LTC1606 Linear Technology, LTC1606 Datasheet - Page 7

• Manufacturer Part Number: LTC1606
• Description: 16-Bit/ 250ksps/ Single Supply ADC
• Manufacturer: Linear Technology

APPLICATIONS
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
Figure 1, V
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 s 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
compare mode. The input switch switches C
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
balances the V
data word) that represents the V
16-bit output latches.
V
IN
R
IN1
R
IN2
Figure 1. LTC1606 Simplified Equivalent Circuit
IN
is connected through the resistor divider to
SAMPLE
IN
HOLD
input charge. The SAR contents (a 16-bit
U
C
SAMPLE
C
V
DAC
DAC
INFORMATION
U
DAC
IN
W
are loaded into the
SAMPLE
–
+
COMPARATOR
SI
U
SAMPLE
16-BIT
LATCH
1606 • F01
R
S
A
to
Driving the Analog Inputs
The nominal input range for the LTC1606 is 10V or
( 4 • V
The input impedance is typically 10k , therefore, it should
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 A
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/ s 16-bit accurate amplifier.
LinearView is a trademark of Linear Technology Corporation
REF
) and the input is overvoltage protected to 25V.
A
IN
Figure 2. Analog Input Filtering
200
1000pF
33.2k
V
CAP
1606 • F02
LTC1606
IN
TM
CD-ROM.
7