LT6700-1/LT6700-2/LT6700-3

10

6700123fb

To create window functions optimized for detecting

entry

into a window (i.e. where the output is to indicate a

“coming into spec” condition, as with the examples in

Figure 1), the nominal resistor values are selected as

follows:

R1

The worst-case variance of the trip-points is related to the

specified threshold limits of the LT6700 device and the

basic tolerance of divider resistors used. For resistor

as follows (italicized values are taken from the datasheet,

expressed in volts):

Generating an External Reference Signal

In some applications, it would be advantageous to have

access to a signal that is directly related to the internal

400mV reference, even though the reference itself is not

available externally. This can be accomplished to a reason-

able degree by using an inverting comparator section as a

“bang-bang” servo, establishing a nominal voltage, on an

integration capacitor, that is scaled to the reference. This

method is used in Figure 2, where the reference level has

APPLICATIO S I FOR ATIO

Figure 1. Simple Window Comparator

been doubled to drive a resistor bridge. The section B

output cycles on and off to swing the section B input

between its hysteresis trip points as the load capacitor

charges and discharges in a shallow, controlled fashion.

The multiplied reference signal also contains ripple that is

the hysteresis multiplied by the same factor, so additional

filtering is performed at the sense node of the bridge to

prevent comparator chatter in the section A comparator,

which is performing the actual conditional decision for the

circuit.

Instrumentation Grade Pulse Width Modulator (PWM)

Comparators with hysteresis are frequently employed to

make simple oscillator structures, and the LT6700 lends

itself nicely to forming a charge-balancing PWM function.

The circuit shown in Figure 3 forms a PWM that is intended

to transmit an isolated representation of a voltage differ-

LT6700-1

GND

1

5

R3

301k

R2

6.04k

33k

+INA

–INB OUTB

OUTA

3.3V

3.3V Supply Monitor

5V Supply Monitor

R1

40.2k

2

6

0.1

µF

HYSTERESIS ZONES

APPROXIMATELY

2% OF TRIP VOLTAGE

3

4

LT6700-1

GND

1

5

487k

6.04k

33k

+INA

–INB OUTB

OUTA

5V

40.2k

2

6

0.1

µF

3

4

6700123 F01

LT6700-1

10k

GND

1

5

+INA

–INB OUTB

OUTA

2

6

3

4

499k

T

*RESISTANCE MAY REQUIRE OPTIMIZATION FOR OPERATION

HYSTERESIS ZONE

≈0.4°C

499k

220k

220k*

3.3

µF

3.3

µF

1.4V TO 18V

0.1

µF

6700123 F02

Figure 2. Micropower Thermostat/Temperature Alarm