ltc1326cms8-trpbf Linear Technology Corporation, ltc1326cms8-trpbf Datasheet - Page 10

• Manufacturer Part Number: ltc1326cms8-trpbf
• Description: Micropower Precision Triple Supply Monitor
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC1326/LTC1326-2.5
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 LTC1326 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
10
CC5
Figure 3. LTC1326 Monitoring a Single 5V Supply.
D1 Used to Avoid RST High Near 3.3V to 4V (See
Figure 2).
5V
RT5
pin to the V
Figure 4. RST Output Voltage
Characteristics of the Circuit in Figure 3
*MMBD914 OR EQUIVALENT
≅ 4.725V (See Figure 4).
5
4
3
2
1
0
0.1µF
D1*
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V
4.7k PULL-UP FROM RST TO V
T
CC5
A
U
= 25°C
1
2
3
4
= V
V
V
V
GND
CC3
CC3
CC5
CCA
CCA
LTC1326
U
= 0V TO 5V
pin. This prevents the part’s
SRST
V
PBR
RST
RST
CC5
(V)
8
7
6
5
W
4.7k
CC5
SYSTEM RESET
1326/2.5 F04
1326/2.5 F03
U
CC5
ADJUSTABLE SUPPLY
*OPTIONAL RESISTOR EXTENDS ESD TOLERANCE OF PBR INPUT TO APPROXIMATELY 10kV
LTC1326-2.5 Override Functions
The V
This is an obvious solution since the trip points for V
and V
V
V
operating off of a 2.5V supply will result in the continuous
assertion of RST.
Extending ESD Tolerance on the PBR Input Pin
The PBR pin is susceptible to ESD since it may be brought
out to a front panel in normal applications. The ESD
tolerance of this pin can be increased by adding a resistor
in series with the PBR pin. A 10k resistor can increase the
ESD tolerance of the PBR pin to approximately 10kV. The
PBR’s internal pull-up current of 7µA typical means there
is only 70mV (150mV max) dropped across the resistor.
See Figure 5.
OR DC/DC FEEDBACK
CCA
CC3
. Likewise, the V
CCA
must always be used. Tying V
CC25
Figure 5. Triple Supply Monitor (3.3V, 2.5V
and Adjustable) with Extended ESD Tolerance
DIVIDER
pin, if unused, can be tied to either V
will always be greater than the trip point for
R1
3.3V
2.5V
CC25
R2
, if unused, can be tied to V
1
2
3
4
V
V
V
GND
LTC1326-2.5
CC3
CC25
CCA
SRST
PBR
RST
RST
CC3
8
7
6
5
to V
10k*
SYSTEM RESET
CC3
PUSH-BUTTON
CC25
or V
RESET
1326/2.5 F05
132625fc
CC25
CC3
and
CC3
.
.