ltc2195 Linear Technology Corporation, ltc2195 Datasheet - Page 19

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

APPLICATIONS INFORMATION
Reference
The LTC2195/LTC2194/LTC2193 have an internal 1.25V
voltage reference. For a 2V input range using the internal
reference, connect SENSE to V
using the internal reference, connect SENSE to ground.
For a 2V input range with an external reference, apply a
1.25V reference voltage to SENSE (Figure 9).
The input range can be adjusted by applying a voltage to
SENSE that is between 0.625V and 1.30V. The input range
will then be 1.6 • V
The V
shown in Figure 8. A low inductance 2.2µF interdigitated
capacitor is recommended for the bypass between REFH
and REFL. This type of capacitor is available at a low cost
from multiple suppliers.
At sample rates below 110Msps an interdigitated capaci-
tor is not necessary for good performance and C1 can be
replaced by a standard 2.2µF capacitor between REFH and
REFL. The capacitors should be as close to the pins as
possible (not on the back side of the circuit board).
TIE TO GND FOR 1V RANGE;
TIE TO V
RANGE = 1.6 • V
0.625V < V
C1: 2.2µF LOW INDUCTANCE
INTERDIGITATED CAPACITOR
TDK CLLE1AX7S0G225M
MURATA LLA219C70G225M
AVX W2L14Z225M
OR EQUIVALENT
0.1µF
REF
DD
0.1µF
C2
C3
FOR 2V RANGE;
SENSE
, REFH and REFL pins should be bypassed as
1.25V
SENSE
–
+
–
+
< 1.300V
C1
FOR
Figure 8a. Reference Circuit
+
–
+
–
SENSE
2.2µF
SENSE
REFH
REFH
V
REFL
REFL
REF
.
LTC2195
CONTROL
5
DETECT
RANGE
AND
DD
. For a 1V input range
1.25V BANDGAP
DIFF AMP
REFERENCE
INTERNAL ADC
HIGH REFERENCE
0.8x
INTERNAL ADC
LOW REFERENCE
0.625V
BUFFER
219543 F08a
Figure 8c and 8d show the recommended circuit board
layout for the REFH/REFL bypass capacitors. Note that in
Figure 8c, every pin of the interdigitated capacitor (C1)
is connected since the pins are not internally connected
in some vendors’ capacitors. In Figure 8d the REFH and
REFL pins are connected by short jumpers in an internal
layer. To minimize the inductance of these jumpers they
can be placed in a small hole in the GND plane on the
second board layer.
Figure 8d. Recommended Layout for the REFH/REFL Bypass
Circuit in Figure 8b
Figure 8c. Recommended Layout for the REFH/REFL Bypass
Circuit in Figure 8a
Figure 8b. Alternative REFH/REFL Bypass Circuit
Figure 9. Using an External 1.25V Reference
CAPACITORS ARE 0402 PACKAGE SIZE
REFERENCE
EXTERNAL
0.1µF
0.1µF
C3
C2
1.25V
LTC2194/LTC2193
C1
2.2µF
SENSE
2.2µF
1µF
V
REF
REFH
REFH
REFL
REFL
219543 F08d
219543 F08c
LTC2195
LTC2195
219543 F09
LTC2195
219543 F08b
19
219543p