Datasheet

LTC2313-14
12
231314fa
For more information www.linear.com/LTC2313-14
applicaTions inForMaTion
Exiting Nap/Sleep Mode
Waking up the LTC2313-14 from either nap or sleep mode,
as shown in Figures 8 and 9, requires SCK to be pulsed
one time. A conversion may be started immediately fol-
lowing nap mode as shown in Figure 8. A period of time
allowing
the reference voltage to recover must follow
waking up from sleep mode as shown in Figure 9. The
wait period required before initiating a conversion for the
recommended value of C
REF
of 2.2µF is 1.1ms.
Power Supply Sequencing
The LTC2313-14 does not have any specific power sup-
ply sequencing
requirements. Care should be taken to
observe the maximum voltage relationships described in
the Absolute Maximum Ratings section.
Single-Ended Analog Input Drive
The analog input of the LTC2313-14 is easy to drive. The
input draws only one small current spike while charging
the sample-and-hold capacitor following the falling edge
of CONV. During the conversion, the analog input draws
only a small leakage current. If the source impedance of
the driving circuit is low, then the input of the LTC2313-14
can be driven directly. As the source impedance increases,
so will the acquisition time. For minimum acquisition time
Figure 8. LTC2313-14 Entering/Exiting Nap Mode
Figure 9. LTC2313-14 Entering/Exiting Sleep Mode
with high source impedance, a buffer amplifier should be
used. The main requirement is that the amplifier driving
the analog input must settle after the small current spike
before the next conversion starts. Settling time must be
less than t
ACQ-MIN
(175ns) for full performance at the
maximum throughput rate. While choosing an input ampli-
fier, also
keep in mind the amount of noise and harmonic
distortion the amplifier contributes.
Choosing an Input Amplifier
Choosing
an input amplifier is easy if a few requirements
are taken into consideration. First, to limit the magnitude
of the voltage spike seen by the amplifier from charging
the sampling capacitor, choose an amplifier that has a low
output impedance (<50Ω) at the closed-loop bandwidth
frequency. For example, if an amplifier is used in a gain
of 1 and has a unity-gain bandwidth of 50MHz, then the
output impedance at 50MHz must be less than 50Ω. The
second requirement is that the closed-loop bandwidth
must be greater than 50MHz to ensure adequate small
signal settling for full throughput rate. If slower op amps
are used, more time for settling can be provided by in
-
creasing the time between
conversions. The best choice
for an op amp to drive the LTC2313-14 will depend on the
application. Generally, applications fall into two categories:
AC applications where dynamic specifications are most
CONV
SCK
Z
1 2
Z
SDO
HI-Z STATE
231314 F08
NAP MODE
HOLD STATIC HIGH or LOW HOLD STATIC HIGH or LOW
START t
ACQ
t
1
CONV
SCK
1 2 3 4
SDO
HI-Z STATE
231314 F09
NAP MODE SLEEP MODE
HOLD STATIC HIGH or LOW
START t
ACQ
V
REF
RECOVERY
t
WAIT
Z Z
t
1