LTC1407ACMSE datasheet(14/24 Pages) LINER

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LTC1407/LTC1407A

1407f

High quality tantalum and ceramic bypass capacitors should

be used at the VDD and VREF pins as shown in the Block

Diagram on the first page of this data sheet. For optimum

performance, a 10

µF surface mount tantalum capacitor

with a 0.1

µFceramicisrecommendedfortheVDDandVREF

pins. Alternatively, 10

µF ceramic chip capacitors such as

X5R or X7R may be used. The capacitors must be located

as close to the pins as possible. The traces connecting the

pins and the bypass capacitors must be kept short and

should be made as wide as possible. The VDD bypass ca-

pacitor returns to GND (Pin 6) and the VREF bypass capaci-

tor returns to the Exposed Pad ground (Pin 11). Care should

be taken to place the 0.1

µF VDD bypass capacitor as close

to Pins 6 and 7 as possible.

Figure 5 shows the recommended system ground connec-

tions. All analog circuitry grounds should be terminated at

the LTC1407/LTC1407A Exposed Pad. The ground return

from the LTC1407/LTC1407A Pin 6 to the power supply

should be low impedance for noise-free operation. The

Exposed Pad of the 10-lead MSE package is also tied to

Pin 6 and the LTC1407/LTC1407A GND. The Exposed Pad

should be soldered on the PC board to reduce ground

connection inductance. Digital circuitry grounds must be

connected to the digital supply common.

APPLICATIO S I FOR ATIO

Integral nonlinearity errors (INL) and differential nonlin-

earity errors (DNL) are largely independent of the common

mode voltage. However, the offset error will vary. CMRR

is typically better than 60dB.

Figure 4 shows the ideal input/output characteristics for

the LTC1407/LTC1407A. The code transitions occur mid-

way between successive integer LSB values (i.e., 0.5LSB,

1.5LSB, 2.5LSB, FS – 1.5LSB). The output code is natural

binary with 1LSB = 2.5V/16384 = 153

µV for the LTC1407A

and 1LSB = 2.5V/4096 = 610

µV for the LTC1407. The

LTC1407A has 1LSB RMS of Gaussian white noise.

Board Layout and Bypassing

Wire wrap boards are not recommended for high resolu-

tion and/or high speed A/D converters. To obtain the best

performance from the LTC1407/LTC1407A, a printed cir-

cuit board with ground plane is required. Layout for the

printed circuit board should ensure that digital and analog

signal lines are separated as much as possible. In particu-

lar, care should be taken not to run any digital track

alongside an analog signal track. If optimum phase match

between the inputs is desired, the length of the four input

wires of the two input channels should be kept matched.

But each pair of input wires to the two input channels

should be kept separated by a ground trace to avoid high

frequency crosstalk between channels.

INPUT VOLTAGE (V)

1407 F04

111...111

111...110

111...101

000...000

000...001

000...010

FS – 1LSB

Figure 4. LTC1407/LTC1407A Transfer Characteristic

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