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LTC2960

2960f

VOLTAGE MONITORING

The LTC2960 is a voltage supervisor with a wide operating

voltage range up to 36V with only 850nA quiescent current.

The supervisor has two outputs, RST and OUT that pro-

vide voltage monitoring capabilities for system power-up,

power-down and brown-out conditions. Built-in hysteresis

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.

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.

If the monitored supply voltage falls to the IN+ (LTC2960-1/

LTC2960-3) threshold, the spare comparator pulls OUT low.

OUT remains low until the IN+ input rises above 0.4V plus

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

(LTC2960-2/LTC2960-4), the spare comparator pulls OUT

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.

Few, if any, external components are necessary for reliable

operation. However, a decoupling capacitor between VCC

and ground is recommended (0.01μF minimum). Use a

capacitor with a compatible voltage rating.

APPLICATIONS INFORMATION

THRESHOLD CONFIGURATION

The LTC2960 monitors voltage applied to its inputs IN+/IN–

and ADJ. A resistive divider connected between a monitored

voltage and ground is used to bias the inputs. Figure 1

demonstrates how the inputs can be made dependent upon

a single voltage (V1). Only three resistors are required.

To calculate their values, specify desired falling reset (VR)

and IN+ (VIN+) thresholds with VIN+ > VR. For example:

VIN+ = 6.4V, VR = 6V

Figure 1. Configuration for Single Voltage Monitoring

ADJ

IN+

RST

OUT

LTC2960-1/

LTC2960-3

2960 F01

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

threshold, V1 = 6V, RSUM = 8MΩ where:

RSUM = R1 + R2 + R3

Both the falling reset and IN+ thresholds are 0.4V, so:

VTH •RSUM

VIN+

0.4V

• 8MΩ

6.4V

= 500k

The closest 1% value is 499k. R2 can be determined

from:

VTH • RSUM

–R1

0.4V

• 8MΩ

– 499k

R2 = 34.33k

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