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LTC6258/LTC6259/LTC6260

6258960fa

For more information www.linear.com/LTC6258

APPLICATIONS INFORMATION

Low Supply Voltage and Low Power Consumption

The LTC6258 family of operational amplifiers can oper-

ate with power supply voltages from 1.8V to 5.25V. Each

amplifier draws 20µA. The low supply voltage capability

and low supply current are ideal for portable applications.

High Capacitive Load Driving Capability and Wide

Bandwidth

The LTC6258 family is optimized for wide bandwidth low

power applications. They have a high gain-bandwidth

to power ratio and are unity gain stable. When the load

capacitance increases, the increased capacitance at the

output pushes the non-dominant pole to lower frequency

in the open loop frequency response, worsening the phase

and gain margin. The LTC6258 family are designed to

directly drive up to 100nF of capacitive load in unity gain

configuration (see Typical Performance Characteristics,

Capacitive Load Handling).

Low Input Referred Noise

The LTC6258 family provides a low input referred noise of

38nV/√Hz at 1kHz. The average noise voltage density over

a 100kHz bandwidth is less than 80nV/√Hz. The LTC6258

family is ideal for low noise and low power signal process-

ing applications.

Low Input Offset Voltage

The LTC6258 family has a low offset voltage of 400μV,

which is essential for precision applications. The offset

voltage is trimmed with a proprietary trim algorithm to

ensure low offset voltage over the entire common mode

voltage range.

Low Input Bias Current

TheLTC6258familyusesabiascurrentcancellationcircuit

tocompensateforthebasecurrentoftheinputtransistors.

When the input common mode voltage is within 200mV of

either rail, the bias cancellation circuit is no longer active.

For common mode voltages ranging from 0.2V above the

negative supply to 0.2V below the positive supply, the

low input bias current allows the amplifiers to be used in

applications with high resistance sources.

Ground Sensing and Rail to Rail Output

The LTC6258 family delivers over 4mA of output drive

current. The output stage is a rail-to-rail topology that

is capable of swinging to within 300mV of either rail. If

output swing to the negative rail is required, an external

pull down resistor to a negative supply can be added.

For 5V/0V op amp supplies, a pull down resistor of 10k

to –2V will allow a ‘true zero’ output swing. In this case,

the output can swing all the way to the bottom rail while

maintaining 45dB of open loop gain. Since the inputs

can go 100mV beyond either rail, the op amp can easily

perform ‘true ground’ sensing.

The maximum output current is a function of total supply

voltage. As the supply voltage to the amplifier increases,

themaximumoutputcurrentalsoincreases.Attentionmust

be paid to keep the junction temperature of the IC below

150°C when the output is in continuous short-circuit. The

output of the amplifier has reverse-biased diodes con-

nected to each supply. The output should not be forced

more than 0.5V beyond either supply, otherwise current

will flow through these diodes.

EMI Rejection

Electromagnetic interference (EMI) rejection is built into

the LTC6258 op amp family. Rejection is measured by

injecting 200mVP-P (–10dBm) RF signal into the pins and

measuring the offset change (delta_VOS). The rejection

ratio is calculated as 20log (100mV/delta_VOS).

Input Protection and Output Overdrive

To prevent breakdown of the input transistors, the input

stages are protected against a large differential input

voltage by two pairs of back-to-back diodes, D5 to D8. If

the differential input voltage exceeds 1.4V, the current in

these diodes must be limited to less than 10mA. These

amplifiersarenotintendedforopenloopapplicationssuch

as comparators. When the output stage is overdriven,

internal limiting circuitry is activated to improve overdrive

recovery. In some applications, this circuitry may draw as

much as 1mA supply current.

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