LTC1726 LINER [Linear Technology], LTC1726 Datasheet - Page 7

• Manufacturer Part Number: LTC1726
• Description: Triple Supply Monitor and uP Supervisor with Adjustable Reset and Watchdog Timer
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
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
predetermined threshold, RST will stay a logic low. Once
all of the V
adjustable 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
ever 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
V
inputs are greater than approximately 4.15V. In this
CC5
is equal to the voltage on V
CCA
CC5
CC5
CC5
will always be greater than the trip point for V
pin, if unused, can be tied to either V
input trip point is disabled if its voltage is equal
CC
trip point is re-enabled when the voltage on
CC
inputs must be above predetermined thresh-
inputs rise above their thresholds, the
CC3
U
CC3
CC3
25mV and the voltage on V
U
and V
or V
CC5
CC5
CC
CC5
CC5
CC3
CC
/V
/V
inputs.
CC
W
/V
CC25
inputs drops below its
CC25
/V
CC25
inputs is below its
CC25
25mV and the two
or V
or V
drop below 1V.
input, which-
CC3
CC3
CC3
U
or V
reaches
pin can
CC5
CC5
CCA
CC3
is
.
.
manner, the part can function as a 5V monitor with the
3.3V monitor disabled.
When monitoring either 3.3V or 5V with V
V
appropriate range. The part handles this situation as
shown in Figure 2. Above 1V and below V
low. From V
sumes 3.3V supply 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
, (see Figure 1) the part determines which is the
CC
CC
3.3V OR 5V
Figure 1. Single Supply Monitor with Others Disabled
V
V
CC
CC
CC
CC3
1V
V
RT3
V
4.15V
CC
Figure 2. RST Voltage vs Supply Voltage
= V
V
5
4
1
3
2
0
RT5
RT3
0
CC5
V
10k PULL-UP FROM RST TO V
T
A
CC3
CC3
= V
= 25 C
to approximately 4.15V, the part as-
= V
CC
1
1
2
3
4
= V
PINS 5, 7 AND 8 NOT SHOWN FOR CLARITY
CC5
)
SUPPLY VOLTAGE (V)
V
V
V
GND
CC3
CC5
CCA
= V
CC5
LTC1726-5
CCA
2
.
= 0V TO 5V
CC3
RST
3
= V
6
CC3
CC5
)
4
R1
10k
1726 F02
RT3
LTC1726
CC3
5
, RST is held
TO SYSTEM
RESET
strapped to
1726 F01
RST
—
0
1
0
1
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