LTC2906 datasheet(9/16 Pages) LINER

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LTC2906/LTC2907

29067f

In margining application, the three-state input pins can be

driven using a three-state buffer. Note however, the low

and high output of the three-state buffer has to satisfy the

VIL and VIH of the three-state pin listed in the Electrical

Characteristics Table. Moreover, when the three-state

buffer is in the high impedance state, the maximum

leakage current allowed from the pin to either GND or V1

is 10

µA.

Monitor Programming

Connecting S1 to either GND, or V1, or leaving it in open

state selects the LTC2906/LTC2907 V1 input voltage

threshold. Table 1 shows the three possible selections of

V1 nominal input voltage and their corresponding S1

connection.

The noninverting input on the VADJ comparator is set

to 0.5V when the TOL pin is set high (5% tolerance)

(Figure 1) and the high impedance inverting input directly

ties to the VADJ pin.

Table 1. Supply Selection Programming

5.0

3.3

OPEN

2.5

GND

Note: Open = open circuit or driven by a three-state buffer

in high impedance state with leakage current less than 10

µA.

R2 =100k

Ω is recommended. Once the resistor divider is

set in the 5% tolerance mode, there is no need to change

the divider for the other tolerance modes (7.5%, 10%)

because the internal reference at the noninverting input on

the VADJ comparator is scaled accordingly, moving the trip

point in 2.5% decrements.

Table 2 shows suggested 1% resistor values for various

adjustable applications.

Table 2. Suggested 1% Resistor Values for the VADJ Inputs

VSUPPLY (V)

VTRIP (V)

R1 (k

Ω)

R2 (k

Ω)

11.25

2150

100

9.4

1780

100

7.5

1400

100

7.5

1300

100

5.6

1020

100

4.725

845

100

3.3

3.055

511

100

2.82

464

100

2.5

2.325

365

100

1.8

1.685

237

100

1.5

1.410

182

100

1.2

1.120

124

100

0.933

86.6

100

0.9

0.840

68.1

100

0.8

0.750

49.9

100

0.7

0.655

30.9

100

0.6

0.561

12.1

100

Tolerance Programming

The three-state input pin TOL, programs the common

supply tolerance for both V1 and VADJ input voltages (5%,

7.5% or 10%). The larger the tolerance the lower the trip

threshold. Table 3 shows the tolerances selection corre-

sponding to a particular connection at the TOL pin.

–

– 0.5V

LTC2906/LTC2907

VTRIP

VADJ

29067 F01

Figure 1. Setting the Adjustable Trip Point

In a typical application, the VADJ pin connects to a tap point

on an external resistive divider between the positive volt-

age being monitored and ground. The following formula

obtains R1 resistor value for a particular value of R2 and

a desired trip voltage at 5% tolerance:

TRIP













(%)

–

APPLICATIO S I FOR ATIO

Table 3. Tolerance Programming

TOLERANCE

TOL

7.5%

OPEN

10%

GND

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