7

LTC1606

Conversion Details

The LTC1606 uses a successive approximation algorithm

and an internal sample-and-hold circuit to convert an

analog signal to a 16-bit or two byte parallel output. The

ADC is complete with a precision reference and an internal

clock. The control logic provides easy interface to micro-

processors and DSPs. (Please refer to the Digital Interface

section for the data format.)

Conversion start is controlled by the CS and R/C inputs. At

the start of conversion the successive approximation

register (SAR) is reset. Once a conversion cycle has

begun, it cannot be restarted.

During the conversion, the internal 16-bit capacitive DAC

output is sequenced by the SAR from the most significant

bit (MSB) to the least significant bit (LSB). Referring to

the sample-and-hold capacitor during the acquire phase

and the comparator offset is nulled by the autozero switches.

In this acquire phase, a minimum delay of 1.5

µs will

provide enough time for the sample-and-hold capacitor to

acquire the analog signal. During the convert phase, the

autozero switches open, putting the comparator into the

ground, injecting the analog input charge onto the sum-

ming junction. This input charge is successively com-

pared with the binary-weighted charges supplied by the

capacitive DAC. Bit decisions are made by the high speed

comparator. At the end of a conversion, the DAC output

16-bit output latches.

Driving the Analog Inputs

The nominal input range for the LTC1606 is

±10V or

(

The input impedance is typically 10k

Ω,therefore,itshould

be driven with a low impedance source. Wideband noise

coupling into the input can be minimized by placing a

1000pF capacitor at the input as shown in Figure 2. An

NPO-type capacitor gives the lowest distortion. Place the

capacitor as close to the device input pin as possible. If an

amplifier is to be used to drive the input, care should be

taken to select an amplifier with adequate accuracy, linear-

ity and noise for the application. The following list is a

summary of the op amps that are suitable for driving the

LTC1606. More detailed information is available in the

Linear Technology data books and LinearView

LT1007 - 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 sup-

ply current.

±5V to ±15V supplies. Good AC/DC specs.

LT1363 - 50MHz voltage feedback amplifier. 6.3mA sup-

ply current. Good AC/DC specs.

LT1364/LT1365 - Dual and quad 50MHz voltage feedback

amplifiers. 6.3mA supply current per amplifier. Good AC/

DC specs.

LT1468 - 90MHz 22V/

µs 16-bit accurate amplifier.

1606 • F01

+

–

DAC

SAMPLE

HOLD

S

A

R

16-BIT

LATCH

COMPARATOR

SAMPLE

SI

Figure 1. LTC1606 Simplified Equivalent Circuit

1606 • F02

1000pF

33.2k

CAP

200

Ω

Figure 2. Analog Input Filtering

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