LTC6702
7
6702fa
APPLICATIONS INFORMATION
The LTC6702 device is a fast (500ns delay), low power,
low voltage (1.7V to 5.5V supply) general purpose dual
comparator. It provides rail-to-rail outputs able to interface
to TTL/CMOS, draws low supply currents (30µA/compara-
tor), and has internal hysteresis (approximately 4mV).
Hysteresis
Each comparator has built-in hysteresis to simplify designs,
to insure stable operation in the presence of noise at the
inputs, and to reject supply rail noise. The reference voltage
applied to the input is not the exact switching threshold
value due to the built-in hysteresis. Actual output switching
typically occurs within ±2.2mV of the reference voltage,
plus or minus the input offset voltage. External positive
feedback circuitry can be employed to increase effective
hysteresis if desired, as shown in Figure 1. This circuitry
will provide an apparent effect on both the rising and fall-
ing input thresholds (the actual internal trip points remain
unaffected). If an inverting confi guration with hysteresis is
needed, simply swap the V
IN
and V
REF
connections.
Unused Inputs
Any unused inputs should be connected in a way that fi xes
the output logic state high or low. One easy way to do this
is to tie +IN to V
+
and –IN to GND.
Input Protection
External input protection circuitry is only needed if currents
would otherwise exceed the absolute maximum rating.
Inputs driven further negative than 100mV below ground
will not cause damage provided the current is limited to
10mA. ESD protection diodes are provided to prevent
damage during handling.
Comparator Input
The allowable input voltage ranges from 100mV below GND
to within 1.2V of the positive supply. The input may be
forced below ground without causing an improper output,
though some additional input current will begin to fl ow
from the ESD input protection diode. The inputs can reach
up to 6V independent of the V
+
supply voltage without
causing additional input current or damage to the part.
As long as one input is within the allowable input voltage
range, the LTC6702 will continue to function normally.
Comparator Output
The comparator output is a push-pull CMOS stage
guaranteed to swing to within 350mV of V
+
and 250mV
of ground, over temperature when sourcing or sinking
15mA. No external pull-up/down resistor is required. To
Figure 1. Additional Hysteresis Circuit for Noninverting Confi guration
Additional Hystersis
R
R
V
Trip Voltages
V
IN
=
+
1
3
•
:
(()
()
••
LH REF
IN H L R
VR
RR R
VV
→
→
=++
⎛
⎝
⎜
⎞
⎠
⎟
=
1
1
1
1
2
1
3
EEF
R
RR R
R
R
V
Examp
•• •1
1
1
1
2
1
3
1
3
++
⎛
⎝
⎜
⎞
⎠
⎟
−
⎛
⎝
⎜
⎞
⎠
⎟
+
lle Additional Hysteresis mV V V
Rk
R
:,==
=
+
50 5
110
2 ==
=
=→=
249
31
05 0525
k
M
FOR V V V L H V
V
REF IN
IN
R
.: ( ) .
(HHL V→=).0 475
–
+
1/2 LTC6702
R2
V
REF
R3
6702 F01
V
IN
R1
