TL75LPxxQ SERIES

TL75LPxxY SERIES

LOW DROPOUT VOLTAGE REGULATORS

SLVS073A − SEPTEMBER 1992 − REVISED AUGUST 1995

3−10

POST OFFICE BOX 655303

POST OFFICE BOX 1443

PARAMETER MEASUREMENT INFORMATION

The TL75LPxx series are low-dropout voltage regulators. This means that the capacitance 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.

Figures 3 and 4 can establish the capacitance value and ESR range for optimum regulator performance.

Figure 3 shows the recommended range of ESR, measured at 120 Hz, for a given load with a 10-

µF capacitor on the

output. In addition, it 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 since it is the worst case. Figure 4

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

limit of 10

µF and a maximum ESR limit of 2 Ω. Figure 4 establishes the amount that the minimum ESR limit of Figure

3 can be adjusted for different capacitor values. For example, when the minimum load needed is 200 mA,

Figure 3 suggests an ESR range of 0.8

Ω to 2 Ω for 10 µF. Figure 4 shows that changing the capacitor from

10

µF to 400 µF 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 now allows an ESR range of 0.13 Ω to 2 Ω. This expanded ESR range is achieved by using

a larger capacitor at the output. For better stability in low-current applications, it is recommended that a small

resistance be placed in series with the capacitor (see Table 1) so that the ESR better approximates those in

Figures 3 and 4.

Table 1. Compensations for Increased Stability at Low Currents

MANUFACTURER

CAPACITANCE

ESR

PART

ADDITIONAL

MANUFACTURER

CAPACITANCE

ESR

TYP

PART

NUMBER

ADDITIONAL

RESISTANCE

AVX

15

µF

0.9

Ω

TAJB156M010S

1

Ω

KEMET

33

µF

0.6

Ω

T491D336M010AS

0.5

Ω

0.02

0.015

0.005

0

0

0.5

1

1.5

2

2.5

3

0.025

0.035

1/ESR

3.5

4

4.5

5

0.01

0.03

2.4

2.2

2

1.8

0

0.1

0.2

0.3

2.6

2.8

3

0.4

0.5

0.04

1.2

0.8

0.6

1.4

1.6

0.4

0.2

0

OUTPUT CAPACITOR

EQUIVALENT SERIES RESISTANCE

vs

LOAD CURRENT

OUTPUT CAPACITOR

STABILITY

vs

EQUIVALENT SERIES RESISTANCE

1

This Region Not

Recommended

for Operation

CL = 10 µF

CI = 0.1 µF

Max ESR Boundary

Min ESR

Boundary

Region of Best Stability

Potential Instability Region

IL − Load Current − A

10

µF

22

µF

100

µF

200

µF

400

µF

Region of

Best Stability

1000

µF

Not Recommended

Potential Instability

Recommended Min ESR

10

µF

Figure 3

Figure 4

Applied

Load

Current

Load

Voltage

∆IL

∆VL

∆VL = ∆IL × ESR