LTC2298CUP datasheet(21/28 Pages) LINER

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LTC2298/LTC2297/LTC2296

229876f

between the digital outputs and sensitive input circuitry.

The output should be buffered with a device such as an

ALVCH16373 CMOS latch. For full speed operation the

capacitive load should be kept under 10pF.

Lower OVDD voltages will also help reduce interference

from the digital outputs.

Data Format

Using the MODE pin, the LTC2298/LTC2297/LTC2296

parallel digital output can be selected for offset binary or

2’s complement format. Note that MODE controls both

Channel A and Channel B. Connecting MODE to GND or

1/3VDD selects straight binary output format. Connecting

MODE to 2/3VDD or VDD selects 2’s complement output

format. An external resistor divider can be used to set the

1/3VDD or 2/3VDD logic values. Table 1 shows the logic

states for the MODE pin.

APPLICATIO S I FOR ATIO

Overflow Bit

When OF outputs a logic high the converter is either

overranged or underranged.

Output Driver Power

Separate output power and ground pins allow the output

drivers to be isolated from the analog circuitry. The power

supply for the digital output buffers, OVDD, should be tied

to the same power supply as for the logic being driven. For

example, if the converter is driving a DSP powered by a 1.8V

supply, then OVDD should be tied to that same 1.8V supply.

OVDD can be powered with any voltage from 500mV up to

3.6V. OGND can be powered with any voltage from GND up

to 1V and must be less than OVDD. The logic outputs will

swing between OGND and OVDD.

Output Enable

The outputs may be disabled with the output enable pin, OE.

OE high disables all data outputs including OF. The data ac-

cess and bus relinquish times are too slow to allow the

outputs to be enabled and disabled during full speed op-

eration. The output Hi-Z state is intended for use during long

periods of inactivity. Channels A and B have independent

output enable pins (OEA, OEB).

Table 1. MODE Pin Function

Clock Duty

MODE Pin

Output Format

Cycle Stabilizer

Straight Binary

Off

1/3VDD

Straight Binary

2/3VDD

2’s Complement

VDD

2’s Complement

Off

Figure 12. Digital Output Buffer

229876 F12

OVDD

VDD

0.1µF

43Ω

TYPICAL

DATA

OUTPUT

OGND

OVDD

0.5V

TO VDD

PREDRIVER

LOGIC

DATA

FROM

LATCH

LTC2298/LTC2297/LTC2296

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