LTC2913

8

2913fa

APPLICATIONS INFORMATION

Power-Up/Power-Down

The LTC2913 is guaranteed to assert UV low and OV high

control.

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

high.

Threshold Accuracy

Resetthresholdaccuracyisimportantinasupply-sensitive

system.Ideally,suchasystemresetsonlyifsupplyvoltages

fall outside the exact thresholds for a specified margin.

All LTC2913 inputs have a relative threshold accuracy of

±1.5% over the full operating temperature range.

For example, when the LTC2913 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 LTC2913, the UV trip point is between 4.433V and

4.567V which is 4.5V ±1.5%.

Using 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

following calculations.

The UV trip point is given as:

V

V

R

R

R

UV

C

A

B

=

+

+









0 5 1

.

The two extreme conditions, with a relative accuracy of

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

V

V

R

R

R

UV MIN

C

A

B

(

)

.

• .

•

• .

• .

=

+

+

(

)





0 5

0 985 1

0 99

1 01







=

+

+

(

and

V

V

R

R

R

UV MAX

C

A

B

(

)

.

• .

•

• .

0 5

1 015 1

1 01

))









• .

0 99

For a desired trip point of 4.55V,

R

R

A

B

+

= 8

Therefore,

V

V

V

a

UV MIN

(

)

.

• .

•

.

.

.

=

+







 =

0 5

0 985 1 8 0 99

1 01

4 354

nnd

V

V

UV MAX

(

)

.

• .

•

.

.

.

=

+







 =

0 5

1 015 1 8 1 01

0 99

4 6500V

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 LTC2913 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

show a graph of the Transient Duration vs. Comparator

Overdrive.