Obsolete Device
TC1025
Linear Building Block – Dual Low Power Comparator
Features
• Rail-to-Rail Inputs and Outputs
• Optimized for Single Supply Operation
• Small Packages: 8-Pin MSOP, 8-Pin SOIC or
8-Pin PDIP
• Ultra Low Input Bias Current: Less than 100pA
• Low Quiescent Current: 8μA (Typ.)
• Operates Down to V
DD
= 1.8V
General Description
The TC1025 is a dual low-power comparator with a
typical supply current of 8μA and operation ensured to
V
DD
= 1.8V. Input and output signal swing is rail-to-rail.
Available in a space-saving 8-pin MSOP package, the
TC1025 consumes half the board area required by a
standard 8-Pin SOIC package. It is also available in
8-Pin SOIC and PDIP packages. It is ideal for applica-
tions requiring high integration, small-size and low
power.
Applications
• Power Management Circuits
• Battery Operated Equipment
• Consumer Products
Functional Block Diagram
OUTA
1
TC1025
8
OUTB
Device Selection Table
Part Number
TC1025CEPA
TC1025CEUA
TC1025CEOA
Package
8-Pin PDIP
8-Pin MSOP
8-Pin SOIC
Temperature
Range
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
INA-
4
5
V
SS
2
A
–
–
B
7
V
DD
+
INA+
3
+
6
INB+
INB-
Package Types
8-Pin PDIP
8-Pin MSOP
8-Pin SOIC
OUTA
V
SS
INA+
INA-
1
2
3
4
8
7
OUTB
V
DD
INB+
INB-
TC1025CEPA
TC1025CEUA
TC1025CEOA
6
5
©
2005 Microchip Technology Inc.
DS21656C-page 1
TC1025
1.0
ELECTRICAL
CHARACTERISTICS
*Stresses above those listed under "Absolute Maximum
Ratings" may cause permanent damage to the device. These
are stress ratings only and functional operation of the device
at these or any other conditions above those indicated in the
operation sections of the specifications is not implied.
Exposure to Absolute Maximum Rating conditions for
extended periods may affect device reliability.
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage ......................................................6.0V
Voltage on Any Pin .......... (V
SS
– 0.3V) to (V
DD
+ 0.3V)
Junction Temperature....................................... +150°C
Operating Temperature Range.............-40°C to +85°C
Storage Temperature Range ..............-55°C to +150°C
TC1025 ELECTRICAL SPECIFICATIONS
Electrical Characteristics:
Typical values apply at 25°C and V
DD
= 3.0V. Minimum and maximum values apply for T
A
= -40° to
+85°C, and V
DD
= 1.8V to 5.5V, unless otherwise specified.
Symbol
V
DD
I
Q
V
ICMR
V
OS
I
B
V
OH
V
OL
CMRR
PSRR
I
SRC
Parameter
Supply Voltage
Supply Current
Common Mode Input Range
Input Offset Voltage
Input Bias Current
Output High Voltage
Output Low Voltage
Common Mode Rejection Ratio
Power Supply Rejection Ratio
Output Source Current
Min
1.8
—
V
SS
– 0.2
-5
-5
-100
V
DD
– 0.3
—
66
60
1
Typ
—
8
—
—
—
—
—
—
—
—
Max
5.5
12
V
DD
+ 0.2
+5
+5
100
—
0.3
—
—
—
Units
V
μA
V
mV
mV
pA
V
V
dB
dB
mA
V
DD
= 3V, V
CM
= 1.5V, T
A
= 25°C
T
A
= 25°C, IN+,IN- = V
DD
to V
SS
R
L
= 10kΩ to V
SS
R
L
= 10kΩ to V
DD
T
A
= 25°C, V
DD
= 5V
V
CM
= V
DD
to V
SS
T
A
= 25°C, V
CM
= 1.2V
V
DD
= 1.8V to 5V
IN+ = V
DD
, IN- = V
SS
,
Output Shorted to V
SS
V
DD
= 1.8V
IN+ = V
SS
, IN- = V
DD
,
Output Shorted to V
DD
V
DD
= 1.8V
100mV Overdrive, C
L
= 100pF
10mV Overdrive, C
L
= 100pF
Test Conditions
Comparator
I
SINK
Output Sink Current
2
—
—
mA
t
PD1
t
PD2
Response Time
Response Time
—
—
4
6
—
—
μsec
μsec
DS21656C-page 2
©
2005 Microchip Technology Inc.
TC1025
2.0
PIN DESCRIPTION
The description of the pins are listed in Table 2-1.
TABLE 2-1:
Pin No.
(8-Pin PDIP)
(8-Pin MSOP)
(8-Pin SOIC)
1
2
3
4
5
6
7
8
PIN FUNCTION TABLE
Symbol
Description
OUTA
V
SS
INA+
INA-
INB-
INB+
V
DD
OUTB
Comparator output.
Negative power supply.
Non inverting input.
Inverting input.
Inverting input.
Non inverting input.
Positive power supply.
Comparator input.
©
2005 Microchip Technology Inc.
DS21656C-page 3
TC1025
3.0
DETAILED DESCRIPTION
4.0
TYPICAL APPLICATIONS
The TC1025 is one of a series of very low-power, linear
building block products targeted at low-voltage, single-
supply applications. The TC1025 minimum operating
voltage is 1.8V, and typical supply current is only 8μA.
It combines two comparators in a single package.
The TC1025 lends itself to a wide variety of
applications, particularly in battery-powered systems.
Typically, it finds application in power management,
processor supervisory, and interface circuitry.
4.1
3.1
Comparators
The TC1025 contains two comparators. The compara-
tor’s input range extends beyond both supply voltages
by 200mV and the outputs will swing to within several
millivolts of the supplies depending on the load current
being driven.
The comparators exhibit propagation delay and supply
current which are largely independent of supply
voltage. The low input bias current and offset voltage
make them suitable for high impedance precision
applications.
2.
3.
External Hysteresis (Comparator)
Hysteresis can be set externally with two resistors
using positive feedback techniques (see Figure 4-1).
The design procedure for setting external comparator
hysteresis is as follows:
1.
Choose the feedback resistor R
C
. Since the
input bias current of the comparator is at most
100pA, the current through R
C
can be set to
100nA (i.e., 1000 times the input bias current)
and retain excellent accuracy. The current
through R
C
at the comparator’s trip point is V
R
/
R
C
where V
R
is a stable reference voltage.
Determine the hysteresis voltage (V
HY
) between
the upper and lower thresholds.
Calculate R
A
as follows:
EQUATION 4-1:
V
HY
-
R
A
= R
C
⎛
----------
⎞
⎝
V
DD
⎠
4.
5.
Choose the rising threshold voltage for V
SRC
(V
THR
).
Calculate R
B
as follows:
EQUATION 4-2:
1
R
B
= ----------------------------------------------------------
-
V
THR
⎞
1
1
⎛
--------------------
–
------
–
-------
-
-
⎝
V
R
×
R
A
⎠
R
A
R
C
6.
Verify the
formulas:
V
SRC
rising:
threshold
voltages
with
these
EQUATION 4-3:
1
1
1
-
-
V
THR
=
(
V
R
) (
R
A
)
⎛
------
⎞
+
⎛
------
⎞
+
⎛
-------
⎞
⎝
R
A
⎠ ⎝
R
B
⎠ ⎝
R
C
⎠
V
SRC
falling:
EQUATION 4-4:
R
A
×
V
DD
V
THF
=
V
THR
–
⎛
------------------------
⎞
-
⎝
R
C
⎠
DS21656C-page 4
©
2005 Microchip Technology Inc.
TC1025
4.2
32.768 kHz “Time of Day Clock”
Crystal Controlled Oscillator
4.4
Oscillators and Pulse Width
Modulators
A very stable oscillator driver can be designed by using
a crystal resonator as the feedback element. Figure 4-2
shows a typical application circuit using this technique
to develop clock driver for a Time Of Day (TOD) clock
chip. The value of R
A
and R
B
determine the DC voltage
level at which the comparator trips – in this case one-
half of V
DD
. The RC time constant of R
C
and C
A
should
be set several times greater than the crystal oscillator’s
period, which will ensure a 50% duty cycle by maintain-
ing a DC voltage at the inverting comparator input
equal to the absolute average age of the output signal.
4.3
Non-Retriggerable One Shot
Multivibrator
Using two comparators, a non-retriggerable one shot
multivibrator can be designed using the circuit configu-
ration of Figure 4-3. A key feature of this design is that
the pulse width is independent of the magnitude of the
supply voltage because the charging voltage and the
intercept voltage are a fixed percentage of V
DD
. In
addition, this one shot is capable of pulse width with as
much as a 99% duty cycle and exhibits input lockout to
ensure that the circuit will not retrigger before the
output pulse has completely timed out. The trigger level
is the voltage required at the input to raise the voltage
at node A higher than the voltage at node B, and is set
by the resistive divider R4 and R10 and the impedance
network composed of R1, R2 and R3. When the one
shot has been triggered, the output of CMPTR2 is high,
causing the reference voltage at the non-inverting input
of CMPTR1 to go to V
DD
. This prevents any additional
input pulses from disturbing the circuit until the output
pulse has timed out.
The value of the timing capacitor C1 must be small
enough to allow CMPTR1 to discharge C1 to a diode
voltage before the feedback signal from CMPTR2
(through R10) switches CMPTR1 to its high state and
allows C1 to start an exponential charge through R5.
Proper circuit action depends upon rapidly discharging
C1 through the voltage set by R6, R9 and D2 to a final
voltage of a small diode drop. Two propagation delays
after the voltage on C1 drops below the level on the
non-inverting input of CMPTR2, the output of CMPTR1
switches to the positive rail and begins to charge C1
through R5. The time delay which sets the output pulse
width results from C1 charging to the reference voltage
set by R6, R9 and D2, plus four comparator propaga-
tion delays. When the voltage across C1 charges
beyond the reference, the output pulse returns to
ground and the input is again ready to accept a trigger
signal.
Microchip’s linear building block comparators adapt
well to oscillator applications for low frequencies (less
than 100kHz). Figure 4-4 shows a symmetrical square
wave generator using a minimum number of compo-
nents. The output is set by the RC time constant of R4
and C1, and the total hysteresis of the loop is set by R1,
R2 and R3. The maximum frequency of the oscillator is
limited only by the large signal propagation delay of the
comparator in addition to any capacitive loading at the
output which degrades the slew rate. To analyze this
circuit, assume that the output is initially high. For this
to occur, the voltage at the inverting input must be less
than the voltage at the non-inverting input. Therefore,
capacitor C1 is discharged. The voltage at the
non-inverting input (V
H
) is:
EQUATION 4-5:
R2
(
V
DD
)
V
H
= --------------------------------------------
-
[
R2 +
(
R1
||
R3
) ]
where, if R1 = R2 = R3, then:
EQUATION 4-6:
2
(
V
DD
)
V
H
= -------------------
3
Capacitor C1 will charge up through R4. When the
voltage at the comparator’s inverting input is equal to
V
H
, the comparator output will switch. With the output
at ground potential, the value at the non-inverting input
terminal (V
L
) is reduced by the hysteresis network to a
value given by:
EQUATION 4-7:
V
DD
-
V
L
= ----------
3
Using the same resistors as before, capacitor C1 must
now discharge through R4 toward ground. The output
will return to a high state when the voltage across the
capacitor has discharged to a value equal to V
L
. The
period of oscillation will be twice the time it takes for the
RC circuit to charge up to one half its final value. The
period can be calculated from:
EQUATION 4-8:
1
---------------- = 2
(
0.694
) (
R4
) (
C1
)
-
FREQ
©
2005 Microchip Technology Inc.
DS21656C-page 5
