LP2951A [SEMTECH]
150mA ADJUSTABLE VOLTAGE REGULATOR; 150毫安可调稳压
| 型号： | LP2951A |
| 厂家： | 
SEMTECH CORPORATION |
| 描述： | 150mA ADJUSTABLE VOLTAGE REGULATOR |
| 文件： | 总5页 (文件大小：115K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
150mA ADJUSTABLE
VOLTAGE REGULATOR
LP2951A
March 17, 1998
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
FEATURES
The LP2951A is an improved version of the LP2951
and features tighter tolerance on the output voltage
and reference voltage specifications. Both the LP2951
and LP2951A feature 150mA output current capability.
The LP2951 series of low power voltage regulators
have low quiescent current and low dropout voltage.
The quiescent current increases minimally during
dropout conditions thereby extending battery life.
•= Guaranteed 150mA current
•= Adjustable output voltage - 1.24V to 29V
•= Accurate 5V output @150mA
•= Low dropout voltage - 450mV @ 150mA
•= Regulator or reference functions
•= Direct replacement for LP2951AC, MIC2951-02,
AS2951AC
Available in the eight lead SOIC package, the LP2951
series includes features such as shutdown and low
output voltage detect (typically due to low battery con-
ditions) . This function may also be used as a power on
reset function when triggered by CMOS or TTL inputs.
The circuit can be used as a fixed voltage 5 volt regula-
tor or adjusted between 1.24 volts and 29 volts using
external resistor pairs.
APPLICATIONS
•= Microcontroller supplies
•= Linear regulators
•= Adjustable supplies
•= Switching power supplies - post-regulation
•= Portable modems
•= Battery powered systems
•= Cellular telephones
•= Voltage references
BLOCK DIAGRAM
ORDERING INFORMATION
DEVICE(1)
LP2951ACM
Note:
VOUTVOLTS
PACKAGE
ADJ
SO-8
(1) Add suffix ‘TR’ for tape and reel.
ABSOLUTE MAXIMUM RATINGS
Parameter
Symbol Maximum Units
Supply Voltage
VIN
-0.3 to 30
-0.3 to 30
V
V
Shutdown Input
Voltage
PIN CONFIGURATION
Error Comp. Output
Voltage
-0.3 to 30
V
Power Dissipation
Internally
Limited
PD
TJ
W
Operating Junction
Temperature Range
-40 to 125
-65 to 150
260
°C
°C
°C
Storage
Temperature Range
TSTG
TLEAD
Lead Temperature
(Soldering) 5 Sec
1
© 1998 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
150mA ADJUSTABLE
VOLTAGE REGULATOR
LP2951A
March 17, 1998
ELECTRICAL CHARACTERISTICS
Unless specified, limits are over operating temperature range (TJ = TA), VIN = VOUT(NOM) + 1V, IL = 100µA, CL = 1µF
Parameter
Symbol
VOUT
Conditions
TJ=25°C, IL = 100µA
0°C ≤ TJ ≤=70°C
6V ≤ VIN=≤=30V
100µA ≤ IL=≤=150mA
IL===100µA
Min
Typ
Max
Units
V
Output Voltage
Temp Coefficient(1)
Line Regulation
Load Regulation
Dropout Voltage
4.975 5.000 5.025
TC
20
0.1
0.1
80
120
0.5
ppm/°C
%
REG(LINE)
REG(LOAD)
VD
0.4
%
150
600
160
mV
380
120
IL===150mA
Ground Current
IGND
µA
IL===100µA
IL===150mA
8
14
mA
µA
mA
V
Dropout Ground Current
Current Limit
IGND(D)
ICL
110
250
250
1.25
VIN = 4.5V, IL===100µA
VOUT = 0
200
Reference Voltage
VREF
1.22
1.235
VREF ≤ VOUT ≤ (VIN - 1V), TJ ==25°C,
100µA ≤ IL=≤=100mA
Feedback Bias Current
IFB
20
60
nA
µA
Error Comparator
Output High Leakage
Current
VOH = 30V
2
Output Low Voltage
Threshold Voltage
VIN = 4.5V, IOL = 400µA
150
60
400
mV
mV
Upper
Lower
25
75
140
0.6
Hysteresis
15
mV
Shutdown Input
Input Logic Voltage
VSD
Low
V
V
High
2.0
Input Current
ISD
VSHUTDOWN = 2.4V
VSHUTDOWN = 30V
SHUTDOWN ≥ 2V, VIN ≤ 30V,
100
750
20
µA
Regulator Shutdown
Output Current
IO(SD)
µA
V
VOUT = 0, Feedback pin to Tap 5V
NOTES:
(1) Temperature coefficient is defined as the worst case voltage change divided by total temperature range.
2
© 1998 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
150mA ADJUSTABLE
VOLTAGE REGULATOR
LP2951A
March 17, 1998
PRINCIPLES OF OPERATION (LP2951 AND LP2951A)
are connected to the output, but this has not been ob-
served in practice. It is also important that the capaci-
tance be mounted close (1cm or less) to the output pin
of the regulator.
Setting the Output Voltage
The LP2951(A) can be set to deliver any output voltage
from 1.24V to 30V by using an external voltage divider.
In addition, an internal voltage divider is provided if a
5V output is desired. To use the internal voltage di-
vider, simply connect the sense pin to the output and
the tap pin to the feedback pin (see block diagram).
When using an external divider the sense and tap pins
are left open, and the divider is installed from the out-
put to ground, with its center connected to the feed-
back pin (see Adjustable Regulator figure below).
When using an external voltage divider, resistances
can be calculated from the following formula:
é
ù
1.235
R2
æ
ç
è
ö
+ 20x10−9 x R1 + 1.235 V
VOUT
=
÷
ê
ø
ë
An upper limit of values for R2 occurs at ~1.2MΩ if the
regulator is to be operated when completely unloaded,
as this allows the feedback divider to provide the 1µA
minimum load recommended for the LP2951(A). If the
regulator always has a load of 1µA or more connected
externally, higher resistor values can be used, but at-
tention must be paid to the -20nA (typical) bias current
required by the feedback pin. Using a 1.2MΩ resistor
for R2, this bias current will already cause a 2% shift in
output voltage between full load and no load. Larger
values of R2 exacerbate the problem. Using a 120KΩ
resistor for R2 reduces the error caused by feedback
bias current to 0.2% while still only requiring 10µA to
feed the divider string.
Adjustable Regulator
If the lead inductance between the input of the
LP2951(A) and its power source exceeds ~500nH
(approximately 10”/25cm of 0.031”/0.78mm trace) it
may also be necessary to add a filter capacitor be-
tween the input terminal and ground. A 1µF tantalum
or aluminum capacitor is usually sufficient. Lower val-
ues can be used if load currents are small. Noise injec-
tion into the feedback terminal of the LP2951(A) from
nearby noise sources can also upset the output. Gen-
erally this can be cured by the addition of 100pF or so
from the feedback terminal to the output.
Output Filtering
An output filter capacitor is always necessary with the
LP2951(A) in order to assure output stability. The size
of this capacitor varies with output voltage (smaller at
higher output voltages) and output current (smaller at
lower output currents). For 5V operation 1µF is suffi-
cient. For regulator operation at a minimum output volt-
age, (1.24V) and output currents of 100mA, the re-
quired filter increases to 3.3µF. Any type of capacitor
may be used, although if aluminum electrolytics are
chosen, the equivalent series resistance (ESR) should
be held to 5Ω or less. For small load currents the ca-
pacitance can be reduced. 0.33µF will be satisfactory
for output currents of 10mA or less, and 0.1µF will
work if output current is below 1mA.
Theoretically, it is also possible for the regulator to be-
come unstable if very large capacitances (>10,000µF)
3
© 1998 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
150mA ADJUSTABLE
VOLTAGE REGULATOR
LP2951A
March 17, 1998
PRINCIPLES OF OPERATION (LP2951 and LP2951A) (cont.)
Reducing Output Noise
In ultra-quiet systems, or when the LP2951(A) is being
used as a reference, it may be desirable to perform
additional output filtering to reduce noise. While this
can be done simply using larger capacitors on the out-
put, that solution tends to be bulky and expensive, and
eventually, with huge capacitors (>1,000µF) may cause
instability in the regulator. Generally, it is more cost-
effective to let the regulator regulate output noise
away. This can be done by bypassing the upper resis-
tor in the feedback divider with a small capacitor to
provide a more direct path for AC feedback. The size
of this capacitor can be calculated from the formula:
1
CBYPASS
=
2πR1fcorner
where R1 is the upper resistor of the feedback divider
and fcorner is the frequency above which the increased
AC feedback is to become active. Because the gain of
the error amplifier in the LP2951(A) begins to roll off at
about 300 Hz, this is generally an optimum choice for
corner frequency.
The reduction of the output noise will be proportional to
the ratio of the two resistors in the feedback divider,
R1
R1+ R2
and will increase 20 dB per decade at frequencies
above the corner frequency chosen, up to the fre-
quency where the error amplifier’s gain has rolled off to
1 (≈100KHz). In order to maintain regulator stability
when using a noise-reducing bypass capacitor, it will
also be necessary to increase the size of the output
filter capacitor by the ratio
R1
R1+ R2
4
© 1998 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
150mA ADJUSTABLE
VOLTAGE REGULATOR
LP2951A
March 17, 1998
OUTLINE DRAWING SO-8
LAND PATTERN SO-8
5
© 1998 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
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