
9
LTC1654
1654fb
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
s (typ) to 14 bits on a 4V
output swing. In the SLOW mode, they will settle in 8.5
s.
The total supply current is 930
A in the FAST mode and
540
A 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
A/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
A.
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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