LTC6362H データシートの表示（PDF） - Linear Technology

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LTC6362H

Precision, Low Power Rail-to-Rail Input/Output Differential Op Amp/SAR ADC Driver

Linear Technology 

LTC6362

APPLICATIONS INFORMATION

Functional Description

The LTC6362 is a low power, low noise, high DC accuracy

fully differential operational amplifier/ADC driver. The

amplifier is optimized to convert a fully differential or

single-ended signal to a low impedance, balanced differ-

ential output suitable for driving high performance, low

power differential successive approximation register (SAR)

ADCs. The balanced differential nature of the amplifier

also provides even-order harmonic distortion cancella-

tion, and low susceptibility to common mode noise (like

power supply noise).

The outputs of the LTC6362 are capable of swinging rail-

to-rail and can source or sink up to 35mA of current. The

LTC6362 is optimized for high bandwidth and low power

applications. Load capacitances above 10pF to ground or

5pF differentially should be decoupled with 10Ω to 100Ω

of series resistance from each output to prevent oscilla-

tion or ringing. Feedback should be taken directly from

the amplifier output. Higher voltage gain configurations

tend to have better capacitive drive capability than lower

gain configurations due to lower closed-loop bandwidth.

Input Pin Protection

The LTC6362 input stage is protected against differential

input voltages which exceed 1.4V by two pairs of series

diodes connected back-to-back between +IN and –IN.

Moreover, all pins have clamping diodes to both power

supplies. If any pin is driven to voltages which exceed

either supply, the current should be limited to under 10mA

to prevent damage to the IC.

SHDN Pin

The LTC6362 has a SHDN pin which when driven to within

0.8V above the negative rail, will shut down amplifier op-

eration such that only 70µA is drawn from the supplies.

Pull-down circuitry should be capable of sinking at least

4µA to guarantee complete shutdown across all condi-

tions. For normal operation, the SHDN pin should be left

floating or tied to the positive rail.

General Amplifier Applications

In Figure 1, the gain to VOUTDIFF from VINP and VINM is

given by:

( ) VOUTDIFF

=

V+OUT

−

V–OUT

≈





RF

RI





•

VINP – VINM

Note from the previous equation, the differential output

voltage (V+OUT – V–OUT) is completely independent of

input and output common mode voltages, or the voltage

at the common mode pin. This makes the LTC6362 ideally

suited for pre-amplification, level shifting and conversion

of single-ended signals to differential output signals for

driving differential input ADCs.

Output Common Mode and VOCM Pin

The output common mode voltage is defined as the aver-

age of the two outputs:

VOUTCM

=

VOCM

=





V+OUT

+

2

V–OUT





As the equation shows, the output common mode voltage

is independent of the input common mode voltage, and

is instead determined by the voltage on the VOCM pin, by

means of an internal common mode feedback loop.

If the VOCM pin is left open, an internal resistor divider

develops a default voltage of 2.5V with a 5V supply. The

VOCM pin can be overdriven to another voltage if desired.

For example, when driving an ADC, if the ADC makes a

reference available for setting the common mode volt-

age, it can be directly tied to the VOCM pin, as long as

the ADC is capable of driving the 170k input resistance

presented by the VOCM pin. The Electrical Characteristics

table specifies the valid range that can be applied to the

VOCM pin (VOUTCMR).

6362fa

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