LTC2960
APPLICATIONS INFORMATION
VOLTAGE MONITORING
THRESHOLD CONFIGURATION
TheLTC2960monitorsvoltageappliedtoitsinputsIN /IN
+
–
The LTC2960 is a voltage supervisor with a wide operating
voltagerangeupto36Vwithonly850nAquiescentcurrent.
The supervisor has two outputs, RST and OUT that pro-
vide voltage monitoring capabilities for system power-up,
power-downandbrown-outconditions. Built-inhysteresis
and a reset timeout period ensure that fluctuations due to
load transients or supply noise do not cause chattering
of the status outputs. The LTC2960 can provide reset and
voltage status signals to a microprocessor based system
or can alternatively be used as an Under Voltage Lock Out
(UVLO) for DC/DC switchers or LDOs for control over a
battery operated system.
andADJ.Aresistivedividerconnectedbetweenamonitored
voltage and ground is used to bias the inputs. Figure 1
demonstrateshowtheinputscanbemadedependentupon
a single voltage (V1). Only three resistors are required.
To calculate their values, specify desired falling reset (V )
R
+
+
+
and IN (V ) thresholds with V > V . For example:
IN
IN
R
+
V
IN
= 6.4V, V = 6V
R
V1
LTC2960-1/
LTC2960-3
R3
ADJ
RST
If the monitored voltage drops below the reset threshold,
RST pulls low until the ADJ input rises above 0.4V plus
2.5% hysteresis. An internal reset timer delays the return
of the RST output to a high state to provide monitored
voltage settling and initialization time. The RST output is
typically connected to a processor reset input.
R2
R1
+
IN
OUT
2960 F01
+
IfthemonitoredsupplyvoltagefallstotheIN (LTC2960-1/
Figure 1. Configuration for Single Voltage Monitoring
LTC2960-3)threshold,thesparecomparatorpullsOUTlow.
+
OUT remains low until the IN input rises above 0.4V plus
The solution for R1, R2 and R3 provides three equations
and three unknowns. Maximum resistor size is governed
by maximum input leakage current. For the LTC2960,
the maximum input leakage current below 85°C is 1nA.
For a maximum error of 1% due to both input currents,
the resistor divider current should be at least 100 times
the sum of the leakage currents, or 0.2μA. At the reset
5% hysteresis. OUT is typically used to signal preparation
for controlled shutdown. For example, the OUT output
may be connected to a processor nonmaskable interrupt
(NMI). Upon interrupt, the processor begins shutdown
procedures such as supply sequencing and/or storage/
erasure of system state in nonvolatile memory.
–
If the monitored supply voltage rises to the IN threshold
threshold, V1 = 6V, R
= 8MΩ where:
SUM
(LTC2960-2/LTC2960-4), the spare comparator pulls OUT
–
R
= R1 + R2 + R3
SUM
low. OUT remains low until the IN falls below 0.4V minus
+
5% hysteresis. The LTC2960-2/LTC2960-4 operates as an
undervoltage and overvoltage monitor.
Both the falling reset and IN thresholds are 0.4V, so:
VTH •RSUM 0.4V•8MΩ
R1=
=
= 500k
Few, ifany, externalcomponentsarenecessaryforreliable
V +
6.4V
IN
operation. However, a decoupling capacitor between V
CC
The closest 1% value is 499k. R2 can be determined
from:
and ground is recommended (0.01μF minimum). Use a
capacitor with a compatible voltage rating.
VTH •RSUM
0.4V • 8MΩ
R2 =
– R1=
– 499k
VR
6V
R2 = 34.33k
2960f
8
Linear Systems [ Linear Systems ]
