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LTC1657

Parallel 16-Bit Rail-to-Rail Micropower DAC

Linear Technology 

LTC1657/LTC1657L

DEFI ITIO S

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

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

states (2n) that divide the full-scale range. Resolution does

not imply linearity.

Full-Scale Voltage (VFS): This is the output of the DAC

when all bits are set to 1.

Voltage Offset Error (VOS): Normally, the DAC offset is the

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.

OUTPUT

VOLTAGE

NEGATIVE 0V

OFFSET

DAC CODE

1657 F01

Figure 1. Effect of Negative Offset

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

sponds to the maximum offset specification:

VOS = VOUT – [(Code)(VFS)/(2n – 1)]

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

difference between two successive codes.

LSB = G • VREF/65536

G = 1 for X1/X2 connected to VOUT

G = 2 for X1/X2 connected to GND

Nominal LSBs: (VREFOUT tie to VREFHI, REFLO tie to GND,

G = 2)

LTC1657 LSB = 4.096V/65536 = 62.5µV

LTC1657L LSB = 2.5V/65536 = 38.1µV

DAC Transfer Characteristic:

( ) VOUT

=

G

•





REFHI – REFLO

65536 

CODE

+ REFLO

G = 1 for X1/X2 connected to VOUT

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:

INL (In LSBs) = [VOUT – VOS – (VFS – VOS)

(code/65535)]

VOUT = The output voltage of the DAC measured at

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 = (∆VOUT – LSB)/LSB

∆VOUT = The measured voltage difference between

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.

9

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