LX8383-33IV Datasheet PDF - Microsemi Corporation
| Part Number | LX8383-33IV | |
| Description | 7.5 A LOW DROPOUT POSITIVE REGULATORS | |
| Manufacturers | Microsemi Corporation | |
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T H E I N F I N I T E P O W E R O F I N N O VAT I O N
L I N D O C #: 8383
LX8383-xx/8383A-xx/8383B-xx
7.5A LOW DROPOUT POSITIVE REGULATORS
PR O D U C T I O N D ATA S H E E T
DESCRIPTION
The LX8383/8383A/8383B series ICs are
positive regulators designed to provide
7.5A output current. All internal circuitry
is designed to operate down to a 1V in-
put-to-output differential, so the LX8383/
83A/83B can operate with greater effi-
ciency than previously available devices.
The dropout voltage for each product is
fully specified as a function of load cur-
rent. Dropout is guaranteed at a maxi-
mum of 1.3V for the LX8383A/83B and
1.5V for the LX8383, at maximum output
current, decreasing at lower load currents.
Fixed versions are also available and speci-
fied in the Available Options table below.
The LX8383B offers a tighter voltage ref-
erence tolerance: 0.8% initial accuracy and
1% over line, load and temperature. The
LX8383/83A have 1% initial accuracy and
2% over line, load and temperature.
The LX8383/83A/83B series devices are
pin-compatible with earlier 3-terminal
regulators, such as the 117 series prod-
ucts. While a 10µF output capacitor is
required on both input and output of these
new devices, this capacitor is generally
included in most regulator designs.
The LX8383/83A/83B 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 LX8383I/8383AI is
specified over the industrial temperature
range of -25°C to +125°C and the
LX8383C/8383AC/8383BC is specified
over the commercial range of 0°C to
+125°C.
PRODUCT HIGHLIGHT
3.3V, 7.5A RE G U L AT O R
VIN ≥ 4.75V
1500µF
6.3V
6MV1500GX
from Sanyo
IN LX8383A OUT
121Ω
ADJ 1%
205Ω
1%
3.38V at 7.5A
2x 330µF, 6.3V
Oscon SA type
from Sanyo
-or-
3x 1500µF, 6.3V
6MV1500GX
from Sanyo
KEY FEATURES
s THREE-TERMINAL ADJUSTABLE OR FIXED
OUTPUT VOLTAGE
s GUARANTEED < 1.3V HEADROOM AT
7.5A (LX8383A/8383B)
s GUARANTEED < 1.5V HEADROOM AT
7.5A (LX8383)
s OUTPUT CURRENT OF 7.5A MINIMUM
p 0.015% LINE REGULATION
p 0.15% LOAD REGULATION
s EVALUATION BOARD AVAILABLE:
REQUEST LXE9001 EVALUATION KIT
A P P L I C AT I O N S
s PENTIUM® PROCESSOR APPLICATIONS
s HIGH EFFICIENCY LINEAR REGULATORS
s POST REGULATORS FOR SWITCHING
POWER SUPPLIES
s BATTERY CHARGERS
s CONSTANT CURRENT REGULATORS
s CYRIX® 6x86TM
s AMD-K5TM
AVAILABLE O PTIONS PER PAR T #
Part #
Output
Voltage
LX8383/83A/83B-00
Adjustable
LX8383/83A/83B-33
3.3V
Other voltage options may be available —
Please contact factory for details.
Application of the LX8383A for the standard voltage (non VRE) Pentium Processor motherboard
with less than 130mV dynamic response to a 7.5A load transient.
Copyright © 1996
Rev. 1.0 12/96
PACKAGE ORDER INFORMATION
TA (°C)
Dropout
Voltage
P
Plastic TO-220
3-pin
V
Plastic TO-247
3-terminal
1.5V
LX8383-xxCP
LX8383-xxCV
0 to 125
1.3V
LX8383A-xxCP
LX8383A-xxCV
1.3V
LX8383B-xxCP
LX8383B-xxCV
-25 to 125
1.5V
LX8383-xxIP
LX8383-xxIV
1.3V
LX8383A-xxIP
LX8383A-xxIV
"xx" refers to output voltage, please see table above.
FOR FURTHER INFORMATION CALL (714) 898-8121
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841
1
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PRODUCT DATABOOK 1996/1997
LX8383-xx/8383A-xx/8383B-xx
7.5A LOW DROPOUT POSITIVE REGULATORS
PR O D U C T I O N D ATA 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 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 * FR * R1)
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:
M = VOUT/VREF
where: M ≡ 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 = 2.5V/1.25V= 2
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 LX8383/83A/83B 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 IADJis very small and constant when compared with the current
through R1, it represents a small error and can usually be ignored.
LX8383/83A/83B
VIN IN OUT
ADJ
VREF
IADJ
50µA
VOUT = VREF
1
+
R2
R1
+ IADJ R2
VOUT
R1
R2
FIGURE 2 — BASIC ADJUSTABLE REGULATOR
LOAD REGULATION
Because the LX8383/83A/83B 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:
RPeff = RP *
R2+R1
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.
LX8383/83A/83B
ParRaPsitic
Line Resistance
VIN IN
OUT
ADJ Connect
R1 to Case
of Regulator
R1
R2 RL
Connect
R2
to Load
FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION
Copyright © 1996
Rev. 1.0 12/96
5
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