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HI5804KCB

12-Bit, 5 MSPS A/D Converter

Intersil 

HI5804

Internal Reference Generator, VROUT and VRIN

The HI5804 has an internal reference voltage generator,

therefore no external reference voltage is required. VROUT

must be connected to VRIN when using the internal refer-

ence voltage.

The HI5804 can be used with an external reference voltage.

The converter requires only one external reference voltage

connected to the VRIN pin with VROUT left open.

The HI5804 is tested with VRIN equal to 3.5V. Internal to the

converter two reference voltages of 1.3V and 3.3V are gen-

erated for a fully differential input signal range of ±2V.

In order to minimize overall converter noise it is recom-

mended that adequate high frequency decoupling be

provided at the reference voltage input pin, VRIN.

Analog Input, Differential Connection

The analog input to the HI5804 can be configured in various

ways depending on the signal source and the required level

of performance. A fully differential connection (Figure 10) will

give the best performance for the converter.

VIN

VIN+

VDC

HI5804

VIN-

FIGURE 11. AC COUPLED SINGLE ENDED INPUT

Again, the difference between the two internal voltage

references is 2V. If VIN is a 4VP-P sinewave, then VIN+ is a

4VP-P sinewave riding on a positive voltage equal to VDC. The

converter will be at positive full scale when VIN+ is at VDC + 2V

(VIN+ - VIN- = 2V) and will be at negative full scale when VIN+ is

equal to VDC - 2V (VIN+ - VIN- = -2V). In this case, VDC could

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

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

VDC bias voltage output of the HI5804.

A single ended source will give better overall system

performance if it is first converted to differential before

driving the analog input of the HI5804.

VIN

VIN+

HI5804

VDC

-VIN

VIN-

FIGURE 10. AC COUPLED DIFFERENTIAL INPUT

Since the HI5804 is powered off a single +5V supply, the

analog input must be biased so it lies within the analog input

common mode voltage range of 1.0V to 4.0V. The perfor-

mance of the ADC does not change significantly with the

value of the common mode voltage.

A 2.3V DC bias voltage source, VDC, half way between the

top and bottom internal reference voltages, is made avail-

able to the user to help simplify circuit design when using a

differential input. This low output impedance voltage source

is not designed to be a reference but makes an excellent

bias source and stays within the analog input common mode

voltage range over temperature.

The difference between the converter’s two internal voltage

references is 2V. For the AC coupled differential input,

(Figure 10), if VIN is a 2VP-P sinewave with -VIN being 180

degrees out of phase with VIN, the converter will be at positive

full scale when the VIN+ input is at VDC + 1V and the VIN-

input is at VDC - 1V (VIN+ - VIN- = 2V). Conversely, the ADC

will be at negative full scale when the VIN+ input is equal to

VDC - 1V and VIN- is at VDC + 1V (VIN+ - VIN- = -2V).

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

or below AGND.

Digital I/O and Clock Requirements

The HI5804 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 HI5804 to be driven by CMOS logic.

The digital CMOS outputs have a separate digital supply.

This allows the digital outputs to operate from a 3.0V to 5.0V

supply. When driving CMOS logic, the digital outputs will

swing to the rails. When driving standard TTL loads, the dig-

ital outputs will meet standard TTL level requirements even

with a 3.0V supply.

In order to ensure rated performance of the HI5804, 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 HI5804 will only be guaranteed at con-

version rates above 0.5 MSPS. This ensures proper perfor-

mance of the internal dynamic circuits.

Supply and Ground Considerations

The HI5804 has separate analog and digital supply and

ground pins to keep digital noise out of the analog signal

path. The part should be mounted on a board that provides

separate low impedance connections for the analog and dig-

ital supplies and grounds. For best performance, the sup-

plies to the HI5804 should be driven by clean, linear

regulated supplies. The board should also have good high

frequency decoupling capacitors mounted as close as possi-

ble to the converter. If the part is powered off a single supply

then the analog supply and ground pins should be isolated

by ferrite beads from the digital supply and ground pins.

Refer to Application Note AN9214, “Using Harris High Speed

A/D Converters” for additional considerations when using

high speed converters.

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