TLV521 datasheet(12/27 Pages) TI1

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VIN

RISO

VOUT

TLV521

SNOSD26 – MAY 2016

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8 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. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The TLV521 is specified for operation from 1.7 V to 5.5 V (±0.85 V to ±2.275 V). The TLV521 features rail to rail

input and rail-to-rail output swings while consuming only nanowatts of power. Parameters that can exhibit

significant variance with regard to operating voltage or temperature are presented in the Typical Characteristics

section.

8.1.1 Driving Capacitive Load

The TLV521 is internally compensated for stable unity gain operation, with a 6-kHz, 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’s output impedance creates a phase

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

will be under damped which causes peaking in the transfer and, when there is too much peaking, the op amp

might start oscillating.

Figure 30. Resistive Isolation of Capacitive Load

In order to drive heavy capacitive loads, an isolation resistor, RISO, should be used, as shown in Figure 30. By

using this isolation resistor, the capacitive load is isolated from the amplifier’s output. The larger the value of

RISO, the more stable the amplifier will be. If the value of RISO is sufficiently large, the feedback loop will be

stable, independent of the value of CL. However, larger values of RISO result in reduced output swing and

reduced output current drive.

Recommended minimum values for RISO are given in the following table, for 5-V supply. Figure 31 shows the

typical response obtained with the CL = 50 pF and RISO = 154 kΩ. The other values of RISO in the table were

chosen to achieve similar dampening at their respective capacitive loads. Notice that for the TLV521 with larger

CL a smaller RISO can be used for stability. However, for a given CL a larger RISO will provide a more damped

response. For capacitive loads of 20 pF and below no isolation resistor is needed.

Table 1. Capacitive Loads vs. Needed Isolation Resistors

RISO

0 – 20 pF

not needed

50 pF

154 k

Ω

100 pF

118 k

Ω

500 pF

52.3 k

Ω

1 nF

33.2 k

Ω

5 nF

17.4 k

Ω

10 nF

13.3 k

Ω

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