LTC2900 Datasheet, PDF (10/16 Pages) Linear Technology – Programmable Quad Supply Monitor with Adjustable Reset Timer

LTC2900
APPLICATIO S I FOR ATIO
V_TRIP
R3
1%
V3 OR V4
R4
1%
LTC2900
+
–
+– _0.5V
2900 F05
Figure 5. Setting the Positive Adjustable Trip Point
sensed and ground, is connected to the high impedance
noninverting inputs (V3, V4). The trip voltage is calculated
from:
V_TRIP = 0.5V^{}1+ _RR34^{}
In the negative adjustable mode, the noninverting input on
the V4 comparator is connected to ground (Figure 6). The
tap point on an external resistive divider, connected be-
tween the negative voltage being sensed and the V_REF pin,
is connected to the high impedance inverting input (V4).
V_REF provides the necessary level shift required to operate
at ground. The trip voltage is calculated from:
V_TRIP = –V_REF^{} _RR34^{}; V_REF = 1.210V Nominal
In a negative adjustable application, the minimum value
for R4 is limited by the sourcing capability of V_REF (±1mA).
With no other load on V_REF, R4 (minimum) is:
1.21V ÷ 1mA = 1.21kΩ.
Tables 2 and 3 offer suggested 1% resistor values for
various adjustable applications.
8
V_REF
R4
1% _{9 V4}
R3
1%
V_TRIP
LTC2900
–
+
2900 F06
Figure 6. Setting the Negative Adjustable Trip Point
Table 2. Suggested 1% Resistor Values for the ADJ Inputs
V_SUPPLY (V)
12
V_TRIP (V)
11.25
R3 (kΩ)
2150
R4 (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
Table 3. Suggested 1% Resistor Values for the –ADJ Input
V_SUPPLY (V)
–2
V_TRIP (V)
–1.87
R3 (kΩ)
187
R4 (kΩ)
121
–5
– 4.64
464
121
– 5.2
– 4.87
487
121
–10
– 9.31
931
121
–12
–11.30
1130
121
2900f
10