MAX1221 datasheet(39/44 Pages) MAXIM

39 / 44 page

12-Bit, Multichannel ADCs/DACs with FIFO,

Temperature Sensing, and GPIO Ports

______________________________________________________________________________________

GPIO INPUT/OUTPUT

tGSU

tGOD

Figure 13. GPIO Timing

LDAC

tLDACPWL

OUT_

±1 LSB

Figure 14.

LDAC Functionality

Layout, Grounding, and Bypassing

For best performance, use PC boards. Ensure that digital

and analog signal lines are separated from each other.

Do not run analog and digital signals parallel to one

another (especially clock signals) or do not run digital

lines underneath the MAX1221/MAX1223/MAX1343

package. High-frequency noise in the AVDD power sup-

ply may affect performance. Bypass the AVDD supply

with a 0.1µF capacitor to AGND, close to the AVDD pin.

Bypass the DVDD supply with a 0.1µF capacitor to

DGND, close to the DVDD pin. Minimize capacitor lead

lengths for best supply-noise rejection. If the power sup-

ply is very noisy, connect a 10Ω resistor in series with the

supply to improve power-supply filtering.

The MAX1221/MAX1223/MAX1343 thin QFN packages

contain an exposed pad on the underside of the device.

Connect this exposed pad to AGND. Refer to the

MAX1258EVKIT for an example of proper layout.

Definitions

Integral Nonlinearity

Integral nonlinearity (INL) is the deviation of the values

on an actual transfer function from a straight line. This

straight line can be either a best-straight-line fit or a line

drawn between the end points of the transfer function,

once offset and gain errors have been nullified. INL for

the MAX1221/MAX1223/MAX1343 is measured using

the end-point method.

Differential Nonlinearity

Differential nonlinearity (DNL) is the difference between

an actual step width and the ideal value of 1 LSB. A

DNL error specification of less than 1 LSB guarantees

no missing codes and a monotonic transfer function.

Unipolar ADC Offset Error

For an ideal converter, the first transition occurs at 0.5

LSB, above zero. Offset error is the amount of deviation

between the measured first transition point and the

ideal first transition point.

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