LTC2309 Linear Technology Corporation, LTC2309 Datasheet - Page 12

• Manufacturer Part Number: LTC2309
• Description: 12-Bit SAR ADC
• Manufacturer: Linear Technology Corporation

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LTC2309
Total Harmonic Distortion (THD)
Total harmonic distortion (THD) is the ratio of the
RMS sum of all harmonics of the input signal to the
fundamental itself. The out-of-band harmonics alias into
the frequency band between DC and half the sampling
frequency(f
where V
frequency and V
second through Nth harmonics.
Internal Reference
The LTC2309 has an on-chip, temperature compen-
sated bandgap reference that is factory trimmed to
2.5V (Refer to Figure 6a). It is internally connected
to a reference amplifi er and is available at V
should be bypassed to GND with a 2.2μF tantalum
capacitor to minimize noise. An 8k resistor is in series
with the output so that it can be easily overdriven by
an external reference if more accuracy and/or lower
drift are required as shown in Figure 6b. The reference
amplifi er gains the V
at REFCOMP . To compensate the reference amplifi er,
bypass REFCOMP with a 10μF ceramic or tantalum
capacitor in parallel with a 0.1μF ceramic capacitor for
best noise performance.
APPLICATIONS INFORMATION
12
THD
=
Figure 5. 1kHz Sine Wave 8192 Point FFT Plot
1
–100
–140
–120
20
–60
–80
–20
–40
is the RMS amplitude of the fundamental
0
SMPL
log
0
2
1
/2). THD is expressed as:
V
through V
2
2
2
FREQUENCY (kHz)
+
REF
V
3
3
2
voltage by 1.638 to 4.096V
V
+
1
N
4
V
are the amplitudes of the
4
SNR = 73.4dB
SINAD = 73.3dB
THD = –88dB
2
...
5
+
V
6
N
2309 G03
2
7
REF
. V
REF
Internal Conversion Clock
The internal conversion clock is factory trimmed to
achieve a typical conversion time (t
a maximum conversion time of 1.8μs over the full
operating temperature range.
I
The LTC2309 communicates through an I
The I
porting multiple devices and multiple masters on a
single bus. The connected devices can only pull the
serial data line (SDA) low and can never drive it high.
SDA is required to be externally connected to the sup-
ply through a pull-up resistor. When the data line is not
being driven low, it is high. Data on the I
transferred at rates up to 100kbits/s in the standard
mode and up to 400kbits/s in the fast mode.
2
C Interface
Figure 6b. Using the LT
0.1μF
4.096V
2.5V
2
10μF
C interface is a 2-wire open-drain interface sup-
Figure 6a. LTC2309 Reference Circuit
2.2μF
0.1μF
LT1790A-2.5
V
5V
V
REFCOMP
GND
IN
REF
V
OUT
+
®
1790A-2.5 as an External Reference
10μF
R3
REFERENCE
R2
AMP
2.2μF
0.1μF
CONV
V
REFCOMP
GND
REF
R1
8k
) of 1.3μs and
2
LTC2309
C bus can be
2
C interface.
REFERENCE
BANDGAP
LTC2309
2309 F06b
2309 F06a
2309f