6

LTC1657L

Figure 1. Effect of Negative Offset

Resolution (n): Resolution is defined as the number of

digital input bits (n). It defines the number of DAC output

not imply linearity.

when all bits are set to 1.

voltage at the output when the DAC is loaded with all zeros.

The DAC can have a true negative offset, but because the

part is operated from a single supply, the output cannot go

below zero. If the offset is negative, the output will remain

near 0V resulting in the transfer curve shown in Figure 1.

DEFI ITIO S

DAC CODE

1657 F01

OUTPUT

VOLTAGE

NEGATIVE

OFFSET

0V

The offset of the part is measured at the code that corre-

sponds to the maximum offset specification:

Least Significant Bit (LSB): One LSB is the ideal voltage

difference between two successive codes.

Nominal LSBs:

LTC1657L LSB = 2.5V/65535 = 38.1

µV

DAC Transfer Characteristic:

VG

REFHI REFLO

CODE

REFLO







+

•

–

65536

G = 2 for X1/X2 connected to GND

CODE = Decimal equivalent of digital input

(0

≤ CODE ≤ 65535)

Zero-Scale Error (ZSE): The output voltage when the

DAC is loaded with all zeros. Since this is a single supply

part, this value cannot be less than 0V.

Integral Nonlinearity (INL): End-point INL is the maxi-

mum deviation from a straight line passing through the

end points of the DAC transfer curve. Because the part

operates from a single supply and the output cannot go

below zero, the linearity is measured between full scale

and the code corresponding to the maximum offset

specification. The INL error at a given input code is

calculated as follows:

(code/65535)]

the given input code

Differential Nonlinearity (DNL): DNL is the difference

between the measured change and the ideal one LSB

change between any two adjacent codes. The DNL error

between any two codes is calculated as follows:

DNL = (

two adjacent codes

Digital Feedthrough: The glitch that appears at the analog

output caused by AC coupling from the digital inputs when

they change state. The area of the glitch is specified in

nV • s.