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LTC1415CG

12-Bit, 1.25Msps, 55mW Sampling A/D Converter

Linear Technology 

LTC1415

APPLICATIONS INFORMATION

The following list is a summary of the op amps that are

suitable for driving the LTC1415, more detailed informa-

tion is available in the Linear Technology databooks and

the LinearViewTM CD-ROM.

LT ®1215/LT1216: Dual and quad 23MHz, 50V/µs single

supply op amps. Single 5V to ±15V supplies, 6.6mA

specifications, 90ns settling to 0.5LSB.

LT1223: 100MHz video current feedback amplifier. ±5V

to ±15V supplies, 6mA supply current. Low distortion up

to and above 400kHz. Low noise. Good for AC applica-

tions.

LT1227: 140MHz video current feedback amplifier. ±5V

to ±15V supplies, 10mA supply current. Lowest distor-

tion at frequencies above 400kHz. Low noise. Best for AC

applications.

LT1229/LT1230: Dual and quad 100MHz current feedback

amplifiers. ±2V to ±15V supplies, 6mA supply current

each amplifier. Low noise. Good AC specs.

LT1360: 37MHz voltage feedback amplifier. ±5V to ±15V

supplies. 3.8mA supply current. Good AC and DC specs.

70ns settling to 0.5LSB.

LT1363: 50MHz, 450V/µs op amps. ±5V to ±15V sup-

plies. 6.3mA supply current. Good AC and DC specs. 60ns

settling to 0.5LSB.

LT1364/LT1365: Dual and quad 50MHz, 450V/µs op amps.

±5V to ±15V supplies, 6.3mA supply current per ampli-

fier. 60ns settling to 0.5LSB.

Input Filtering

The noise and the distortion of the input amplifier and

other circuitry must be considered since they will add to

the LTC1415 noise and distortion. The small-signal band-

width of the sample-and-hold circuit is 20MHz. 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 100Ω source resistor

to limit the input bandwidth to 1.6MHz. The 1000pF

LinearView is a trademark of Linear Technology Corporation.

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.

100Ω

ANALOG INPUT

1000pF

1

+AIN

2

– AIN

LTC1415

3

VREF

4

REFCOMP

10µF

5

AGND

LTC1415 • F07

Figure 7. RC Input Filter

Input Range

The 4.096V input range of the LTC1415 is optimized for

low noise. Most single supply op amps also perform well

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

LTC1415 differential inputs and reference circuitry can

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 LTC1415 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

2k resistor is in series with the output so that it can be

easily overdriven by an external reference or other

11

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