LTC1040
Dual Micropower
Comparator
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
Micropower
1.5µW (1 Sample/Second)
Power Supply Flexibility
Single Supply 2.8V to 16V
Split Supply
±2.8V
to
±8V
Guaranteed
Max Offset 0.75mV
Guaranteed
Max Tracking Error Between Input
Pairs
±
0.1%
Input Common Mode Range to Both Supply Rails
TTL/CMOS Compatible with
±5V
or Single 5V
Supply
Input Errors are Stable with Time and Temperature
The LTC
®
1040 is a monolithic CMOS dual comparator
manufactured using Linear Technology’s enhanced
LTCMOS
TM
silicon gate process. Extremely low operating
power levels are achieved by internally switching the
comparator ON for short periods of time. The CMOS
output logic holds the output information continuously
while not consuming any power.
In addition to switching power ON, a switched output is
provided to drive external loads during the comparator’s
active time. This allows not only low comparator power,
but low total system power.
Sampling is controlled by an external strobe input or an
internal oscillator. The oscillator frequency is set by an
external RC network.
Each comparator has a unique input structure, giving two
differential inputs. The output of the comparator will be
high if the algebraic sum of the inputs is positive and low
if the algebraic sum of the inputs is negative.
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTCMOS™ is a trademark of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
Battery-Powered Systems
Remote Sensing
Window Comparator
BANG-BANG Controllers
TYPICAL APPLICATIO
Window Comparator with Symmetric Window Limits
1000
Typical LTC1040 Supply Current
vs Sampling Frequency
V
S
=
±5V
LTC1040
A
OUT
= “1” WHEN
V
IN
> V
C
+
∆
COMP A
SUPPLY CURRENT, I
S
(µA)
V
IN
+
–
+
–
100
10
A + B = “1” WHEN
V
C
–
∆ ≤
V
IN
≤
V
C
+
∆
V
C
∆
1
R
EXT
= 10M
+
–
+
–
COMP B
B
OUT
= “1” WHEN
V
IN
< V
C
–
∆
0.10
0.01
0.1
1
100
1,000
10
SAMPLING FREQUENCY, f
S
(Hz)
LTC1040 • TA01
U
EXTERNALLY STROBED
10,000
LTC1040 • TA02
U
U
1040fa
1
LTC1040
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
STROBE
ON/OFF
A+B
A
OUT
A1
+
A1
–
A2
+
A2
–
GND
1
2
3
4
5
6
7
8
9
18
V
+
17 V
P-P
16 OSC
15 B
OUT
14 B1
+
13 B1
–
12 B2
+
11 B2
–
10 V
–
SW PACKAGE
18-LEAD PLASTIC SO WIDE
Total Supply Voltage (V
+
to V
–
) ............................... 18V
lnput Voltage ........................ (V
+
+ 0.3V) to (V
–
– 0.3V)
Operating Temperature Range
LTC1040C ..................................... – 40°C
≤
T
A
≤
85°C
LTC1040M
(OBSOLETE)
.................... – 55°C to 125°C
Storage Temperature Range ................. – 55°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
Output Short-Circuit Duration .......................Continuous
ORDER PART
NUMBER
LTC1040CN
LTC1040CSW
N PACKAGE
18-LEAD PDIP
T
JMAX
= 110°C,
θ
JA
= 120°C/W (N)
T
JMAX
= 125°C,
θ
JA
= 85°C/W (SW)
J PACKAGE
18-LEAD CERDIP
T
JMAX
= 150°C,
θ
JA
= 80°C/W
LTC1040MJ
LTC1040CJ
OBSOLETE PACKAGE
Consider the N18 Package as an Alternate Source
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
OS
PARAMETER
Offset Voltage (Note 2)
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. Test conditions: V
+
= 5V, V
–
= – 5V, unless otherwise noted.
CONDITIONS
Split Supplies
±2.8V
to
±6V
Single Supply (V
–
= GND) 2.8V to 6V
Split Supplies
±6V
to
±8V
Single Supply (V
–
= GND) 6V to 15V
Tracking Error Between
Input Pairs (Notes 2 and 3)
Split Supplies
±2.8V
to
±8V
Single Supplies (V
–
= GND) 2.8 to 16V
OSC = GND
f
S
= 1kHz (Note 4)
Split Supplies
Single Supplies (V
–
= GND)
V
+
= 5V, V
P-P
On
V
+
= 5V, V
P-P
Off
LTC1040C
LTC1040M
q
q
q
q
q
q
q
q
q
q
LTC1040M/LTC1040C
MIN
TYP
MAX
±0.3
±1
0.05
±0.3
20
V
–
±2.8
2.8
1.2
0.001
0.001
60
80
30
V
+
±8
16
3
0.5
5
100
±
0.75
±4.5
0.1
UNITS
mV
mV
%
nA
MΩ
V
V
V
mA
µA
µA
µs
I
BIAS
R
IN
CMR
PSR
I
S(ON)
I
S(OFF)
t
D
Input Bias Current
Average Input Resistance
Common Mode Range
Power Supply Range
Power Supply ON Current (Note 5)
Power Supply OFF Current (Note 5)
Response Time (Note 6)
A, B, A + B and
ON/OFF Outputs (Note 7)
Logic “1” Output Voltage
Logic “0” Output Voltage
V
OH
V
OL
V
+
= 4.75V, l
OUT
= – 360µA
V
+
= 4.75V, l
OUT
= 1.6mA
q
q
2.4
4.4
0.25
0.4
2
U
V
V
1040fa
W
U
U
W W
W
LTC1040
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IH
V
IL
R
EXT
f
S
PARAMETER
STROBE Input (Note 7)
Logic “1” Input Voltage
Logic “0” Input Voltage
External Timing Resistor
Sampling Frequency
The
q
denotes the specifications which apply over the full operating
temperature range otherwise specifications are at T
A
= 25°C. Test conditions: V
+
= 5V, V
–
= – 5V, unless otherwise specified
CONDITIONS
V
+
= 5.25V
V
+
= 4.75V
Resistor Tied Between V
+
and OSC Pin
R
EXT
= 1M, C
EXT
= 0.1µF
q
q
MIN
2.0
100
LTC1040M/LTC1040C
TYP
MAX
1.6
1.0
5
UNITS
V
V
kΩ
Hz
0.8
10,000
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Applies over input voltage range limit and includes gain
uncertainty.
Note 3:
Tracking error = (V
IN1
– V
IN2
)/ V
IN1
.
Note 4:
R
IN
is guaranteed by design and is not tested.
R
IN
= 1/(f
S
• 33pF).
Note 5:
Average supply current = t
D
• l
S(ON)
• f
S
+ (1 – t
D
x f
S
) • l
S(OFF)
.
Note 6:
Response time is set by an internal oscillator and is independent
of overdrive voltage.
Note 7:
Inputs and outputs also capable of meeting EIA/JEDEC B series
CMOS specifications.
TYPICAL PERFOR A CE CHARACTERISTICS
Peak Supply Current
vs Supply Voltage
20
NORMALIZED SAMPLING FREQUENCY
(fS/fS AT 5V, 25°C)
18
16
14
T
A
= 125°C
1.6
1.4
1.2
1.0
0.8
0.6
T
A
= –55°C
0
2
8
10 12
4
6
SUPPLY VOLTAGE, V
+
(V)
14
16
T
A
= 25°C
SAMPLE RATE, f
S
(Hz)
I
S(ON)
(mA)
12
10
8
6
4
2
0
2
4
10
8
6
12
+
(V)
SUPPLY VOLTAGE, V
125°C
–55°C
25°C
LTC1040 • TPC01
Response Time
vs Supply Voltage
AVERAGE INPUT RESISTANCE, R
IN
(1/f
S
• 33pF) (Ω)
300
250
10
11
T
A
= 25°C
TYPICAL OUTPUT VOLTAGE DROP, V
+
–V
P-P
(V)
RESPONSE TIME, t
D
(µs)
200
150
100
50
0
2
4
10
14
8
12
6
+
SUPPLY VOLTAGE, V (V)
16
U W
14
16
LTL1040 • TPC04
Normalized Sampling Frequency
vs Supply Voltage and Temperature
2.2
2.0
1.8
Sampling Rate vs R
EXT
, C
EXT
10
3
C
EXT
= 1000pF
10
2
C
EXT
= 0.01µF
C
EXT
= 0.05µF
10
C
EXT
= 0.1µF
1
C
EXT
= 1µF
R = 1M
C = 0.1µF
0.1
100k
1M
R
EXT
(Ω)
10M
LT1040 • TPC03
LTC1040 • TPC02
Input Resistance
vs Sampling Frequency
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
V
P-P
Output Voltage
vs Load Current
10
10
V
+
= 10V
V
+
= 2.8V
V
+
= 16V
10
9
10
8
V
+
= 5V
10
7
1
10
10
2
10
3
SAMPLING FREQUENCY, f
S
(Hz)
10
4
0
1
2
3 4 5 6 7 8
LOAD CURRENT, I
L
(mA)
9
10
LTC1040 • TPC05
LTC1040 • TPC06
1040fa
3
LTC1040
TYPICAL PERFOR A CE CHARACTERISTICS
Response Time
vs Temperature
130
120
RESPONSE TIME, t
D
(µs)
V
+
= 5V
110
100
90
80
70
60
50
40
–50
0
25
–25
50
75 100
AMBIENT TEMPERATURE, T
A
(°C)
125
9
LTC1040
TEST CIRCUIT
V
IN
BLOCK DIAGRA
4
U W
LTC1040 • TPC07
Quick Hookup Guide
Self-Oscillating
1
18
17
16
V+
EXTERNAL
STROBE
INPUT
1
External Strobe
18
17
16
V+
R
EXT
C
EXT
LTC1040
10
9
10
LTC1040 • TPC08
V
+
(18)
+
–
+
–
GND (9)
V
–
(10)
OUTPUT
ALL INPUTS ON OPPOSITE COMPARATOR AT GROUND
LTC1040 • TA01
W
V
IN1
A1
+
5
A1
–
6
V
IN2
A2
+
7
A2
–
8
V
+
18
+
–
+
–
COMP A
4
4 A
OUT
2 ON/OFF
V
IN1
B1
+
14
B1
–
13
B2
+
12
B2
–
11
V
IN2
+
–
+
–
3 A+B
COMP B
15 B
OUT
4
TIMING
SWITCH
GENERATOR TIMING
STROBE 1
OSC 16
V
+
POWER ON
V
P-P
CIRCUIT
17 V
P-P
80µs
9
GND
10
V
–
1040fa
LTC1040 • BD01
LTC1040
APPLICATIO S I FOR ATIO
The LTC1040 uses sampled data techniques to achieve its
unique characteristics. Some of the experience acquired
using classic linear comparators does not apply to this
circuit, so a brief description of internal operation is
essential to proper application.
The most obvious difference between the LTC1040 and
other comparators is the dual differential input structure.
Functionally, when the sum of inputs is positive, the
comparator output is high and when the sum of the inputs
is negative, the output is low. This unique input structure
is achieved with CMOS switches and a precision capacitor
array. Because of the switching nature of the inputs, the
concept of input current and input impedance needs to be
examined.
The equivalent input circuit is shown in Figure 1. Here, the
input is being driven by a resistive source, R
S
, with a
bypass capacitor, C
S
. The bypass capacitor may or may
not be needed, depending on the size of the source
resistance and the magnitude of the input voltage, V
IN
.
C
IN
≈
33pF
R
S
V
IN
C
S
S1
+
S2
–
V
–
LTC1040 DIFFERENTIAL INPUT
LTC1040 • AI01
Figure 1. Equivalent Input Circuit
For R
S
< 1Ok
Assuming C
S
is zero, the input capacitor, C
IN
, charges to
V
IN
with a time constant of R
S
C
IN
. When R
S
is too large,
C
IN
does not have a chance to fully charge during the
sampling interval (≈ 80µs) and errors will result. If R
S
exceeds 10kΩ, a bypass capacitor is necessary to mini-
mize errors.
U
For R
S
> 1OkΩ
For R
S
greater than 10kΩ, C
IN
cannot fully charge and a
bypass capacitor, C
S
, is needed. When switch S1 closes,
charge is shared between C
S
and C
IN
. The change in
voltage on C
S
because of this charge sharing is:
C
IN
C
IN
+ C
S
This represents an error and can be made arbitrarily small
by increasing C
S
.
∆V
= V
IN
•
With the addition of C
S
, a second error term caused by the
finite input resistance of the LTC1040 must be considered.
Switches S1 and S2 alternately open and close, charging
and discharging C
IN
between V
IN
and ground. The
alternate charge and discharge of C
IN
causes a current to
flow into the positive input and out of the negative input.
The magnitude of this current is:
I
IN
= q • f
S
= V
IN
C
IN
f
S
where f
S
is the sampling frequency. Because the input
current is directly proportional to input voltage, the LTC1040
can be said to have an average input resistance of:
V
1
1
R
IN
=
IN
=
=
I
IN
f
S
C
IN
f
S
• 33pF
(see typical curve of Input Resistance vs Sampling Fre-
quency). A voltage divider is set up between R
S
and R
IN
causing error.
The input voltage error caused by these two effects is:
C
IN
R
S
+
V
ERROR
= V
IN
C
IN
+ C
S
R
S
+ R
IN
W
U U
(
(
)
Example: f
S
= 10Hz, R
S
= 1MΩ,
C
S
= 1µF, V
IN
= 1V
V
ERROR
= 1V
33 • 10
–12
+
10
6
1 • 10
– 6
10
6
+ 3 • 10
9
)
= 33µV + 330µV = 363µV.
Notice that most of the error is caused by R
IN
. If the
sampling frequency is reduced to 1Hz, the voltage error is
reduced to 66µV.
1040fa
5
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