LTC1040CSW#TR Linear Technology, LTC1040CSW#TR Datasheet - Page 6

• Manufacturer Part Number: LTC1040CSW#TR
• Description: IC COMPARATOR DUAL LOWPWR 18SOIC
• Manufacturer: Linear Technology
• Series: LTCMOS™r
• Type: General Purposer

Specifications of LTC1040CSW#TR

• Number Of Elements: 2
• Output Type: CMOS, TTL
• Voltage - Supply: 2.8 V ~ 16 V, ±2.8 V ~ 8 V
• Mounting Type: Surface Mount
• Package / Case: 18-SOIC (0.300", 7.50mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LTC1040
APPLICATIO S I FOR ATIO
Minimizing Comparison Errors
The two differential input voltages, V1 and V2, are con-
verted to charge by the input capacitors C
Figure 2). The charge is summed at the virtual ground
point; if the net charge is positive, the comparator output
is high and if negative, it is low. There is an optimum way
to connect these inputs, in a specific application, to
minimize error.
Ignoring internal offset, the LTC1040 will be at its switch-
ing point when:
Optimum error will be achieved when the differential
voltages, V1 and V2, are individually minimized. Figure 3
shows two ways to connect the LTC1040 to compare an
input voltage, V
above equation, each method will be at null when:
(a) (V
(b) (V
Notice that in method (a) the null point depends on the
ratio of C
ratio. Also, because method (b) has zero differential input
voltage, the errors due to finite input resistance are
negligible. The LTC1040 has a high accuracy capacitor
array and even the non-optimum connection will only
result in 0.1% more error, worst-case compared to the
optimum connection.
6
or V
or V
Figure 2. Dual Differential Equivalent Input Circuit
REF
REF
V1
V2
V1 • C
IN1
IN
IN
– 0V) C
– V
= V
= V
/C
+
–
+
–
IN1
IN2
IN
REF
REF
IN
LTC1040 DUAL DIFFERENTIAL INPUT
) C
, but method (b) is independent of this
, to a reference voltage, V
S1
+ V2 • C
.
IN1
(C
U
IN1
IN1
– (0V – V
– (0V – 0V) C
S2
/C
U
IN2
IN2
)
= 0.
C
C
IN1
IN2
IN
) C
W
GROUND
VIRTUAL
IN2
IN2
LTC1040 • AI02
= 0
= 0
IN1
REF
and C
. Using the
U
IN2
(see
Tracking Error
Tracking error is caused by the ratio error between C
and C
consider Figure 3a with V
because C
Common Mode Range
The input switches of the LTC1040 are capable of
switching to either the V
input common mode range includes both supply rails.
Many applications, not feasible with conventional com-
parators, are possible with the LTC1040. In the load
current detector shown in Figure 4, a 0.1 resistor is used
to sense the current in the V
requires the dual differential input and common mode
capabilities of the LTC1040.
V
REF
V
IN
IN2
V
and is expressed as a percentage. For example,
S
IN1
+
(a) OK
V
is guaranteed to equal C
–
–
+
+
Figure 4. Load Current Detector
IN
Figure 3. Two Ways to Do It
= V
REF
100mV
0.1
I
L
+
C
C
or V
REF
IN1
IN2
–
+
–
+
–
= 1V. Then at null,
LTC1040
= 1V 1mV
supply. This means that the
+
V
REF
V
1/2
IN
supply. This application
OUT = HI IF I
OUT = LO IF I
(b) Optimum
IN2
OUT
+
–
+
–
to within 0.1%.
LTC1040 • AI04
L
L
> 1A
< 1A
R
L
LTC1040 • TA03
1040fa
IN1