TLV172IDCKT.B datasheet(20/49 Pages) TI2

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LOAD

ISO

LOAD

1 + C

× R

× s

T(s) =

1 + R + R

× C

× s

CLOAD

VIN

VOUT

+VS

RISO

-VS

TLV172, TLV2172, TLV4172

SBOS784C – NOVEMBER 2016 – REVISED JANUARY 2019

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Product Folder Links: TLV172 TLV2172 TLV4172

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9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The TLVx172 operational amplifier provides high overall performance in a large number of general-purpose

applications. As with all amplifiers, applications with noisy or high-impedance power supplies require decoupling

capacitors placed close to the device pins. In most cases, 0.1-µF capacitors are adequate. Follow the additional

recommendations in the Layout Guidelines section to achieve the maximum performance from this device. Many

applications introduce capacitive loading to the output of the amplifier (which potentially causes instability). To

stabilize the amplifier, add an isolation resistor between the amplifier output and the capacitive load. Typical

Application section shows the process for selecting a resistor.

9.2 Typical Application

This circuit can drive capacitive loads (such as cable shields, reference buffers, MOSFET gates, and diodes).

The circuit uses an isolation resistor (RISO) to stabilize the output of an operational amplifier. RISO modifies the

open-loop gain of the system to ensure that the circuit has sufficient phase margin.

Figure 29. Unity-Gain Buffer With RISO Stability Compensation

9.2.1 Design Requirements

The design requirements are:

•

Supply voltage: 30 V (±15 V)

•

Capacitive loads: 100 pF, 1000 pF, 0.01 μF, 0.1 μF, and 1 μF

•

Phase margin: 45° and 60°

9.2.2 Detailed Design Procedure

Figure 29 shows a unity-gain buffer driving a capacitive load. Equation 1 shows the transfer function for the

circuit in Figure 29.Figure 29 does not show the open-loop output resistance of the operational amplifier (Ro).

(1)

The transfer function in Equation 1 has a pole and a zero. The frequency of the pole (fp) is determined by (Ro +

RISO) and CLOAD. The RISO and CLOAD components determine the frequency of the zero (fz). A stable system is

obtained by selecting RISO so that the rate of closure (ROC) between the open-loop gain (AOL) and 1/β is 20 dB

per decade. Figure 30 shows the concept. The 1/β curve for a unity-gain buffer is 0 dB.

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