9

LTC1650

OPERATIO

Serial Interface

on the rising edge of the clock. Data is loaded as one

16-bit word, MSB first. The DAC register loads the data

from the shift register when CS/LD is pulled high. The

clock is disabled internally when CS/LD is high. Note: CLK

must be low before CS/LD is pulled low to avoid an extra

internal clock pulse.

The buffered output of the 16-bit shift register is available

Multiple LTC1650s may be daisy-chained together by

while the clock and CS/LD signals remain common to all

chips in the daisy chain. The serial data is clocked to all of

the chips, then the CS/LD signal is pulled high to update all

of them simultaneously.

When CLR is pulled low or when the part powers up, the

RSTOUT pin goes low and stays low as long as the supply

is below 2.5V. The power-on reset is also activated when

one of the supplies drops below 2.5V and the output is

when any of three conditions occur: CLR goes low, the part

powers up or one of the supplies drops below 2.5V. This

condition exists as long as CS/LD is low. As soon as CS/

LD goes high, the DAC register is loaded with the data in

the shift register and the output will settle to its new value.

Voltage Output

The LTC1650 rail-to-rail buffered output can source or

sink 5mA over the entire operating temperature range. The

output can swing to within a few millivolts of either supply

rail when unloaded and has an equivalent output resis-

tance of 50

Ω when driving a load to the rails. The buffer

amplifier can drive 1000pF without going into oscillation.

The LTC1650 has a deglitched voltage output. The midscale

glitch is less than 2nV-s. The digital feedthrough is about

0.05nV-s.

Output Ranges

The LTC1650 is capable of unipolar or bipolar output

is configured for unipolar operation and the output will

swing from REFLO to REFHI. When UNI/BIP is connected

to REFHI the part is configured in bipolar mode and the

output will swing from (2 • REFLO – REFHI) to REFHI and

will be at REFLO at midscale. With REFLO = 0V the output

swing is

±REFHI in bipolar mode and 0V to REFHI in

unipolar mode.