lt6700hdcb-3-trpbf Linear Technology Corporation, lt6700hdcb-3-trpbf Datasheet - Page 9

• Manufacturer Part Number: lt6700hdcb-3-trpbf
• Description: Micropower, Low Voltage, Dual Comparator With 400mv Reference
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
The LT6700-1/LT6700-2/LT6700-3 devices are a family of
dual micropower comparators with a built-in 400mV ref-
erence. Features include wide supply voltage range (1.4V
to 18V), Over-The-Top input and output range, 2% accu-
rate rising input threshold voltage and 6.5mV typical built-
in hysteresis. The comparator’s open-collector outputs
can sink up to 40mA typical.
Internal Reference
Each of the comparator sections has one input available
externally, with the three versions of the part differing by
the polarity of those available inputs (i.e., inverting or
noninverting). The other comparator inputs are connected
internally to the 400mV reference. The rising input thresh-
old voltage of the comparators is designed to be equal to
that of the reference (i.e., ≈ 400mV). The reference voltage
is established with respect to the device GND connection.
Hysteresis
Each comparator has built-in 6.5mV (typical) hysteresis to
simplify designs, insure stable operation in the presence
of noise at the inputs, and to reject supply rail noise that
might be induced by state change load transients. The
hysteresis is designed such that the falling input threshold
voltage is nominally 393.5mV. External positive feedback
circuitry can be employed with noninverting comparator
inputs to increase effective hysteresis if desired, but such
circuitry will provide an apparent effect on both the rising
and falling input thresholds (the actual internal thresholds
remain unaffected).
Comparator Inputs
A comparator input can swing from ground to 18V,
regardless of the supply voltage used. The typical input
current for inputs well above threshold (i.e., >800mV) is
a few pA leaking into an input. With decreasing input
voltage, a small bias current begins to be drawn out of the
input, reaching a few nA when at ground potential. The
input may be forced 100mV below ground without causing
an improper output, though some additional bias current
will begin to flow from the parasitic ESD input protection
diode. Inputs driven further negative than 100mV below
ground will not cause comparator malfunction or damage
U
U
W
U
(provided the current is limited to 10mA), but the accuracy
of the reference cannot be guaranteed, in which case the
output state of the alternate comparator may be effected.
Comparator Outputs
The comparator outputs are open collector and capable of
sinking 40mA typical. Load currents are directed out the
GND pin of the part. The output off-state voltage may range
between –0.3V and 18V with respect to ground, regardless
of the supply voltage used. As with any open-collector
device, the outputs may be tied together to implement
wire-AND logic functions.
Power Supplies
The comparator family core circuitry operates from a
single 1.4V to 18V supply. A minimum 0.1µF bypass
capacitor is required between the V
an output load is connected to the supply rail near the part
and the output is sinking more than 5mA, a 1µF bypass
capacitor is recommended. In instances where the supply
is relatively “soft” (such as with small batteries) and
susceptible to load steps, an additional 47Ω series de-
coupling resistor can further improve isolation of supply
transients from the V
Flexible Window Comparator
Using the LT6700-1 as shown in the circuits of Figure 1,
the wire-AND configuration permits high accuracy win-
dow functions to be implemented with a simple 3-resistor
voltage divider network. The section A comparator pro-
vides the V
provides the V
providing about 1.7% recovery level at each trip point to
prevent output chatter.
For designs that are to be optimized to detect departure
from a window limit, the nominal resistor divider values
are selected as follows (refer to the resistor designators
shown on the first circuit of Figure 1):
LT6700-1/LT6700-2/LT6700-3
R1 ≤ 400k (this sets the divider current >> I
R2 = R1 • (0.98 • V
R3 = R1 • (2.5 • V
L
trip-point and the section B comparator
H
trip-point, with the built-in hysteresis
H
S
H
– 0.98 • V
pin.
/V
L
– 1)
H
/V
S
L
pin and GND. When
)
B
of inputs)
6700123fd
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