5

LTC1560-1

sn15601 15601fs

PIN FUNCTIONS

GND (Pins 1, 3): Analog Ground Pins. The quality of the

analog ground can affect the filter performance. For dual

supply operation the analog ground pin should be con-

nected to an analog ground plane surrounding the pack-

age. The analog ground plane should be connected to a

digital ground plane (if any) at a single point. For single

supply operation, the analog ground pin should be biased

at one-half the power supply across the device (see

Figure 1) and the analog ground plane should then be

connected to V – (Pin 4).

VIN (Pin 2): The filter input is internally connected to the

inverting input of a high frequency op amp through an 8k

resistor.

V –, V + (Pins 4, 6): Power Supply Pins. The negative and

positive power supply (Pins 4 and 6 respectively) should

be decoupled with a 0.1

µF capacitor in parallel with a

0.01

µF. Both capacitors should be types designed for

decoupling video frequencies and they should be placed

as close as possible to the power supply pins of the filter.

Parallel routing of high frequency signal paths should be

avoided; they will couple into the device’s power supply

pins and cause gain inaccuracy and stopband degrada-

tion. The power supplies can be applied in any order, that

is, the positive supply can be applied before the negative

supply and vice versa. Switching power supplies are not

recommended.

0.5fC/fC (Pin 5): By tying Pin 5 high the filter cutoff

frequency is internally programmed for 500kHz. By tying

Pin 5 low the cutoff frequency will switch to 1MHz. Pin 5

should not be left floating. The logic threshold of Pin 5 is

approximately 0.4 times the total power supply across the

device.

SHDN (Pin 7): Shutdown. Under normal operating condi-

tions, Pin 7 should be shorted either to the analog ground

(Pin 1) or to V – (Pin 4). If Pin 7 is pulled high to V +, the filter

operation will stop and the IC will be placed in a power

saving mode. The power supply current will then be

reduced to 1mA. For a

±5V supply, the logic threshold of

Pin 7 is 2.5V. Pin 7 is internally connected to the analog

ground pin via a 50k resistor.

VOUT (Pin 8): The filter output pin can sink or source 1mA.

The total harmonic distortion of the filter will degrade

when driving coaxial cables or loads less than 10k without

an output buffer.

Figure 1. Connections for Single Supply Operation

V +

1560-1 F01

VIN

VOUT

0.01

µF

0.1

µF

0.01

µF

1

µF

10k

10k

GND OR V+

ANALOG GROUND PLANE

SYSTEM GROUND

DIGITAL GROUND

PLANE

GND

V –

V +

GND

VIN

1

4

3

2

8

5

6

7

VOUT

SHDN

0.5fC/fC

LTC1560-1