SBOA283 March 2021 LMV861 , OPA377 , TLV9002

**Design Goals**

Input | Output | BW | Gain | Supply | |||
---|---|---|---|---|---|---|---|

V_{iMin} | V_{iMax} | V_{oMin} | V_{oMax} | f_{p} | G | V_{cc} | V_{ee} |

–200V | 200V | –2V | 2V | 1MHz | –40dB | 2.5V | –2.5V |

**Design Description**

This circuit inverts the input
signal, V_{i}, and applies a signal gain of –40dB. The common-mode voltage
of an inverting amplifier is equal to the voltage applied to the non-inverting
input, which is ground in this design.

**Design Notes**

- The common-mode voltage in this circuit does not vary with input voltage.
- The input impedance is determined by the input resistor. Make sure this value is large when compared to the output impedance of the source.
- Using high-value resistors can
degrade the phase margin of the circuit and introduce additional noise in
the circuit. The capacitor in parallel with R
_{2}provides filtering and improves stability of the circuit if high-value resistors are used for both the input and feedback resistances. - Avoid placing capacitive loads directly on the output of the amplifier to minimize stability issues.
- Small-signal bandwidth is determined by the noise gain (or non-inverting gain) and op amp gain-bandwidth product (GBP).
- Large signal performance may be limited by slew rate. Therefore, check the maximum output swing versus frequency plot in the data sheet to minimize slew-induced distortion.
- For more information on op amp
linear operating region, stability, slew-induced distortion, capacitive load
drive, driving ADCs, and bandwidth see the
*Design References*section. - Note that higher input voltage
levels may require the use of multiple resistors in series to help reduce
the voltage drop across the individual resistors. For more information, see
the
*Design References*section.

**Design Steps**

The transfer function of this circuit follows:

Equation 1. ${V}_{o}={V}_{i}\times \left(\u2013\frac{{R}_{2}}{{R}_{1}}\right)$

- Calculate the gain required for the
circuit. Equation 1. $\text{G=}\frac{{\text{V}}_{\mathrm{oMax}}\text{}\u2013{\text{V}}_{\mathrm{oMin}}}{{\text{V}}_{\mathrm{iMax}}\text{}\u2013{\text{V}}_{\mathrm{iMin}}}=\frac{\text{2V}\u2013\text{(}\u2013\text{2V)}}{\text{200V}\u2013\text{(}\u2013\text{200V)}}\text{= 0.01}\frac{\text{V}}{\text{V}}\text{=\u201340dB}$
- Choose the starting value of
R
_{1}.Equation 1. ${R}_{1}=\mathrm{100k\Omega}$ - Calculate for a desired signal
attenuation of 0.01 V/V. Equation 1. $\text{G =}\frac{{\text{R}}_{\text{2}}}{{\text{R}}_{\text{1}}}\text{\u2192}{\text{R}}_{\text{2}}={\text{R}}_{\text{1}}\text{\xd7 G}=\text{0.01}\frac{\text{V}}{\text{V}}\text{\xd7 100k\u2126}\text{= 1k\u2126}$
- Select the feedback capacitor, C
_{1}, to meet the circuit bandwidth.Equation 1. ${\text{C}}_{\text{1}}\text{\u2264}\frac{\text{1}}{{\text{2\pi \xd7 R}}_{\text{2}}{\text{\xd7 f}}_{\text{p}}}\text{\u2192}$C 1 ≤ 1 2π × 1kΩ × 1MHz ≤ 159.15pF ≈ 160pF (Standard Value) - Calculate the minimum slew rate
required to minimize slew-induced distortion. Equation 1. ${V}_{p}<\frac{\mathrm{SR}}{2\pi \times {f}_{p}}\to \mathrm{SR}2\pi \times f\times {V}_{p}\to $
SR > 2 π × 1 MHz × 2 V = 12.6 V μS - SR
_{LMV861}= 18V/µs; therefore, it meets this requirement.

- SR
- Calculate the circuit bandwidth to ensure it meets
the 1-MHz requirement. Be sure to use the noise gain, NG, or non-inverting gain,
of the circuit. Equation 1. $\text{NG=1 +}\frac{{\text{R}}_{2}}{{\text{R}}_{1}}\text{=1.01}\frac{\text{V}}{\text{V}}\text{\u2192}$
BW = GBP NG = 30MHz 1.01 V V = 29.7MHz - BW
_{LMV861}= 30MHz; therefore, it meets this requirement.

- BW
- If C
_{1}is not used to limit the circuit bandwidth, to avoid stability issues ensure that the zero created by the gain setting resistors and input capacitance of the device is greater than the bandwidth of the circuit.Equation 1. $\frac{\text{1}}{{\text{2\pi \xd7 (C}}_{\text{cm}}{\text{+ C}}_{\text{diff}}{\text{) \xd7 (R}}_{\text{2}}{\text{|| R}}_{\text{1}}\text{)}}\text{>}\frac{{\text{GBP}}_{\text{LMV861}}}{\text{NG}}$- C
_{cm}and C_{diff}are the common-mode and differential input capacitance of the LMV861, respectively.

- C

**Design Simulations**

**DC Simulation Results**

**AC Simulation Results**

**Transient Simulation Results**

A 1-kHz, 400-Vpp input sine wave yields a 4-Vpp output sine wave.

**Design References**

- See
*Analog Engineer's Circuit Cookbooks*for the comprehensive TI circuit library. - SPICE Simulation File SBOC522.
- TI Precision Labs
- For more information on
circuits with larger input voltages, see
*Considerations for High-Voltage Measurements*.

**Design Featured Op
Amp**

LMV861 | |
---|---|

V_{ss} | 2.7V to 5.5V |

V_{inCM} | (Vee – 0.1V) to (Vcc – 1.1V) |

V_{out} | Rail-to-rail |

V_{os} | 0.273mV |

I_{q} | 2.25mA |

I_{b} | 0.1pA |

UGBW | 30MHz |

SR | 18V/µs |

#Channels | 1, 2 |

www.ti.com/product/LMV861 |

**Design Alternate Op Amp**

TLV9002 | OPA377 | |
---|---|---|

V_{ss} | 1.8V to 5.5V | 2.2V to 5.5V |

V_{inCM} | Rail-to-rail | Rail-to-rail |

V_{out} | Rail-to-rail | Rail-to-rail |

V_{os} | 0.4mV | 0.25mV |

I_{q} | 0.06mA | 0.76mA |

I_{b} | 5pA | 0.2pA |

UGBW | 1MHz | 5.5MHz |

SR | 2V/µs | 2V/µs |

#Channels | 1, 2, 4 | 1, 2, 4 |

www.ti.com/product/TLV9002 | www.ti.com/product/OPA377 |