Datasheet

6
LTC1608
A
IN
+
(Pin 1): Positive Analog Input. The ADC converts the
difference voltage between A
IN
+
and A
IN
–
with a differen-
tial range of ±2.5V. A
IN
+
has a ±2.5V input range when
A
IN
–
is grounded.
A
IN
–
(Pin 2): Negative Analog Input. Can be grounded, tied
to a DC voltage or driven differentially with A
IN
+
.
V
REF
(Pin 3): 2.5V Reference Output. Bypass to AGND with
2.2µF tantalum in parallel with 0.1µF ceramic.
REFCOMP (Pin 4): 4.375V (Nominal) Reference Compen-
sation Pin. Bypass to AGND with 22µF tantalum in parallel
with 0.1µF ceramic. This is not recommended for use as
an external reference due to part-to-part output voltage
variations and glitches that occur during the conversion.
AGND (Pins 5 to 8): Analog Grounds. Tie to analog ground
plane.
DV
DD
(Pin 9): 5V Digital Power Supply. Bypass to DGND
with 10µF tantalum in parallel with 0.1µF ceramic.
DGND (Pin 10): Digital Ground for Internal Logic. Tie to
analog ground plane.
D15 to D0 (Pins 11 to 26): Three-State Data Outputs. D15
is the Most Significant Bit.
BUSY (Pin 27): The BUSY output shows the converter
status. It is low when a conversion is in progress. Data is
valid on the rising edge of BUSY.
OGND (Pin 28): Digital Ground for Output Drivers.
OV
DD
(Pin 29): Digital Power Supply for Output Drivers.
Bypass to OGND with 10µF tantalum in parallel with 0.1µF
ceramic.
RD (Pin 30): Read Input. A logic low enables the output
drivers when CS is low.
CONVST (Pin 31): Conversion Start Signal. This active
low signal starts a conversion on its falling edge when CS
is low.
CS (Pin 32): The Chip Select Input. Must be low for the ADC
to recognize CONVST and RD inputs.
SHDN (Pin 33): Power Shutdown. Drive this pin low with
CS low for nap mode. Drive this pin low with CS high for
sleep mode.
V
SS
(Pin 34): –5V Negative Supply. Bypass to AGND with
10µF tantalum in parallel with 0.1µF ceramic.
AV
DD
(Pin 35): 5V Analog Power Supply. Bypass to AGND
with 10µF tantalum in parallel with 0.1µF ceramic.
AV
DD
(Pin 36): 5V Analog Power Supply. Bypass to AGND
with 10µF tantalum in parallel with 0.1µF ceramic and
connect this pin to Pin 35 with a 10Ω resistor.
UU
U
PI FU CTIO S
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Intermodulation Distortion
Power Supply Feedthrough
vs Ripple Frequency
Input Common Mode Rejection
vs Input Frequency
FREQUENCY (kHz)
0
–40
–20
0
200
1608 G07
–60
–80
50 100 150 250
–100
–120
–140
AMPLITUDE (dB)
f
SAMPLE
= 500kHz
f
IN1
= 96.56kHz
f
IN2
= 99.98kHz
INPUT FREQUENCY (Hz)
1k
AMPLITUDE OF POWER SUPPLY
FEEDTHROUGH (dB)
0
–20
–40
–60
–80
–100
–120
–140
10k 100k 1M
1608 G08
f
SAMPLE
= 500kHz
V
RIPPLE
= 10mV
V
SS
A
VDD
INPUT FREQUENCY (Hz)
1k
COMMON MODE REJECTION (dB)
80
70
60
50
40
30
20
10
0
10k 100k
1608 G14a
1M