LTC1067-50IS#TRPBF Linear Technology, LTC1067-50IS#TRPBF Datasheet - Page 14

• Manufacturer Part Number: LTC1067-50IS#TRPBF
• Description: IC FILTR BLDNGBLK R-R DUAL16SOIC
• Manufacturer: Linear Technology

Specifications of LTC1067-50IS#TRPBF

• Filter Type: Universal Switched Capacitor
• Frequency - Cutoff Or Center: 40kHz
• Number Of Filters: 2
• Max-order: 4th
• Voltage - Supply: 2.7 V ~ 11 V, ±2.7 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS
LTC1067/LTC1067-50
the output of the first section is near the positive rail
(operating modes invert the signal). The output of the first
stage will saturate at about 250mV (typical for 5V supply)
from positive supply. The output from the second stage
will be 250mV from the negative supply rail (assuming
inversion again) even though the op amp’s output is
capable of swinging to within 15mV.
The positive output voltage swing being less than the
negative swing, coupled with the AGND potential set at the
midpoint of the supplies and inverting of the signal, yields
the following equation for peak-to-peak output swing:
14
V
P-P
Figure 12. LTC1067/LTC1067-50 Positive Output Voltage
Swing vs Load Resistance, 3.3V/3V Supplies
Figure 11. LTC1067/LTC1067-50 Positive Output Voltage
Swing vs Load Resistance, 5V Supply
Swing = (V
5.0
4.5
4.0
3.5
3.0
2.5
3.3
3.0
2.7
2.4
2.1
1.8
1.5
0
0
2
2
+
U
LOAD RESISTANCE (k TO V
LOAD RESISTANCE (k TO V
LTC1067-50
4
– V
4
LTC1067
V
6
S
6
–
LTC1067
INFORMATION
= 3.3V
LTC1067-50
V
) – 2(V
U
S
8
8
= 3V
10
10
12 14 16 18 20
+
12 14 16 18 20
– V
W
POSITIVE SWING
–
–
)
)
1067 F11
1067 F12
U
)
Many applications are more concerned with the negative
output swing than the positive output swing. Interfacing to
an ADC running on a single 5V supply with a 4.096
reference voltage is a standard example. The LTC1067 or
LTC1067-50 will easily reach the 4.096V level for a full-
scale reading. The issue is how close does the output go
to ground. The further the output is from ground, the more
codes that are essentially lost. The previous example
demonstrated that the lowest output voltage would be
about 250mV, although, as is shown below, 15mV is
achievable.
To achieve a lower negative output swing voltage, the
AGND voltage must be adjusted down below the midpoint.
The AGND voltage is determined by two equal, on-chip
resistors. These resistors are typically 15k each. While the
ratio of these two resistors is tightly matched, the absolute
value of the resistors is not tightly controlled. Adjusting
the AGND voltage by simply adding an external resistor
can be done, but caution must be exercised.
In Figure 13, a resistor is used to adjust the AGND voltage
for use with a 5V powered ADC with a full-scale input of
4.096V. The resistor value was chosen carefully to assure
that a 4.096V input signal to the filter yields a full-scale
reading from the ADC and a 0V input signal gives the
lowest possible value (15mV for the LTC1067 and 10mV
for the LTC1067-50). The circuit works well over tempera-
ture and part variations. For this application, the 5V supply
must be above 4.75V.
(4.75V
MIN
0.1 F
5V
)
Figure 13. Power and AGND Connections for
5V ADC with 4.096V Full Scale
1
2
3
4
5
6
7
8
V
NC
V
SA
LPA
BPA
HPA/NA
INV A
+
+
LTC1067-50
LTC1067
HPB/NB
AGND
INV B
BPB
CLK
LPB
V
SB
–
16
15
14
13
12
11
10
9
1067 F13
1 F
64.9k
1%