LTC2907 データシートの表示（PDF） - Linear Technology
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LTC2907
Linear Technology
LTC2907 Datasheet PDF : 16 Pages
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LTC2906/LTC2907
APPLICATIO S I FOR ATIO
In margining application, the three-state input pins can be
driven using a three-state buffer. Note however, the low
and high output of the three-state buffer has to satisfy the
VIL and VIH of the three-state pin listed in the Electrical
Characteristics Table. Moreover, when the three-state
buffer is in the high impedance state, the maximum
leakage current allowed from the pin to either GND or V1
is 10µA.
Monitor Programming
Connecting S1 to either GND, or V1, or leaving it in open
state selects the LTC2906/LTC2907 V1 input voltage
threshold. Table 1 shows the three possible selections of
V1 nominal input voltage and their corresponding S1
connection.
Table 1. Supply Selection Programming
V1
S1
5.0
V1
3.3
OPEN
2.5
GND
Note: Open = open circuit or driven by a three-state buffer
in high impedance state with leakage current less than 10µA.
The noninverting input on the VADJ comparator is set
to 0.5V when the TOL pin is set high (5% tolerance)
(Figure␣ 1) and the high impedance inverting input directly
ties to the VADJ pin.
VTRIP
R1
1%
VADJ
R2
1%
LTC2906/LTC2907
–
+
–+ 0.5V
29067 F01
Figure 1. Setting the Adjustable Trip Point
In a typical application, the VADJ pin connects to a tap point
on an external resistive divider between the positive volt-
age being monitored and ground. The following formula
obtains R1 resistor value for a particular value of R2 and
a desired trip voltage at 5% tolerance:
R1 =
VTRIP(5%)
0.5V
–
1R2
R2 =100kΩ is recommended. Once the resistor divider is
set in the 5% tolerance mode, there is no need to change
the divider for the other tolerance modes (7.5%, 10%)
because the internal reference at the noninverting input on
the VADJ comparator is scaled accordingly, moving the trip
point in 2.5% decrements.
Table 2 shows suggested 1% resistor values for various
adjustable applications.
Table 2. Suggested 1% Resistor Values for the VADJ Inputs
VSUPPLY (V)
12
VTRIP (V)
11.25
R1 (kΩ)
2150
R2 (kΩ)
100
10
9.4
1780
100
8
7.5
1400
100
7.5
7
1300
100
6
5.6
1020
100
5
4.725
845
100
3.3
3.055
511
100
3
2.82
464
100
2.5
2.325
365
100
1.8
1.685
237
100
1.5
1.410
182
100
1.2
1.120
124
100
1
0.933
86.6
100
0.9
0.840
68.1
100
0.8
0.750
49.9
100
0.7
0.655
30.9
100
0.6
0.561
12.1
100
Tolerance Programming
The three-state input pin TOL, programs the common
supply tolerance for both V1 and VADJ input voltages (5%,
7.5% or 10%). The larger the tolerance the lower the trip
threshold. Table 3 shows the tolerances selection corre-
sponding to a particular connection at the TOL pin.
Table 3. Tolerance Programming
TOLERANCE
TOL
5%
V1
7.5%
OPEN
10%
GND
29067f
9
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