LTC1416 Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Fabricante

LTC1416

Low Power 14-Bit, 400ksps Sampling ADC

Linear Technology 

LTC1416

APPLICATIONS INFORMATION

Input Filtering

The noise and the distortion of the input amplifier and

other circuitry must be considered since they will add to

the LTC1416 noise and distortion. The small-signal band-

width of the sample-and-hold circuit is 15MHz. Any noise

or distortion products that are present at the analog inputs

will be summed over this entire bandwidth. Noisy input

circuitry should be filtered prior to the analog inputs to

minimize noise. A simple 1-pole RC filter is sufficient for

many applications. For example, Figure 7 shows a 1000pF

capacitor from AIN+ to ground and a 200Ω source resistor

to limit the input bandwidth to 800kHz. The 1000pF

capacitor also acts as a charge reservoir for the input

sample-and-hold and isolates the ADC input from sam-

pling glitch sensitive circuitry. High quality capacitors and

resistors should be used since these components can add

distortion. NPO and silver mica type dielectric capacitors

have excellent linearity. Carbon surface mount resistors

can also generate distortion from self-heating and from

damage that may occur during soldering. Metal film

surface mount resistors are much less susceptible to both

problems.

ANALOG 200Ω

INPUT

1 AIN+

1000pF

2 AIN–

3

LTC1416

VREF

22µF

4

REFCOMP

5

AGND

1416 F07

accommodate other input ranges often with little or no

additional circuitry. The following sections describe the

reference and input circuitry and how they affect the input

range.

Internal Reference

The LTC1416 has an on-chip, temperature compensated,

curvature corrected, bandgap reference that is factory

trimmed to 2.500V. It is connected internally to a reference

amplifier and is available at VREF (Pin 3). See Figure 8a. A

4k resistor is in series with the output so that it can be

easily overdriven by an external reference or other cir-

cuitry (see Figure 8b). The reference amplifier gains the

voltage at the VREF pin by 1.625 to create the required

internal reference voltage. This provides buffering be-

tween the VREF pin and the high speed capacitive DAC. The

3 VREF

2.5V

4.0625V 4 REFCOMP

22µF

5 AGND

REF

AMP

R2

80k

R3

128k

R1

4k

BANDGAP

REFERENCE

LTC1416

1416 F08a

Figure 8a. LTC1416 Reference Circuit

Figure 7. RC Input Filter

Input Range

The ±2.5V input range of the LTC1416 is optimized for low

noise and low distortion. Most op amps also perform best

over this same range, allowing direct coupling to the

analog inputs and eliminating the need for special transla-

tion circuitry.

Some applications may require other input ranges. The

LTC1416 differential inputs and reference circuitry can

5V

VIN

LT1019A-2.5

VOUT

ANALOG

INPUT

22µF

1 AIN+

2 AIN–

3

LTC1416

VREF

4

REFCOMP

5

AGND

1416 F08b

Figure 8b. Using the LT1019-2.5 as an External Reference

11

Share Link: