7

LTC1564

1564fa

AGND (Pin 15): Analog Ground. The AGND pin is at the

midpoint of an internal resistive voltage divider, develop-

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

LTC1564

DIGITAL GROUND PLANE

(IF ANY)

ANALOG

GROUND PLANE

1

SINGLE-POINT

SYSTEM GROUND

23

4

5

6

7

1564 F01

8

16

15

14

13

12

11

0.1

µF

10

9

0.1

µF

Figure 1. Dual Supply Ground Plane Connection

LTC1564

DIGITAL GROUND PLANE

(IF ANY)

ANALOG

GROUND PLANE

1

SINGLE-POINT

SYSTEM GROUND

23

4

5

6

7

1564 F01

8

16

REFERENCE

15

14

13

12

11

0.1

µF

1

µF

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

bypassed to the ground plane by at least a 0.1

µF high

quality capacitor (at least 1

µF 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

XX

X

X

Shutdown Mode. Filter Disabled. Latch Holds F and G Inputs Present

when Last CS/HOLD = 0

1

1

0

XXXX

XX

X

X

Shutdown Mode. Filter Disabled. Latch Accepts F and G Inputs

1

0

X

XXXX

XX

X

X

Shutdown Mode. Filter Disabled. Latch Contents (F and G) Reset to All Zeros

0

1

0

0000

X

X

X

X

Mute Mode. Filter Active, Zero Gain, Reduced Noise

0

0

X

XXXX

XX

X

X

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