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PDF LT1580CT Data sheet ( Hoja de datos )
| Número de pieza | LT1580CT | |
| Descripción | 7A/ Very Low Dropout Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1580/LT1580 -2.5
7A, Very Low
Dropout Regulator
FEATURES
s Low Dropout, 540mV at 7A Output Current
s Fast Transient Response
s Remote Sense
s 1mV Load Regulation
s Fixed 2.5V Output and Adjustable Output
s No Supply Sequencing Problems in
Dual Supply Mode
U
APPLICATIONS
s Microprocessor Supplies
s Post Regulators for Switching Supplies
s High Current Regulators
s 5V to 3.XXV for Pentium® Processors Operating
at 90MHz to 166MHz and Beyond
s 3.3V to 2.9V for Portable Pentium Processor
s PowerPCTM Series Power Supplies
DESCRIPTION
The LT ®1580 is a 7A low dropout regulator designed to
power the new generation of microprocessors. The drop-
out voltage of this device is 100mV at light loads rising to
just 540mV at 7A. To achieve this dropout, a second low
current input voltage 1V greater than the output voltage, is
required. The device can also be used as a single supply
device where dropout is comparable to an LT1584.
Several other new features have been added to the LT1580.
A remote SENSE pin is brought out. This feature virtually
eliminates output voltage variations due to load changes.
Typical load regulation, measured at the SENSE pin, for a
load current step of 100mA to 7A is less than 1mV.
The LT1580 has fast transient response, equal to the
LT1584. On fixed voltage devices, the ADJ pin is brought
out. A small capacitor on the ADJ pin further improves
transient response.
This device is ideal for generating processor supplies of
2V to 3V on motherboards where both 5V and 3.3V
supplies are available.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
PowerPC is a trademark of IBM Corporation.
TYPICAL APPLICATION
2.5V Microprocessor Supply
3.3V
7A +
VPOWER
330µF
VOUT
OS-CON
LT1580-2.5
2.5V/7A
+ 100µF TANT
AVX TPS
×7
5V
0.2A + 10µF
VCONTROL
GND
TANT
SENSE
ADJ
0.1µF
1580 TA01
Dropout Voltage —
Minimum Power Voltage
1.0
INDICATES GUARANTEED TEST POINTS
0°C ≤ TJ ≤ 125°C
DATA SHEET LIMIT
0.5
TJ = 125°C
TJ = 25°C
0
012 34 567
OUTPUT CURRENT (A)
1580 G03
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1580/LT1580 -2.5
LT1580 Reference Voltage
vs Temperature
1.258
1.256
1.254
1.252
1.250
1.248
1.246
1.244
1.242
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
1580 G04
LT1580-2.5 Output Voltage
vs Temperature
2.508
Load Current Step Response
2.506
2.504
VOUT
50mV/DIV
2.502
2.500
2.498
7A
LOAD
2.496
2.494
400mA
50µs/DIV
1580 TA02
2.492
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
1580 G05
PIN FUNCTIONS (5-Lead/7-Lead)
SENSE (Pin 1): This pin is the positive side of the reference
voltage for the device. With this pin it is possible to Kelvin
sense the output voltage at the load.
ADJ (Pin 2/5): This pin is the negative side of the
reference voltage for the device. Transient response can
be improved by adding a small bypass capacitor from the
ADJ pin to ground. For fixed voltage devices the ADJ pin
is also brought out to allow the user to add a bypass
capacitor.
GND (Pin 2, 7-Lead Only): For fixed voltage devices this
is the bottom of the resistor divider that sets the output
voltage.
VPOWER (Pin 5/6): This is the collector to the power device
of the LT1580. The output load current is supplied through
this pin. For the device to regulate, the voltage at this pin
must be between 0.1V and 0.8V greater than the output
voltage (see Dropout specifications).
VCONTROL (Pin 4/3): This pin is the supply pin for the
control circuitry of the device. The current flow into this
pin will be about 1% of the output current. For the device
to regulate, the voltage at this pin must be between 1.0V
and 1.3V greater than the output voltage (see Dropout
specifications).
VOUT (Pin 3/4): This is the power output of the device.
5
5 Page 
LT1580/LT1580 -2.5
APPLICATIONS INFORMATION
low dropout applications the power dissipation will be less
than 12W.
The power in the device is made up of two main compo-
nents: the power in the output transistor and the power in
the drive circuit. The additional power in the control circuit
is negligible.
The power in the drive circuit will be equal to:
PDRIVE = (VCONTROL – VOUT)(ICONTROL)
where ICONTROL is equal to between IOUT/100 (typ) and
IOUT/58 (max).
ICONTROL is a function of output current. A curve of
ICONTROL vs IOUT can be found in the Typical Performance
Characteristics curves.
The power in the output transistor is equal to:
POUTPUT = (VPOWER – VOUT)(IOUT)
The total power is equal to:
PTOTAL = PDRIVE + POUTPUT
Junction-to-case thermal resistance is specified from the
IC junction to the bottom of the case directly below 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 electroni-
cally isolated, a thermally conductive spacer can be used
as long as the added contribution to thermal resistance is
considered. Please consult Linear Technology’s “ Mount-
ing Considerations for Power Semiconductors,” 1990
Linear Applications Handbook, Volume 1, Pages RR3-1 to
RR3-20. Note that the case of the LT1580 is electrically
connected to the output.
The following example illustrates how to calculate
maximum junction temperature. Using an LT1580 and
assuming:
VCONTROL (max continuous) = 5.25V (5V + 5%),
VPOWER (max continuous) = 3.465V (3.3V + 5%),
VOUT = 2.5V, Iout = 4A,
TA = 70°C, θHEATSINK = 4°C/W,
θCASE-HEATSINK = 1°C/W (with thermal compound)
Power dissipation under these conditions is equal to:
Total Power Dissipation = PDRIVE + POUTPUT
PDRIVE = (VCONTROL – VOUT) (ICONTROL)
ICONTROL = IOUT/58 = 4A/58 = 69mA
PDRIVE = (5.25V – 2.5V)(69mA) = 190mW
POUTPUT = (VPOWER – VOUT)(IOUT)
= ( 3.465V – 2.5V)(4A) = 3.9W
Total Power Dissipation = 4.05W
Junction temperature will be equal to:
TJ = TA + PTOTAL (θHEATSINK + θCASE-HEATSINK + θJC)
For the Control section:
TJ = 70°C + 4.05W(4°C/W +1°C/W + 0.65°C/W) = 93°C
93°C < 125°C = TJMAX for Control Section
For the Power section:
TJ = 70°C + 4.05W (4°C/W + 1°C/W + 2.7°C/W) = 101°C
101°C < 150°C = TJMAX for Power Section
In both cases the junction temperature is below the
maximum rating for the respective sections, ensuring
reliable operation.
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1580CT.PDF ] | |
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