7 Applications 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, as well as validating and testing their design

implementation to confirm system functionality.

7.1 Application Information

The LPV521 is specified for operation from 1.6V to 5.5V (±0.8V to ±2.25V). Many of the specifications apply

from –40°C to +125°C. The LMV521 features rail-to-rail input and rail-to-rail output swings while consuming only

nanowatts of power. Parameters that exhibit significant variance with regard to operating voltage or temperature

are presented in Section 5.6.

7.1.1 Driving Capacitive Load

The LPV521 is internally compensated for stable unity gain operation, with a 6.2kHz, typical gain bandwidth.

However, the unity gain follower is the most sensitive configuration to capacitive load. The combination of a

capacitive load placed at the output of an amplifier along with the amplifier output impedance creates a phase

lag, which reduces the phase margin of the amplifier. If the phase margin is significantly reduced, the response

is underdamped, and causes peaking in the transfer. When there is too much peaking, the op amp can start

oscillating.

+

-

VIN

RISO

VOUT

CL

Figure 7-1. Resistive Isolation of Capacitive Load

To drive heavy capacitive loads, use an isolation resistor, RISO, as in Figure 7-1. By using this isolation resistor,

the capacitive load is isolated from the amplifier output. The larger the value of RISO, the more stable the

amplifier. If the value of RISO is sufficiently large, the feedback loop is stable, independent of the value of CL.

However, larger values of RISO result in reduced output swing and reduced output current drive.

Table 7-1 shows the recommended minimum RISO values for a 5V supply. Figure 7-2 shows the typical response

obtained with the CL = 50pF and RISO = 154kΩ. The other values of RISO in Table 7-1 are chosen to achieve

similar dampening at the respective capacitive loads. Notice that for the LPV521 with larger a CL, a smaller

RISO can be used for stability. However, for a given CL, a larger RISO provides a more damped response. For

capacitive loads of 20pF and less, no isolation resistor is needed.

Table 7-1. Recommended Minimum RISO Values for a

5V Supply

CL

RISO

0pF to 20pF

Not needed

50pF

154kΩ

100pF

118kΩ

500pF

52.3kΩ

1nF

33.2kΩ

5nF

17.4kΩ

10nF

13.3kΩ

www.ti.com

LPV521

SNOSB14E – AUGUST 2009 – REVISED JULY 2024

Copyright © 2024 Texas Instruments Incorporated

Submit Document Feedback

19

Product Folder Links: LPV521