltage between 3.5V
and 5V depending on input voltage. (See V
OH
in Electrical
Characteristics).
If the V
IN
pin falls below the UVLO threshold then the OUT
pin is pulled low regardless of the PS pin state.
Figure 1. Monitor Threshold
vs Comparator Reference Inputs
COMPARATOR REFERENCE INPUT (INL, INH) (V)
MONITOR THRESHOLD, V
IN
(V)
2965 F01
100
10
1
0.5 2.521.51
40x
10x
