LTC1605-1/LTC1605-2
9
160512fa
For more information www.linear.com/LTC1605-1
applicaTions inForMaTion
LT
®
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. 300µA
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 feedback
amplifiers. 6.3mA supply current per amplifier. Good AC/
DC specs.
LT1468 - 90MHz, 22V/µs 16-Bit Accurate Amplifier
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 (1.6V
REF
) or nominally 0V to 4V
for the LTC1605-1 and (±1.6V
REF
) 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.
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
(2.2µF tantalum).
Offset and Gain Adjustments
The LTC1605-1/LTC1605-2 offset and full-scale er
-
rors 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 off
-
set 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
30.5µV
(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 V
IN
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 –61µV
(–0.5LSB) and adjust R3 so the code is changing between
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 V
IN
and R4 is
adjusted until the output code is changing between 0111
1111 1111 1110 and 0111 1111 1111 1111. Figure 6b
shows the bipolar transfer characteristics 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 result
-
ing 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.
1605-1/2 F02
1000pF 33.2k
V
IN
CAP
A
IN
200Ω
Figure 2. Analog Input Filtering
