LTC1850CFW datasheet(16/28 Pages) LINER

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LTC1850/LTC1851

18501f

LT1468/LT1469: Single and Dual 90MHz Voltage Feed-

back Amplifier.

±5V to ±15V supplies. 7mA supply current

per amplifier. Lowest noise and low distortion.

LT1630/LT1631: Dual and Quad 30MHz Rail-to-Rail Volt-

age Feedback Amplifiers. Single 3V to

±15V supplies.

3.5mA supply current per amplifier. Low noise and low

distortion.

LT1632/LT1633: Dual and Quad 45MHz Rail-to-Rail Volt-

age Feedback Amplifiers. Single 3V to

±15V supplies.

4.3mA supply current per amplifier. Low distortion.

LT1806/LT1807: Single and Dual 325MHz Rail-to-Rail

Voltage Feedback Amplifier. Single 3V to

±5V supplies.

13mA supply current. Lowest distortion.

LT1809/LT1810: Single and Dual 180MHz Rail-to-Rail

Voltage Feedback Amplifier. Single 3V to

±15V supplies.

20mA supply current. Lowest distortion.

LT1812/LT1813: 100MHz Voltage Feedback Amplifier.

Single 5V to

±5V supplies. 3.6mA supply current. Low

noise and low distortion.

Input Filtering

The noise and the distortion of the input amplifier and

other circuitry must be considered since they will add to

the LTC1850/LTC1851 noise and distortion. 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 instance, a 100

Ω source resistor

and a 1000pF capacitor to ground on the input will limit the

input bandwidth to 1.6MHz. The capacitor also acts as a

charge reservoir for the input sample-and-hold and iso-

lates the ADC input from sampling glitch sensitive cir-

cuitry. High quality capacitors and resistors should be

used since these components can add distortion. NPO and

silver mica type dielectric capacitors have excellent linear-

ity. 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.

APPLICATIO S I FOR ATIO

REFERENCE

The LTC1850/LTC1851 include an on-chip, temperature

compensated, curvature corrected, bandgap reference

that is factory trimmed to 2.500V and has a very flexible

3-pin interface. REFOUT is the 2.5V bandgap output,

REFIN is the input to the reference buffer and REFCOMP

is the reference buffer output. REFOUT must be bypassed

with a 1

µF or greater capacitor to ground for stability. The

input span is determined by the voltage appearing on the

REFCOMP pin as shown in Table 2. The reference buffer

has a gain of 1.6384 and is factory trimmed by forcing an

external 2.500V on the REFIN pin and trimming REFCOMP

to 4.096V. The 3-pin interface allows for three pin-

strappable Reference modes as well as two additional

external Reference modes. For voltages on the REFIN pin

ranging from 1V to 2.6V, the output voltage on REFCOMP

will equal 1.6384 times the voltage on the REFIN pin. In

this mode, the REFIN pin can be tied to REFOUT to utilize

the internal 2.5V reference to get 4.096V on REFCOMP or

driven with an external reference or DAC. If REFIN is tied

low, the internal 2.5V reference divided by 2 (1.25V) is

connected internally to the input of the reference buffer

resulting in 2.048V on REFCOMP. If REFIN is tied high, the

reference buffer is disabled and REFCOMP can be tied to

REFOUT to achieve a 2.5V span or driven with an external

reference or DAC. Table 3 summarizes the Reference

modes.

Table 3. Reference Mode Table

MODE

REFIN

REFCOMP

REFIN Tied Low

= GND

2.048V Output

REFIN is Buffer Input

1V to 2.6V Input

1.6384V to 4.26V Output

(1.6384 • REFIN)

REFIN Tied High

= VDD

Input, 6.4k

Ω to Ground

Full Scale and Offset

In applications where absolute accuracy is important,

offset and full-scale errors can be adjusted to zero during

a calibration sequence. Offset error must be adjusted

before full-scale error. Zero offset is achieved by adjusting

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