LTC1605-1 datasheet(8/20 Pages) LINER

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LTC1605-1/LTC1605-2

APPLICATIONS INFORMATION

®1007 - Low noise precision amplifier. 2.7mA supply

current

±5V to ±15V supplies. Gain bandwidth product

8MHz. DC applications.

LT1097 - Low cost, low power precision amplifier. 300

µA

supply current.

±5V to ±15V supplies. Gain bandwidth

product 0.7MHz. DC applications.

LT1227 - 140MHz video current feedback amplifier.

10mA supply current.

±5V to ±15V supplies. Low noise

and low distortion.

LT1360 - 37MHz voltage feedback amplifier. 3.8mA

supply current.

±5V to ±15V supplies. Good AC/DC

specs.

LT1363 - 50MHz voltage feedback amplifier. 6.3mA

supply current. Good AC/DC specs.

LT1364/LT1365 - Dual and quad 50MHz voltage feed-

back amplifiers. 6.3mA supply current per amplifier.

Good AC/DC specs.

LT1468 - 90MHz, 22V/

µs 16-Bit Accurate Amplifier

For minimum code transition noise the REF pin and the

CAP pin should each be decoupled with a capacitor to

filter wideband noise from the reference and the buffer

(2.2

µF tantalum).

Offset and Gain Adjustments

The LTC1605-1/LTC1605-2 offset and full-scale errors

have been trimmed at the factory with the external

resistors shown in Figure 4. This allows for external

adjustment of offset and full scale in applications where

absolute accuracy is important. See Figure 5 for the offset

and gain trim circuit for the LTC1605-1/LTC1605-2.

First adjust the offset to zero by adjusting resistor R3.

Apply an input voltage of 30.5

µV (0.5LSB) and adjust R3

so the code is changing between 0000 0000 0000 0001

and 0000 0000 0000 0000. The gain error is trimmed by

adjusting resistor R4. An input voltage of 3.999908V (FS

– 1.5LSB) is applied to VIN and R4 is adjusted until the

output code is changing between 1111 1111 1111 1110

and 1111 1111 1111 1111. Figure 6a shows the unipolar

transfer characteristic of the LTC1605-1.

For the LTC1605-2, first adjust the offset to zero by

adjusting resistor R3. Apply an input voltage of – 61

µV

(– 0.5LSB) and adjust R3 so the code is changing be-

tween 1111 1111 1111 1111 and 0000 0000 0000 0000.

The gain error is trimmed by adjusting resistor R4. An

input voltage of 3.999817V (+ FS – 1.5LSB) is applied to

VIN and R4 is adjusted until the outut code is changing

between 0111 1111 1111 1110 and 0111 1111 1111

1111. Figure 6b shows the bipolar transfer characteris-

tics of the LTC1605-2.

DC Performance

One way of measuring the transition noise associated

with a high resolution ADC is to use a technique where a

DC signal is applied to the input of the ADC and the

resulting output codes are collected over a large number

of conversions. For example, in Figure 7 the distribution

of output code is shown for a DC input that has been

digitized 10000 times. The distribution is Gaussian and

the RMS code transition is about 1LSB.

Figure 2. Analog Input Filtering

1605-1/2 F02

1000pF

33.2k

VIN

CAP

AIN

200

Ω

Internal Voltage Reference

The LTC1605-1/LTC1605-2 has an on-chip, temperature

compensated, curvature corrected, bandgap reference,

which is factory trimmed to 2.50V. The full-scale range of

the ADC is equal to (1.6VREF) or nominally 0V to 4V for the

LTC1605-1 and (

±1.6VREF) or nominally ±4V for the

LTC1605-2. The output of the reference is connected to

the input of a unity-gain buffer through a 4k resistor (see

Figure 3). The input to the buffer or the output of the

reference is available at REF (Pin 3). The internal refer-

ence can be overdriven with an external reference if more

accuracy is needed. The buffer output drives the internal

DAC and is available at CAP (Pin 4). The CAP pin can be

used to drive a steady DC load of less than 2mA. Driving

an AC load is not recommended because it can cause the

performance of the converter to degrade.

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