Datasheet

LTC2389-16
28
238916f
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 fundamen-
tal frequency and V2 through V
N
are the amplitudes
of the second through Nth harmonics, respectively.
Figure 11 shows that the LTC2389-16 achieves a typical
THD of –116dB (fully differential) at a 2.5MHz sampling
rate with a 2kHz input.
POWER CONSIDERATIONS
The LTC2389-16 provides two sets of power supply pins:
the 5V core power supply (V
DD
) and the digital input/
output interface power supply (OV
DD
). The flexible OV
DD
supply allows the LTC2389-16 to communicate with any
digital logic operating between 1.8V and 5V, including
2.5V and 3.3V systems. Both the V
DD
and OV
DD
supply
networks should be bypassed to GND with a 0.1μF ceramic
capacitor close to each pin and a 10μF ceramic capacitor
in parallel.
Figure 12. Nap Mode Timing for the LTC2389-16
Power Supply Sequencing
The LTC2389-16 does not have any specific power supply
sequencing requirements. Care should be taken to adhere
to the maximum voltage relationships described in the
Absolute Maximum Ratings section. The LTC2389-16
has an internal power-on reset (POR) circuit which resets
the converter on initial power-up or whenever the power
supply voltage drops below 2.5V. Once the supply
volt-
age
re-enters the nominal supply voltage range, the POR
reinitializes the ADC. With the POR, the result of the first
conversion is valid after power-up as long as the reference
has been given sufficient time to settle.
Nap Mode
The LTC2389-16 can be put into nap mode after a conver-
sion has been completed to reduce the power consumption
between conversions. In this mode some of the circuitry on
the device is turned off. Nap mode is enabled by keeping
CNVST low between conversions, as shown in Figure 12.
To initiate a new conversion after entering nap mode, bring
CNVST high and hold for at least 200ns before bringing
it low again.
applications inFormation
CNVST
BUSY
NAP
t
CONV
t
ACQ
NAP MODE
238916 F12
t
CNVSTH