LTC1564 LINER [Linear Technology], LTC1564 Datasheet - Page 7

• Manufacturer Part Number: LTC1564
• Description: 10kHz to 150kHz Digitally Controlled Antialiasing Filter and 4-Bit P.G.A
• Manufacturer: LINER [Linear Technology]

AGND (Pin 15): Analog Ground. The AGND pin is at the
midpoint of an internal resistive voltage divider, develop-
ing a potential halfway between the V
an equivalent series resistance to the pin of nominally 7k.
(In the shutdown state, analog switch FETs interrupt the
voltage-divider resistors and the AGND pin assumes a
high impedance.) AGND also serves as the internal half-
supply reference in the LTC1564, tied to the noninverting
inputs of all internal op amps and establishing the ground
reference voltage for the IN and OUT pins. Because of this,
very “clean” grounding is recommended, including an
PI FU CTIO S
Table 3. Summary of LTC1564 Digital Controls and Modes
X = Doesn’t Matter
EN
SYSTEM GROUND
1
1
1
0
0
0
0
U
SINGLE-POINT
Figure 1. Dual Supply Ground Plane Connection
RST
1
1
0
1
0
1
1
U
CS/HOLD
ANALOG
GROUND PLANE
1
0
X
0
X
1
0
U
16
1
F3
X
X
X
0
X
V
Other Than 0000
Other Than 0000
–
15
2
0.1 F
F2
V
X
X
X
0
X
+
14
3
0.1 F
LTC1564
F1
X
X
X
0
X
13
4
F0
DIGITAL GROUND PLANE
X
X
X
0
X
12
5
+
and V
11
6
G3 G2 G1
(IF ANY)
X
X
X
X
X
X
X
10
7
–
X
X
X
X
X
X
X
pins, with
9
8
X
X
X
X
X
X
X
1564 F01
G0
X
X
X
X
X
X
X
FUNCTION
Shutdown Mode. Filter Disabled. Latch Holds F and G Inputs Present
when Last CS/HOLD = 0
Shutdown Mode. Filter Disabled. Latch Accepts F and G Inputs
Shutdown Mode. Filter Disabled. Latch Contents (F and G) Reset to All Zeros
Mute Mode. Filter Active, Zero Gain, Reduced Noise
Mute Mode. Filter Active, Zero Gain, Reduced Noise. Latch Contents
(F and G) Reset to All Zeros
Normal Filtering Operation. Latch Holds F and G Inputs Present
when Last CS/HOLD = 0
Normal Filtering Operation. Filter Responds Directly to F and G Input
Pins (See Separate Pin Descriptions)
analog ground plane surrounding the package. For dual
supply operation, this ground plane will be tied to the 0V
point and the AGND pin should connect directly to the
ground plane (Figure 1). For single supply operation, in
contrast, if the system signal ground is at V
plane should tie to V
bypassed to the ground plane by at least a 0.1 F high
quality capacitor (at least 1 F for best AC performance)
(Figure 2). As with all high dynamic range analog circuits,
performance in an application will reflect the quality of the
grounding.
SYSTEM GROUND
SINGLE-POINT
Figure 2. Single Supply Ground Plane Connection
ANALOG
GROUND PLANE
REFERENCE
V
+
1 F
/2
–
and the AGND pin should be AC-
16
1
15
2
V
+
14
3
0.1 F
LTC1564
13
4
DIGITAL GROUND PLANE
12
5
LTC1564
(IF ANY)
11
6
–
, the ground
10
7
9
8
1564 F01
7