LTC1654
OPERATIO
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: (X
1
/X
1/2
tied to REFLO)
V
OUT
= (V
REFHI
– V
REFLO
)(CODE/16384) + V
REFLO
b) GAIN of 1/2: (X
1
/X
1/2
tied to V
OUT
)
V
OUT
= (1/2)(V
REFHI
– V
REFLO
)(CODE/16384) + V
REFLO
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 3µs (typ) to 14 bits on a 4V
output swing. In the SLOW mode, they will settle in 8.5µs.
U
The total supply current is 930µA in the FAST mode and
540µA 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 5µA/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 0.1µA.
The amplifiers’ output stage is also three-stated but the
V
OUT
pins still have the internal gain-setting resistors
connected to them resulting in an effective resistance from
V
OUT
to REFLO. This resistance is typically 90k when the
X
1
/X
1/2
pin is tied to V
OUT
and 36k when X
1
/X
1/2
is tied to
REFLO. Because of this resistance, V
OUT
will go to V
REFLO
when the DAC is powered down and V
OUT
is unloaded.
1654fb
9
LINER [ LINEAR TECHNOLOGY ]
