ltc2195 Linear Technology Corporation, ltc2195 Datasheet - Page 25

• Manufacturer Part Number: ltc2195
• Description: Ltc2195/ltc2194/ltc2193 - 16-bit, 125/105/80msps Low Power Dual Adcs
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
GROUNDING AND BYPASSING
The LTC2195/LTC2194/LTC2193 require a printed circuit
board with a clean unbroken ground plane. A multilayer
board with an internal ground plane in the first layer be-
neath the ADC is recommended. 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 or underneath the ADC.
High quality ceramic bypass capacitors should be used at
the V
capacitors must be located as close to the pins as possible.
Size 0402 ceramic capacitors are recommended. The traces
connecting the pins and bypass capacitors must be kept
short and should be made as wide as possible.
Of particular importance is the capacitor between REFH
and REFL. This capacitor should be on the same side of
TYPICAL APPLICATIONS
DD
, OV
C3 0.1µF
C2 0.1µF
DD
, V
CM
, V
–
+
–
+
PAR/SER
REF
CN1
A
A
A
A
IN1 +
IN1 –
IN2 +
IN2 –
, REFH and REFL pins. Bypass
+
–
+
–
0.1µF
0.1µF
C37
C29
V
DD
0.1µF
10
11
12
13
14
1
2
3
4
5
6
7
8
9
C5
V
V
GND
A
A
GND
REFH
REFL
REFH
REFL
PAR/SER
A
A
GND
V
DD
0.1µF
CM1
IN1 +
IN1 –
IN2 +
IN2 –
CM2
C7
SENSE
ENCODE
INPUT
2.2µF
C4
LTC2195
the circuit board as the A/D, and as close to the device
as possible. A low inductance interdigitated capacitor is
suggested for REFH/REFL if the sampling frequency is
greater than 110Msps.
The analog inputs, encode signals, and digital outputs
should not be routed next to each other. Ground fill and
grounded vias should be used as barriers to isolate these
signals from each other.
HEAT TRANSFER
Most of the heat generated by the LTC2195/LTC2194/
LTC2193 is transferred from the die through the bottom-
side exposed pad and package leads onto the printed circuit
board. For good electrical and thermal performance, the
exposed pad must be soldered to a large grounded pad
on the PC board. This pad should be connected to the
internal ground planes by an array of vias.
SDO
SPI
PORT
OUT1C
OUT1C
OUT1D
OUT1D
OUT2A
OUT2A
OUT2B
OUT2B
OGND
DCO
DCO
OV
FR–
FR
DD
+
–
+
–
+
–
+
+
–
+
–
LTC2194/LTC2193
40
39
38
37
36
35
34
33
32
31
30
29
28
27
C16 0.1µF
219543 TA02
OV
DD
DIGITAL
OUTPUTS
LTC2195
25
219543p