LTC2301CDEXPBF datasheet(14/24 Pages) LINER

14 / 24 page

LTC2301/LTC2305

23015f

APPLICATIONS INFORMATION

The magnitude of the DC current is then approximately IDC

= (VIN – VREFCOMP/2)/REQ, which is roughly proportional to

VIN. To prevent large DC drops across the resistor RFILTER,

a ﬁlter with a small resistor and large capacitor should be

chosen. When running at the maximum throughput rate

of 14ksps, the input current equals 1.5μA at VIN = 4.096V,

which amounts to a full-scale error of 0.5LSBs when using

a ﬁlter resistor (RFILTER) of 333Ω. Applications requiring

lower sample rates can tolerate a larger ﬁlter resistor for

the same amount of full-scale error.

Figures 3a and 3b show respective examples of input

ﬁltering for single-ended and differential inputs. For the

single-ended case in Figure 4a, a 50Ω source resistor

and a 2000pF capacitor to ground on the input will limit

the input bandwidth to 1.6MHz. High quality capacitors

and resistors should be used in the RC ﬁlter since these

components can add distortion. NPO and silver mica type

dielectric capacitors have excellent linearity. Carbon surface

mount resistors can generate distortion from self heating

Figure 2a. Analog Input Equivalent Circuit

Figure 2b. Analog Input Equivalent

Circuit for Large Filter Capacitances

VIN

INPUT

CH0, CH1,

IN+, IN–

RON =

100Ω

CIN =

55pF

CFILTER

RSOURCE

23015 F02a

LTC2301

LTC2305

VIN

INPUT

(CH0, CH1,

IN+, IN–)

REQ =

1/(fSMPL • CIN)

VREFCOMP/2

CFILTER

RFILTER

IDC

23015 F02b

LTC2301

LTC2305

–

and from damage that may occur during soldering. Metal

ﬁlm surface mount resistors are much less susceptible

to both problems.

Dynamic Performance

Fast Fourier Transform (FFT) test techniques are used to

test the ADC’s frequency response, distortion and noise

at the rated throughput. By applying a low distortion

sine wave and analyzing the digital output using an FFT

algorithm, the ADC’s spectral content can be examined

for frequencies outside the fundamental.

Signal-to-Noise and Distortion Ratio (SINAD)

The signal-to-noise and distortion ratio (SINAD) is the

ratio between the RMS amplitude of the fundamental input

frequency to the RMS amplitude of all other frequency

components at the A/D output. The output is band-limited

to frequencies from above DC and below half the sampling

Figure 3a. Optional RC Input Filtering for Single-Ended Input

Figure 3b. Optional RC Input Filtering for Differential Inputs

23015 F03a

CH0, CH1

LTC2305

REFCOMP

2000pF

0.1μF

10μF

50Ω

ANALOG

INPUT

1000pF

23015 F03b

CH0, IN+

CH1, IN–

LTC2301

LTC2305

REFCOMP

1000pF

0.1μF

10μF

50Ω

DIFFERENTIAL

ANALOG

INPUTS

LTC2301CDEXPBF Datasheet(PDF) 14 Page - Linear Technology

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