LTC2914IDHC-2 データシートの表示（PDF） - Linear Technology

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LTC2914IDHC-2

Quad UV/OV Positive/Negative Voltage Monitor

Linear Technology 

LTC2914

APPLICATIONS INFORMATION

Power-Up/Power-Down

As soon as VCC reaches 1V during power-up, the UV output

asserts low and the OV output weakly pulls to VCC.

The LTC2914 is guaranteed to assert UV low and OV high

under conditions of low VCC, down to VCC = 1V. Above VCC =

2V (2.1V maximum) the VH and VL inputs take control.

Once all VH inputs and VCC become valid an internal timer

is started. After an adjustable delay time, UV weakly pulls

high.

( ) VUV(MIN)

=

0.5V

•

0.985

•



1+

R AR+C R• B0.9•91.01

and

( ) VUV(MAX)

=

0.5V

•

1.015

•



1+

R

RC • 1.01

A + RB • 0.99





For a desired trip point of 4.5V,

RC

RA + RB

=8

Threshold Accuracy

Reset threshold accuracy is important in a supply-sensitive

system. Ideally, such a system resets only if supply voltages

fall outside the exact thresholds for a specified margin.

All LTC2914 inputs have a relative threshold accuracy of

±1.5% over the full operating temperature range.

For example, when the LTC2914 is programmed to moni-

tor a 5V input with a 10% tolerance, the desired UV trip

point is 4.5V. Because of the ±1.5% relative accuracy of

the LTC2914, the UV trip point is between 4.433V and

4.567V which is 4.5V ±1.5%.

Likewise, the accuracy of the resistances chosen for RA,

RB and RC affect the UV and OV trip points as well. Us-

ing the example just given, if the resistances used to set

the UV trip point have 1% accuracy, the UV trip range is

between 4.354V and 4.650V. This is illustrated in the fol-

lowing calculations.

The UV trip point is given as:

VUV

=

0.5V



1+

RC

RA + RB





The two extreme conditions, with a relative accuracy of

1.5% and resistance accuracy of 1%, result in:

Therefore,

VUV(MIN)

=

0.5V

•

0.985

•



1+

8

0.99 

1.01

=

4.354V

and

VUV(MAX)

=

0.5V

•

1.015

•



1+

8

1.01

0.99 

=

4.650V

Glitch Immunity

In any supervisory application, noise riding on the moni-

tored DC voltage causes spurious resets. To solve this

problem without adding hysteresis, which causes a new

error term in the trip voltage, the LTC2914 lowpass filters

the output of the first stage comparator at each input. This

filter integrates the output of the comparator before as-

serting the UV or OV logic. A transient at the input of the

comparator of sufficient magnitude and duration triggers

the output logic. The Typical Performance Characteristics

section shows a graph of the Transient Duration vs Com-

parator Overdrive.

2914fa

10

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