LTC1604 Linear Technology, LTC1604 Datasheet - Page 15

• Manufacturer Part Number: LTC1604
• Description: High Speed/ 16-Bit/ 333ksps Sampling A/D Converter with Shutdown
• Manufacturer: Linear Technology

APPLICATIONS
– 38 V (i.e., – 0.5LSB) at A
A
0000 0000 0000 and 1111 1111 1111 1111. For full-scale
adjustment, an input voltage of 2.499886V (FS/2 – 1.5LSBs)
is applied to A
flickers between 0111 1111 1111 1110 and 0111 1111
1111 1111.
BOARD LAYOUT AND GROUNDING
Wire wrap boards are not recommended for high resolu-
tion or high speed A/D converters. To obtain the best
performance from the LTC1604, a printed circuit board
with ground plane is required. Layout should ensure that
digital and analog signal lines are separated as much as
possible. Particular care should be taken not to run any
digital track alongside an analog signal track or under-
neath the ADC.The analog input should be screened by
AGND.
An analog ground plane separate from the logic system
ground should be established under and around the ADC.
Pin 5 to Pin 8 (AGNDs), Pin 10 (ADC’s DGND) and all other
analog grounds should be connected to this single analog
ground point. The REFCOMP bypass capacitor and the
DV
IN
DD
–
50k
R8
input until the output code flickers between 0000
+
bypass capacitor should also be connected to this
–5V
Figure 15b. Offset and Full-Scale Adjust Circuit
47 F
R5
47k
IN
50k
R7
+
24k
R3
and R2 is adjusted until the output code
R6
24k
U
0.1 F
ANALOG
INPUT
INFORMATION
U
R4
100
IN
+
and adjust the offset at the
W
4
1
3
5
2
A
A
V
REFCOMP
AGND
IN
IN
REF
+
–
LTC1604
U
1604 F15b
analog ground plane. No other digital grounds should be
connected to this analog ground plane. Low impedance
analog and digital power supply common returns are
essential to low noise operation of the ADC and the foil
width for these tracks should be as wide as possible. In
applications where the ADC data outputs and control
signals are connected to a continuously active micropro-
cessor bus, it is possible to get errors in the conversion
results. These errors are due to feedthrough from the
microprocessor to the successive approximation com-
parator. The problem can be eliminated by forcing the
microprocessor into a WAIT state during conversion or by
using three-state buffers to isolate the ADC data bus. The
traces connecting the pins and bypass capacitors must be
kept short and should be made as wide as possible.
The LTC1604 has differential inputs to minimize noise
coupling. Common mode noise on the A
will be rejected by the input CMRR. The A
used as a ground sense for the A
will hold and convert the difference voltage between A
and A
be kept as short as possible. In applications where this is
not possible, the A
by side to equalize coupling.
SUPPLY BYPASSING
High quality, low series resistance ceramic, 10 F or 47 F
bypass capacitors should be used at the V
pins as shown in Figure 16 and in the Typical Application
on the first page of this data sheet. Surface mount ceramic
capacitors such as Murata GRM235Y5V106Z016 provide
excellent bypassing in a small board space. Alternatively,
10 F tantalum capacitors in parallel with 0.1 F ceramic
capacitors can be used. Bypass capacitors must be lo-
cated as close to the pins as possible. The traces connect-
ing the pins and the bypass capacitors must be kept short
and should be made as wide as possible.
IN
–
. The leads to A
IN
+
and A
IN
+
(Pin 1) and A
IN
–
traces should be run side
IN
+
input; the LTC1604
IN
IN
DD
+
IN
–
LTC1604
and A
and REFCOMP
–
(Pin 2) should
input can be
IN
15
–
leads
IN
+