LTC1726IS8-5 Linear Technology, LTC1726IS8-5 Datasheet - Page 9

• Manufacturer Part Number: LTC1726IS8-5
• Description: IC MON TRPL SPPLY SUPERVSR 8SOIC
• Manufacturer: Linear Technology
• Type: Multi-Voltage Supervisorr

Specifications of LTC1726IS8-5

• Number Of Voltages Monitored: 3
• Output: Open Drain or Open Collector
• Reset: Active Low
• Reset Timeout: Adjustable/Selectable
• Voltage - Threshold: 3.085V, 4.675V, Adj
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

applicaTions inForMaTion
Figure 3 contains a simple circuit for 5V systems that can’t
risk the RST output going high in the 3.1V to 4.15V range
(possibly due to very slow rise time on the 5V supply).
Diode D1 powers the LTC1726-5 while dropping ≈ 0.6V
from the V
internal override circuit from being activated. Without the
override circuit active, the RST pin stays low until V
reaches V
5V
0.1µF
Figure 3. LTC1726-5 Monitoring a Single 5V
Supply. D1 Used to Avoid RST High Near 3.1V
to 4V (See Figure 2).
RT5
CC5
Figure 4. RST Output Voltage
Characteristics of the Circuit in Figure 3
5
4
3
2
1
0
≅ 4.675V. (See Figure 4.)
pin to the V
D1
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V
10k PULL-UP FROM RST TO V
T
A
CC5
= 25°C
1
2
3
4
= V
D1: MMBD914 OR EQUIVALENT
PINS 5, 7 AND 8 NOT SHOWN FOR CLARITY
V
V
V
GND
CCA
CC3
CC5
CCA
LTC1726-5
= 0V TO 5V
CC3
V
CC5
RST
pin. This prevents the part’s
(V)
6
CC5
R1
10k
1726 F04
TO SYSTEM
RESET
1726 F03
CC5
LTC1726-2.5 Override Functions
The V
V
V
for V
V
operating off of a 2.5V supply will result in the continuous
assertion of RST.
Watchdog Timer
The watchdog circuit monitors a µP’s activity. The µP is
required to change the logic state of the WDI pin on a
periodic basis in order to clear the watchdog timer and
prevent the LTC1726 from issuing a reset.
During power-up, the watchdog timer remains cleared
while reset is asserted. As soon as the reset timer times
out, the watchdog timer is started. The watchdog timer
will continue to run until a transition is detected on the
WDI input or until the watchdog timer times out. Once the
watchdog timer times out, the internal circuitry asserts
the reset and starts the reset timer. When the reset timer
times out and reset is deasserted, the watchdog timer is
again started. If no WDI transition is received within the
watchdog time-out period, the reset will be reasserted at
the end of the watchdog time-out period. If a transition is
received on the WDI input during the watchdog time-out
period, the watchdog timer will be restarted and reset will
remain deasserted.
CC25
CC3
CC3
. V
CCA
and V
. This is an obvious solution since the trip points for
CCA
CC3
. Likewise, the V
pin, if unused, can be tied to either V
CC25
must always be used. Tying V
will always be greater than the trip point
CC25
, if unused, can be tied to
CC3
LTC1726
to V
CC25
CC3
1726fc
and
9
or