ltc6910-2 Linear Technology Corporation, ltc6910-2 Datasheet - Page 14

• Manufacturer Part Number: ltc6910-2
• Description: Digitally Controlled Programmable Gain Amplifiers In Sot-23
• Manufacturer: Linear Technology Corporation

LTC6910-1
LTC6910-2/LTC6910-3
OUT (Pin 1): Analog Output. This is the output of an
internal operational amplifier and swings to near the
power supply rails (V
Characteristics table. The internal op amp remains active
at all times, including the zero gain setting (digital input
000). As with other amplifier circuits, loading the output as
lightly as possible will minimize signal distortion and gain
error. The Electrical Characteristics table shows perfor-
mance at output currents up to 10mA and current limits
that occur when the output is shorted to midsupply at 2.7V
and 5V supplies. Signal outputs above 10mA are pos-
sible but current-limiting circuitry will begin to affect
amplifier performance at approximately 20mA. Long-term
operation above 20mA output is not recommended. Do
not exceed maximum junction temperature of 150 C. The
output will drive capacitive loads up to 50pF. Capacitances
higher than 50pF should be isolated by a series resistor to
preserve AC stability.
AGND (Pin 2): Analog Ground. The AGND pin is at the
midpoint of an internal resistive voltage divider, develop-
ing a potential halfway between the V
equivalent series resistance to the pin of nominally 5k
(Figure 4). AGND is also the noninverting input of the
internal op amp, which makes it the ground reference
voltage for the IN and OUT pins. Because of this, very
“clean” grounding is important, including an analog ground
plane surrounding the package.
PI FU CTIO S
SYSTEM GROUND
14
SINGLE-POINT
U
Ground Plane Connection
U
ANALOG
GROUND
PLANE
Figure 1. Single Supply
0.1 F
V
+
8
1
LTC6910-X
DIGITAL GROUND PLANE
7
2
U
+
1 F
and V
(IF ANY)
6
3
V
2
+
5
4
REFERENCE
–
) as specified in the Electrical
6910 F01
+
and V
SYSTEM GROUND
SINGLE-POINT
–
pins, with an
Figure 2. Symmetrical Dual Supply
Ground Plane Connection
ANALOG
GROUND
PLANE
0.1 F
V
+
8
1
LTC6910-X
DIGITAL GROUND PLANE
7
2
Recommended analog ground plane connection depends
on how power is applied to the LTC6910-X (Figures 1, 2,
and 3). Single power supply applications typically use V
for the system signal ground. The analog ground plane in
single-supply applications should therefore tie to V
the AGND pin should be bypassed to this ground plane by
a high quality capacitor of at least 1 F (Figure 1). The
AGND pin then provides an internal analog reference
voltage at half the supply voltage (with internal resistance
of approximately 5k ) which is the center of the swing
range for both input and output. Dual supply applications
with symmetrical supplies (such as 5V) have a natural
system ground at zero volts, which can drive the analog
ground plane; AGND then connects directly to the ground
plane, making zero volts the input and output reference
voltage for the LTC6910-X (Figure 2). Finally, if a dual
power supply is asymmetrical, the supply ground is still
the natural ground plane voltage. To maximize signal
swing capability with an asymmetrical supply, however, it
is often desirable to refer the LTC6910-X’s analog input
and output to a voltage equidistant from the two supply
rails V
when open-circuited and bypassed with a capacitor (Fig-
ure 3), just as with a single power supply, but now the
ground plane connection is different and the LTC6910-X’s
V
(IF ANY)
6
3
+
V
and V
5
4
–
0.1 F
+
and V
6910 F02
–
pins are both isolated from this ground plane.
–
. The AGND pin will provide such a potential
SYSTEM GROUND
SINGLE-POINT
Supply Ground Plane Connection
ANALOG
GROUND
PLANE
Figure 3. Asymmetrical Dual
0.1 F
V
+
8
1
LTC6910-X
7
2
1 F
6
3
MID-SUPPLY
REFERENCE
DIGITAL GROUND PLANE
5
4
(IF ANY)
V
–
0.1 F
6910123fa
–
, and
6910 F03
–