LTC1726IS8-5 Linear Technology, LTC1726IS8-5 Datasheet - Page 8

• 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

Supply Monitoring
The LTC1726 is a low power, high accuracy triple supply
monitor and watchdog timer. The watchdog and reset
periods are both adjustable using external capacitors.
All three V
olds for reset not to be asserted. The LTC1726 will assert
reset during power-up, power-down and brownout condi-
tions on any one or all of the V
Upon power-up, either the V
power the drive circuits for the RST pin. This ensures that
RST will be low when either V
1V. As long as any one of the V
determined threshold, RST will stay a logic low. Once all of
the V
reset timer is started and RST is released after the reset
time-out period.
On power-down, once any of the V
threshold, RST is held at a logic low. A logic low of 0.3V is
guaranteed until both V
3V or 5V/2.5V Power Detect
Since the LTC1726 is a multisupply monitor, it will be
required to assert reset as soon as there is power on any
one of the monitor inputs. Therefore, the part derives its
power from either the V
pin has the greatest potential. This ensures the part pulls
the RST pin low as soon as either input pin is ≥1V. The
adjustable input is excluded from being a potential supply
pin because of its 1V nominal operating range.
Override Functions (5V Versions Only)
The V
This is an obvious solution since the trip points for V
and V
The V
to the voltage on V
less than 4.15V. In this manner the LTC1726-5 behaves
as a 3.3V monitor and the 5V reset function is disabled.
The V
is equal to the voltage on V
are greater than approximately 4.15V. In this manner, the
LTC1726
applicaTions inForMaTion
8
CC
CCA
CC5
CC5
CC5
inputs rise above their thresholds, the adjustable
will always be greater than the trip point for V
trip point is re-enabled when the voltage on V
pin, if unused, can be tied to either V
input trip point is disabled if its voltage is equal
CC
inputs must be above predetermined thresh-
CC3
CC3
±25mV and the voltage on V
CC3
or V
and V
CC3
CC5
CC5
CC5
±25mV and the two inputs
CC
CC
CC5
CC
/V
/V
/V
inputs.
inputs is below its pre-
CC25
inputs drops below its
/V
CC25
CC25
CC25
or V
input, whichever
or V
drop below 1V.
CC3
CC3
CC3
reaches
or V
pin can
CC5
CC5
CCA
CC3
CC5
is
.
.
part can function as a 5V monitor with the 3.3V monitor
disabled.
When monitoring either 3.3V or 5V with V
V
propriate range. The part handles this situation as shown in
Figure 2. Above 1V and below V
V
monitoring and RST is deasserted. Above approximately
4.15V, the part operates as a 5V monitor. In most systems,
the 5V supply will pass through the 3.1V to 4.15V region in
<200ms during power-up, and the RST output will behave
as desired. Table 1 summarizes the state of RST at various
operating voltages with V
Table 1. Override Truth Table (V
INPUTS (V
0V ≤ V
1V ≤ V
V
4.15V ≤ V
V
RT3
RT5
CC5
RT3
≤ V
≤ V
, (see Figure 1) the part determines which is the ap-
to approximately 4.15V, the part assumes 3.3V supply
CC
CC
3.3V OR 5V
Figure 1. Single Supply Monitor with Others Disabled
CC
CC
≤ 1V
≤ V
CC
CC3
≤ 4.15V
≤ V
RT3
V
Figure 2. RST Voltage vs Supply Voltage
CC
= V
RT5
CC5
5
4
1
3
2
0
0
= V
V
10k PULL-UP FROM RST TO V
T
A
CC3
= 25°C
CC
1
2
3
4
PINS 5, 7 AND 8 NOT SHOWN FOR CLARITY
= V
)
1
V
V
V
GND
CC5
CC3
CC5
CCA
LTC1726-5
SUPPLY VOLTAGE (V)
= V
CC3
CCA
2
CC3
RST
= V
= 0V TO 5V
= V
RT3
CC5
6
3
CC5
, RST is held low. From
CC3
.
)
4
R1
10k
CC3
1726 F02
TO SYSTEM
RESET
5
strapped to
RST
—
1726 F01
0
1
0
1
1726fc