10

LTC2901

2901is sn2901

APPLICATIO S I FOR ATIO

Power-Up

and the COMPX pins. This ensures that the RST and COMPX

outputs will be low as soon as V1 or V2 reaches 1V. The

RST and COMPX outputs will remain low until the part is

is below its programmed threshold, RST will be a logic low.

nal timer is started and RST is released after the pro-

V3 input impedance will be low (1k

Ω typ).

Monitor Programming

The LTC2901 input voltage combination is selected by

Figure 4. Table 1 offers recommended 1% resistor values

for the various modes. The last column in Table 1 specifies

gramming with a ratiometric DAC.

During power-up, once V1 or V2 reaches 2.4V max, the

monitor enters a programming period of approximately

150

and the monitor is configured to the desired input combi-

after programming, the comparators are enabled and

supply monitoring will begin.

Supply Monitoring

The LTC2901 is a low power, high accuracy program-

mable quad supply monitoring circuit with four nondelayed

monitor outputs, a common reset output and a watchdog

timer. Watchdog and reset timing are both adjustable

using external capacitors. Single pin programming selects

1 of 16 input voltage monitor combinations. All four

voltage inputs must be above predetermined thresholds

for the reset not to be invoked. The LTC2901 will assert the

reset and comparator outputs during power-up, power-

down and brownout conditions on any one of the voltage

inputs.

The inverting inputs on the V3 and/or V4 comparators are

set to 0.5V when the positive adjustable modes are selected

(Figure 5). The tap point on an external resistive divider,

connected between the positive voltage being sensed and

ground, is connected to the high impedance noninverting

inputs (V3, V4). The trip voltage is calculated from:

VV

R

R









05

1

3

4

.

In the negative adjustable mode, the noninverting input on

the V4 comparator is connected to ground (Figure 6). The

tap point on an external resistive divider, connected be-

is connected to the high impedance inverting input (V4).

at ground. The trip voltage is calculated from:

VV

R

R

V

V No

al

TRIP

REF

REF

=









=

–

;

.

min

3

4

1 210

Figure 4. Monitor Programming

12

11

10

R1

1%

R2

1%

2901 F04

GND

LTC2901

Table 1. Voltage Threshold Programming

MODE

V1 (V) V2 (V) V3 (V) V4 (V) R1 (k

0

5.0

3.3

ADJ

ADJ

Open

Short

0.000

1

5.0

3.3

ADJ

–ADJ

93.1

9.53

0.094

2

3.3

2.5

ADJ

ADJ

86.6

16.2

0.156

3

3.3

2.5

ADJ

–ADJ

78.7

22.1

0.219

4

3.3

2.5

1.5

ADJ

71.5

28.0

0.281

5

5.0

3.3

2.5

ADJ

66.5

34.8

0.344

6

5.0

3.3

2.5

1.8

59.0

40.2

0.406

7

5.0

3.3

2.5

1.5

53.6

47.5

0.469

8

5.0

3.0

2.5

ADJ

47.5

53.6

0.531

9

5.0

3.0

ADJ

ADJ

40.2

59.0

0.594

10

3.3

2.5

1.8

1.5

34.8

66.5

0.656

11

3.3

2.5

1.8

ADJ

28.0

71.5

0.719

12

3.3

2.5

1.8

–ADJ

22.1

78.7

0.781

13

5.0

3.3

1.8

–ADJ

16.2

86.6

0.844

14

5.0

3.3

1.8

ADJ

9.53

93.1

0.906

15

5.0

3.0

1.8

ADJ

Short

Open

1.000