LTC1654IGN datasheet(9/16 Pages) LINER

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LTC1654

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Voltage Output

The LTC1654 comes complete with rail-to-rail voltage

output buffer amplifiers. These amplifiers will swing to

within a few millivolts of either supply rail when unloaded

and to within a 450mV of either supply rail when sinking

or sourcing 5mA.

There are two GAIN configuration modes for the LTC1654:

a) GAIN of 1: (X1/X1/2 tied to REFLO)

VOUT = (VREFHI – VREFLO)(CODE/16384) + VREFLO

b) GAIN of 1/2: (X1/X1/2 tied to VOUT)

VOUT = (1/2)(VREFHI – VREFLO)(CODE/16384) + VREFLO

The LTC 1654 has two SPEED modes: A FAST mode and

a SLOW mode. When operating in the FAST mode, the

output amplifiers will settle in 3

µs (typ) to 14 bits on a 4V

output swing. In the SLOW mode, they will settle in 8.5

µs.

The total supply current is 930

µA in the FAST mode and

540

µA in the SLOW mode. The output noise voltage

density at 10kHz is 170nV/

√Hz in SLOW mode and

150nV/

√Hz in FAST mode.

Power Down

Each DAC can also be independently powered down to less

than 5

µA/DAC of supply current. The reference pin also

goes into a high impedance state when the DAC is powered

down and the reference current will drop to below 0.1

µA.

The amplifiers’ output stage is also three-stated but the

VOUT pins still have the internal gain-setting resistors

connected to them resulting in an effective resistance from

VOUT to REFLO. This resistance is typically 90k when the

X1/X1/2 pin is tied to VOUT and 36k when X1/X1/2 is tied to

REFLO. Because of this resistance, VOUT will go to VREFLO

when the DAC is powered down and VOUT is unloaded.

OPERATIO

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