Datasheet

LTC2938/LTC2939
11
293839ff
APPLICATIONS INFORMATION
A less accurate supervisor increases the required system
voltage margin and increases the probability of system
malfunction. The LTC2938 and LTC2939 ±1.5% specifi ca-
tion improves the reliability of the system over supervisors
with wider threshold tolerances.
Monitor Confi guration
Select the LTC2938/LTC2939 input voltage combination
by placing the recommended resistive divider from V
REF
to GND and connect the tap point to V
PG
, as shown in
Figure 2.
Table 1 offers recommended 1% resistor values for the
various modes. The rightmost column in Table 1 specifi es
optimum V
PG
/V
REF
ratios (±0.01), when confi guring with
a ratiometric DAC.
Table 1. Voltage Threshold Modes
MODE V1 (V) V2 (V) V3 (V) V4 (V) R1 (kΩ) R2 (kΩ) V
PG
/V
REF
0 5 3.3 ADJ ADJ Open Short 0
1 5 3.3 ADJ –ADJ 93.1 9.53 0.094
2 3.3 2.5 ADJ ADJ 86.6 16.2 0.156
3 3.3 2.5 ADJ –ADJ 78.7 22.1 0.219
4 3.3 1.8 1.5 ADJ 71.5 28 0.281
5 5 3.3 2.5 ADJ 66.5 34.8 0.344
6 5 3.3 2.5 1.8 59 40.2 0.406
7 3.3 1.8 1.5 1.2 53.6 47.5 0.469
8 3.3 1.8 1.2 ADJ 47.5 53.6 0.531
9 3.3 1.8 ADJ ADJ 40.2 59 0.594
10 3.3 2.5 1.8 1.5 34.8 66.5 0.656
11 3.3 2.5 1.8 ADJ 28 71.5 0.719
12 3.3 1.8 ADJ –ADJ 22.1 78.7 0.781
13 3.3 1.5 ADJ ADJ 16.2 86.6 0.844
14 5 3.3 1.8 ADJ 9.53 93.1 0.906
15 3.3 1.2 ADJ ADJ Short Open 1
Upon power-up, the LTC2938 or LTC2939 enters a con-
fi guration period of approximately 150μs during which
the voltage on the V
PG
input is sampled and the monitor
is confi gured to the desired input combination. Do not
add capacitance to the V
PG
input. Immediately after
programming, the comparators are enabled and supply
monitoring begins.
Figure 2. Monitor Programming
R1
1%
R2
1%
293839 F02
V
REF
V
PG
GND
LTC2938/
LTC2939