9

Analog Input, Single-Ended Connection

The configuration shown in Figure 11 may be used with a

single ended AC coupled input. Sufficient headroom must be

provided such that the input voltage never goes above +5V

Again, the difference between the two internal voltage

could range between 2V and 3V without a significant change in

ADC performance. The simplest way to produce VDC is to use

The single ended analog input can be DC coupled (Figure

12) as long as the input is within the analog input common

mode voltage range.

The resistor, R, in Figure 12 is not absolutely necessary but

may be used as a load setting resistor. A capacitor, C,

frequency noise on the inputs, also improving performance.

Values around 20pF are sufficient and can be used on AC

coupled inputs as well. Note, however, that the value of

capacitor C chosen must take into account the highest

frequency component of the analog input signal.

A single ended source will give better overall system

performance if it is first converted to differential before

driving the HI5905.

Digital I/O and Clock Requirements

The HI5905 provides a standard high-speed interface to

external TTL/CMOS logic families. The digital CMOS clock

input has TTL level thresholds. The low input bias current

allows the HI5905 to be driven by CMOS logic. The digital

CMOS outputs have a separate +5.0V digital supply input pin.

In order to ensure rated performance of the HI5905, the duty

cycle of the clock should be held at 50%

±5%. It must also

have low jitter and operate at standard TTL levels.

Performance of the HI5905 will only be guaranteed at

conversion rates above 0.5MSPS. This ensures proper

performance of the internal dynamic circuits.

TABLE 1. A/D CODE TABLE

CODE

CENTER

DESCRIPTION

DIFFERENTIAL

INPUT

VOLTAGE

†

(USING

INTERNAL

REFERENCE)

TWO’S COMPLEMENT BINARY OUTPUT CODE

MSB

LSB

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

+Full Scale

(+FS) - 1/4 LSB

+1.99994V

0

1

1

1

1

1

1

1

1

1

1

1

1

1

+FS

1.99969V

0

1

1

1

1

1

1

1

1

1

1

1

1

0

+ 3/4 LSB

183.105

µV

0

0

0

0

0

0

0

0

0

0

0

0

0

0

- 1/4 LSB

-61.035

µV

1

1

1

1

1

1

1

1

1

1

1

1

1

1

-FS + 1 3/4 LSB

-1.99957V

1

0

0

0

0

0

0

0

0

0

0

0

0

1

-Full Scale

(-FS) + 3/4 LSB

-1.99982V

1

0

0

0

0

0

0

0

0

0

0

0

0

0

HI5905

VDC

FIGURE 11. AC COUPLED SINGLE ENDED INPUT

HI5905

VDC

R

C

VDC

FIGURE 12. DC COUPLED SINGLE ENDED INPUT

HI5905