Datasheet

LTC2370 -16
13
237016fa
APPLICATIONS INFORMATION
code. In applications where the transient response of the
reference is important, the fast settling LTC6655-5 refer-
ence is also recommended.
In applications where power management is critical and
the external reference may be powered down, it is rec-
ommended that REF is kept greater than 2V in order to
guarantee a maximum shutdown current of 140µA. In such
applications, a Schottky diode can be placed between REF
and V
DD
, as shown in Figure 7.
the RMS amplitude of all other frequency components
except the first five harmonics and DC. Figure 8 shows
that the LTC2370-16 achieves a typical SNR of 94dB at a
2MHz sampling rate with a 2kHz input.
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
SMPL
/2).
THD is expressed as:
THD= 20log
V2
2
+ V3
2
+ V4
2
+…+ V
N
2
V1
where V1 is the RMS amplitude of the fundamental fre-
quency and V2 through V
N
are the amplitudes of the second
through Nth harmonics.
POWER CONSIDERATIONS
The LTC2370-16 provides two power supply pins: the
2.5V power supply (V
DD
), and the digital input/output
interface power supply (OV
DD
). The flexible OV
DD
supply
allows the LTC2370-16 to communicate with any digital
logic operating between 1.8V and 5V, including 2.5V and
3.3V systems.
Figure 8. 32k Point FFT with f
IN
= 2kHz of the LTC2370-16
FREQUENCY (kHz)
0 100 200 300 400 800 9001000700600500
–180
AMPLITUDE (dBFS)
–60
–40
–20
–80
–100
–120
–140
–160
0
237016 F08
SNR = 94dB
THD = –112dB
SINAD = 93.9dB
SFDR = 117dB
REF
237016 F07
LTC2370-16
V
DD
Figure 7. A Schottky Diode Between REF and V
DD
Maintains
REF > 2V for Applications Where the Reference May Be
Powered Down
DYNAMIC PERFORMANCE
Fast Fourier Transform (FFT) techniques are used to test
the ADC’s frequency response, distortion and noise at the
rated throughput. By applying a low distortion sine wave
and analyzing the digital output using an FFT algorithm,
the ADC’s spectral content can be examined for frequen-
cies outside the fundamental. The LTC2370-16 provides
guaranteed tested limits for both AC distortion and noise
measurements.
Signal-to-Noise and Distortion Ratio (SINAD)
The signal-to-noise and distortion ratio (SINAD) is the
ratio between the RMS amplitude of the fundamental input
frequency and the RMS amplitude of all other frequency
components at the A/D output. The output is band-limited
to frequencies from above DC and below half the sampling
frequency. Figure 8 shows that the LTC2370-16 achieves
a typical SINAD of 93.9dB at a 2MHz sampling rate with
a 2kHz input.
Signal-to-Noise Ratio (SNR)
The signal-to-noise ratio (SNR) is the ratio between the
RMS amplitude of the fundamental input frequency and