TLV170 Datasheet, PDF (20/38 Pages) Texas Instruments – 36-V, Single-Supply, EMI-Hardened, Low-Power Operational Amplifiers for Cost-Sensitive Systems

TLV170, TLV2170, TLV4170
SBOS782 – NOVEMBER 2016
9 Application and Implementation
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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 TLVx170 family of op amps 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 in order to achieve the maximum performance from this
device. Many applications can introduce capacitive loading to the output of the amplifier (potentially causing
instability). One method of stabilizing the amplifier in such applications is to add an isolation resistor between the
amplifier output and the capacitive load. The design process for selecting this resistor is given in the Typical
Application section.
9.2 Typical Application
This circuit can be used to drive capacitive loads (such as cable shields, reference buffers, MOSFET gates, and
diodes). The circuit uses an isolation resistor (R_ISO) to stabilize the output of an op amp. R_ISO modifies the open-
loop gain of the system to ensure the circuit has sufficient phase margin.
+V_S
R_ISO
V_OUT
+
V_{IN ±}
-V_S
C_LOAD
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Figure 30. Unity-Gain Buffer With R_ISO 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 30 shows a unity-gain buffer driving a capacitive load. Equation 1 shows the transfer function for the
circuit in Figure 30. Not shown in Figure 30 is the open-loop output resistance of the op amp, R_o.
T(s) =
1 + C_LOAD × R_ISO × s
1 + R_o + R_ISO × C_LOAD × s
(1)
The transfer function in Equation 1 has a pole and a zero. The frequency of the pole (f_p) is determined by (R_o +
R_ISO) and C_LOAD. Components R_ISO and C_LOAD determine the frequency of the zero (f_z). A stable system is
obtained by selecting R_ISO such that the rate of closure (ROC) between the open-loop gain (A_OL) and 1/β is
20 dB per decade; see Figure 31. The 1/β curve for a unity-gain buffer is 0 dB.
20
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