LTC1966IMS8 Linear Technology, LTC1966IMS8 Datasheet - Page 15

• Manufacturer Part Number: LTC1966IMS8
• Description: IC PREC RMS/DC CONV MCRPWR 8MSOP
• Manufacturer: Linear Technology

Specifications of LTC1966IMS8

• Current - Supply: 155µA
• Voltage - Supply: 2.7 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
For single-ended DC-coupled applications, simply con-
nect one of the two inputs (they are interchangeable) to
the signal, and the other to ground. This will work well for
dual supply configurations, but for single supply con-
figurations it will only work well for unipolar input sig-
nals. The LTC1966 input voltage range is from rail-to-rail,
and when the input is driven above V
(ground for single supply operation) the gain and offset
errors will increase substantially after just a few hundred
millivolts of overdrive. Fortunately, most single supply
circuits measuring a DC-coupled RMS value will include
some reference voltage other than ground, and the
second LTC1966 input can be connected to that point.
For single-ended AC-coupled applications, Figure 9 shows
three alternate topologies. The first one, shown in Figure
9a uses a coupling capacitor to one input while the other
is grounded. This will remove the DC voltage difference from
the input to the LTC1966, and it will therefore not be part
of the resulting output voltage. Again, this connection will
work well with dual supply configurations, but in single
supply configurations it will be necessary to raise the volt-
age on the grounded input to assure that the signal at the
active input stays within the range of V
is already a suitable voltage reference available, connect the
second input to that point. If not, a midsupply voltage can
be created with two resistors as shown in Figure 9b.
Finally, if the input voltage is known to be between V
V
shown in Figure 9c. Whereas the DC return path was
provided through Pin 3 in Figures 9a and 9b, in this case,
the return path is provided on Pin 2, through the input
signal voltages. The switched capacitor action between
the two input pins of the LTC1966 will cause the voltage on
DD
, it can be AC coupled by using the configuration
V
IN
U
C
C
2
3
U
(9a)
IN1
IN2
LTC1966
V
V
Figure 9. Single-Ended AC-Coupled Input Connection Alternatives
DD
SS
W
SS
DD
V
to V
V
DD
IN
or below V
DD
100k
U
R1
. If there
C
C
SS
R2
100k
2
3
and
(9b)
SS
IN1
IN2
LTC1966
V
DD
the coupling capacitor connected to the second input to
follow the DC average of the input voltage.
For differential input applications, connect the two inputs to
the differential signal. If AC coupling is desired, one of the
two inputs can be connected through a series capacitor.
In all of these connections, to choose the input coupling
capacitor, C
constant desired, and divide by the LTC1966 differential
input impedance. Because the LTC1966 input impedance
is about 100 times its output impedance, this capacitor is
typically much smaller than the output averaging capaci-
tor. Its requirements are also much less stringent, and a
ceramic chip capacitor will usually suffice.
Output Connections
The LTC1966 output is differentially, but not symmetri-
cally, generated. That is to say, the RMS value that the
LTC1966 computes will be generated on the output (Pin 5)
relative to the output return (Pin 6), but these two pins are
not interchangeable. For most applications, Pin 6 will be
tied to ground (Pin 1), and this will result in the best
accuracy. However, Pin 6 can be tied to any voltage
between V
output voltage swing desired. This last restriction keeps
V
reference level other than ground is used, it should be a
low impedance, both AC and DC, for proper operation of
the LTC1966.
Use of a voltage in the range of V
lead to errors due to the switch dynamics as the NMOS
transistor is cut off. For this reason, it is recommended
that OUT RTN = 0V if V
OUT
itself (Pin 5) within the range of V
V
V
SS
DC
IN
C
, calculate the low frequency coupling time
(Pin 4) and V
+
–
2
3
C
(9c)
C
IN1
IN2
DD
V
SS
LTC1966
V
OR GND
is 3V.
DD
DD
1966 F07
(Pin 7) less the maximum
DD
– 1V to V
LTC1966
SS
DD
to V
– 1.3V can
sn1966 1966fas
DD
15
. If a