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LX8117B-05CDT

Datasheet LX8117B-05CDT, LX8117B-05CDD, LX8117B-00CST, LX8117B-00CDT, LX8117B-00CDD Datasheet (Microsemi Corporation)

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LIN DOC #:
8117
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A L OW DROPOUT POSITIVE REGULATORS
T HE I NFINITE P OWER OF I NNOVATION
DESCRIPTION KEY FEATURES
The LX8117/8117A/8117B series are positive Low Dropout (LDO) regulators. At the designed maximum load current, the LX8117 series dropout voltage is guar­anteed 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 trimming of the internal voltage reference 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
NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.
PRODUCT HIGHLIGHT
operate at input-to-output differential voltages down to 1V.
Most regulator circuit designs include output capacitors with values in the range of tens to hundreds of microfarads or more. The LX8117/17A/17B typically requires at least 10µF of output capaci­tance 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-use efficiency and allowing cooler operation.
The LX8117 is available in low-profile plastic SOT-223 and D-Pak packages for applications where space is at a premium. 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.
ACTIVE TERMINATOR FOR SCSI-2 BUS
110
Ω
110
Ω
P RODUCTION DATA SHEET
■ 0.2% Line Regulation Maximum
■ 0.4% Load Regulation Maximum
■ Output Current Of 800mA
■ Regulates Down To 1.2V Dropout
(LX8117) And 1.3V Dropout (LX8117A)
■ 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 #
Part #
LX8117/8117A/8117B-00 Adjustable LX8117/8117A/8117B-25 2.5V LX8117/8117A/8117B-28 2.85V LX8117/8117A/8117B-33 3.3V LX8117/8117A/8117B-05 5V
Output
Voltage
4.75V to
5.25V
Copyright © 1999 Rev. 1.4 3/99
LX8117-28
OUTIN
110
Ω
18 to 27 Lines
GND
10µF
PACKAGE ORDER INFORMATION
T
(°C)
A
0 to 125 1.0A LX8117A-xxCST LX8117A-xxCDD LX8117A-xxCDT
Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number
O/P
Current
0.8A LX8117-xxCST LX8117-xxCDD LX8117-xxCDT
1.2A LX8117B-xxCST LX8117B-xxCDD LX8117B-xxCDT
(i.e. LX8117-28CSTT). "xx" refers to output voltage, please see table above.
ST
22µF
Plastic SOT-223 3-pin
110
DD
Ω
Plastic T0-263 3-pin
Plastic T0-252
DT
(D-Pak) 3-pin
L INF INITY MICROELECTRONICS INC.
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
1
PRODUCT DATABOOK 1996/1997
A
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A L OW DROPOUT POSITIVE REGULATORS
RODUCTION DATA SHEET
P
ABSOLUTE MAXIMUM RATINGS (Note 1)
Power Dissipation .................................................................................. Internally Limited
Input Voltage
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
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
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.
THERMAL DATA
ST PACKAGE:
THERMAL RESISTANCE-JUNCTION TO TAB,
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
DD PACKAGE:
THERMAL RESISTANCE-JUNCTION TO TAB,
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
DT PACKAGE:
THERMAL RESISTANCE-JUNCTION TO TAB,
THERMAL RESISTANCE-JUNCTION TO AMBIENT,
Junction Temperature Calculation: TJ = TA + (P thermal performance of the device/pc-board system. All of the above assume no ambient airflow.
* θ
can be improved with package soldered to 0.5IN2 copper area over backside ground
JA
plane or internal power plane. θ mounting technique. (See Application Notes Section: Thermal Considerations)
can vary from 20ºC/W to > 40ºC/W depending on
JA
θθ
θ
θθ
JT
θθ
θ
θθ
JA
θθ
θ
θθ
JT
θθ
θ
θθ
JA
θθ
θ
θθ
JC
θθ
θ
θθ
JA
x θJA). The θ
D
15°C/W
*150°C/W
10°C/W
*60°C/W
9°C/W
*80°C/W
numbers are guidelines for the
JA
PACKAGE PIN OUTS
TAB IS V
OUT
3. IN
2. OUT
1. ADJ / GND
ST PACKAGE
(Top View)
TAB IS V
OUT
3
IN
2
OUT
1
ADJ / GND
DD PACKAGE (D2 Pak)
(Top View)
TAB IS V
OUT
3. IN
2. OUT
1. ADJ / GND
DT PACKAGE (D-Pak)
(Top View)
BLOCK DIAGRAM
V
IN
Bias
Circuit
Thermal
Limit Circuit
Bandgap
Circuit
Control
Circuit
DJ
2
Output
Circuit
Current
Limit Circuit
V
OUT
Copyright © 1999
Rev. 1.4 3/99
PRODUCT DATABOOK 1996/1997
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A L OW DROPOUT POSITIVE REGULATORS
P RODUCTION DATA SHEET
RECOMMENDED OPERATING CONDITIONS (Note 2)
Parameter
Symbol
Input Voltage
Operating Voltage LX8117(A/B)-00 / 8117(A/B)-05
LX8117(A/B)-25 / -28 / -33
Input-Output Differential LX8117(A/B)-00 Operating Ambient Temperature Range
Note 2. Range over which the device is functional.
ELECTRICAL CHARACTERISTICS
(Unless otherwise specified: 0°C ≤ TJ ≤ 125°C, I
= 0.8A for the LX8117-xx, I
MAX
= 1.0A for the LX8117A-xx, and I
MAX
LX8117-00 / 8117A-00 / 8117B-00 (Adjustable)
Parameter
Reference Voltage V
Line Regulation (Note 3) Load Regulation (Note 3)
Dropout Voltage ∆VI
(Note 4)
LX8117-00 I
LX8117A/B-00 I
Current Limit LX8117-00 I
LX8117A-00 (VIN - V
LX8117B-00 (VIN - V Minimum Load Current (Note 5) I
Thermal Regulation
Ripple Rejection f Adjust Pin Current I
Adjust Pin Current Change ∆I Temperature Stability ∆V Long Term Stability ∆V
RMS Output Noise (% of V
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.
)V
OUT
Symbol
REFIOUT
∆V
REF(VIN
∆V
REF(IOUT
OUT (MAX)(VIN
OUT (MIN)VIN
∆V
(Pwr)
OUT
ADJ
ADJ
OUT
OUT
OUT (RMS)
= 10mA, (VIN - V
10mA ≤ I
)
I
)
(VIN - V
I
OUT
= 10mA, 1.5V ≤ (V
OUT
) = 3V, 10mA ≤ I
OUT
= 100mA
OUT
= 500mA
OUT
= I
OUT
OUT (MAX)
= I
OUT
OUT (MAX)
- V
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
≤ 10V
TA = 25°C, 30ms pulse
=120Hz, (VIN - V
RIPPLE
10mA ≤ I
OUT
(T)
(t) TA = 125°C, 1000 hours
10Hz ≤ f ≤ 10kHz
≤ I
≤ I
Test Conditions Units
) = 2V, TJ = 25°C
OUT
, 1.4V ≤ (V
OUT (MAX)
- V
) ≤ 7V
IN
OUT
≤ I
OUT
OUT (MAX)
) = 3V, V
OUT
, 1.4V ≤ (V
OUT (MAX)
Recommended Operating Conditions
Min. Typ. Max.
0 125 °C
MAX
LX8117 / 17A / 17B-00
- V
) ≤ 10V
IN
OUT
= 1Vp-p
RIPPLE
- V
) ≤ 10V
IN
OUT
Units
15 V
12 V 10 V
= 1.2A for the LX8117B-xx.)
Min. Typ. Max.
1.238 1.250 1.262 V
1.225 1.250 1.270 V
0.05 0.2 %
0.15 0.4 %
0.97 1.10 V
1.00 1.15 V
1.05 1.20 V
1.15 1.30 V
800 950 mA 1000 1200 mA 1200 1500 mA
0.5 5 mA
0.08 0.2 %/W
60 75 dB
45 100 µA
0.2 5 µA
0.5 %
0.3 %
0.003 %
Copyright © 1999 Rev. 1.4 3/99
(Other Voltage Options on following pages.)
3
PRODUCT DATABOOK 1996/1997
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A L OW DROPOUT POSITIVE REGULATORS
RODUCTION DATA SHEET
P
ELECTRICAL CHARACTERISTICS (continued)
LX8117-25 / 8117A-25 / 8117B-25 (2.5V Fixed)
Parameter
Output Voltage V
Line Regulation (Note 3)
Load Regulation (Note 3)
Dropout Voltage ∆VI
(Note 4)
LX8117-25 I
LX8117A/B-25 I
Current Limit LX8117-25 I
LX8117A-25 (VIN - V LX8117B-25 (VIN - V
Quiescent Current I
Thermal Regulation Ripple Rejection f
Temperature Stability ∆V Long Term Stability ∆V
RMS Output Noise (% of V
)V
OUT
Symbol
OUTIOUT
∆V
OUT
∆V
OUT(IOUT
OUT (MAX)(VIN
Q
∆V
(Pwr)
OUT
OUT
OUT
OUT (RMS)
= 10mA, VIN = 5V, TA = 25°C
0mA ≤ I
(VIN)
)
OUT
I
= 0mA, 4.25V ≤ VIN ≤ 10V
OUT
V
= 4.25V, 0mA ≤ I
IN
= 100mA
OUT
I
= 500mA
OUT
= I
OUT
OUT (MAX)
= I
OUT
OUT (MAX)
- V
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
V
≤ 10V
IN
TA = 25°C, 30ms pulse
=120Hz, (VIN - V
RIPPLE
(T)
(t) TA = 125°C, 1000 hours
10Hz ≤ f ≤ 10kHz
≤ I
, 4.75V ≤ VIN ≤ 10V
OUT (MAX)
OUT
OUT
Test Conditions Units
≤ I
OUT (MAX)
) = 3V, V
RIPPLE
= 1Vp-p
LX8117 / 17A / 17B-25
Min. Typ. Max.
2.475 2.500 2.525 V
2.450 2.500 2.550 V 16mV
210mV
0.97 1.10 V
1.00 1.15 V
1.05 1.20 V
1.15 1.30 V
800 950 mA 1000 1200 mA 1200 1500 mA
4.5 10 mA
0.08 0.2 %/W
60 75 dB
0.5 %
0.3 %
0.003 %
LX8117-28 / 8117A-28 / 8117B-28 (2.8V Fixed)
Parameter
Output Voltage V
Line Regulation (Note 3) Load Regulation (Note 3)
Dropout Voltage ∆VI
(Note 4)
LX8117-28 I LX8117A/B-28 I
Current Limit LX8117-28 I
LX8117A-28 (VIN - V
LX8117B-28 (VIN - V Quiescent Current I
Thermal Regulation Ripple Rejection f
Temperature Stability ∆V Long Term Stability ∆V
RMS Output Noise (% of V
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.
)V
OUT
Symbol
OUTIOUT
∆V
OUT
∆V
OUT(IOUT
OUT (MAX)(VIN
Q
∆V
(Pwr)
OUT
OUT
OUT
OUT (RMS)
= 10mA, VIN = 4.85V, TA = 25°C
0mA ≤ I
OUT
0mA ≤ I
(VIN)
)
OUT
I
= 0mA, 4.25V ≤ VIN ≤ 10V
OUT
V
= 4.25V, 0mA ≤ I
IN
= 100mA
OUT
I
= 500mA
OUT
= I
OUT
OUT (MAX)
= I
OUT
OUT (MAX)
- V
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
V
≤ 10V
IN
TA = 25°C, 30ms pulse
=120Hz, (VIN - V
RIPPLE
(T)
(t) TA = 125°C, 1000 hours
10Hz ≤ f ≤ 10kHz
≤ I
OUT (MAX)
≤ 500mA, V
OUT
Test Conditions Units
, 4.25V ≤ VIN ≤ 10V
= 3.95V
IN
≤ I
OUT (MAX)
) = 3V, V
OUT
RIPPLE
= 1Vp-p
LX8117 / 17A / 17B-28
Min. Typ. Max.
2.820 2.850 2.880 V
2.790 2.850 2.910 V
2.790 2.850 2.910 V
16mV 210mV
0.97 1.10 V
1.00 1.15 V
1.05 1.20 V
1.15 1.30 V
800 950 mA 1000 1200 mA
1200 1500 mA
4.5 10 mA
0.08 0.2 %/W
60 75 dB
0.5 %
0.3 %
0.003 %
4
Copyright © 1999
Rev. 1.4 3/99
PRODUCT DATABOOK 1996/1997
0.8, 1 & 1.2A L OW DROPOUT POSITIVE REGULATORS
P RODUCTION DATA SHEET
ELECTRICAL CHARACTERISTICS (continued)
LX8117-33 / 8117A-33 / 8117B-33 (3.3V Fixed)
Parameter
Output Voltage V
Line Regulation (Note 3)
Load Regulation (Note 3)
Dropout Voltage ∆VI
(Note 4)
LX8117-33 I
LX8117A/B-33 I
Current Limit LX8117-33 I
LX8117A-33 (VIN - V LX8117B-33 (VIN - V
Quiescent Current I
Thermal Regulation Ripple Rejection f
Temperature Stability ∆V Long Term Stability ∆V
RMS Output Noise (% of V
)V
OUT
Symbol
OUTIOUT
∆V
OUT
∆V
OUT(IOUT
OUT (MAX)(VIN
Q
∆V
(Pwr)
OUT
OUT
OUT
OUT (RMS)
= 10mA, VIN = 5V, TA = 25°C
0mA ≤ I
(VIN)
I
= 0mA, 4.25V ≤ VIN ≤ 10V
OUT
)
V
= 4.25V, 0mA ≤ I
IN
= 100mA
OUT
I
= 500mA
OUT
= I
OUT
= I
OUT
- V
V
≤ 10V
IN
TA = 25°C, 30ms pulse
=120Hz, (VIN - V
RIPPLE
(T)
(t) TA = 125°C, 1000 hours
10Hz ≤ f ≤ 10kHz
LX8117-xx/8117A-xx/8117B-xx
≤ I
OUT
OUT (MAX)
OUT (MAX)
OUT (MAX)
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
Test Conditions Units
LX8117 / 17A / 17B-33
Min. Typ. Max.
3.267 3.300 3.333 V
, 4.75V ≤ VIN ≤ 10V
3.235 3.300 3.365 V 16mV
OUT
≤ I
OUT (MAX)
210mV
0.97 1.10 V
1.00 1.15 V
1.05 1.20 V
1.15 1.30 V
800 950 mA 1000 1200 mA 1200 1500 mA
4.5 10 mA
0.08 0.2 %/W
) = 3V, V
OUT
RIPPLE
= 1Vp-p
60 75 dB
0.5 %
0.3 %
0.003 %
LX8117-05 / 8117A-05 / 8117B-05 (5.0V Fixed)
Parameter
Output Voltage V
Line Regulation (Note 3)
Load Regulation (Note 3)
Dropout Voltage ∆VI
(Note 4)
LX8117-05 I
LX8117A/B-05 I
Current Limit LX8117-05 I
LX8117A-05 (VIN - V LX8117B-05 (VIN - V
Quiescent Current I
Thermal Regulation Ripple Rejection f
Temperature Stability ∆V Long Term Stability ∆V
RMS Output Noise (% of V
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.
)V
OUT
Symbol
OUTIOUT
∆V
OUT
∆V
OUT(IOUT
OUT (MAX)(VIN
Q
∆V
(Pwr)
OUT
OUT
OUT
OUT (RMS)
= 10mA, VIN = 7V, TA = 25°C
0mA ≤ I
(VIN)
)
OUT
I
= 0mA, 6.5V ≤ VIN ≤ 10V
OUT
V
= 6.5V, 0mA ≤ I
IN
= 100mA
OUT
I
= 500mA
OUT
= I
OUT
OUT (MAX)
= I
OUT
OUT (MAX)
- V
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
) = 5V, TJ = 25°C
OUT
V
≤ 10V
IN
TA = 25°C, 30ms pulse
=120Hz, (VIN - V
RIPPLE
(T)
(t) TA = 125°C, 1000 hours
10Hz ≤ f ≤ 10kHz
≤ I
, 6.50V ≤ VIN ≤ 10V
OUT (MAX)
≤ I
OUT
OUT
Test Conditions Units
OUT (MAX)
) = 3V, V
RIPPLE
= 1Vp-p
LX8117 / 17A / 17B-05
Min. Typ. Max.
4.950 5.000 5.050 V
4.900 5.000 5.100 V 110mV
2.5 15 mV
0.97 1.10 V
1.00 1.15 V
1.05 1.20 V
1.15 1.30 V
800 950 mA 1000 1200 mA 1200 1500 mA
4.5 10 mA
0.08 0.2 %/W
60 75 dB
0.5 %
0.3 %
0.003 %
Copyright © 1999 Rev. 1.4 3/99
5
PRODUCT DATABOOK 1996/1997
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A L OW DROPOUT POSITIVE REGULATORS
RODUCTION DATA SHEET
P
APPLICATION NOTES
The LX8117 series ICs are easy to use Low-Dropout (LDO) voltage 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.
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.
STABILITY
The output capacitor is part of the regulator’s frequency compen­sation 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 pin bypassing is used, the required output capacitor value increases. 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. The table below shows recommended minimum capacitance values for stable operation.
RECOMMENDED CAPACITOR VALUES
INPUT OUTPUT ADJ
10µF 15µF Tantalum, 100µF Aluminum None 10µF 47µF Tantalum, 220µF Aluminum 15µF
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.
The circuit shown in Figure 1 can be used to observe the transient 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 under­shoot, can be quickly compared in order to develop an optimum solution.
Power Supply
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 progres­sively 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.
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.
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 case where the regulator is supplying regulated voltage to a resistive 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 through the regulator to develop the designed output voltage across the load resistance. If the output resistor is short-circuited to ground, the input-to-output voltage difference across the regulator suddenly becomes larger by the amount of voltage that had appeared across the load resistor. The SOA circuit reads the increased input-to­output voltage, and cuts back the amount of current that it will permit the regulator to supply to its output terminal. When the short 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 by the SOA circuit, based on the large input-to-output voltage across the regulator at the time the short circuit is removed from the output.
Minumum Load
IN
LX8117-xx
ADJ
C
1
FIGURE 1 — DYNAMIC INPUT and OUTPUT TEST
OUT
Star Ground
C
2
(Larger resistor)
Full Load (Smaller resistor)
R
<< R
DSON
1 sec
10ms
Under some conditions, a correctly operating SOA circuit may
When the power system is started “cold”, both the input and
L
6
Copyright © 1999
Rev. 1.4 3/99
PRODUCT DATABOOK 1996/1997
LX8117-xx
OUT
IN
ADJ
V
IN
R1
R2
R
L
R
P
Parasitic
Line Resistance
Connect R1 to Case of Regulator
Connect R2 to Load
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A L OW DROPOUT POSITIVE REGULATORS
P RODUCTION DATA SHEET
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 will never 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.
RIPPLE REJECTION
Ripple rejection can be improved by connecting a capacitor between the ADJ pin and ground. The value of the capacitor should 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:
C = 1 / (6.28 * F where: C ≡ the value of the capacitor in Farads;
F R1 ≡ the value of resistor R1 in ohms
At a ripple frequency of 120Hz, with R1 = 100Ω:
C = 1 / (6.28 * 120Hz
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:
M = V
OUT/VREF
where: M ≡ a multiplier for the ripple seen when the
V
For example, if V
M = 2.5V/1.25V= 2
* R1)
R
select an equal or larger standard value.
≡ the ripple frequency in Hz
R
100Ω) = 13.3µF
*
ADJ pin is optimally bypassed.
= 1.25V.
REF
= 2.5V the output ripple will be:
OUT
LX8117-xx
ADJ
OUT
V
OUT
V
R1
REF
V
IN
IN
I
ADJ
50µA
V
= V
OUT
REF
FIGURE 2 — BASIC ADJUSTABLE REGULATOR
R2
1 + + I
R1
ADJ
R2
R2
LOAD REGULATION
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 connected to the load, the effective resistance between the regulator and the load would be:
R2+R1
= RP
R
Peff
where: R

*
R1

≡ Actual parasitic line resistance.
P
When the circuit is connected as shown in Figure 3, the parasitic
resistance appears as its actual value, rather than the higher R
Peff
.
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.
OUTPUT VOLTAGE
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. Because I through R1, it represents a small error and can usually be ignored.
Copyright © 1999 Rev. 1.4 3/99
is very small and constant when compared with the current
ADJ
FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION
7
PRODUCT DATABOOK 1996/1997
T
J
T
C
T
S
T
A
R
q
JT
R
q
CS
R
q
SA
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A L OW DROPOUT POSITIVE REGULATORS
RODUCTION DATA SHEET
P
APPLICATION NOTES
LOAD REGULATION (continued)
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 room temperature. If a 3-terminal regulator used to supply 2.50 volts is connected by 2 inches of this trace to a load which draws 5 amps of current, a 50 millivolt drop will appear between the regulator and 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.
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 capaci­tance, 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 enough that the voltage at the input pin does not drop below V during transients.
V
= V
IN (MIN)
where: V
+ V
OUT
IN (MIN)
V
OUT
V
DROPOUT (MAX)
DROPOUT (MAX)
≡ the lowest allowable instantaneous
voltage at the input pin.
≡ the designed output voltage for the
power supply system.
≡ the specified dropout voltage
for the installed regulator.
IN (MIN)
THERMAL CONSIDERATIONS
The LX8117 regulators have internal power and thermal limiting circuitry designed to protect each device under overload conditions. For continuous normal load conditions, however, maximum junc­tion temperature ratings must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. This includes junction to case, case to heat sink interface, and heat sink thermal resistance itself.
THERMAL CONSIDERATIONS (continued)
Example
Given: V
= 5.0V ±5%, V
IN
= 0.5A, TA = 55°C, TJ = 125°C
I
OUT
R
= 15°C/W, R
θJT
= 2.5V ±3%
OUT
= 5°C/W
θTS
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:
where: P
= PD (R
T
J
D
R
θJT
R
θTS
+ R
+ R
θJT
θCS
θSA
) + T
A
≡ Dissipated power.
≡ Thermal resistance from the junction to the
mounting tab of the package.
≡ Thermal resistance through the interface
between the IC and the surface on which it is mounted.
R
≡
Thermal resistance from the mounting surface
θSA
of the heatsink to ambient.
T
≡ Heat sink temperature.
S
First, find the maximum allowable thermal resistance of the
heat sink:
P
= [[V
D
(1 + Tol
*
IN
VIN
)] - [V
* (1 - Tol
OUT
VOUT
)]] * I
OUT
PD= 1.4W
TJ - T
R
= - (R
θSA
A
P
D
θJT
+ R
) , R
θTS
= 29.6°C/W
θSA
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.
= in
Area
SINK
R
θSA
Substituting the value for R square pad with area:
3.1°C/W
- 22.3°C/W
calculated above, we find that a
θSA
2
Area
= 0.43 in2 (0.66" x 0.66"), 280mm2 (17 x 17 mm)
SINK
will be required to maintain the LX8117 junction temperature within specified limits.
8
Copyright © 1999
Rev. 1.4 3/99
PRODUCT DATABOOK 1996/1997
LX8117-xx
OUT
IN
ADJ
V
OUT
**
V
IN
R1 121
Ω
R2 1k
C1* 10µF
* Needed if device is far from filter capacitors.
** V
OUT
= 1.25V 1 +
C2 100µF
R2 R1
(Note A)
LX8117-xx/8117A-xx/8117B-xx
0.8, 1 & 1.2A L OW DROPOUT POSITIVE REGULATORS
P RODUCTION DATA SHEET
TYPICAL APPLICATIONS
(Note A)
V
IN
10µF
LX8117-xx
IN
ADJ
* C1 improves ripple rejection.
should be ≈ R1 at ripple
X
C
frequency.
or 100µF Aluminum
OUT
R1 121 1%
R2
Ω
365
1%
V
IN
10µF Tantalum
5V
V
OUT
Ω
150µF
C1 10µF*
FIGURE 5 — 1.2V - 8V ADJUSTABLE REGULATORFIGURE 4 — IMPROVING RIPPLE REJECTION
LX8117-33
IN
GND
OUT
3.3V
Min. 15µF Tantalum or 100µF Aluminum capacitor. May be increased without limit. ESR must be less than 50mΩ.
Note A: V
= (Intended V
IN (MIN)
Copyright © 1999 Rev. 1.4 3/99
FIGURE 6 — FIXED 3.3V OUTPUT REGULATOR
OUT
) + (V
DROPOUT (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.
9
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