Bay Linear, Inc 2478 Armstrong Street, Livermore, CA 94550 Tel: (925) 989-7144, Fax: (925) 940-9556 www.baylinear.com
LM2931
Note 1: Output or referenc e voltage t emperature coeffici ents defined as the worst ca se voltage chan ge divid ed by the total temperatu r e range.
Note 2: Unless otherwise specif ied all lim its 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 ≤ 0.8 V
Note 2: Regulation is measured at constant jun ction temperat ure , usi ng pulse test ing with a low duty cycle. Changes in ou tput volta ge due to
heating effects are covered under specification for th ermal regulation.
Note 3: Line regulation for is tested at 150°C for IL = 1mA. For IL = 100µA and TJ = 125°C, line regu lation is guaranteed by design to 0.2%. for
B2931-15 16V ≤ VIN ≤ 26V.
Note 4: Dropout voltage is defined as the inpu t to output differential at which the output voltage drops 2% below its nominal value measured at
1V diff e r ential.
Note 5: Ground pin Current is the regulator quiescent current. The total current drawn from the source is the sum of the ground pin curre nt an d
output load cu rrent.
Note 6: Thermal regulation is the change in output volta ge at a time T after a change in power dissipation , excludi ng load or li ne 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 H ints
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 stabilit y can be o btained with a ta ntal u m
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 maintai n 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.