LTC2938 LINER [Linear Technology], LTC2938 Datasheet - Page 12

• Manufacturer Part Number: LTC2938
• Description: Confi gurable 4- and 6-Supply Monitors with Watchdog Timer
• Manufacturer: LINER [Linear Technology]

LTC2938/LTC2939
APPLICATIONS INFORMATION
Using the Adjustable Thresholds
The reference inputs on the V3 and/or V4 comparators are
set to 0.5V when the positive adjustable modes are se-
lected (Figure 3). The LTC2939 V5 and V6 comparators are
always in positive adjustable mode with a 0.5V reference.
The tap point on an external resistive divider, connected
between the positive voltage being sensed and ground, is
connected to the high impedance, adjustable inputs (V3,
V4, V5 and V6). Calculate the trip voltage from:
In the negative adjustable mode, the high impedance,
adjustable input on the V4 comparator is connected to
ground (Figure 4). The tap point on an external resistive
divider, connected between the negative voltage being
sensed and the V
impedance adjustable input (V4). V
essary level shift required to operate at ground. The nega-
tive trip voltage is calculated from:
12
V
V
TRIP
TRIP
V3, V4, V5 OR V6
Figure 4. Setting the Negative Adjustable Trip Point
Figure 3. Setting the Positive Adjustable Trip Point
= −
=
V
0 5
TRIP
.
V
R4
1%
R3
1%
V
REF
V
TRIP
•
R3
1%
R4
1%
REF
⎛
⎝ ⎜
•
1
V
V4
R
R
REF
+
output, is connected to the high
3
4
R
R
;
LTC2938/LTC2839
3
4
+
–
V
⎞
⎠ ⎟
REF
0.5V
LTC2938/LTC2939
=
1 210
REF
.
293839 F04
provides the nec-
V No
293839 F03
min
al
In a negative adjustable application, the minimum value for
R4 is limited by the sourcing capability of V
With no other load on V
Tables 2 and 3 offer suggested 1% resistor values for
various adjustable applications assuming 5% monitor
thresholds.
Table 2. Suggested 1% Resistor Values for the ADJ Inputs
Table 3. Suggested 1% Resistor Values for the Negative
ADJ Inputs
Although all of the supply monitor comparators have
built-in glitch immunity, bypass capacitors on V1 and V2
are recommended because the greater of V1 or V2 is also
the supply for the device. Filter capacitors on the V3, V4,
V5 and V6 inputs are allowed.
V
V
1 210
SUPPLY
SUPPLY
.
1
–5.2
–10
–12
7.5
3.3
2.5
1.8
1.5
1.2
0.9
mA
12
10
–2
–5
8
6
5
3
1
(V)
(V)
V
=
1 210
.
V
V
–11.30
TRIP
TRIP
11.25
4.725
3.055
2.325
1.685
1.410
1.120
0.933
0.840
–1.87
–4.64
–4.87
–9.31
2.82
9.4
7.5
5.6
7
(V)
(V)
k
REF
, R4 (minimum) is:
R3 (kΩ)
R3 (kΩ)
2150
1780
1400
1300
1020
1130
86.6
68.1
1.87
845
511
464
365
237
182
124
464
487
931
REF
R4 (kΩ)
R4 (kΩ)
100
100
100
100
100
100
100
100
100
100
100
100
100
100
121
121
121
121
121
(±1mA).
293839ff