Datasheet

7
LTC1564
1564fa
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
+
and V
–
pins, with
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
UU
U
PI FU CTIO S
LTC1564
DIGITAL GROUND PLANE
(IF ANY)
ANALOG
GROUND PLANE
1
SINGLE-POINT
SYSTEM GROUND
234567
1564 F01
8
16 15 14 13 12 11
0.1µF
V
+
10 9
0.1µF
V
–
Figure 1. Dual Supply Ground Plane Connection
LTC1564
DIGITAL GROUND PLANE
(IF ANY)
ANALOG
GROUND PLANE
1
SINGLE-POINT
SYSTEM GROUND
234567
1564 F01
8
16
V
+
/2
REFERENCE
15 14 13 12 11
0.1µF
1µF
V
+
10 9
Figure 2. Single Supply Ground Plane Connection
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
–
, the ground
plane should tie to V
–
and the AGND pin should be AC-
bypassed to the ground plane by at least a 0.1µF high
quality capacitor (at least 1µF 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.
Table 3. Summary of LTC1564 Digital Controls and Modes
EN RST CS/HOLD F3 F2 F1 F0 G3 G2 G1 G0 FUNCTION
1 1 1 XXXX XXX X Shutdown Mode. Filter Disabled. Latch Holds F and G Inputs Present
when Last CS/HOLD = 0
1 1 0 XXXX XXX X Shutdown Mode. Filter Disabled. Latch Accepts F and G Inputs
1 0 X XXXX XXXX Shutdown Mode. Filter Disabled. Latch Contents (F and G) Reset to All Zeros
0 1 0 0000 XXXX Mute Mode. Filter Active, Zero Gain, Reduced Noise
0 0 X XXXX XXXX Mute Mode. Filter Active, Zero Gain, Reduced Noise. Latch Contents
(F and G) Reset to All Zeros
0 1 1 Other Than 0000 X X X X Normal Filtering Operation. Latch Holds F and G Inputs Present
when Last CS/HOLD = 0
0 1 0 Other Than 0000 X X X X Normal Filtering Operation. Filter Responds Directly to F and G Input
Pins (See Separate Pin Descriptions)
X = Doesn’t Matter