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LM2931

100mA Low Dropout Voltage Regulator

Bay Linear 

LM2931

Note 1: Output or reference voltage temperature coefficients defined as the worst case voltage change divided by the total temperature range.

Note 2: Unless otherwise specified all limits guaranteed for TJ = 25°C, VIN = VO +1V, IL = 100µA and CL = 1µF. Additional conditions for the 8-

pin versions are feedback tied to –XX Voltage tap and output tied to output Sense pin ( VOUT = XX V) and VSHUTDOWN ≤ 0.8V

Note 2: Regulation is measured at constant junction temperature , using pulse testing with a low duty cycle. Changes in output voltage due to

heating effects are covered under specification for thermal regulation.

Note 3: Line regulation for is tested at 150°C for IL = 1mA. For IL = 100µA and TJ = 125°C, line regulation is guaranteed by design to 0.2%. for

B2931-15 16V ≤ VIN ≤ 26V.

Note 4: Dropout voltage is defined as the input to output differential at which the output voltage drops 2% below its nominal value measured at

1V differential.

Note 5: Ground pin Current is the regulator quiescent current. The total current drawn from the source is the sum of the ground pin current and

output load current.

Note 6: Thermal regulation is the change in output voltage at a time T after a change in power dissipation, excluding load or line regulation

effects. Specifications are for a 50 mA load pulse (1.25W) for T = 10ms.

Note 7: VREF ≤ VOUT ≤ (VIN –1V), 2.3V ≤ VIN ≤ 26V, 100µA ≤ IL ≤100mA, TJ ≤ TJMAX

Note 8: VSHUTDOWN ≥ 2V, VIN ≤ 26V, VOUT = 0

Application Hints

The LM2931 requires an output capacitor for device

stability. The value required varies greatly

depending upon the application circuit and other

factors. The high frequency characteristics of

electrolytic capacitors depend greatly on the type and

also on the manufacturer. Sometimes only bench

testing is the only means to determine the proper

capacitor type and value. The high quality 100 µF

aluminum electrolytic covers all general application

circuits, this stability can be obtained with a tantalum

electrolytic value of 47 µF.

Another critical point of electrolytic characteristics is

its performance over temperature. The LM2931 is

designed to operate starting at -40°C which may not

be true in the case of electrolytic. Higher

temperatures generally no problem. The electrolytic.

type in aluminum will freeze around -30°C. This

could cause an oscillation at output of regulator. At a

lower temperature requirement by many applications

the capacitor should maintain its performance. So as

a result, for an application which regulator junction

temperature does not exceed 25°C, the output

capacitor can be reduced by the

factor of two over the value needed for the entire

temperature range.

Other points with linear regulators are that the twitch

higher output current stability decreases. In most

applications the LM2931 is operating at few

milliamps. In these applications the output capacitance

can be further reduced. For example, when the

regulator is running at 10mA output current the output

capacitance value is half compared to the same

regulator that is running at 100 mA.

With the LM2931 adjustable regulator, the minimum

value of output capacitance is a function of the output

voltage. The value decreases with higher output

voltages, since the internal loop gain is reduced.

The worst case occurs at the lower temperature and

maximum operating currents, the entire circuit and the

electrolytic, should be cooled down to the minimum

temperature. The minimum of 0.6 volts required at

the input of regulator above the output to keep the

power dissipation and die heating to its minimum.

After the value for the capacitor has been determined

for actual use, the value should be doubled.

Bay Linear, Inc 2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 989-7144, Fax: (925) 940-9556

www.baylinear.com

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