LTC1326 View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC1326 Datasheet PDF : 16 Pages
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LTC1326/LTC1326-2.5
APPLICATIO S I FOR ATIO
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 VCC5 pin to the VCC3 pin. This prevents the part’s
internal override circuit from being activated. Without the
override circuit active, the RST pin stays low until VCC5
reaches VRT5 ≅ 4.725V (See Figure 4).
LTC1326-2.5 Override Functions
The VCCA pin, if unused, can be tied to either VCC3 or VCC25.
This is an obvious solution since the trip points for VCC3
and VCC25 will always be greater than the trip point for
VCCA. Likewise, the VCC25, if unused, can be tied to VCC3.
VCC3 must always be used. Tying VCC3 to VCC25 and
operating off of a 2.5V supply will result in the continuous
assertion of RST.
LTC1326
D1* 1
8
VCC3 PBR
4.7k
2
7
5V
VCC5 SRST
3
6
VCCA RST
SYSTEM RESET
0.1µF 4
5
GND RST
*MMBD914 OR EQUIVALENT
1326/2.5 F03
Figure 3. LTC1326 Monitoring a Single 5V Supply.
D1 Used to Avoid RST High Near 3.3V to 4V (See
Figure 2).
5
VCC5 = VCCA = 0V TO 5V
4.7k PULL-UP FROM RST TO VCC5
4 TA = 25°C
3
2
1
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.
ADJUSTABLE SUPPLY
OR DC/DC FEEDBACK
DIVIDER
3.3V
2.5V
R1
R2
LTC1326-2.5
1
VCC3
2
VCC25
3
VCCA
4
GND
8
PBR
7
SRST
6
RST
5
RST
PUSH-BUTTON
RESET
10k*
SYSTEM RESET
*OPTIONAL RESISTOR EXTENDS ESD TOLERANCE OF PBR INPUT TO APPROXIMATELY 10kV
1326/2.5 F05
Figure 5. Triple Supply Monitor (3.3V, 2.5V
and Adjustable) with Extended ESD Tolerance
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
VCC5 (V)
1326/2.5 F04
Figure 4. RST Output Voltage
Characteristics of the Circuit in Figure 3
10
132625fc
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