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LTC1695

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LTC1695

DEFINITIONS

Resolution: The number of DAC output states (2N) that

divide the full-scale range. The resolution does not imply

linearity.

Full-Scale Voltage (VFS): The regulator output voltage

(VOUT) if all DAC bits are set to ones (code 63).

Voltage Offset Error (VOS): The regulator output voltage

if all DAC bits are set to zeros. The LDO amplifier can have

a true negative offset, but due to the LTC1695’s single

supply operation, VOUT cannot go below ground. If the

offset is negative, VOUT will remain near 0V resulting in the

transfer curve shown in Figure 1.

OUTPUT

VOLTAGE

0V

NEGATIVE

OFFSET

DAC CODE

1695 • F01

Figure 1. Effect of Negative Offset

The offset of the part is measured at the first code (code␣ 1)

that produces an output voltage 0.5LSB greater than the

previous code.

VOS = VOUT – [(Code • VFS)/(2N – 1)]

Least Significant Bit (VLSB): The least significant bit or the

ideal voltage difference between two successive codes.

VLSB = (VFS – VOS)/(2N – 1)

Table 1. Nominal VLSB and VFS values

VCC

VLSB

4.5V

70.3mV

5.0V

78.1mV

5.5V

85.9mV

VFS

4.430V

4.922V

5.414V

INL: Integral nonlinearity is the maximum deviation from

a straight line passing through the endpoints of the DAC

transfer curve. Due to the LTC1695’s single supply opera-

tion and the fact that VOUT cannot go below ground,

linearity is measured between full scale and the first code

(code 01) that guarantees a positive output. The INL error

at a given input code is calculated as follows:

INL = (VOUT – VIDEAL))/VLSB

VIDEAL = (Code • VLSB) + VOS

VOUT = The output voltage of the DAC

measured at the given input code

DNL: Differential nonlinearity is the difference between the

measured change and the ideal 1LSB change between any

two adjacent codes. The DNL error between any two codes

is calculated as below:

DNL = (∆VOUT – VLSB)/VLSB

∆VOUT = The measured voltage difference

between two adjacent codes

The ∆VOUT calculation includes the VOS values to account

for the effect of negative offset in Figure 1. This is relevant

for code 1’s DNL.

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