Microsemi LX8385B-XXCDT 3a low dropout positive regulator Datasheet

LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
KEY FEATURES
DESCRIPTION
The LX8385/85A/85B Series devices are
pin-compatible with earlier 3-terminal
regulators, such as the 117 series products,
but they do require input and output
capacitors. A minimum 10µF capacitor is
required on the input and a 15µF or greater
on the output of these new devices for
stability. Although, these capacitors are
generally included in most regulator designs.
The LX8385/85A/85B Series quiescent
current flows into the load, thereby
increasing efficiency. This feature contrasts
with PNP regulators where up to 10% of the
output current is wasted as quiescent
current.
The LX8385-xxI is specified over the
industrial temperature range of -25°C to
125°C, while the LX8385-xxC / 85A-xxC /
85B-xxC is specified over the commercial
range of 0°C to 125°C.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
PRODUCT HIGHLIGHT
IN
5V
LX8385A
OUT
3.3V
at 3A
+
*1500µF
6MV1500GX
Sanyo
121 Ω
1%
ADJ
+
1500µF
2x 6MV1500GX
Sanyo
200 Ω
1%
ƒ Three-Terminal Adjustable Or
Fixed Output
ƒ Guaranteed 1% Voltage
Reference Accuracy Over Line,
Load, And Temperature
(LX8385B)
ƒ Guaranteed < 1.5V Headroom At
3A (LX8385)
ƒ Guaranteed < 1.3V Headroom At
3A (LX8385A/8385B)
ƒ 0.015% Line Regulation
ƒ 0.15% Load Regulation
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The LX8385/85A/85B Series ICs are
positive regulators designed to provide 3A
output current. These regulators yield
higher efficiency than currently available
devices with all internal circuitry designed
to operate down to a 1V input-to-output
differential. In each of these products, the
dropout voltage is fully specified as a
function of load current. Dropout is
guaranteed at a maximum of 1.3V
(8385A/B) and 1.5V (8385) at maximum
output current, decreasing at lower load
currents.
In addition, on-chip trimming adjusts the
reference voltage tolerance to 1% maximum
at room temperature and 2% maximum over
the 0 to 125°C range for the LX8385A. The
LX8385B offers 0.8% tolerance at room
temperature and 1.0% maximum over line,
load and temperature. Fixed versions are
also available and specified in the Available
Options table below.
APPLICATIONS
ƒ High Efficiency Linear
Regulators
ƒ Post Regulators For Switching
Power Supplies
ƒ Battery Chargers
ƒ Constant Current Regulators
ƒ Graphics & Standard Supplies
ƒ Processor I/O Supply
ƒ Low Voltage Memory & Chipset
Supplies
PART #
OUTPUT
VOLTAGE
LX8385/85A/85B-00
Adjustable
LX8385/85A/85B-33
3.3V
LX8385/85A/85B-05
5.0V
Table 1 - Available Options
0 to 125
-25 to 125
2.0%
2.0%
1.0%
2.0%
1.5V
1.3V
1.3V
1.5V
DD
LX8385X
TA (°C)
PACKAGE ORDER INFO
Plastic TO-220
Plastic TO-252
Max Ref Max Dropout DT (D-Pak) 3-Pin
P 3-Pin
Accuracy
Voltage
RoHS Compliant
RoHS Compliant
Plastic TO-263
3-Pin
Transition DC: 0532
Transition DC: 0543
RoHS Compliant
Transition DC: 0535
LX8385-xxCDT
LX8385A-xxCDT
LX8385B-xxCDT
LX8385-xxIDT
LX8385-xxCP
LX8385A-xxCP
LX8385B-xxCP
LX8385-xxIP
LX8385-xxCDD
LX8385A-xxCDD
LX8385B-xxCDD
LX8385-xxIDD
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX8385-xxCP-TR)
Copyright © 2000
Rev. 2.0b, 2005-10-25
Microsemi Inc.
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
PACKAGE PIN OUT
Power Dissipation ................................................................................... Internally Limited
Input Voltage ................................................................................................................ 10V
Input to Output Voltage Differential............................................................................. 10V
Operating Junction Temperature................................................................................ 150°C
Storage Temperature Range....................................................................... -65°C to 150 °C
Peak Package Solder Reflow Temp (40 seconds max. exposure) .................260°C (+0, -5)
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ABSOLUTE MAXIMUM RATINGS (NOTE 1)
TAB is V OUT
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 specified terminal.
3
V IN
2
V OUT
1
ADJ /
GND*
DD PACKAGE (3-PIN)
(Top View)
TAB is V OUT
V IN
3
THERMAL DATA
2
DD
Plastic TO-263 3-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
ADJ/
GND*
1
60°C/W
2.7°C/W
DT PACKAGE (3-PIN)
(Top View)
TAB is V OUT
P
Plastic TO-220 3-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
V OUT
60°C/W
2.7°C/W
3
V IN
2
V OUT
ADJ /
GND*
1
DT
Plastic TO-252 3-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
60°C/W
2.7°C/W
P PACKAGE (3-PIN)
(Top View)
*Pin 1 is GND for fixed voltage versions
Junction Temperature Calculation: TJ = TA + (PD x θJT).
The θJA & θJT numbers are guidelines for the thermal performance of the device/pc-board
system. All of the above assume no ambient airflow.
RoHS 100% Matte Tin Lead Finish
BLOCK DIAGRAM
V IN
Bias Circuit
Bandgap
Circuit
Control
Circuit
Output
Circuit
SOA
Protection
Circuit
ADJ or
GND*
PACKAGE DATA
Therm al
Lim it Circuit
V OUT
Current
Lim it Circuit
*Pin 1 is GND for fixed voltage versions
Copyright © 2000
Rev. 2.0b, 2005-10-25
Microsemi Inc.
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
ELECTRICAL CHARACTERISTICS
Parameter
`
Symbol
Min
LX8385x-xx
Typ
Max
Units
LX8385-00 / 8385A-00 / 8385B-00 (ADJUSTABLE)
Reference Voltage
(Note 4)
LX8385/85A-00
VREF
LX8385B-00
Line Regulation (Note 2)
Load Regulation (Note 2)
Thermal Regulation
Δ VREF
(VIN)
Δ VREF
(IOUT)
ΔVOUT
(Pwr)
Adjust Pin Current
1.238
1.250
1.262
V
1.225
1.250
1.270
V
1.240
1.250
1.260
V
1.238
1.250
1.262
V
1.5V < (VIN -VOUT), VIN < 7V, IOUT = 10mA
0.015
0.2
%
VOUT > VREF, VIN - VOUT = 3V,
10mA < IOUT < 3A
0.15
0.5
%
TA = 25°C, 20ms pulse
0.01
0.04
%/W
65
IADJ
Adjust Pin Current Change (Note 4)
Dropout Voltage
IOUT = 10mA, TA = 25°C
10mA < IOUT < 3A, 1.5V < (VIN -VOUT),
VIN < 10V, P < PMAX
IOUT = 10mA, TA = 25°C
10mA < IOUT < 3A, 1.5V < (VIN -VOUT),
VIN < 10V, P < PMAX
VOUT = 5V, f= 120Hz, COUT = 100µF Tantalum,
VIN = 6.5V, CADJ = 10µF, IOUT = 3A
Ripple Rejection (Note 3)
LX8385-00
LX8385A/85B-00
Minimum Load Current
`
Test Conditions
ΔIADJ
ΔV
IOUT(MIN)
55
100
µA
0.2
5
µA
ΔVREF = 1%, IOUT = 3A
1.2
1.5
V
ΔVREF = 1%, IOUT = 3A
1.1
1.3
V
2
10
mA
1
%
VIN < 10V
IOUT(MAX)
(VIN - VOUT) < 7V, VIN < 10V
Long Term Stability (Note 3)
ΔVOUT(t)
TA = 125°C, 1000 hours
3
VOUT
LX8385B-33
Load Regulation (note 2)
Thermal Regulation
ΔVOUT
(VIN)
ΔVOUT
(IOUT)
ΔVOUT
(Pwr)
Ripple Rejection (note 3)
Quiescent Current
Dropout Voltage
LX8385A/85B-33
Copyright © 2000
Rev. 2.0b, 2005-10-25
ΔV
0.25
%
0.003
%
VIN = 5V, IOUT = 0mA, TA = 25°C
3.267
3.3
3.333
V
4.75V < VIN < 10V, 0mA < IOUT < 3A, P < PMAX
3.235
3.3
3.365
V
VIN = 5V, IOUT = 0mA, TA = 25°C
3.274
3.3
3.326
V
4.75V < VIN < 10V, 0A < IOUT < 3A, P < PMAX
3.267
3.3
3.333
V
4.75V < VIN < 7V
1
6
mV
4.75V < VIN < 10V
2
10
mV
VIN = 5V, 0mA < IOUT < IOUT(MAX)
5
15
mV
0.01
0.02
%/W
TA = 25°C, 20ms pulse
COUT = 100µF (Tantalum), IOUT = 3A
IQ
LX8385-33
A
60
0mA < IOUT < IOUT(MAX), 4.75V < V < 10V
83
dB
4
10
mA
ΔVOUT = 1%, IOUT < IOUT(MAX)
1.2
1.5
V
ΔVOUT = 1%, IOUT < IOUT(MAX)
1.1
1.3
V
Microsemi Inc.
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
ELECTRICALS
Line Regulation (note 2)
3.5
0.3
Temperature Stability (Note 3)
ΔVOUT(T)
RMS Output Noise (% of VOUT)
ΔVOUT(RMS) TA = 25°C, 10Hz < f < 10kHz
(Note 3)
LX8385-33/ 8385A-33/ 8385B-33 (3.3V FIXED)
LX8385/85A-33
dB
10mA < IOUT < IOUT(MAX), 1.5V < (VIN -VOUT), VIN<10V
Maximum Output Current
Output Voltage
(Note 4)
83
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Unless otherwise specified, the following specifications apply over the operating ambient temperature for the LX8385x-xxC with
0°C ≤ TA ≤ 125°C and the LX8385-xxI with -25°C ≤ TA ≤ 125°C except where otherwise noted. Test conditions: VIN -VOUT = 3V;
IOUT = 3A. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient
temperature.
LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
ELECTRICAL CHARACTERISTICS (CONTINUED)
Parameter
`
`
Symbol
Test Conditions
Min
LX8385x-xx
Typ
Max
Units
LX8385-33 / 8385A-33 / 8385B- (3.3V FIXED)(CONTINUED)
Maximum Output Current
IOUT(MAX)
VIN < 7V
Temperature Stability (Note 3)
ΔVOUT(T)
Long Term Stability (Note 3)
ΔVOUT (t)
TA=125°C, 1000 hours
RMS Output Noise (% of VOUT)
(Note 3)
VOUT (RMS)
TA=25°C, 10Hz < f < 10kHz
3
3.5
A
0.25
0.3
%
1
0.003
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Unless otherwise specified, the following specifications apply over the operating ambient temperature for the LX8385x-xxC with
0°C ≤ TA ≤ 125°C and the LX8385-xxI with -25°C ≤ TA ≤ 125°C except where otherwise noted. Test conditions: VIN -VOUT = 3V;
IOUT = 3A. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient
temperature.
%
%
LX8385-05 / 8385A-05 / 8385B-05 (5.0V FIXED)
Output Voltage
(Note 4)
LX8385/85A-05
VOUT
LX8385B-05
Line Regulation (Note 2)
Load Regulation (Note 2)
Thermal Regulation
Dropout Voltage
ΔVOUT
(IOUT)
ΔVOUT
(Pwr)
LX8385A/85B-33
Maximum Output Current
5.00
5.050
V
4.900
5.00
5.100
V
VIN=7V, IOUT=0mA, TA=25°C
4.960
5.00
5.040
V
7V < VIN < 10V, 0mA < IOUT < 3A, P < PMAX
4.950
5.00
5.050
V
2
10
mV
5
25
mV
0.01
0.02
%/W
4
10
mA
ΔVOUT=1%, IOUT < IOUT(MAX)
1.2
1.5
V
ΔVOUT=1%, IOUT < IOUT(MAX)
1.1
1.3
V
VIN=7V, 0mA < IOUT < IOUT(MAX)
TA=25°C, 20ms pulse
COUT=100µF (Tantalum), IOUT=3A
IQ
LX8385-33
4.950
7V < VIN < 10V, 0mA < IOUT < 3A, P < PMAX
ΔVOUT(VIN) 7V < VIN < 10V
Ripple Rejection (Note 3)
Quiescent Current
VIN=7V, IOUT=0mA, TA=25°C
ΔV
IOUT(MAX)
VIN < 10V
Temperature Stability (Note 3)
ΔVOUT (T)
Long Term Stability (Note 3)
ΔVOUT (t)
TA=125°C, 1000 hours
RMS Output Noise (% of VOUT)
(Note 3)
VOUT (RMS)
TA=25°C, 10Hz < f < 10kHz
Note 2
3
83
dB
3.5
A
0.25
%
0.3
1
0.003
%
%
Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output
voltage due to heating effects are covered under the specification for thermal regulation.
These parameters, although guaranteed are not tested in production.
See Maximum Output Current Section
Copyright © 2000
Rev. 2.0b, 2005-10-25
Microsemi Inc.
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
ELECTRICALS
Note 3
Note 4
60
0mA < IOUT < IOUT(MAX), 4.75V < VIN < 10V
Page 4
LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
APPLICATION NOTES
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 (<400mΩ ESR) 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 operation.
Minimum Capacitor Values
INPUT
10µF
10µF
OUTPUT
15µF Tantalum, 100µF Aluminum
47µF Tantalum, 220µF Aluminum
ADJ
None
15µF
Copyright © 2000
Rev. 2.0b, 2005-10-25
IN
LX8385x
OUT
Minim um Load
(Larger resistor)
Full Load
(Sm aller
resistor)
ADJ
R DSON << R L
Star Ground
10m s
1 sec
FIGURE 1 - DYNAMIC INPUT AND OUTPUT TEST
OVERLOAD RECOVERY
Like almost all IC power regulators, the LX8385/85A/85B
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 LX8385/85A/85B 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.
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 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-to-output
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
Microsemi Inc.
Integrated Products Division
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Page 5
APPLICATIONS
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 under-shoot, can be compared quickly in order to
develop an optimum solution.
Power
Supply
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The LX8385/85A/85B Series ICs are easy to use LowDropout (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
LX8385/85A/85B 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.
LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
APPLICATION NOTES (CONTINUED)
where:
1
(6.28 × FR × R1)
≡ 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
C=
1
= 13.3μF
(6.28 × 120Hz ×100Ω )
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=
where:
VOUT
VREF
≡ a multiplier for the ripple seen when the
ADJ pin is optimally bypassed.
VREF = 1.25V
For example, if VOUT = 2.5V the output ripple will be:
M
⎛
R2 ⎞
⎝
R1 ⎠
VOUT = V REF ⎜⎜ 1 +
⎟ + I ADJ R 2
FIGURE 2 - BASIC ADJUSTABLE REGULATOR
LOAD REGULATION
Because the LX8385/85A/85B 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:
⎛ R 2 + R1 ⎞
RPeff = RP × ⎜
⎟
⎝ R1 ⎠
where:
RP ≡ Actual parasitic line resistance.
When the circuit is connected as shown in Figure 3, the
parasitic resistance appears as its actual value, rather than the
higher RPeff.
IN
LX8385x
ADJ
O UT
R1
R P Parasitic Line
Resistance
Connect R1 to
Case of Regulator
RL
R2
Connect R2 to
Load
FIGURE 3 - CONNECTIONS FOR BEST LOAD REGULATION
Microsemi Inc.
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Page 6
APPLICATIONS
Copyright © 2000
Rev. 2.0b, 2005-10-25
R1
R2
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 LX8385/85A/85B 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 IADJ is very small and
constant when compared with the current through R1, it
represents a small error and can usually be ignored.
V REF
V OUT
I ADJ
50µA
V IN
2 .5 V
M =
=2
1.25V
OUT
LX8385x
ADJ
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=
IN
V IN
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OVERLOAD RECOVERY (continued)
voltage across the regulator at the time the short circuit is
removed from the output. 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.
LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
APPLICATION NOTES (CONTINUED)
Even when the circuit is configured optimally, parasitic
resistance can be a significant source of error. A 20 mil. wide PC
trace built from 1 oz. copper-clad circuit board material has a
parasitic resistance of about 25 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
1.5 amps of current, a 75 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 2.43 volts, which is a
3% 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 regulator 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
VIN(MIN) during transients.
VΙΝ(ΜΙΝ) = VOUT + VDROPOUT(MAX)
≡ the lowest allowable instantaneous
voltage at the input pin.
VOUT
≡ the designed output voltage for the
power supply system.
VDROPOUT(MAX) ≡ the specified dropout voltage for the
installed regulator.
where: VIN(MIN)
Copyright © 2000
Rev. 2.0b, 2005-10-25
Find:
VIN
VOUT
IOUT
TA
RθJT
=
=
=
=
=
5V
2.5V
1.5A
50°C
2.7°C/W for TO-220
Proper Heat Sink to keep IC’s junction temperature
below 125°C.**
Solution: The junction temperature is:
TJ = PD (R θJT + R θCS + R θSA ) + TA
where: PD
RθJT
≡
≡
RθCS
≡
RθSA
≡
TS
≡
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.
(1.0°C/W at 6 in-lbs mounting screw
torque).
Thermal resistance from the mounting
surface to ambient (thermal resistance
of the heat sink).
Heat Sink Temperature.
TJ
TC
R θ JT
TS
R θ CS
TA
R θ SA
First, find the maximum allowable thermal resistance of the
heat sink:
R θSA =
TJ − TA
− (R θJT + R θCS )
PD
PD = (VIN(MAX) − VOUT ) I OUT = (5.0V − 2.5V ) × 1.5A
PD = 3.75W
R θSA =
125°C − 50°C
− (2.7°C/W + 1.0°C/W)
(5.0V − 2.5V) * 1.5A
R θSA = 16.3°C/W
Next, select a suitable heat sink. The selected heat sink must
have RθSA < 3.1°C/W. Thermalloy heatsink 6230B has RθSA =
12°C/W.
Finally, verify that junction temperature remains within specification using the selected heat sink:
TJ = 3.75W(2.7°C/W + 1.0°C/W + 12.0°C/W) + 50°C
TJ = 109°C
** Although the device can operate up to 150°C junction, it is recommended for long
term reliability to keep the junction temperature below 125°C whenever possible.
Microsemi Inc.
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
APPLICATIONS
THERMAL CONSIDERATIONS
The LX8385/85A/85B 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.
Junction-to-case thermal resistance is specified from the IC
junction to the back surface of the case directly opposite the die.
This is the lowest resistance path for heat flow. Proper mounting
is required to ensure the best possible thermal flow from this area
of the package to the heat sink. Thermal compound at the case to
heat sink interface is strongly recommended. If the case of the
device must be electrically isolated, a thermally conductive
spacer can be used, as long as its added contribution to thermal
resistance is considered. Note that the case of all devices in this
series is electrically connected to the output.
Example
Given:
WWW . Microsemi .C OM
LOAD REGULATION (continued)
LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
TYPICAL APPLICATIONS
LX8385x
V IN
IN
V IN
(Note A)
OUT
LX8385x
C1*
10µF
V OUT
R1
121 Ω 1%
ADJ
R1
121 Ω 1%
ADJ
V OUT **
+
+
10µF
OUT
+
C2
100µF
150µF
+
R2
365 Ω 1%
R2
1k
C1
10µF*
* C1 im proves ripple rejection.
X C should be ≈ R1 at ripple
frequency.
WWW . Microsemi .C OM
IN
(Note A)
* Needed if device is far from filter capacitors.
⎛
FIGURE 4 - IMPROVING RIPPLE REJECTION
* *VOUT = 1.25V ⎜ 1 +
⎝
⎞
⎟
R1 ⎠
R2
FIGURE 5 - 1.2V - 8V ADJUSTABLE REGULATOR
IN
V IN
(note A)
LX8385x
OUT
+
10µF
5V
121 Ω
1%
ADJ
+
1k
100µF
2N3904
TTL
Output
365 Ω
1%
1k
FIGURE 6 - 5V REGULATOR W ITH SHUTDOW N
10µF Tantalum or
100µF Alum inum
LX8385x
O UT
ADJ
APPLICATIONS
IN
V IN
3.3V
Min. 15µF Tantalum or
100µF Alum inum capacitor. May
be increased without lim it. ESR
m ust be less than <400m Ω .
FIGURE 7 - FIXED 3.3V OUTPUT REGULATOR
Note A:
VIN(MIN) = (Intended VOUT ) + VDROPOUT(MAX)
Copyright © 2000
Rev. 2.0b, 2005-10-25
Microsemi Inc.
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
P
WWW . Microsemi .C OM
PACKAGE DIMENSIONS
3-Pin Plastic TO-220
B
S
F
Dim
T
Q
A
B
C
D
F
G
H
J
K
L
N
Q
R
S
T
U
U
A
1
2
C
3
R
H
K
D
L
J
G
N
DD
MILLIMETERS
MIN
MAX
14.22
15.88
9.65
10.67
3.56
4.83
0.51
1.14
3.53
4.09
2.54 BSC
6.35
0.30
1.14
12.70
14.73
1.14
1.27
5.08 TYP
2.54
3.05
2.03
2.92
1.14
1.40
5.84
6.86
0.508
1.14
INCHES
MIN
MAX
0.560
0.625
0.380
0.420
0.140
0.190
0.020
0.045
0.139
0.161
0.100 BSC
0.250
0.012
0.045
0.500
0.580
0.045
0.050
0.200 TYP
0.100
0.120
0.080
0.115
0.045
0.055
0.230
0.270
0.020
0.045
MILLIMETERS
MIN
MAX
10.03
10.67
8.51
9.17
4.19
4.59
1.14
1.40
0.330
0.51
1.19
1.34
2.41
2.66
2.29
2.79
–
1.65
0
0.25
14.60
15.87
7°
3°
INCHES
MIN
MAX
0.395
0.420
0.335
0.361
0.165
0.181
0.045
0.055
0.013
0.020
0.047
0.053
0.095
0.104
0.090
0.110
–
0.065
0
0.010
0.575
0.625
7°
3°
3-Pin Plastic TO-263
I
A
Dim
D
C
B
K
M
N
H
G
0° -8°
J
Seating Plane
MECHANICALS
E
F
A
B
C
D
E
F
G
H
I
J
K
M
N
Note: Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006”) on any side. Lead dimension shall
not include solder coverage.
Copyright © 2000
Rev. 2.0b, 2005-10-25
Microsemi Inc.
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
LX8385x-xx
®
TM
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
DT
WWW . Microsemi .C OM
PACKAGE DIMENSIONS
3-Pin Plastic TO-252
P
U
J
Dim
G
N
W
L
A
F
Q
O
V
0.23
M
H
C
R
D
E
B
X
I
K
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
U
V
W
X
MILLIMETERS
MIN
MAX
6.47
6.73
5.97
6.23
2.16
2.42
0.68
0.94
0.38
0.64
0.63
0.89
2.16
2.42
0.84
1.10
0.89
1.15
2.44
2.70
9.55
9.81
5.20
5.46
7.0°
0.51
0.77
0.51
0.77
4.19
4.45
0.76
1.02
0.48
0.74
0.51
0.77
45°
1.44
1.70
0
0.10
INCHES
MIN
MAX
0.255
0.265
0.235
0.245
0.085
0.095
0.027
0.037
0.015
0.025
0.025
0.035
0.085
0.095
0.033
0.043
0.035
0.045
0.096
0.106
0.376
0.386
0.205
0.215
7.0°
0.020
0.030
0.020
0.030
0.165
0.175
0.030
0.040
0.019
0.029
0.020
0.030
45°
0.057
0.067
0
0.004
MECHANICALS
Copyright © 2000
Rev. 2.0b, 2005-10-25
Microsemi Inc.
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 10
LX8385x-xx
TM
®
3A Low Dropout Positive Regulators
P RODUCTION D ATA S HEET
WWW . Microsemi .C OM
NOTES
NOTES
PRODUCTION DATA – Information contained in this document is proprietary to
Microsemi and is current as of publication date. This document may not be modified in
any way without the express written consent of Microsemi. Product processing does not
necessarily include testing of all parameters. Microsemi reserves the right to change the
configuration and performance of the product and to discontinue product at any time.
Copyright © 2000
Rev. 2.0b, 2005-10-25
Microsemi Inc.
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 11