LTC4263CDE-TRPBF View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC4263CDE-TRPBF

14-Bit, 65Msps ADC

Linear Technology 

LTC2205-14

APPLICATIONS INFORMATION

ANALOG

INPUT

HIGH SPEED

DIFFERENTIAL

AMPLIFIER 25Ω

++

CM

––

25Ω

AMPLIFIER = LTC6600-20,

LTC1993, ETC.

VCM

2.2μF

AIN+

12pF

LTC2205-14

AIN–

12pF

220514 F05

Figure 5. DC Coupled Input with Differential Amplifier

LTC2205-14

TIE TO VDD TO USE

INTERNAL 2.5V

REFERENCE

OR INPUT FOR

EXTERNAL 2.5V

REFERENCE

OR INPUT FOR

EXTERNAL 1.25V

REFERENCE

SENSE

RANGE

SELECT

AND GAIN

CONTROL

VCM

2.2μF

BUFFER

1.25V

INTERNAL

ADC

REFERENCE

PGA

2.5V

BANDGAP

REFERENCE

Reference Operation

Figure 6 shows the LTC2205-14 reference circuitry

consisting of a 2.5V bandgap reference, a programmable

gain amplifier and control circuit. The LTC2205-14 has

three modes of reference operation: Internal Reference,

1.25V external reference or 2.5V external reference. To

use the internal reference, tie the SENSE pin to VDD. To

use an external reference, simply apply either a 1.25V or

2.5V reference voltage to the SENSE input pin. Both 1.25V

and 2.5V applied to SENSE will result in a full-scale range

of 2.25VP-P (PGA = 0). A 1.25V output, VCM is provided

for a common mode bias for input drive circuitry. An

external bypass capacitor is required for the VCM output.

This provides a high frequency low impedance path to

ground for internal and external circuitry. This is also the

compensation capacitor for the reference; it will not be

stable without this capacitor. The minimum value required

for stability is 2.2μF.

The internal programmable gain amplifier provides the

internal reference voltage for the ADC. This amplifier has

very stringent settling requirements and is not accessible

for external use.

Figure 6. Reference Circuit

220514 F06

3.3V

1μF

1.25V

2 LTC1461-2.5 6

4

VCM

2.2μF

SENSE LTC2205-14

2.2μF

220514 F07

Figure 7. A 2.25V Range ADC with an External 2.5V Reference

The SENSE pin can be driven ±5% around the nominal 2.5V

or 1.25V external reference inputs. This adjustment range

can be used to trim the ADC gain error or other system

gain errors. When selecting the internal reference, the

SENSE pin should be tied to VDD as close to the converter

as possible. If the sense pin is driven externally it should

be bypassed to ground as close to the device as possible

with 1μF (or larger) ceramic capacitor.

18

220514fb

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