ADCMP341_07 AD [Analog Devices], ADCMP341_07 Datasheet - Page 10

• Manufacturer Part Number: ADCMP341_07
• Description: Dual 0.275% Comparators and Reference with Programmable Hysteresis
• Manufacturer: AD [Analog Devices]

ADCMP341/ADCMP343
APPLICATION INFORMATION
The ADCMP341/ADCMP343 are dual, low power comparators
with a built-in 400 mV reference that operates from 1.7 V to 5.5 V.
The comparators are 0.275% accurate with fully programmable
hysteresis, implemented using a new technique of a three-resistor
string on the input. These open-drain outputs are capable of
sinking up to 40 mA.
COMPARATORS AND INTERNAL REFERENCE
Each of the comparators has one input available externally; the
other comparator inputs are connected internally to the 400 mV
reference. The ADCMP341 has two noninverting comparators
and the ADCMP343 has two inverting comparators.
There are two input pins available to each comparator. However,
these two input pins (±INx_U, ±INx_L) connect to the same
input leg of the comparator via a muxing system. This is to
provide fully programmable rising and falling trip points. The
output of the comparator determines which pin is connected to
the input of the same comparator. Using Figure 28 as an
example, when OUTA is high, +INA_U is connected to the
comparator input. When the input voltage drops and passes
below the 400 mV reference, the output goes low. This in turn
disconnects +INA_U from the comparator and connects
+INA_L. This leg of the string is at a lower voltage and thus
instantaneously the effect of hysteresis is applied. Therefore,
using a resistor string on the input as shown in Figure 28, the
voltages for the rising and falling trip points can be programmed
by selecting the appropriate resistors in the string.
POWER SUPPLY
The ADCMP341/ADCMP343 are designed to operate from 1.7 V
to 5.5 V. A 0.1 μF decoupling capacitor is recommended between
V
INPUTS
The comparator inputs are limited to the maximum V
range. The voltage on these inputs can be above V
above the maximum allowed V
OUTPUTS
The open-drain comparator outputs are limited to the maximum
specified V
outputs are capable of sinking up to 40 mA. Outputs can be tied
together to provide a common output signal.
PROGRAMMING HYSTERESIS
When choosing the resistor values, the input bias current must
be considered as a potential source of error. Begin by choosing a
resistor value for R3, which takes into account the acceptable
error introduced by the maximum specified input bias current.
To reduce this error, the current flowing through the Resistor R3
should be considerably greater than the input bias current.
DD
and GND.
DD
voltage range, regardless of the V
DD
voltage.
DD
voltage. These
DD
but never
DD
voltage
Rev. 0 | Page 10 of 12
R3 is therefore
Now R2 can be calculated from the following:
R1 can then be calculated using the following equation:
where:
V
I
R1, R2, and R3 are the three resistors as shown in Figure 28.
I
V
V
LAYOUT RECOMMENDATIONS
Correct layout is very important to increase noise immunity.
Long tracks from the input resistors to the device can lead to
noise being coupled onto the inputs. To avoid this, it is best to
place the input resistors as close as possible to the device. It is
also recommended that a GND plane is used under this layout.
The combination of small hysteresis and the use of a large R3
resistor further increases susceptibility to noise. In this case, a
decoupling capacitor (CA, CB) may be required on the ±INx_U
node to help reduce any noise. A recommended layout example
can be seen in Figure 29.
BIAS
R3
REF
FALLING
RISING
is the current flowing through R3.
is the maximum specified input bias current.
is the specified on chip reference.
R =
I
R
R
R3
1
3
2
is the desired rising trip voltage and higher of the two.
is the desired falling trip voltage and lower of the two.
=
=
>>
⎛
⎜
⎜
⎝
V
R
I
R
VINA
REF
R
3
I
3
3
(
BIAS
Figure 28. Programming Hysteresis Example
V
×
Figure 29. Recommended Layout Example
R1
R2
R3
RISING
⎛
⎜
⎜
⎝
OUTA
V
V
R1A
R2A
R3A
V
INA
+INA_U
+INA_L
FALLING
RISING
REF
−
V
FALLING
−
CA
GND
1
⎞
⎟
⎟
⎠
⎞
⎟
⎟
⎠
ADCMP341
−
C1
U1
)
R
V
2
DD
V
400mV
DD
CB
OUTB
INB
R1B
R2B
R3B
OUTA