LM2925 [NSC]
Low Dropout Regulator with Delayed Reset; 低压差稳压器与延迟复位
| 型号： | LM2925 |
| 厂家： | 
National Semiconductor |
| 描述： | Low Dropout Regulator with Delayed Reset |
| 文件： | 总8页 (文件大小：226K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
April 1998
LM2925
Low Dropout Regulator with Delayed Reset
LM2925 cannot be harmed by temporary mirror-image inser-
tion. Familiar regulator features such as short circuit and
thermal overload protection are also provided.
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.
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
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
Typical Application Circuit
Connection Diagram
TO-220 5-Lead
DS005268-2
Order Number LM2925T
See NS Package Number T05A
DS005268-1
*
Required if regulator is located far from power supply filter.
**
C
must be at least 10 µF to maintain stability. May be increased
OUT
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
© 1998 National Semiconductor Corporation
DS005268
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Internal Power Dissipation (Note 2)
Operating Temperature Range
Maximum Junction Temperature
Storage Temperature Range
Lead Temperature
Internally Limited
−40˚C to + 125˚C
150˚C
−65˚C to + 150˚C
Input Voltage
(Soldering, 10 seconds)
260˚C
Operating Range
26V
60V
ESD rating is to be determined
Overvoltage Protection
VOUT
Electrical Characteristics
=
=
=
=
VIN 14V, C2 10 µf, IO 500 mA, TJ 25˚C (Note 4) (unless otherwise specified)
Parameter
Conditions
Min
Typ
Max
Units
(Note 3)
Output Voltage
6V≤ VIN ≤ 26V, IO ≤ 500 mA,
−40˚C≤ TJ ≤ +125˚C
V
4.75
5.00
4
5.25
25
=
Line Regulation
9V ≤ VIN ≤ 16V, IO 5 mA
mV
mV
mV
mΩ
=
6V ≤ VIN ≤ 26V, IO 5 mA
10
50
Load Regulation
5 mA ≤ IO ≤ 500 mA
500 mADC and 10 mArms,
100 Hz-10 kHz
10
50
Output Impedance
200
Quiescent Current
IO ≤ 10 mA
3
40
mA
=
IO 500 mA
100
0.6
mA
=
IO 750 mA
90
mA
Output Noise Voltage
Long Term Stability
Ripple Rejection
10 Hz-100 kHz
100
20
µVrms
mV/1000 hr
=
fo 120 Hz
66
dB
V
=
Dropout Voltage
IO 500 mA
0.45
0.82
1.2
31
=
IO 750 mA
V
Current Limit
0.75
26
A
Maximum Operational
Input Voltage
V
Maximum Line Transient
Reverse Polarity Input
Voltage, DC
VO ≤ 5.5V
60
70
V
V
VO ≥ − 0.6V, 10Ω Load
−15
−30
Reverse Polarity Input
Voltage, Transient
1% Duty Cycle, τ ≤ 100 ms,
10Ω Load
−50
−80
V
Reset Output
Electrical Characteristics
=
=
=
VIN 14V, C3 0.1 µF, TA 25˚C (Note 4) (unless otherwise specified)
Parameter Conditions
Min
Typ
Max
Units
(Note 3)
Reset Voltage
Output Low
Output High
=
=
ISINK 1.6 mA, VIN 35V
0.3
5.0
30
0.6
5.5
V
V
=
ISOURCE
0
4.5
Reset Internal Pull-up Resistor
Reset Output Current Limit
VOUT Threshold
kΩ
mA
V
=
VRESET 1.2 V
5
4.5
12
=
Delay Time
C3 .005 µF
ms
ms
s
=
C3 0.1 µF
150
250
12
300
=
C3 4.7 µF tantalum
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2
Reset Output
Electrical Characteristics (Continued)
=
=
=
VIN 14V, C3 0.1 µF, TA 25˚C (Note 4) (unless otherwise specified)
Parameter Conditions
Min
Typ
(Note 3)
1.95
Max
Units
Delay Current
Pin 4
1.2
2.5
µA
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating Conditions.
Note 2: Thermal resistance without a heat sink for junction to case temperature is 3˚C/W (TO-220). Thermal resistance for TO-220 case to ambient temperature is
50˚C/W.
Note 3: These parameters are guaranteed and 100% production tested.
Note 4: To ensure constant junction temperature, low duty cycle pulse testing is used.
Typical Circuit Waveforms
DS005268-3
FIGURE 2.
Typical Performance Characteristics
Reset Voltage
Reset Voltage
Delay Time
DS005268-5
DS005268-4
DS005268-6
3
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Typical Performance Characteristics (Continued)
Reset Voltage
on Power-up
Delay Time
Reset Pull-up
Resistor R10
DS005268-8
DS005268-7
DS005268-9
Dropout Voltage
Line Transient Response
Ripple Rejection
DS005268-11
DS005268-12
DS005268-10
Ripple Rejection
Quiescent Current
Output Voltage
DS005268-15
DS005268-13
DS005268-14
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4
Typical Performance Characteristics (Continued)
Quiescent Current
Quiescent Current
Load Transient Response
DS005268-18
DS005268-19
DS005268-17
Peak Output Current
Maximum Power
Output Capacitor ESR
Dissipation (TO-220)
DS005268-20
DS005268-22
DS005268-21
Quiescent Current: The part of the positive input current
that does not contribute to the positive load current. The
regulator ground lead current.
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.
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.
Input Voltage: The DC voltage applied to the input terminals
with respect to ground.
Application Hints
Input-Output Differential: The voltage difference between
the unregulated input voltage and the regulated output volt-
age for which the regulator will operate.
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.
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.
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
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Application Hints (Continued)
Capacitors must also be rated at all ambient temperatures
expected in the system. Many aluminum type electrolytics
will freeze at temperatures less than −30˚C, reducing their
effective capacitance to zero. To maintain regulator stability
down to −40˚C, capacitors rated at that temperature (such as
tantalums) must be used.
RESET OUTPUT
The range of values for the delay capacitor is limited only by
stray capacitances on the lower extreme and capacitance
leakage on the other. Thus, delay times from microseconds
to seconds are possible. The low charging current, typically
2.0 microamps, allows the use of small, inexpensive disc ca-
pacitors for the nominal range of 100 to 500 milliseconds.
This is the time required in many microprocessor systems for
the clock oscillator to stabilize when initially powered up. The
RESET output of the regulator will thus prevent erroneous
data and/or timing functions to occur during this part of op-
eration. The same delay is incorporated after any other fault
condition in the regulator output is corrected.
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6
Circuit Schematic
7
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Physical Dimensions inches (millimeters) unless otherwise noted
5-Lead TO-220 Power Package (T)
Order Number LM2925T
NS Package Number T05A
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DE-
VICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMI-
CONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or sys-
tems which, (a) are intended for surgical implant into
the body, or (b) support or sustain life, and whose fail-
ure to perform when properly used in accordance
with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
2. A critical component in any component of a life support
device or system whose failure to perform can be rea-
sonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
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