ltc2258cuj-12 Linear Technology Corporation, ltc2258cuj-12 Datasheet - Page 19

• Manufacturer Part Number: ltc2258cuj-12
• Description: 12-bit, 65/40/2 5msps Ultralow Power 1.8v Adcs
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Reference
The LTC2258-12/2257-12/2256-12 has an internal 1.25V
voltage reference. For a 2V input range using the internal
reference, connect SENSE to V
using the external 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
ANALOG
INPUT
Figure 7. Front-End Circuit Using a High Speed
Differential Amplifi er
DIFFERENTIAL
HIGH SPEED
+
–
AMPLIFIER
+
–
0.1μF
0.1μF
SENSE
.
200Ω
200Ω
DD
25Ω
25Ω
. For a 1V input range
12pF
0.1μF
V
A
A
CM
IN
IN
+
–
LTC2258-12
225812 F07
The V
shown in Figure 8. The 0.1μF capacitor between REFH and
REFL 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
0.65V < V
REF
DD
LTC2257-12/LTC2256-12
2.2μF
FOR 2V RANGE;
SENSE
0.1μF
0.1μF
Figure 9. Using an External 1.25V Reference
, REFH and REFL pins should be bypassed as
1.25V
SENSE
< 1.300V
REFERENCE
EXTERNAL
FOR
Figure 8. Reference Circuit
1.25V
0.1μF
1μF
SENSE
REFH
V
REFL
REF
LTC2258-12
SENSE
1μF
1μF
CONTROL
V
5Ω
DETECT
RANGE
REF
AND
LTC2258-12
LTC2258-12
1.25V BANDGAP
DIFF AMP
REFERENCE
INTERNAL ADC
HIGH REFERENCE
0.8x
INTERNAL ADC
LOW REFERENCE
225812 F09
0.625V
BUFFER
19
225812p
225812 F08