LTC1326 LINER [Linear Technology], LTC1326 Datasheet - Page 9

• Manufacturer Part Number: LTC1326
• Description: Micropower Precision Triple Supply Monitors
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
During a supply induced reset condition, the ability of the
PBR pin to force a soft reset condition on the SRST pin
is disabled. In other words SRST will remain high. If the
PBR pin is held low, both during and after a supply
induced reset (low RST), the RST pin will remain low until
200ms after the PBR goes high.
Power Detect/Gate Drive
The LTC1326/LTC1326-2.5 for the most part are powered
internally from the V
drive of the output FET on the RST pin. On the input to this
FET is power detection circuitry used to detect and drive
the gate from either the 3.3V input pin (V
input pin (V
(V
from the pin with the highest potential. This ensures the
part pulls the RST pin low as soon as either input pin is
Early versions of the LTC1326 did not have the power
detect/gate drive circuitry. These early versions were
powered off of V
concerning this circuitry change. All date codes of the
LTC1326-2.5 have the power detect/gate drive circuits.
Dual and Single Supply Monitor Operation
The V
disabled by the following override techniques which allow
the LTC1326 or LTC1326-2.5 to be used as a dual or single
supply monitor.
LTC1326 Override Functions
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 part will behave as a
3.3V monitor and the V
The V
is equal to the voltage on V
are greater than approximately 4.15V. In this manner the
LTC1326 can function as a 5V monitor with the 3.3V
monitor disabled.
1V.
CC25
CCA
CC5
CC5
CC5
CC3
) on the LTC1326-2.5. The gate drive is derived
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
, V
CC5
CC5
) on the LTC1326 or the 2.5V input pin
CC3
and V
CC3
U
alone. Consult factory for date codes
CC3
CCA
CC5
25mV and the voltage on V
pin. The exception is at the gate
U
CC3
reset will be disabled.
inputs may be individually
25mV and the two inputs
W
CC3
CC3
) or the 5V
U
or V
CC5
CC5
CCA
CC5
CC3
is
.
.
When monitoring either 3.3V or 5V with V
V
appropriate range. The LTC1326 handles this situation as
shown in Figure 2. Above 1V and below V
low. From V
assumes 3.3V supply monitoring and RST is deasserted.
Above approximately 4.15V the LTC1326 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 and 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
ADJUSTABLE
, (see Figure 1) the LTC1326 determines which is the
SUPPLY
CC
CC
V
V
CC3
CC
CC
CC
CC3
1V
V
RT3
= V
4.15V
Figure 2. RST Voltage vs Supply Voltage
= V
V
RT5
R1
RT3
5
4
2
1
0
CC5
CC5
3
0
3.3V OR
V
4.7k PULL-UP FROM RST TO V
= V
LTC1326/LTC1326-2.5
.
CC3
to approximately 4.15V the LTC1326
5V
R2
CC
= V
)
1
CC5
SUPPLY VOLTAGE (V)
1
2
3
4
= V
Figure 1
CCA
V
V
V
GND
2
CC3
CC5
CCA
CC3
LTC1326
= 0V TO 5V
= V
SRST
3
PBR
RST
RST
CC5
RST
—
0
1
0
1
CC3
)
8
7
6
5
4
1326/2.5 F02
RT3
CC3
4.7k
SYSTEM RESET
, RST is held
5
strapped to
RST
—
1
0
1
0
1326/2.5 F01
9