LX8117-28CDTT [MICROSEMI]
Positive Fixed Voltage Regulator ; 正固定电压稳压器\n型号: | LX8117-28CDTT |
厂家: | Microsemi |
描述: | Positive Fixed Voltage Regulator
|
文件: | 总9页 (文件大小:223K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LIN DOC #: 8117
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS
P R O D U C T I O N D A T A S H E E T
T H E I N F I N I T E P O W E R O F I N N O V A T I O N
DESCRIPTION
KEY FEATURES
■ 0.2% Line Regulation Maximum
The LX8117/8117A/8117B series are
positive Low Dropout (LDO) regulators.
At the designed maximum load current,
theLX8117seriesdropoutvoltageisguar-
anteed to be 1.2V or lower at 0.8A
(LX8117A 1.3V @ 1A). The dropout
voltage decreases with load current.
An adjustable output voltage version
of the LX8117/17A/17B is available, as
well as versions with fixed outputs of
2.5V, 2.85V, 3.3V and 5V. The 2.85V
version is specifically designed for use
as a component of active termination
networks for the SCSI bus. On-chip
trimmingoftheinternalvoltagereference
allows specification of the initial output
voltage to within ±1% of its nominal
value. The output current-limit point is
also trimmed, which helps to minimize
stress on both the regulator and the
system power source when they are
operated under short-circuit conditions.
The regulator's internal circuitry will
operate at input-to-output differential
voltages down to 1V.
■ 0.4% Load Regulation Maximum
■ Output Current Of 800mA
Most regulator circuit designs include
outputcapacitorswithvaluesintherange
of tens to hundreds of microfarads or
more. The LX8117/17A/17B typically
requires at least 10µF of output capaci-
tance for stable operation.
PNP-type regulators can waste current
equal to as much as 10 percent of their
output as a quiescent current which flows
directly to ground, bypassing the load.
Quiescent current from the LX8117/17A/
17B flows through the load, increasing
power-useefficiencyandallowingcooler
operation.
The LX8117 is available in low-profile
plastic SOT-223 and D-Pak packages for
applicationswherespaceisatapremium.
The LX8117 is also available in a plastic
TO-263 package for instances when the
thermal resistance from the circuit die to
the environment must be minimized.
■ Regulates Down To 1.2V Dropout
(LX8117) And 1.3V Dropout (LX8117A)
■ Operates Down To 1V Dropout
■ Space Saving SOT-223 Surface
Mount Package
■ Guaranteed Dropout Voltage At Multiple
Current Levels
■ Three-Terminal Adjustable Or Fixed 2.5V,
2.85V, 3.3V & 5V
APPLICATIONS
■ Battery Chargers
■ Active SCSI Terminators
■ 5V To 3.3V Linear Regulators
■ High-Efficiency Linear Regulators
■ Post Regulators For Switching Supplies
AVAILABLE OPTIONS PER PART #
NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.
Output
Part #
Voltage
PRODUCT HIGHLIGHT
LX8117/8117A/8117B-00 Adjustable
LX8117/8117A/8117B-25
LX8117/8117A/8117B-28
LX8117/8117A/8117B-33
LX8117/8117A/8117B-05
2.5V
2.85V
3.3V
5V
ACTIVE TERMINATOR FOR SCSI-2 BUS
110
110
110
Ω
Ω
Ω
LX8117-28
IN OUT
18 to 27
Lines
GND
4.75V to
5.25V
22µF
10µF
110Ω
PACKAGE ORDER INFORMATION
O/P
Current
Plastic SOT-223
3-pin
Plastic T0-263
DD
3-pin
Plastic T0-252
DT
TA (°C)
ST
(D-Pak) 3-pin
0.8A
1.0A
1.2A
LX8117-xxCST
LX8117A-xxCST
LX8117B-xxCST
LX8117-xxCDD
LX8117-xxCDT
LX8117A-xxCDT
LX8117B-xxCDT
0 to 125
LX8117A-xxCDD
LX8117B-xxCDD
Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number
(i.e. LX8117-28CSTT). "xx" refers to output voltage, please see table above.
L I N F I N I T Y M I C R O E L E C T R O N I C S I N C .
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
Copyright © 1999
Rev. 1.4 3/99
1
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS
P R O D U C T I O N D A T A S H E E T
ABSOLUTE MAXIMUM RATINGS (Note 1)
PACKAGE PIN OUTS
Power Dissipation .................................................................................. Internally Limited
Input Voltage
TAB IS VOUT
LX8117-00/8117A-00/8117B-00 (Adj.) ..................................................................... 15V
LX8117-33/8117A-33/8117B-33 (3.3V), LX8117-05/8117A-05/8117B-05 (5.0V).... 15V
LX8117-25/8117A-25/8117B-25 (2.5V), LX8117-28/8117A-28/8117B-28 (2.85V).. 12V
Surge Voltage ............................................................................................................... 15V
Operating Junction Temperature
3. IN
2. OUT
1. ADJ / GND
Plastic (ST, DD & DT Packages) .......................................................................... 150°C
Storage Temperature Range ...................................................................... -65°C to 150°C
Lead Temperature (Soldering, 10 seconds) ............................................................. 300°C
Short-Circuit Protection....................................................................................... Indefinite
ST PACKAGE
(Top View)
TAB IS VOUT
Note 1. Exceeding these ratings could cause damage to the device. All voltages are with
respect to Ground. Currents are positive into, negative out of the specified terminal.
3
2
1
IN
OUT
THERMAL DATA
ADJ / GND
ST PACKAGE:
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
DD PACKAGE:
15°C/W
DD PACKAGE (D2 Pak)
*150°C/W
(Top View)
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
DT PACKAGE:
10°C/W
TAB IS VOUT
*60°C/W
3. IN
2. OUT
THERMAL RESISTANCE-JUNCTION TO TAB, θJC
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
9°C/W
*80°C/W
1. ADJ / GND
Junction Temperature Calculation: TJ = TA + (PD x θJA). The θJA numbers are guidelines for the
thermalperformanceofthedevice/pc-boardsystem. Alloftheaboveassumenoambientairflow.
* θJAcan be improved with package soldered to 0.5IN2 copper area over backside ground
plane or internal power plane. θJAcan vary from 20ºC/W to > 40ºC/W depending on
mounting technique. (See Application Notes Section: Thermal Considerations)
DT PACKAGE (D-Pak)
(Top View)
BLOCK DIAGRAM
VIN
Bias
Circuit
Bandgap
Circuit
Control
Circuit
Output
Circuit
Thermal
Limit Circuit
VOUT
Current
Limit Circuit
ADJ
Copyright © 1999
Rev. 1.4 3/99
2
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS
P R O D U C T I O N D A T A S H E E T
RECOMMENDED OPERATING CONDITIONS
(Note 2)
Recommended Operating Conditions
Parameter
Symbol
Units
Min.
Typ.
Max.
Input Voltage
Operating Voltage
LX8117(A/B)-00 / 8117(A/B)-05
15
12
10
V
V
V
LX8117(A/B)-25 / -28 / -33
LX8117(A/B)-00
Input-Output Differential
0
125
°C
Operating Ambient Temperature Range
Note 2. Range over which the device is functional.
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified: 0°C ≤ T ≤ 125°C, IMAX = 0.8A for the LX8117-xx, IMAX = 1.0A for the LX8117A-xx, and IMAX = 1.2A for the LX8117B-xx.)
J
LX8117-00 / 8117A-00 / 8117B-00 (Adjustable)
LX8117 / 17A / 17B-00
Parameter
Symbol
Test Conditions
Units
Min. Typ.
Max.
1.238 1.250 1.262
1.225 1.250 1.270
V
V
Reference Voltage
VREF
IOUT = 10mA, (VIN - VOUT) = 2V, TJ = 25°C
10mA ≤ IOUT ≤ IOUT (MAX), 1.4V ≤ (V - VOUT) ≤ 10V
IN
0.05
0.15
0.97
1.00
1.05
1.15
950
1200
1500
0.5
0.2
0.4
1.10
1.15
1.20
1.30
%
Line Regulation (Note 3)
Load Regulation (Note 3)
∆VREF(V ) IOUT = 10mA, 1.5V ≤ (VIN - VOUT) ≤ 7V
IN
∆VREF(IOUT
)
(VIN - VOUT) = 3V, 10mA ≤ IOUT ≤ IOUT (MAX)
IOUT = 100mA
%
V
V
Dropout Voltage
(Note 4)
∆V
IOUT = 500mA
V
V
LX8117-00
IOUT = IOUT (MAX)
LX8117A/B-00
LX8117-00
IOUT = IOUT (MAX)
IOUT (MAX) (VIN - VOUT) = 5V, TJ = 25°C
(VIN - VOUT) = 5V, TJ = 25°C
800
1000
1200
mA
mA
mA
mA
%/W
dB
µA
µA
%
Current Limit
LX8117A-00
LX8117B-00
Minimum Load Current (Note 5)
Thermal Regulation
(VIN - VOUT) = 5V, TJ = 25°C
5
0.2
IOUT (MIN)
V ≤ 10V
IN
0.08
75
45
∆VOUT(Pwr) TA = 25°C, 30ms pulse
60
Ripple Rejection
Adjust Pin Current
fRIPPLE =120Hz, (V - VOUT) = 3V, VRIPPLE = 1Vp-p
IN
100
5
IADJ
∆IADJ
0.2
Adjust Pin Current Change
Temperature Stability
Long Term Stability
10mA ≤ IOUT ≤ IOUT (MAX) , 1.4V ≤ (V - VOUT) ≤ 10V
IN
0.5
0.3
∆VOUT (T)
%
∆VOUT (t) TA = 125°C, 1000 hours
VOUT (RMS) 10Hz ≤ f ≤ 10kHz
0.003
%
RMS Output Noise (% of VOUT
)
Notes: 3. See thermal regulation specification for changes in output voltage due to heating effects. Load regulation and line regulation are measured at a constant junction
temperature by low duty cycle pulse testing.
4. Dropout voltage is specified over the full output current range of the device. Dropout voltage is defined as the minimum input/output differential measured
at the specified output current. Test points and limits are also shown on the Dropout Voltage Curve.
5. Minimum load current is defined as the minimum output current required to maintain regulation.
(Other Voltage Options on following pages.)
Copyright © 1999
Rev. 1.4 3/99
3
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS
P R O D U C T I O N D A T A S H E E T
ELECTRICAL CHARACTERISTICS (continued)
LX8117-25 / 8117A-25 / 8117B-25 (2.5V Fixed)
LX8117 / 17A / 17B-25
Min. Typ. Max.
Parameter
Symbol
Test Conditions
Units
2.475 2.500 2.525
2.450 2.500 2.550
V
V
mV
mV
V
Output Voltage
VOUT
IOUT = 10mA, VIN = 5V, TA = 25°C
0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V
IOUT = 0mA, 4.25V ≤ VIN ≤ 10V
VIN = 4.25V, 0mA ≤ IOUT ≤ IOUT (MAX)
IOUT = 100mA
(VIN)
∆VOUT
Line Regulation (Note 3)
Load Regulation (Note 3)
Dropout Voltage
(Note 4)
1
6
∆VOUT (IOUT
)
2
10
∆V
0.97
1.00
1.05
1.15
950
1200
1500
4.5
1.10
1.15
1.20
1.30
V
IOUT = 500mA
IOUT = IOUT (MAX)
LX8117-25
V
V
LX8117A/B-25
LX8117-25
LX8117A-25
LX8117B-25
IOUT = IOUT (MAX)
800
1000
1200
mA
mA
mA
mA
%/W
dB
%
Current Limit
IOUT (MAX) (VIN - VOUT) = 5V, TJ = 25°C
(VIN - VOUT) = 5V, TJ = 25°C
(VIN - VOUT) = 5V, TJ = 25°C
10
Quiescent Current
Thermal Regulation
Ripple Rejection
Temperature Stability
Long Term Stability
IQ
∆VOUT(Pwr) TA = 25°C, 30ms pulse
fRIPPLE =120Hz, (VIN - VOUT) = 3V, VRIPPLE = 1Vp-p
VIN ≤ 10V
0.08
75
0.2
60
0.5
0.3
∆VOUT (T)
%
∆VOUT (t) TA = 125°C, 1000 hours
VOUT (RMS) 10Hz ≤ f ≤ 10kHz
0.003
%
RMS Output Noise (% of VOUT
)
LX8117-28 / 8117A-28 / 8117B-28 (2.8V Fixed)
LX8117 / 17A / 17B-28
Min. Typ. Max.
Parameter
Symbol
Test Conditions
Units
2.820 2.850 2.880
2.790 2.850 2.910
2.790 2.850 2.910
V
V
V
Output Voltage
VOUT
IOUT = 10mA, VIN = 4.85V, TA = 25°C
0mA ≤ IOUT ≤ IOUT (MAX) , 4.25V ≤ VIN ≤ 10V
0mA ≤ IOUT ≤ 500mA, VIN = 3.95V
IOUT = 0mA, 4.25V ≤ VIN ≤ 10V
VIN = 4.25V, 0mA ≤ IOUT ≤ IOUT (MAX)
IOUT = 100mA
(VIN)
∆VOUT
Line Regulation (Note 3)
Load Regulation (Note 3)
1
6
mV
mV
V
∆VOUT (IOUT
)
2
10
0.97
1.00
1.05
1.15
950
1200
1500
4.5
1.10
1.15
1.20
1.30
Dropout Voltage
(Note 4)
∆V
IOUT = 500mA
V
V
LX8117-28
LX8117A/B-28
LX8117-28
LX8117A-28
LX8117B-28
IOUT = IOUT (MAX)
IOUT = IOUT (MAX)
V
800
1000
1200
mA
mA
mA
mA
%/W
dB
%
Current Limit
IOUT (MAX) (VIN - VOUT) = 5V, TJ = 25°C
(VIN - VOUT) = 5V, TJ = 25°C
(VIN - VOUT) = 5V, TJ = 25°C
VIN ≤ 10V
10
Quiescent Current
Thermal Regulation
Ripple Rejection
IQ
∆VOUT(Pwr) TA = 25°C, 30ms pulse
fRIPPLE =120Hz, (VIN - VOUT) = 3V, VRIPPLE = 1Vp-p
0.08
75
0.2
60
0.5
Temperature Stability
Long Term Stability
∆VOUT (T)
∆VOUT (t) TA = 125°C, 1000 hours
VOUT (RMS) 10Hz ≤ f ≤ 10kHz
0.3
0.003
%
%
RMS Output Noise (% of VOUT
)
Notes: 3. See thermal regulation specification for changes in output voltage due to heating effects. Load regulation and line regulation are measured at a constant junction
temperature by low duty cycle pulse testing.
4. Dropout voltage is specified over the full output current range of the device. Dropout voltage is defined as the minimum input/output differential measured
at the specified output current. Test points and limits are also shown on the Dropout Voltage Curve.
5. Minimum load current is defined as the minimum output current required to maintain regulation.
Copyright © 1999
Rev. 1.4 3/99
4
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS
P R O D U C T I O N D A T A S H E E T
ELECTRICAL CHARACTERISTICS (continued)
LX8117-33 / 8117A-33 / 8117B-33 (3.3V Fixed)
LX8117 / 17A / 17B-33
Min. Typ. Max.
Parameter
Symbol
Test Conditions
Units
3.267 3.300 3.333
3.235 3.300 3.365
V
V
Output Voltage
VOUT
IOUT = 10mA, V = 5V, TA = 25°C
0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V
IN
(VIN)
∆VOUT
Line Regulation (Note 3)
Load Regulation (Note 3)
Dropout Voltage
(Note 4)
IOUT = 0mA, 4.25V ≤ VIN ≤ 10V
VIN = 4.25V, 0mA ≤ IOUT ≤ IOUT (MAX)
IOUT = 100mA
1
2
6
mV
mV
V
∆VOUT (IOUT
)
10
∆V
0.97
1.00
1.05
1.15
950
1200
1500
4.5
1.10
1.15
1.20
1.30
V
IOUT = 500mA
IOUT = IOUT (MAX)
LX8117-33
V
V
LX8117A/B-33
LX8117-33
IOUT = IOUT (MAX)
800
1000
1200
mA
mA
mA
mA
%/W
dB
%
Current Limit
IOUT (MAX) (VIN - VOUT) = 5V, TJ = 25°C
(VIN - VOUT) = 5V, TJ = 25°C
LX8117A-33
LX8117B-33
(VIN - VOUT) = 5V, TJ = 25°C
10
0.2
Quiescent Current
Thermal Regulation
Ripple Rejection
Temperature Stability
Long Term Stability
IQ
∆VOUT(Pwr) TA = 25°C, 30ms pulse
fRIPPLE =120Hz, (VIN - VOUT) = 3V, VRIPPLE = 1Vp-p
VIN ≤ 10V
0.08
75
0.5
60
∆VOUT (T)
0.3
%
∆VOUT (t) TA = 125°C, 1000 hours
VOUT (RMS) 10Hz ≤ f ≤ 10kHz
0.003
%
RMS Output Noise (% of VOUT
)
LX8117-05 / 8117A-05 / 8117B-05 (5.0V Fixed)
LX8117 / 17A / 17B-05
Min. Typ. Max.
Parameter
Symbol
Test Conditions
Units
4.950 5.000 5.050
4.900 5.000 5.100
V
V
Output Voltage
VOUT
IOUT = 10mA, V = 7V, TA = 25°C
0mA ≤ IOUT ≤ IOUT (MAX) , 6.50V ≤ VIN ≤ 10V
IN
(VIN)
∆VOUT
Line Regulation (Note 3)
Load Regulation (Note 3)
Dropout Voltage
(Note 4)
IOUT = 0mA, 6.5V ≤ VIN ≤ 10V
VIN = 6.5V, 0mA ≤ IOUT ≤ IOUT (MAX)
IOUT = 100mA
1
10
mV
mV
V
∆VOUT (IOUT
)
2.5
15
∆V
0.97
1.00
1.05
1.15
950
1200
1500
4.5
1.10
1.15
1.20
1.30
V
IOUT = 500mA
IOUT = IOUT (MAX)
LX8117-05
V
V
LX8117A/B-05
LX8117-05
IOUT = IOUT (MAX)
800
1000
1200
mA
mA
mA
mA
%/W
dB
%
Current Limit
IOUT (MAX) (VIN - VOUT) = 5V, TJ = 25°C
(VIN - VOUT) = 5V, TJ = 25°C
LX8117A-05
LX8117B-05
(VIN - VOUT) = 5V, TJ = 25°C
10
0.2
Quiescent Current
Thermal Regulation
Ripple Rejection
Temperature Stability
Long Term Stability
IQ
∆VOUT(Pwr) TA = 25°C, 30ms pulse
fRIPPLE =120Hz, (VIN - VOUT) = 3V, VRIPPLE = 1Vp-p
VIN ≤ 10V
0.08
75
0.5
60
∆VOUT (T)
0.3
%
∆VOUT (t) TA = 125°C, 1000 hours
VOUT (RMS) 10Hz ≤ f ≤ 10kHz
0.003
%
RMS Output Noise (% of VOUT
)
Notes: 3. See thermal regulation specification for changes in output voltage due to heating effects. Load regulation and line regulation are measured at a constant junction
temperature by low duty cycle pulse testing.
4. Dropout voltage is specified over the full output current range of the device. Dropout voltage is defined as the minimum input/output differential measured
at the specified output current. Test points and limits are also shown on the Dropout Voltage Curve.
5. Minimum load current is defined as the minimum output current required to maintain regulation.
Copyright © 1999
Rev. 1.4 3/99
5
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS
P R O D U C T I O N D A T A S H E E T
APPLICATION NOTES
Minumum Load
(Larger resistor)
The LX8117 series ICs are easy to use Low-Dropout (LDO) voltage
Power Supply
IN
OUT
LX8117-xx
regulators. They have all of the standard self-protection features
expected of a voltage regulator: short circuit protection, safe
operating area protection and automatic thermal shutdown if the
device temperature rises above approximately 165°C.
Use of an output capacitor is REQUIRED with the LX8117 series.
Please see the table below for recommended minimum capacitor
values.
Full Load
(Smaller resistor)
ADJ
RDSON << RL
C1
C2
1 sec
10ms
Star Ground
These regulators offer a more tightly controlled reference voltage
tolerance and superior reference stability when measured against
the older pin-compatible regulator types that they replace.
FIGURE 1 — DYNAMIC INPUT and OUTPUT TEST
OVERLOAD RECOVERY
Like almost all IC power regulators, the LX8117 regulators are
equipped with Safe Operating Area (SOA) protection. The SOA
circuit limits the regulator's maximum output current to progres-
sively lower values as the input-to-output voltage difference
increases. By limiting the maximum output current, the SOA circuit
keeps the amount of power that is dissipated in the regulator itself
within safe limits for all values of input-to-output voltage within the
operating range of the regulator. The LX8117 SOA protection
system is designed to be able to supply some output current for all
values of input-to-output voltage, up to the device breakdown
voltage.
Under some conditions, a correctly operating SOA circuit may
prevent a power supply system from returning to regulated
operation after removal of an intermittent short circuit at the output
of the regulator. This is a normal mode of operation which can be
seen in most similar products, including older devices such as 7800
series regulators. It is most likely to occur when the power system
input voltage is relatively high and the load impedance is relatively
low.
STABILITY
The output capacitor is part of the regulator’s frequency compen-
sation system. Many types of capacitors are available, with different
capacitance value tolerances, capacitance temperature coefficients,
and equivalent series impedances. For all operating conditions,
connection of a 220µF aluminum electrolytic capacitor or a 47µF
solid tantalum capacitor between the output terminal and ground
will guarantee stable operation.
If a bypass capacitor is connected between the output voltage
adjust (ADJ) pin and ground, ripple rejection will be improved
(please see the section entitled “RIPPLE REJECTION”). When ADJ
pinbypassingisused,therequiredoutputcapacitorvalueincreases.
Output capacitor values of 220µF (aluminum) or 47µF (tantalum)
provide for all cases of bypassing the ADJ pin. If an ADJ pin bypass
capacitor is not used, smaller output capacitor values are adequate.
Thetablebelowshowsrecommendedminimumcapacitancevalues
for stable operation.
When the power system is started “cold”, both the input and
output voltages are very close to zero. The output voltage closely
follows the rising input voltage, and the input-to-output voltage
difference is small. The SOA circuit therefore permits the regulator
to supply large amounts of current as needed to develop the
designed voltage level at the regulator output. Now consider the
casewheretheregulatorissupplyingregulatedvoltagetoaresistive
load under steady state conditions. A moderate input-to-output
voltage appears across the regulator but the voltage difference is
small enough that the SOA circuitry allows sufficient current to flow
throughtheregulatortodevelopthedesignedoutputvoltageacross
theloadresistance. Iftheoutputresistorisshort-circuitedtoground,
theinput-to-outputvoltagedifferenceacrosstheregulatorsuddenly
becomes larger by the amount of voltage that had appeared across
the load resistor. The SOA circuit reads the increased input-to-
output voltage, and cuts back the amount of current that it will
permittheregulatortosupplytoitsoutputterminal. Whentheshort
circuit across the output resistor is removed, all the regulator output
current will again flow through the output resistor. The maximum
current that the regulator can supply to the resistor will be limited
bytheSOAcircuit,basedonthelargeinput-to-outputvoltageacross
theregulatoratthetimetheshortcircuitisremovedfromtheoutput.
RECOMMENDED CAPACITOR VALUES
INPUT
OUTPUT
ADJ
None
15µF
10µF
10µF
15µF Tantalum, 100µF Aluminum
47µF Tantalum, 220µF Aluminum
In order to ensure good transient response from the power supply
system under rapidly changing current load conditions, designers
generally use several output capacitors connected in parallel. Such
an arrangement serves to minimize the effects of the parasitic
resistance (ESR) and inductance (ESL) that are present in all
capacitors. Cost-effective solutions that sufficiently limit ESR and
ESL effects generally result in total capacitance values in the range
of hundreds to thousands of microfarads, which is more than
adequate to meet regulator output capacitor specifications. Output
capacitance values may be increased without limit.
ThecircuitshowninFigure1canbeusedtoobservethetransient
response characteristics of the regulator in a power system under
changing loads. The effects of different capacitor types and values
on transient response parameters, such as overshoot and under-
shoot, can be quickly compared in order to develop an optimum
solution.
Copyright © 1999
Rev. 1.4 3/99
6
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS
P R O D U C T I O N D A T A S H E E T
APPLICATION NOTES
OVERLOAD RECOVERY (continued)
If this limited current is not sufficient to develop the designed
voltage across the output resistor, the voltage will stabilize at some
lower value, and willnever reach the designed value. Under these
circumstances, it may be necessary to cycle the input voltage down
to zero in order to make the regulator output voltage return to
regulation.
LX8117-xx
OUT
IN
VIN
VOUT
ADJ
VREF
R1
R2
IADJ
50µA
RIPPLE REJECTION
R2
R1
VOUT = VREF 1 +
+ IADJ R2
Ripple rejection can be improved by connecting a capacitor
betweentheADJpinandground. Thevalueofthecapacitorshould
be chosen so that the impedance of the capacitor is equal in
magnitude to the resistance of R1 at the ripple frequency. The
capacitor value can be determined by using this equation:
FIGURE 2 — BASIC ADJUSTABLE REGULATOR
LOAD REGULATION
C = 1 / (6.28 F R1)
*
*
Because the LX8117 regulators are three-terminal devices, it is not
possible to provide true remote load sensing. Load regulation will
be limited by the resistance of the wire connecting the regulator to
the load. The data sheet specification for load regulation is
measured at the bottom of the package. Negative side sensing is a
true Kelvin connection, with the bottom of the output divider
returned to the negative side of the load. Although it may not be
immediately obvious, best load regulation is obtained when the top
of the resistor divider, (R1), is connected directly to the case of the
regulator, not to the load. This is illustrated in Figure 3. If R1 were
connectedtotheload,theeffectiveresistancebetweentheregulator
and the load would be:
R
where: C ≡ the value of the capacitor in Farads;
select an equal or larger standard value.
FR ≡ the ripple frequency in Hz
R1 ≡ the value of resistor R1 in ohms
At a ripple frequency of 120Hz, with R1 = 100Ω:
C = 1 / (6.28 120Hz 100Ω) = 13.3µF
*
*
The closest equal or larger standard value should be used, in this
case, 15µF.
When an ADJ pin bypass capacitor is used, output ripple
amplitude will be essentially independent of the output voltage. If
an ADJ pin bypass capacitor is not used, output ripple will be
proportional to the ratio of the output voltage to the reference
voltage:
R2+R1
R1
RPeff = RP
*
where: RP ≡ Actual parasitic line resistance.
M = VOUT/VREF
When the circuit is connected as shown in Figure 3, the parasitic
resistance appears as its actual value, rather than the higher RPeff.
where: M ≡ a multiplier for the ripple seen when the
ADJ pin is optimally bypassed.
VREF = 1.25V.
R
ParaPsitic
LX8117-xx
OUT
Line Resistance
For example, if VOUT = 2.5V the output ripple will be:
M = 2.5V/1.25V= 2
IN
VIN
ADJ
Connect
R1 to Case
of Regulator
Output ripple will be twice as bad as it would be if the ADJ pin
were to be bypassed to ground with a properly selected capacitor.
R1
R2
RL
OUTPUT VOLTAGE
Connect
R2
The LX8117 ICs develop a 1.25V reference voltage between the output
and the adjust terminal (See Figure 2). By placing a resistor, R1,
between these two terminals, a constant current is caused to flow
through R1 and down through R2 to set the overall output voltage.
Normally this current is the specified minimum load current of 10mA.
BecauseIADJisverysmallandconstantwhencomparedwiththecurrent
through R1, it represents a small error and can usually be ignored.
to Load
FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION
Copyright © 1999
Rev. 1.4 3/99
7
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS
P R O D U C T I O N D A T A S H E E T
APPLICATION NOTES
LOAD REGULATION (continued)
THERMAL CONSIDERATIONS (continued)
Example
Given: VIN = 5.0V ±5%, VOUT = 2.5V ±3%
Even when the circuit is optimally configured, parasitic resistance
can be a significant source of error. A 100 mil (2.54 mm) wide PC
trace built from 1 oz. copper-clad circuit board material has a
parasitic resistance of about 5 milliohms per inch of its length at
roomtemperature. Ifa3-terminalregulatorusedtosupply2.50volts
is connected by 2 inches of this trace to a load which draws 5 amps
of current, a50 millivoltdrop will appear between theregulatorand
the load. Even when the regulator output voltage is precisely
2.50 volts, the load will only see 2.45 volts, which is a 2% error. It
is important to keep the connection between the regulator output
pin and the load as short as possible, and to use wide traces or
heavy-gauge wire.
IOUT = 0.5A, TA = 55°C, TJ = 125°C
RθJT = 15°C/W, RθTS = 5°C/W
Find: The size of a square area of 1oz. copper circuit-
board trace-foil that will serve as a heatsink,
adequate to maintain the junction temperature of the
LX8117 in the ST (SOT-223) package within
specified limits.
Solution: The junction temperature is:
TJ = PD (RθJT + RθCS + RθSA) + TA
The minimum specified output capacitance for the regulator
should be located near the reglator package. If several capacitors
are used in parallel to construct the power system output capaci-
tance, any capacitors beyond the minimum needed to meet the
specified requirements of the regulator should be located near the
sections of the load that require rapidly-changing amounts of
current. Placing capacitors near the sources of load transients will
help ensure that power system transient response is not impaired
by the effects of trace impedance.
To maintain good load regulation, wide traces should be used on
the input side of the regulator, especially between the input
capacitors and the regulator. Input capacitor ESR must be small
enoughthatthevoltageattheinputpindoesnotdropbelowVIN(MIN)
during transients.
where: PD ≡ Dissipated power.
RθJT ≡ Thermal resistance from the junction to the
mounting tab of the package.
RθTS ≡ Thermal resistance through the interface
between the IC and the surface on which
it is mounted.
RθSA
≡
Thermal resistance from the mounting surface
of the heatsink to ambient.
TS ≡ Heat sink temperature.
TJ TC TS
TA
RqJT
RqCS
RqSA
First, find the maximum allowable thermal resistance of the
heat sink:
VIN (MIN) = VOUT + VDROPOUT (MAX)
PD = [[VIN (1 + Tol )] - [V
(1 - Tol )]] I
*
VOUT OUT
*
*
VIN
OUT
where: VIN (MIN)
VOUT
≡ the lowest allowable instantaneous
voltage at the input pin.
≡ the designed output voltage for the
power supply system.
PD = 1.4W
TJ - TA
RθSA
=
- (RθJT + RθTS) ,
RθSA = 29.6°C/W
PD
VDROPOUT (MAX) ≡ the specified dropout voltage
for the installed regulator.
A test was conducted to determine the thermal characteristics of
1 oz. copper circuit-board trace material. The following equation
describes the observed relationship between the area of a square
copper pad, and the thermal resistance from the tab of a SOT-223
package soldered at the center of the pad to ambient.
THERMAL CONSIDERATIONS
The LX8117 regulators have internal power and thermal limiting
circuitrydesignedtoprotecteachdeviceunderoverloadconditions.
For continuous normal load conditions, however, maximum junc-
tion temperature ratings must not be exceeded. It is important to
give careful consideration to all sources of thermal resistance from
junctiontoambient. Thisincludesjunctiontocase, casetoheatsink
interface, and heat sink thermal resistance itself.
3.1°C/W
AreaSINK
=
in2
RθSA - 22.3°C/W
Substituting the value for RθSA calculated above, we find that a
square pad with area:
AreaSINK = 0.43 in2 (0.66" x 0.66"), 280mm2 (17 x 17 mm)
will be required to maintain the LX8117 junction temperature
within specified limits.
Copyright © 1999
Rev. 1.4 3/99
8
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS
P R O D U C T I O N D A T A S H E E T
TYPICAL APPLICATIONS
LX8117-xx
OUT
LX8117-xx
OUT
VIN
(Note A)
(Note A)
VIN
IN
VOUT**
5V
VOUT
IN
ADJ
R1
121
R1
ADJ
Ω
10µF
121
Ω
C2
100µF
C1*
10µF
1%
150µF
R2
1k
R2
C1
10µF*
* C1 improves ripple rejection.
365
Ω
XC should be
frequency.
≈ R1 at ripple
1%
* Needed if device is far from filter capacitors.
R2
R1
**VOUT = 1.25V 1 +
FIGURE 4 — IMPROVING RIPPLE REJECTION
FIGURE 5 — 1.2V - 8V ADJUSTABLE REGULATOR
LX8117-33
VIN
OUT
IN
3.3V
GND
10µF Tantalum
or 100µF Aluminum
Min. 15µF Tantalum or
100µF Aluminum capacitor.
May be increased without
limit. ESR must be less
than 50mΩ.
FIGURE 6 — FIXED 3.3V OUTPUT REGULATOR
Note A: VIN (MIN) = (Intended VOUT) + (VDROPOUT (MAX)
)
PRODUCTION DATA - Information contained in this document is proprietary to Linfinity, and is current as of publication date. This document
may not be modified in any way without the express written consent of Linfinity. Product processing does not necessarily include testing of
all parameters. Linfinity reserves the right to change the configuration and performance of the product and to discontinue product at any time.
Copyright © 1999
Rev. 1.4 3/99
9
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