Applied Load

Current

Load

Voltage

0

1

2

3

4

5

4.5

3.5

2.5

1.5

0.5

0

0.01

0.015

0.02

0.025

0.03

0.035

0.04

200

µF

1000

µF

1/ESR

0.005

400

µF

Not Recommended

Recommended Min ESR

Potential Instability

Region of

Best Stability

100

µF

22

µF

10

µF

Max ESR Boundary

Region of Best Stability

Min ESR

Boundary

3

2.8

2.6

2.4

2.2

2

1.8

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

0

0.1

0

0.2

0.3

0.4

0.5

This Region Not

Recommended for

Operation

f = 120 Hz

Potential Instability Region

TL750M SERIES

SLVS021N – JANUARY 1988 – REVISED AUGUST 2010

www.ti.com

PARAMETER MEASUREMENT INFORMATION

The TL750Mxx is a low-dropout regulator. This means that the capacitance loading is important to the

performance of the regulator because it is a vital part of the control loop. The capacitor value and the equivalent

series resistance (ESR) both affect the control loop and must be defined for the load range and the temperature

range. Figure 1 and Figure 2 can establish the capacitance value and ESR range for the best regulator

performance.

Figure 1 shows the recommended range of ESR for a given load with a 10-mF capacitor on the output. This

figure also shows a maximum ESR limit of 2

Ω and a load-dependent minimum ESR limit.

For applications with varying loads, the lightest load condition should be chosen because it is the worst case.

Figure 2 shows the relationship of the reciprocal of ESR to the square root of the capacitance with a minimum

capacitance limit of 10 mF and a maximum ESR limit of 2 Ω. This figure establishes the amount that the minimum

ESR limit shown in Figure 1 can be adjusted for different capacitor values.

For example, where the minimum load needed is 200 mA, Figure 1 suggests an ESR range of 0.8

Ω to 2 Ω for

10 mF. Figure 2 shows that changing the capacitor from 10 mF to 400 mF can change the ESR minimum by

greater than 3/0.5 (or 6). Therefore, the new minimum ESR value is 0.8/6 (or 0.13

Ω ). This allows an ESR range

of 0.13

Ω to 2 Ω , achieving an expanded ESR range by using a larger capacitor at the output. For better stability

in low-current applications, a small resistance placed in series with the capacitor (see Table 1) is recommended,

so that ESRs better approximate those shown in Figure 1 and Figure 2.

Table 1. Compensation for Increased Stability at Low Currents

MANUFACTUR

ESR

PART

ADDITIONAL

CAPACITANCE

ER

TYP

NUMBER

RESISTANCE

<br/>

AVX

15 mF

0.9

Ω

TAJB156M010S

1

Ω

<br/>

<br/>

T491D336M010

KEMET

33 mF

0.6

Ω

0.5

Ω

AS

<br/>

OUTPUT CAPACITOR

<br/>

EQUIVALENT SERIES RESISTANCE (ESR)

STABILITY

vs

vs

LOAD CURRENT RANGE

EQUIVALENT SERIES RESISTANCE (ESR)

Figure 1.

Figure 2.

6

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