TS1001

Page 10

TS1001DS r1p0

RTFDS

Configuring the TS1001 as Nanowatt Analog

Comparator

Although optimized for use as an operational

amplifier, the TS1001 can also be used as a rail-to-

rail I/O comparator as illustrated in Figure 7.

External hysteresis can be employed to minimize the

risk of output oscillation. The positive feedback

circuit causes the input threshold to change when

the output voltage changes state. The diagram in

Figure 8 illustrates the TS1001’s analog comparator

hysteresis band and output transfer characteristic.

The design of an analog comparator using the

TS1001 is straightforward. In this application, a 1.5-

divider network formed by RD1 and RD2 generated

at ½ the supply voltage, or 0.75V, while keeping the

current drawn by this resistor divider low. Capacitor

C1 is used to filter any extraneous noise that could

couple into the TS1001’s inverting input.

In this application, the desired hysteresis band was

at 0.9V.

Since the TS1001 is a very low supply current

amplifier (0.6µA, typical), it is desired that the design

of an analog comparator using the TS1001 should

also use as little current as practical. The first step in

the design, therefore, was to set the feedback

resistor R3:

R3 = 10MΩ

Calculating a value for R1 is given by the following

expression:

10MΩ into the equation above yields:

R1 = 667kΩ

The following expression was then used to calculate

a value for R2:

and R3 = 10MΩ into the above expression yields:

R2 = 2.5MΩ

Printed Circuit Board Layout Considerations

Even though the TS1001 operates from a single

0.65V to 2.5V power supply and consumes very little

supply current, it is always good engineering

practice to bypass the power supplies with a 0.1μF

ceramic capacitor placed in close proximity to the

Good pcb layout techniques and analog ground

plane management improve the performance of any

analog circuit by decreasing the amount of stray

capacitance that could be introduced at the op amp's

inputs and outputs. Excess stray capacitance can

easily couple noise into the input leads of the op

amp and excess stray capacitance at the output will

add to any external capacitive load. Therefore, PC

board trace lengths and external component leads

should be kept a short as practical to any of the

TS1001’s package pins. Second, it is also good

engineering practice to route/remove any analog

ground plane from the inputs and the output pins of

the TS1001.

Figure 8: Analog Comparator Hysteresis Band and Output

Switching Points.

Figure 7: A NanoWatt Analog Comparator with User-

Programmable Hysteresis.