LM2941, LM2941C

SNVS770G – JUNE 1999 – REVISED APRIL 2013

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Definition of Terms

Dropout Voltage: The input-voltage differential at which the circuit ceases to regulate against further reduction

in input voltage. Measured when the output voltage has dropped 100mV from the nominal value obtained at

Input Voltage: The DC voltage applied to the input terminals with respect to ground.

Input-Output Differential: The voltage difference between the unregulated input voltage and the regulated

output voltage for which the regulator will operate.

Line Regulation: The change in output voltage for a change in the input voltage. The measurement is made

under conditions of low dissipation or by using pulse techniques such that the average chip temperature is not

significantly affected.

Load Regulation: The change in output voltage for a change in load current at constant chip temperature.

Long Term Stability: Output voltage stability under accelerated life-test conditions after 1000 hours with

maximum rated voltage and junction temperature.

Output Noise Voltage: The rms AC voltage at the output, with constant load and no input ripple, measured over

a specified frequency range.

Quiescent Current: That part of the positive input current that does not contribute to the positive load current.

The regulator ground lead current.

Ripple Rejection: The ratio of the peak-to-peak input ripple voltage to the peak-to-peak output ripple voltage.

temperature to either temperature extreme.

APPLICATION HINTS

Output Capacitor

A Tantalum capacitor with a minimum capacitance value of 22

μF, and ESR in the range of 0.01Ω to 5Ω, 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 1.0Ω.

Setting the Output Voltage

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

Applications. The output voltage is given by the formula:

(1)

Using 1.00 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

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