Datasheet

LTC1407-1/LTC1407A-1
16
14071fb
APPLICATIONS INFORMATION
Board Layout and Bypassing
Wire wrap boards are not recommended for high resolu-
tion and/or high speed A/D converters. To obtain the best
performance from the LTC1407-1/LTC1407A-1, a printed
circuit board with ground plane is required. Layout for
the printed circuit board should ensure that digital and
analog signal lines are separated as much as possible. In
particular, care should be taken not to run any digital track
alongside an analog signal track. If optimum phase match
between the inputs is desired, the length of the four input
wires of the two input channels should be kept matched.
But each pair of input wires to the two input channels
should be kept separated by a ground trace to avoid high
frequency crosstalk between channels.
High quality tantalum and ceramic bypass capacitors
should be used at the V
DD
and V
REF
pins as shown in the
Block Diagram on the fi rst page of this data sheet. For
optimum performance, a 10µF surface mount tantalum
capacitor with a 0.1µF ceramic is recommended for the V
DD
and V
REF
pins. Alternatively, 10µF ceramic chip capacitors
such as X5R or X7R may be used. The capacitors must be
located as close to the pins as possible. The traces con-
necting the pins and the bypass capacitors must be kept
short and should be made as wide as possible. The V
DD
bypass capacitor returns to GND (Pin 6) and the V
REF
by-
pass capacitor returns to the Exposed Pad ground (Pin 11).
Care should be taken to place the 0.1µF V
DD
bypass ca-
pacitor as close to Pins 6 and 7 as possible.
Figure 7 shows the recommended system ground connec-
tions. All analog circuitry grounds should be terminated
Figure 6a. The LT1819 Driving the LTC1407A-1 Differentially
Figure 6b. LTC1407-1 6MHz Sine Wave 4096 Point FFT Plot
with the LT1819 Driving the Inputs Differentially
Figure 7. Recommended Layout
–CH0 OR
–CH1
LTC1407A-1
+CH0 OR
+CH1
C1
47pF
R1
51
C3
1µF
C5
0.1µF
5V
–5V
C4
1µF
R5
1k
1.5V
CM
R3
499
R4
499
R6
1k
C2
47pF
R2
51
C6
0.1µF
V
IN
1.25V
P-P
MAX
1407A F06a
–
+
U1
1/2 LT1819
–
+
U2
1/2 LT1819
FREQUENCY (Hz)
MAGNITUDE (dB)
–60
–30
–20
14031 F06b
–70
–80
–120
–100
0
–10
–40
–50
–90
–110
0
371k185k 556k 741k
1407-1 F07