LTC1402 Datasheet, PDF (11/20 Pages) Linear Technology – Serial 12-Bit, 2.2Msps Sampling ADC with Shutdown

LTC1402
APPLICATIONS INFORMATION
LT1630: Dual 30MHz Rail-to-Rail Voltage FB Amplifier.
2.7V to ±15V supplies. Very high A_VOL, 500µV offset and
520ns settling to 0.5LSB for a 4V swing. THD and noise
are – 93dB to 40kHz and below 1LSB to 320kHz (A_V = 1,
2V_P-P into 1kΩ, V_S = 5V), making the part excellent for AC
applications (to 1/3 Nyquist) where rail-to-rail perfor-
mance is desired. Quad version is available as LT1631.
LT1632: Dual 45MHz Rail-to-Rail Voltage FB Amplifier.
2.7V to ±15V supplies. Very high A_VOL, 1.5mV offset and
400ns settling to 0.5LSB for a 4V swing. It is suitable for
applications with a single 5V supply. THD and noise are
– 93dB to 40kHz and below 1LSB to 800kHz (A_V = 1,
2V_P-P into 1kΩ, V_S = 5V), making the part excellent for AC
applications where rail-to-rail performance is desired.
Quad version is available as LT1633.
LT1813: Dual 100MHz 750V/µs 3mA Voltage Feedback
Amplifier. 5V to ±5V supplies. Distortion is – 86dB to
100kHz and – 77dB to 1MHz with ±5V supplies (2V_P-P into
500Ω). Excellent part for fast AC applications with ±5V
supplies.
INPUT FILTERING AND SOURCE IMPEDANCE
The noise and the distortion of the input amplifier and
other circuitry must be considered since they will add to
the LTC1402 noise and distortion. The small-signal band-
width of the sample-and-hold circuit is 80MHz. Any noise
or distortion products that are present at the analog inputs
will be summed over this entire bandwidth. 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 example, Figure 2 shows a 68pF
capacitor from A_IN+ to ground and a 51Ω source resistor
to limit the input bandwidth to 47MHz. The 68pF capacitor
also acts as a charge reservoir for the input sample-and-
hold and isolates the ADC input from sampling glitch-
sensitive circuitry.
High quality capacitors and resistors should be used since
these components can add distortion. NPO and silver mica
type dielectric capacitors have excellent linearity.
Carbon surface mount resistors can generate distortion
from self heating and from damage that may occur during
soldering. Metal film surface mount resistors are much
ANALOG ^51Ω
INPUT
3 _AIN+
68pF
4 _AIN–
2
5
10µF
6
AGND1
LTC1402
V_REF
AGND2
7
GAIN
1402 F02
Figure 2. RC Input Filter
less susceptible to both problems. When high amplitude
unwanted signals are close in frequency to the desired signal
frequency, a multiple pole filter is required. Figure 3 shows
a simple implementation using an LTC1560-1 fifth order
elliptic continuous-time 1MHz filter.
1
8
V_IN ²
7
3 ^LTC1560-1 6
4
– 5V
0.1µF
5
5V
0.1µF
3 _AIN+
4 _AIN–
2
5
10µF
6
AGND1
LTC1402
V_REF
AGND2
7
GAIN
1402 F03
Figure 3. 1MHz Fifth Order Elliptic Lowpass Filter
BIPOLAR AND UNIPOLAR INPUT RANGES
The ±2V bipolar input range of the LTC1402 is optimized
for low noise and low distortion. Most op amps also
perform best over this same range, allowing direct cou-
pling to the analog inputs and eliminating the need for
special translation circuitry. The inputs of the LTC1402
may also be driven fully differential in bipolar mode with
a single supply. Each input should not swing more than
2V_P-P individually to get the best performance from single
supply amplifiers.
The 0V to 4V range is ideal for single ended input use with
single supply applications.
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