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LM2931
(Rev.:2007)

100 mA, Adjustable Output, LDO Voltage Regulator with 60 V Load Dump Protection

ON Semiconductor 

LM2931, NCV2931 Series

Vout = 5.0 V

RL = 500 W

18.5

CO = 100 mF

CO(ESR) = 0.3 W

100

TA = 25°C

14

0

t, TIME (10 ms/DIV)

Figure 13. Line Regulation

Vin = 14 V

Vout = 5.0 V

Cin = 1000 mF

CO = 100 mF

CO(ESR) = 0.3 W

TA = 25°C

t, TIME (10 ms/DIV)

Figure 14. Load Regulation

1.240

1.220

1.200

LM2931C Adjustable

IO = 10 mA

Vin = Vout + 1.0 V

TA = 25°C

1.180

1.160

0 3.0 6.0 9.0 12 15 18 21 24

VO, OUTPUT VOLTAGE (V)

Figure 15. Reference Voltage versus Output Voltage

2.6

LM2931C Adjustable

2.5

IO = 10 mA

Vin = Vout + 1.0 V

TA = 25°C

2.4

Output Off"

2.3

2.2

2.1

Output On"

2.0

0 3.0 6.0 9.0 12 15 18 21 24

VO, OUTPUT VOLTAGE (V)

Figure 16. Output Inhibit−Thresholds

versus Output Voltage

APPLICATIONS INFORMATION

The LM2931 series regulators are designed with many

protection features making them essentially blow−out

proof. These features include internal current limiting,

thermal shutdown, overvoltage and reverse polarity input

protection, and the capability to withstand temporary

power−up with mirror−image insertion. Typical application

circuits for the fixed and adjustable output device are shown

in Figures 17 and 18.

The input bypass capacitor Cin is recommended if the

regulator is located an appreciable distance (≥ 4″) from the

supply input filter. This will reduce the circuit’s sensitivity

to the input line impedance at high frequencies.

This regulator series is not internally compensated and

thus requires an external output capacitor for stability. The

capacitance value required is dependent upon the load

current, output voltage for the adjustable regulator, and the

type of capacitor selected. The least stable condition is

encountered at maximum load current and minimum output

voltage. Figure 22 shows that for operation in the “Stable”

region, under the conditions specified, the magnitude of the

output capacitor impedance |ZO| must not exceed 0.4 W. This

limit must be observed over the entire operating temperature

range of the regulator circuit.

With economical electrolytic capacitors, cold temperature

operation can pose a serious stability problem. As the

electrolyte freezes, around −30°C, the capacitance will

decrease and the equivalent series resistance (ESR) will

increase drastically, causing the circuit to oscillate. Quality

electrolytic capacitors with extended temperature ranges of

−40° to +85°C and −55° to +105°C are readily available.

Solid tantalum capacitors may be a better choice if small size

is a requirement, however, the maximum ⏐ZO⏐ limit over

temperature must be observed.

Note that in the stable region, the output noise voltage is

linearly proportional to ⏐ZO⏐. In effect, CO dictates the high

frequency roll−off point of the circuit. Operation in the area

titled “Marginally Stable” will cause the output of the

regulator to exhibit random bursts of oscillation that decay

in an under−damped fashion. Continuous oscillation occurs

when operating in the area titled “Unstable”. It is suggested

that oven testing of the entire circuit be performed with

maximum load, minimum input voltage, and minimum

ambient temperature.

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