Datasheet

LTC2953
15
2953f
APPLICATIONS INFORMATION
2953 F14
LTC2953-1
–
+
–
+
+
0.5V
0.5V
R14
2150k
R13
23.2k
R12
196k
V
TH
= 5.4V
V
TH
= 6.04V
UVLO
COMPARATOR
POWER FAIL
COMPARATOR
PFOPFI
UVLO
EN
INT
V
IN
8.4V
DEBOUNCE
AND DELAY
DEBOUNCE
50mV
4mV
Which Input Initiated Power Down:
⎯
P
⎯
B or UVLO?
The circuit in Figure 14 determines whether a power
down was initiated by a user pressing the push button
or by a battery drooping too low. If both
⎯
I
⎯
N
⎯
T and
⎯
P
⎯
F
⎯
O
outputs are low, then a low battery condition initiated a
power down.
PFI and UVLO Thresholds
The circuit depicted in Figure 14 uses one resistive divider
network for both power fail and low battery comparators.
The power fail comparator trips at a higher battery voltage
than the low battery comparator, thus providing a battery
warning before a power down sequence is initiated. Due
to the low offset architecture of the comparators, the
UVLO and
⎯
P
⎯
F
⎯
I thresholds can be set to as close as ±5mV
apart. The trip thresholds of the circuit of Figure 14 are
6.04V and 5.40V for the power fail and low battery (UVLO)
comparators, respectively.
Push Button Lockout
The LTC2953 provides a push button lock out feature that
prevents a user from turning on a system with a dead
battery. The push button input is ignored when the UVLO
input voltage is less than the falling threshold (0.5V). See
Figure 15B.
t
DB, OFF
t
INT, Min
UVLO
INT
2953 F15a
0.5V
0.55V
SUPPLY
GLITCH
t
DB, OFF
t
PD, Min
+ t
PDT
UVLO
EN
INT
2953 F15b
0.5V
LOW SUPPLY
LOCKS OUT
ENABLE
LOW SUPPLY CONDITION
Figure 14. Dual Function Battery Comparators
Figure 15A. Supply Glitch Generates μP Interrupt
Figure 15B. Low Supply Initiates System
Power Down and Locks Out Enable