TS1002 TOUCHSTONE [Touchstone Semiconductor Inc], TS1002 Datasheet - Page 10

• Manufacturer Part Number: TS1002
• Description: THE ONLY 0.8V/0.6uA RAIL-TO-RAIL DUAL/QUAD OP AMPS
• Manufacturer: TOUCHSTONE [Touchstone Semiconductor Inc]

TS1002/TS1004
In the event that an external R
C
results in gain accuracy loss because the external
series R
load resistor R
Figure 6: TS1002/TS1004 Transient Response for R
Configuring the TS1002 or the TS1004 into a
Nanowatt Analog Comparator
Although optimized for use as an operational
amplifier, these amplifiers 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 amplifiers’ analog comparator
hysteresis band and output transfer characteristic.
The design of an analog comparator using the
TS1002 or the TS1004 is straightforward. In this
application, a 1.5-V power supply (V
and the resistor divider network formed by RD1 and
RD2 generated a convenient reference voltage
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Figure 7: A NanoWatt Analog Comparator with User-
LOAD
appears in the application, the use of an R
and C
ISO
Programmable Hysteresis.
forms a voltage-divider with the external
LOAD
LOAD
= 500pF
V
IN
.
.
LOAD
V
OUT
in parallel with
DD
) was used
ISO
= 50kΩ
ISO
(V
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
amplifer’s inverting input.
In this application, the desired hysteresis band was
set to 100mV (V
(V
at 0.9V.
Since these amplifers draw very little supply current
(0.6µA per amplifier, typical), it is desired that the
design of an analog comparator using these
amplfiers should also use as little current as
practical. The first step in the design, therefore, was
to set the feedback resistor R3:
Calculating a value for R1 is given by the following
expression:
Substituting V
10MΩ into the equation above yields:
The following expression was then used to calculate
a value for R2:
Substituting V
and R3 = 10MΩ into the above expression yields:
Figure 8: Analog Comparator Hysteresis Band and Output
REF
HI
) set at 1V and a desired low trip-point (V
) for the circuit at ½ the supply voltage, or
R2 = 1/[V
Switching Points.
HYB
HI
HI
R1 = R3 x (V
/(V
= 1V, V
HYB
= 100mV, V
REF
R2 = 2.5MΩ
R1 = 667kΩ
R3 = 10MΩ
) with a desired high trip-point
x R1) – (1/R1) – (1/R3)]
REF
HYB
= 0.75V, R1 = 667kΩ,
DD
/V
DD
TS1002_4DS r1p0
= 1.5V, and R3 =
)
LO
RTFDS
) set