LTC2965_15 Datasheet, PDF (10/18 Pages) Linear Technology – 100V Micropower Single Voltage Monitor

LTC2965
Applications Information
The closest 1% value is 301kΩ. Plugging the standard
values back into the equation for V_INL yields the design
voltage for V_INL:
V_INL
=
(R1• V_REF)
(R1+ R2)
=
(909kΩ • 2.402V)
(301kΩ + 909kΩ)
=
1.804V
At this point in the independent divider example only the
values required to set the voltage at INL have been found.
Repeat the process for the INH input by substituting the
above equations with V_INH for V_INL, R3 for R1, R4 for R2
and V_INH = 2.0V.
V_IN
V_IN
REF ^VIN OUT
R3
LTC2965
RS
INH
PS
R2
INL
GND
R1
REF ^VIN OUT
R2 R4
LTC2965
RS
INH
PS
INL
GND
R1 R3
Figure 2a. Three-Resistor
Threshold Configuration
2965 F02ab
Figure 2b.Two-Resistor
Threshold Configuration
Using built-in hysteresis, the V_INA thresholds are:
V_IN(RISE) = RANGE • (INL + V_HYS)
V_IN(FALL) = RANGE • INL
Figure 3b introduces built-in hysteresis on the falling edge
because INL is pulled to ground. Similarly, a two-resistor
network, R3 and R4, is used to set the voltage on INH using:
R4 ₌ V_{REF – 1}
R3 V_INH
Using built-in hysteresis the V_IN thresholds are:
V_IN(FALL) = RANGE • INH
V_IN(FALL) = RANGE • (INH – V_HYS)
Consider V_INH = 2V with built-in hysteresis activated on
the falling edge. For 10x range, 1.1% falling hysteresis is
obtained. If a larger percentage of hysteresis is desired then
V_INH is alternatively set to 0.5V and the range is selected
to be 40x to obtain the same V_IN threshold but with 4.4%
falling hysteresis. The amount of built-in hysteresis is
scaled according to Table 2. If more hysteresis is needed
then it is implemented in the external resistive divider as
described in the Threshold Configuration section.
Using Built-In Hysteresis
The LTC2965 has the capability of simplifying the threshold
configuration such that only two resistors are required.
The device pins can be configured to select a built-in hys-
teresis voltage, V_HYS, which can be applied to either the
rising or falling threshold depending on whether the INH
or INL pin is grounded. Note that the hysteresis voltage
at each range setting remains at a fixed value. Figure 3
introduces examples of each configuration. For example,
if INH is biased from an external divider and the INL pin is
grounded, then hysteresis is enabled on the low or falling
threshold. The low threshold is then –V_HYS relative to the
high threshold determined by INH. Figure 3a introduces
built-in hysteresis on the rising edge because INH is pulled
to ground. A two-resistor network, R1 and R2, is used to
set the voltage on INL using:
V_IN
V_IN
REF
OUT
LTC2965
R2
INH
INL
RS
R1
GND ^PS
V_IN
V_IN
REF
OUT
LTC2965
R4
INH
INL
RS
R3
GND ^PS
2965 F03ab
Figure 3a. Rising Edge
Built-In Hysteresis
Figure 3b. Falling Edge
Built-In Hysteresis
Table 2. Built-In Hysteresis Voltage vs Range
RANGE
V_IN REFERRED BUILT-IN HYSTERESIS
10x
220mV
40x
880mV
R2
R1
=
V_REF
V_INL
–1
2965f
10
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