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PDF LM2925T Data sheet ( Hoja de datos )
| Número de pieza | LM2925T | |
| Descripción | Low Dropout Regulator with Delayed Reset | |
| Fabricantes | National Semiconductor | |
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April 1998
LM2925
Low Dropout Regulator with Delayed Reset
General Description
The LM2925 features a low dropout, high current regulator.
Also included on-chip is a reset function with an externally
set delay time. Upon power up, or after the detection of any
error in the regulated output, the reset pin remains in the ac-
tive low state for the duration of the delay. Types of errors de-
tected include any that cause the output to become unregu-
lated: low input voltage, thermal shutdown, short circuit,
input transients, etc. No external pull-up resistor is neces-
sary. The current charging the delay capacitor is very low, al-
lowing long delay times.
Designed primarily for automotive applications, the LM2925
and all regulated circuitry are protected from reverse battery
installations or two-battery jumps. During line transients,
such as a load dump (60V) when the input voltage to the
regulator can momentarily exceed the specified maximum
operating voltage, the 0.75A regulator will automatically shut
down to protect both internal circuits and the load. The
LM2925 cannot be harmed by temporary mirror-image inser-
tion. Familiar regulator features such as short circuit and
thermal overload protection are also provided.
Features
n 5V, 750 mA output
n Externally set delay for reset
n Input-output differential less than 0.6V at 0.5A
n Reverse battery protection
n 60V load dump protection
n −50V reverse transient protection
n Short circuit protection
n Internal thermal overload protection
n Available in plastic TO-220
n Long delay times available
n P+ Product Enhancement tested
Typical Application Circuit
Connection Diagram
TO-220 5-Lead
DS005268-1
*Required if regulator is located far from power supply filter.
**COUT must be at least 10 µF to maintain stability. May be increased
without bound to maintain regulation during transients. Locate as close as
possible to the regulator. This capacitor must be rated over the same
operating temperature range as the regulator. The equivalent series
resistance (ESR) of this capacitor is critical; see curve.
FIGURE 1. Test and Application Circuit
Order Number LM2925T
See NS Package Number T05A
DS005268-2
© 1998 National Semiconductor Corporation DS005268
www.national.com
1 page  
Typical Performance Characteristics (Continued)
Quiescent Current
Quiescent Current
Load Transient Response
Peak Output Current
DS005268-19
Maximum Power
Dissipation (TO-220)
DS005268-17
DS005268-18
Output Capacitor ESR
DS005268-20
Definition of Terms
Dropout Voltage: The input-output voltage differential at
which the circuit ceases to regulate against further reduction
in input voltage. Measured when the output voltage has
dropped 100 mV from the nominal value obtained at 14V in-
put, dropout voltage is dependent upon load current and
junction temperature.
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 volt-
age 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 condi-
tions of low dissipation or by using pulse techniques such
that the average chip temperature is not significantly af-
fected.
Load Regulation: The change in output voltage for a
change in load current at constant chip temperature.
Long Term Stability: Output voltage stability under acceler-
ated 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.
DS005268-21
DS005268-22
Quiescent Current: The 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 Stability of VO: The percentage change in ou-
put voltage for a thermal variation from room temperature to
either temperature extreme.
Application Hints
EXTERNAL CAPACITORS
The LM2925 output capacitor is required for stability. Without
it, the regulator output will oscillate, sometimes by many
volts. Though the 10 µF shown is the minimum recom-
mended value, actual size and type may vary depending
upon the application load and temperature range. Capacitor
effective series resistance (ESR) also effects the IC stability.
Since ESR varies from one brand to the next, some bench
work may be required to determine the minimum capacitor
value to use in production. Worst-case is usually determined
at the minimum junction and ambient temperature and maxi-
mum load expected.
Output capacitors can be increased in size to any desired
value above the minimum. One possible purpose of this
would be to maintain the output voltages during brief condi-
tions of negative input transients that might be characteristic
of a particular system.
5 www.national.com
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| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LM2925T.PDF ] | |
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