Datasheet

LTC2364-16
13
236416fa
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 LTC2364-16 achieves a typical SNR of 94.7dB at
a 250kHz sampling rate with a 2kHz input.
Figure 8. 32k Point FFT with f
IN
= 2kHz of the LTC2364-16
FREQUENCY (kHz)
0 25 50 75 100 125
–180
AMPLITUDE (dBFS)
–60
–40
–20
–80
–100
–120
–140
–160
0
236416 F08
SNR = 94.7dB
THD = –121dB
SINAD = 94.7dB
SFDR = 125dB
REF
236416 F07
LTC2364-16
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 LTC2364-16 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 LTC2364-16 achieves
a typical SINAD of 94.7dB at a 250kHz 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
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 LTC2364-16 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 LTC2364-16 to communicate with any digital
logic operating between 1.8V and 5V, including 2.5V and
3.3V systems.
Power Supply Sequencing
The
LTC2364-16 does not have any specific power supply
sequencing requirements. Care should be taken to adhere