Datasheet

LTC1726
10
1726fc
Typical applicaTions
Disabling the Watchdog Timer
Triple Supply Monitor (3.3V, 5V and Adjustable) Dual Supply Monitor (3.3V and 5V, Defeat V
CCA
Input)
Selecting the Reset and Watchdog
Time-Out Capacitors
The reset time-out period is adjustable in order to accom-
modate a variety of µP applications. The reset time-out
period, t
RT
, is adjusted by connecting a capacitor, C
RT
,
between the RT pin and ground. The value of this capacitor
is determined as follows:
C
RT
= t
RT
/3.30
with C
RT
in pF and t
RT
in µs (i.e., 1500pF ⇒ 4.95ms).
The capacitor should be a low leakage type. A ceramic
capacitor is recommended.
The watchdog period is also adjustable so that the watchdog
time-out period can be optimized for software execution.
The watchdog time-out period, t
WT
, is adjusted by connect-
ing a capacitor, C
WT
, between the WT pin and ground. Once
the optimum watchdog time-out period (t
WT
) is determined,
the value of the capacitor is calculated as follows:
C
WT
= t
WT
/21.8
with C
WT
in pF and t
WT
in µs (i.e., 1500pF ⇒ 32.7ms).
The capacitor should be a low leakage type. A ceramic
capacitor is recommended.
applicaTions inForMaTion
1
2
3
4
8
7
6
5
V
CC3
V
CCA
GND
RT
WT
RST
WDI
LTC1726-5/LTC1726-2.5
3.3V
SYSTEM
RESET
*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL
COMBINATION OF R1 AND R2 ≤ 66.5k
THE WATCHDOG TIMER CAN BE DISABLED BY CONNECTING
THE WDI AND WT PINS TO GROUND. THE PART WILL ACT
STRICTLY AS A TRIPLE SUPPLY MONITOR WITH AN
ADJUSTABLE RESET TIME-OUT PERIOD
C
RT
5V/2.5V
R2*
R1*
1726 TA03
ADJUSTABLE
SUPPLY
V
CC5
/V
CC25
1
2
3
4
8
7
6
5
V
CC3
V
CC5
V
CCA
GND
RT
WT
RST
WDI
LTC1726-5
3.3V
SYSTEM RESET
*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL
COMBINATION OF R1 AND R2 ≤ 66.5k
C
RT
C
WT
WDI
5V
R2*
R1*
1726 TA04
ADJUSTABLE SUPPLY
OR DC/DC FEEDBACK
DIVIDER
1
2
3
4
8
7
6
5
V
CC3
V
CC5
V
CCA
GND
RT
WT
RST
WDI
LTC1726-5
3.3V
SYSTEM RESET
WDI
5V
1726 TA05
C
RT
C
WT