LM2941, LM2941C

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SNVS770I – JUNE 1999 – REVISED JANUARY 2015

8.2.2 Detailed Design Procedure

8.2.2.1 Output Capacitor

A tantalum capacitor with a minimum capacitance value of 22

μF, and ESR in the range of 0.01 Ω to 5 Ω, is

required at the output pin for loop stability. It must be located less than 1 cm from the device. There is no

limitation on any additional capacitance.

Alternately, a high quality X5R/X7R 22

μF ceramic capacitor may be used for the output capacitor only if an

appropriate value of series resistance is added to simulate the ESR requirement. The ceramic capacitor selection

must include an appropriate voltage de-rating of the capacitance value due to the applied output voltage. The

series resistor (for ESR simulation) should be in the range of 0.1

Ω to 1 Ω.

8.2.2.2 Setting the Output Voltage

The output voltage range is 5 V to 20 V and is set by the two external resistors, R1 and R2. See the Figure 18.

The output voltage is given by the formula:

where

•

(1)

Using 1 k

Ω for R1 will ensure that the bias current error of the adjust pin will be negligible. Using a R1 value

higher than 10 k

Ω may cause the output voltage to shift across temperature due to variations in the adjust pin

bias current.

Calculating the upper resistor (R2) value of the pair when the lower resistor (R1) value is known is accomplished

with the following formula:

(2)

The resistors used for R1 and R2 should be high quality, tight tolerance, and with matching temperature

8.2.3 Application Curves

Figure 19. Low Voltage Behavior

Figure 20. Output at Voltage Extremes

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