LTC1727 Linear Technology, LTC1727 Datasheet - Page 10

• Manufacturer Part Number: LTC1727
• Description: Micropower Precision Triple Supply Monitors in 8-Lead MSOP and 5-Lead SOT-23 Packages
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC1727/LTC1728
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 LTC1727-5/
LTC1728-5 will behave as a 3.3V monitor and V
capability will be disabled.
The V
is equal to the voltage on V
are greater than approximately 4.15V. In this manner, the
part can function as a 5V monitor with the 3.3V monitor
disabled.
10
CCA
CC5
CC5
CC5
will always be greater than the trip point for V
pin, if unused, can be tied to either V
trip point is reenabled when the voltage on V
input trip point is disabled if its voltage is equal
CC3
U
25mV and the voltage on V
U
CC3
25mV and the two inputs
W
3.3V OR 5V
Figure 2. Single Supply Monitor with Others Disabled
V
CC
Figure 3. RST Voltage vs Supply Voltage
1
5
4
3
2
0
0
V
10k PULL-UP FROM RST TO V
CC3
CC3
U
CC5
= V
or V
1
5
4
3
2
CC5
CC5
reset
SUPPLY VOLTAGE (V)
V
V
V
GND
CC5
CCA
CC3
CC5
CCA
= V
CC5
CC3
LTC1728-5
is
CCA
2
.
.
= 0V TO 5V
RST
When monitoring either 3.3V or 5V with V
V
appropriate range. The part handles this situation as
shown in Figure 3. Above 1V and below V
low. From V
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
3
RT3
RT5
CC5
CC3
1
CC3
CC
CC
= V
V
V
(see Figure 2), the part determines which is the
CC
4
CC
CC
CC3
1727/28 F03
1V
V
CC5
R1
10k
RT3
4.15V
= V
V
RT3
.
RT5
5
CC5
TO SYSTEM
RESET
to approximately 4.15V the part assumes
= V
1727/28 F02
CC
)
CC3
= V
CC5
)
RT3
CC3
, RST is held
strapped to
RST
—
0
1
0
1