LT1580CQ#PBF [Linear]
暂无描述;
Linear 
LT1580/LT1580-2.5
7A, Very Low
Dropout Regulator
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FEATURES
DESCRIPTION
■
Low Dropout, 540mV at 7A Output Current
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.
■
Fast Transient Response
■
Remote Sense
■
1mV Load Regulation
■
Fixed 2.5V Output and Adjustable Output
No Supply Sequencing Problems in
■
Dual Supply Mode
SeveralothernewfeatureshavebeenaddedtotheLT1580.
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.
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APPLICATIONS
■
Microprocessor Supplies
■
Post Regulators for Switching Supplies
■
High Current Regulators
5V to 3.XXV for Pentium® Processors Operating
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.
■
at 90MHz to 166MHz and Beyond
■
3.3V to 2.9V for Portable Pentium Processor
PowerPCTM Series Power Supplies
■
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.
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TYPICAL APPLICATION
Dropout Voltage—
Minimum Power Voltage
2.5V Microprocessor Supply
1.0
INDICATES GUARANTEED TEST POINTS
0°C ≤ T ≤ 125°C
2.5V/7A
J
3.3V
7A
V
V
OUT
POWER
+
+
+
100µF TANT
AVX TPS
× 7
330µF
DATA SHEET LIMIT
OS-CON
LT1580-2.5
0.5
T
= 125°C
J
5V
0.2A
V
SENSE
ADJ
CONTROL
T
= 25°C
J
GND
10µF
TANT
0.1µF
1580 TA01
0
0
3
5
6
7
1
2
4
OUTPUT CURRENT (A)
1580 G03
1
LT1580/LT1580-2.5
W W
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ABSOLUTE MAXIMUM RATINGS
VPOWER Input Voltage ................................................ 6V
VCONTROL Input Voltage ........................................... 13V
Storage Temperature ............................ –65°C to 150°C
Operating Junction Temperature Range
Power Transistor
LT1580C............................................ 0°C to 150°C
LT1580I........................................ –40°C to 150°C
Lead TemperaU ture (Soldering, 10 sec).................. 300°C
U U
Control Section
PRECONDITIONING
LT1580C............................................ 0°C to 125°C
LT1580I........................................ –40°C to 125°C
100% Thermal Limit Functional Test
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W U
PACKAGE/ORDER INFORMATION
ORDER PART
ORDER PART
NUMBER
FRONT VIEW
FRONT VIEW
NUMBER
5
4
3
2
1
V
V
V
5
4
3
2
1
V
V
V
POWER
CONTROL
OUT
POWER
CONTROL
OUT
TAB
IS
OUTPUT
TAB
IS
OUTPUT
LT1580CQ
LT1580IQ
LT1580CT
LT1580IT
ADJ
ADJ
SENSE
SENSE
T PACKAGE
5-LEAD PLASTIC TO-220
Q PACKAGE
5-LEAD PLASTIC DD
θJA = XX°C/ W
θJA = 50°C/ W
ORDER PART
NUMBER
ORDER PART
NUMBER
FRONT VIEW
FRONT VIEW
NC
POWER
7
6
5
4
3
2
1
7
6
5
4
3
2
1
NC
POWER
ADJ
V
V
ADJ
V
TAB
IS
OUTPUT
TAB
IS
OUTPUT
OUT
V
V
OUT
CONTROL
GND
V
CONTROL
LT1580CR-2.5
LT1580IR-2.5
LT1580CT7-2.5
LT1580IT7-2.5
GND
SENSE
SENSE
T7 PACKAGE
7-LEAD PLASTIC TO-220
R PACKAGE
7-LEAD PLASTIC DD
θJA = XX°C/ W
θJA = 50°C/ W
Consult factory for Military grade parts.
(Note 1)
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Output Voltage: LT1580-2.5
V
V
V
= 5V, V
= 4V to 12V, V
= 4V to 12V, V
= 0mA to 7A, 0°C ≤ T ≤ 125°C
= 4V to 12V, V
= 3.3V, I = 0mA
LOAD
2.485
2.475
2.475
2.500 2.515
2.500 2.525
2.500 2.525
V
V
V
CONTROL
CONTROL
CONTROL
POWER
= 3V to 5.5V, I
= 3V to 5.5V,
= 0mA to 4A
LOAD
●
●
POWER
POWER
I
LOAD
J
V
= 3V to 5.5V,
POWER
2.460
2.500 2.525
V
CONTROL
I
= 0mA to 6.5A, –40°C ≤ T < 0°C
LOAD
J
Reference Voltage: LT1580
V
V
V
= 2.75V, V
= 2.7V to 12V, V
= 2.7V to 12V, V
= 2V, I = 10mA
LOAD
1.243
1.237
1.237
1.250 1.257
1.250 1.263
1.250 1.263
V
V
V
CONTROL
CONTROL
CONTROL
POWER
(V
ADJ
= 0V)
= 1.75V to 5.5V, I
= 10mA to 4A
LOAD
POWER
= 2.05V to 5.5V,
POWER
I
= 10mA to 7A, 0°C ≤ T ≤ 125°C
LOAD
J
V
= 2.7V to 12V, V
= 2.05V to 5.5V,
POWER
1.232
1.250 1.263
V
CONTROL
I
= 10mA to 6.5A, –40°C ≤ T < 0°C
LOAD
J
Line Regulation: LT1580-2.5
LT1580
V
V
= 3.65V to 12V, V
= 3V to 5.5V, I = 10mA
LOAD
●
●
1
1
3
3
mV
mV
CONTROL
CONTROL
POWER
= 2.5V to 12V, V
= 1.75V to 5.5V, I
= 10mA
POWER
LOAD
2
LT1580/LT1580-2.5
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Load Regulation: LT1580-2.5
V
V
= 5V, V
= 2.75V, V
= 3.3V, I = 0mA to 7A
LOAD
●
●
1
1
5
5
mV
mV
CONTROL
CONTROL
POWER
LT1580 (V = 0V)
= 2.1V, I
= 10mA to 7A
ADJ
POWER
LOAD
Minimum Load Current: LT1580
V
= 5V, V
= 3.3V, V
= 0V (Note 3)
●
5
6
10
mA
CONTROL
POWER
ADJ
Control Pin Current: LT1580-2.5
(Note 4)
V
V
V
V
V
V
V
V
= 5V, V
= 5V, V
= 5V, V
= 5V, V
= 5V, V
= 5V, V
= 5V, V
= 5V, V
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 100mA, 0°C ≤ T ≤ 125°C
= 100mA, –40°C ≤ T < 0°C
= 4A, 0°C ≤ T ≤ 125°C
= 4A, –40°C ≤ T < 0°C
10
12
60
70
70
80
120
130
mA
mA
mA
mA
mA
mA
mA
mA
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
LOAD
LOAD
LOAD
LOAD
J
J
30
33
60
J
J
= 3V, I
= 3V, I
= 4A, 0°C ≤ T ≤ 125°C
LOAD
J
= 4A, –40°C ≤ T < 0°C
= 7A, 0°C ≤ T ≤ 125°C
= 6.5A, –40°C ≤ T < 0°C
LOAD
J
= 3.3V, I
= 3.3V, I
LOAD
LOAD
J
J
Control Pin Current: LT1580
(Note 4)
V
V
V
V
V
V
V
V
= 2.75V, V
= 2.75V, V
= 2.75V, V
= 2.75V, V
= 2.75V, V
= 2.75V, V
= 2.75V, V
= 2.75V, V
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 1.75V, I
= 1.75V, I
= 2.05V, I
= 2.05V, I
= 100mA, 0°C ≤ T ≤ 125°C
6
10
12
60
70
70
80
120
130
mA
mA
mA
mA
mA
mA
mA
mA
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
J
= 100mA, –40°C ≤ T < 0°C
J
= 4A, 0°C ≤ T ≤ 125°C
30
33
60
J
= 4A, –40°C ≤ T < 0°C
J
= 4A, 0°C ≤ T ≤ 125°C
J
= 4A, –40°C ≤ T < 0°C
J
= 7A, 0°C ≤ T ≤ 125°C
J
= 6.5A, –40°C ≤ T < 0°C
J
Ground Pin Current: LT1580-2.5
V
V
= 5V, V
= 3.3V, I
= 0mA
●
●
6
50
8
10
mA
CONTROL
CONTROL
POWER
LOAD
ADJ Pin Current: LT1580 (V = 0V)
= 2.75V, V
= 2.05V, I = 10mA
LOAD
120
µA
ADJ
POWER
Current Limit: LT1580-2.5
V
V
V
V
= 5V, V
= 5V, V
= 2.75V, V
= 3.3V, ∆V
= 3.3V, ∆V
= 100mV, 0°C ≤ T ≤ 125°C
= 100mV, –40°C ≤ T < 0°C
7.1
6.6
7.1
6.6
A
A
A
A
CONTROL
CONTROL
CONTROL
CONTROL
POWER
POWER
OUT
OUT
J
J
LT1580 (V
= 0V)
= 2.05V, ∆V
= 2.05V, ∆V
= 100mV, 0°C ≤ T ≤ 125°C
= 100mV, –40°C ≤ T < 0°C
8
ADJ
POWER
POWER
OUT
OUT
J
= 2.75V, V
J
Ripple Rejection: LT1580-2.5
LT1580
V = V = 5V Avg, V
= 1V , I
= 4A, T = 25°C
60
60
80
80
dB
dB
C
P
RIPPLE
P-P OUT
J
V = V = 3.75V Avg, V
= 1V , V
= 0V, I
= 4A, T = 25°C
OUT J
C
P
RIPPLE
P-P ADJ
Thermal Regulation
30ms Pulse
0.002
0.020
%/W
Thermal Resistance, Junction-to-Case T, T7 Packages, Control Circuitry/Power Transistor
0.65/2.70
°C/W
Dropout Voltage (Note 2)
Minimum V
: LT1580-2.5
V
V
V
V
V
V
V
V
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 100mA, 0°C ≤ T ≤ 125°C
1.00
1.00
1.06
1.15
1.15
1.20
1.15
1.20
1.20
1.25
1.30
1.35
V
V
V
V
V
V
V
V
CONTROL
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
J
(V
CONTROL
– V
)
= 100mA, –40°C ≤ T < 0°C
OUT
J
= 1A, 0°C ≤ T ≤ 125°C
J
= 1A, –40°C ≤ T < 0°C
J
= 4A, 0°C ≤ T ≤ 125°C
J
= 4A, –40°C ≤ T < 0°C
J
= 7A, 0°C ≤ T ≤ 125°C
J
= 6.5A, –40°C ≤ T < 0°C
J
Minimum V
: LT1580
V
V
V
V
V
V
V
V
V
V
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 2.05V, I
= 100mA, 0°C ≤ T ≤ 125°C
1.00
1.00
1.05
1.06
1.15
1.15
1.20
1.15
1.20
1.18
1.23
1.20
1.25
1.30
1.35
V
V
V
V
V
V
V
V
V
V
CONTROL
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
J
(V
– V
= 0V)
)
= 100mA, –40°C ≤ T < 0°C
CONTROL
OUT
J
(V
ADJ
= 1A, 0°C ≤ T ≤ 125°C
J
= 1A, –40°C ≤ T < 0°C
J
= 2.75A, 0°C ≤ T ≤ 125°C
J
= 2.75A, –40°C ≤ T < 0°C
J
= 4A, 0°C ≤ T ≤ 125°C
J
= 4A, –40°C ≤ T < 0°C
J
= 7A, 0°C ≤ T ≤ 125°C
J
= 6.5A, –40°C ≤ T < 0°C
J
3
LT1580/LT1580-2.5
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Minimum V
: LT1580-2.5
V
V
V
V
V
V
V
= 5V, I
= 5V, I
= 5V, I
= 5V, I
= 5V, I
= 5V, I
= 5V, I
= 100mA
= 1A
●
●
0.10
0.15
0.34
0.17
0.22
0.40
0.50
0.62
0.80
0.80
V
V
V
V
V
V
V
POWER
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
(V
POWER
– V
)
OUT
= 4A, T = 25°C
J
= 4A
●
= 7A, T = 25°C
0.54
0.70
0.70
J
= 7A, 0°C ≤ T ≤ 125°C
= 6.5A, –40°C ≤ T ≤ 0°C
J
J
Minimum V
: LT1580
V
V
V
V
V
V
V
V
= 2.75V, I
= 2.75V, I
= 2.75V, I
= 2.75V, I
= 2.75V, I
= 2.75V, I
= 2.75V, I
= 2.75V, I
= 100mA
= 1A
2.75A
●
●
●
0.10
0.15
0.26
0.34
0.17
0.22
0.38
0.40
0.50
0.62
0.80
0.80
V
V
V
V
V
V
V
V
POWER
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
(V
(V
– V
= 0V)
)
POWER
OUT
ADJ
= 4A, T = 25°C
J
= 4A
●
= 7A, T = 25°C
0.54
0.70
0.70
J
= 7A, 0°C ≤ T ≤ 125°C
= 6.5A, –40°C ≤ T ≤ 0°C
J
J
The
●
denotes specifications which apply over the full operating
Note 3: For the LT1580 adjustable device the minimum load current is the
minimum current required to maintain regulation. Normally the current in
the resistor divider used to set the output voltage is selected to meet the
minimum load current requirement.
temperature range.
Note 1: Unless otherwise specified V
adjustable device V
= V
. For the LT1580
OUT
SENSE
= 0V.
ADJ
Note 4: The control pin current is the drive current required for the output
transistor. This current will track output current with roughly a 1:100 ratio.
The minimum value is equal to the quiescent current of the device.
Note 2: For the LT1580, dropout is caused by either minimum control
voltage (V ) or minimum power voltage (V ). Both parameters
are specified with respect to the output voltage. The specifications represent
the minimum input/output voltage required to maintain 1% regulation.
CONTROL
POWER
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TYPICAL PERFORMANCE CHARACTERISTICS
Control Pin Current
vs Output Current
Dropout Voltage—
Minimum Power Voltage
Minimum Control Voltage
140
120
100
80
2
1.0
0.5
INDICATES GUARANTEED TEST POINTS
INDICATES GUARANTEED TEST POINTS
INDICATES GUARANTEED TEST POINTS
0°C ≤ T ≤ 125°C
0°C ≤ T ≤ 125°C
0°C ≤ T ≤ 125°C
J
J
J
DATA SHEET LIMIT
DATA SHEET LIMIT
DATA SHEET LIMIT
1
TYPICAL
DEVICE
60
T
= 125°C
T = 25°C
J
J
T = 125°C
J
T
= 25°C
J
40
20
0
0
0
0
1
2
3
4
5
6
7
0
3
5
6
7
1
2
4
0
3
5
6
7
1
2
4
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
1580 G01
1580 G02
1580 G03
4
LT1580/LT1580-2.5
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TYPICAL PERFORMANCE CHARACTERISTICS
LT1580-2.5 Output Voltage
vs Temperature
LT1580 Reference Voltage
vs Temperature
Load Current Step Response
2.508
2.506
2.504
2.502
2.500
2.498
2.496
2.494
2.492
1.258
1.256
1.254
1.252
1.250
1.248
1.246
1.244
1.242
VOUT
50mV/DIV
7A
LOAD
400mA
50µs/DIV
1580 TA02
50
TEMPERATURE (°C)
–50 –25
0
25
75 100 125 150
50
–50 –25
0
25
75 100 125 150
TEMPERATURE (°C)
1580 G05
1580 G04
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PIN FUNCTIONS
(5-Lead/7-Lead)
VPOWER (Pin 5/6): This is the collector to the power device
oftheLT1580. Theoutputloadcurrentissuppliedthrough
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).
SENSE(Pin1):Thispinisthepositivesideofthereference
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
beimprovedbyaddingasmallbypasscapacitorfromthe
ADJ pin to ground. For fixed voltage devices the ADJ pin
is also brought out to allow the user to add a bypass
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).
capacitor
.
GND (Pin 2, 7-Lead Only): For fixed voltage devices this
is the bottom of the resistor divider that sets the output
voltage.
VOUT (Pin 3/4): This is the power output of the device.
5
LT1580/LT1580-2.5
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BLOCK DIAGRA
V
CONTROL
V
POWER
+
–
SENSE
V
OUT
FOR FIXED
VOLTAGE
DEVICE
1580 BD
ADJ
GND
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APPLICATIONS INFORMATION
reducing the dropout voltage by a VBE compared to
conventional designs. The current requirement for the
control voltage is relatively small, equal to approximately
1% of the output current or about 70mA for a 7A load. The
bulk of this current is drive current for the NPN output
transistor. This drive current becomes part of the output
current.
The LT1580 is a low dropout regulator designed to power
the new generation of microprocessors. Low dropout
regulators have become more common in desktop com-
puter systems as microprocessor manufacturers have
moved away from 5V only CPUs. A wide range of supply
requirements exists today with new voltages just over the
horizon. Inmanycasestheinput-outputdifferentialisvery
small, effectively disqualifying many of the low dropout
regulatorsonthemarkettoday. TheLT1580isdesignedto
make use of multiple power supplies, present in most
systems, to reduce the dropout voltage. This two supply
approach maximizes efficiency.
The control voltage must be at least 1V greater than the
outputvoltagetoobtainoptimumperformance. Themaxi-
mum voltage on the VCONTROL pin is 13V. The maximum
voltage at the VPOWER pin is limited to 7V. GDN pin current
for fixed voltage devices is 6mA (typ) and is constant as a
function of load. ADJ pin current for adjustable devices is
60µAat25°Candvariesproportionaltoabsolutetempera-
ture.
The second supply, at least 1V greater than the output
voltage, is used to provide power for the control circuitry
and supply the drive current to the NPN output transistor.
This allows the NPN to be driven into saturation, thereby
6
LT1580/LT1580-2.5
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APPLICATIONS INFORMATION
TheLT1580hasimprovedfrequencycompensationwhich
permits the use of capacitors with very low ESR. This is
critical in addressing the needs of modern, low voltage,
high speed microprocessors. Current generation micro-
processors cycle load current from several hundred mil-
liamperes to several amperes in tens of nanoseconds.
Output voltage tolerances are tighter and include transient
response as part of the specification. The LT1580 is
designed to meet the fast current load step requirements
of these microprocessors and saves total cost by needing
less output capacitance to maintain regulation.
bined with ratiometrically accurate internal divider resis-
tors the part can easily hold 1% output accuracy over the
full temperature range and load current range, guaran-
teed, while operating with an input/output differential of
well under 1V.
Typical applications for the LT1580 include 3.3V to 2.5V
conversion with a 5V control supply, 5V to 4.2V conver-
sion with a 12V control supply or 5V to 3.6V conversion
with a 12V control supply. It is easy to obtain dropout
voltages of less than 0.5V at 4A along with excellent static
and dynamic specifications. The LT1580 is capable of 7A
of output current with a maximum dropout of 0.8V. The
LT1580hasfasttransientresponsethatallowsittohandle
the large current changes associated with today’s micro-
processors. The device is fully protected against
overcurrent and overtemperature conditions. Both fixed
voltage (2.5V) and adjustable output versions are avail-
able. ThedeviceisavailableinamultileadTO-220package
withfiveleadsfortheadjustabledeviceandsevenleadsfor
the fixed voltage device.
Careful design has eliminated any supply sequencing
issues associated with a dual supply system. The output
voltage will not turn on until both supplies are operating.
Ifthecontrolvoltagecomesupfirst,theoutputcurrentwill
be limited to a few milliamperes until the power input
voltage comes up. If the power input comes up first the
outputwillnotturnonatalluntilthecontrolvoltagecomes
up. The output can never come up unregulated. The
LT1580 can also be operated as a single supply device by
tying the control and power inputs together. Dropout in
single supply operation will be determined by the mini-
mum control voltage.
Grounding and Output Sensing
The LT1580 allows true Kelvin sensing for both the high
and low side of the load. This means that the voltage
regulation at the load can be easily optimized. Voltage
drops due to parasitic resistances between the regulator
andtheloadwhichwouldnormallydegraderegulationcan
beplacedinsidetheregulationloopoftheLT1580. Figures
1 through 3 illustrate the advantages of remote sensing.
Figure 1 shows the LT1580 connected as a conventional
3-terminal regulator with the SENSE lead connected di-
rectly to the output of the device. RP represents the
parasiticresistanceoftheconnectionsbetweentheLT1580
and the load. The load is typically a microprocessor and
RP is made up of the PC traces and/or connector resis-
tances, in the case of a modular regulator, between the
regulator and the processor. The effect of RP can be seen
in trace A of Figure 3. Very small resistances cause
significant load regulation steps. For example, at 7A out-
put current the output voltage will shift by 7mV for every
0.001Ω of resistance. In Figure 2 the LT1580 is connected
to take advantage of the remote sense feature. The SENSE
The LT1580 includes several innovative features that
require additional pins over the traditional 3-terminal
regulator. Both the fixed and adjustable devices have
remoteSENSEpins,permittingveryaccurateregulationof
output voltage at the load, where it counts, rather than at
the regulator. As a result the typical load regulation over
anoutputcurrentrangeof100mAto7Awitha2.5Voutput
istypicallylessthan1mV. Forthefixedvoltagedevicesthe
ADJ pin is also brought out. This allows the user to
improve transient response by bypassing the internal
resistor divider. In the past fixed output voltage devices
did not provide this capability. Bypassing the ADJ pin with
a capacitor in the range of 0.1µF to 1µF will provide
optimum transient response. The value chosen will de-
pend on the amount of output capacitance in the system.
In addition to the enhancements mentioned above the
reference accuracy has been improved by a factor of two
with a guaranteed initial tolerance of ±0.6% at 25°C.
Temperature drift is also very well controlled. When com-
7
LT1580/LT1580-2.5
U
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APPLICATIONS INFORMATION
pin and the top of the resistor divider are connected to the
top of the load. The bottom of the resistor divider is
connected to the bottom of the load. RP is now effectively
connectedinsidetheregulatingloopoftheLT1580andthe
load regulation at the load will be negligible for reasonable
values of RP. Trace B of Figure 3 illustrates the effect on
output regulation. It is important to note that the voltage
drops due to RP are not eliminated. They will add to the
dropout voltage of the regulator regardless of whether
they are inside the loop as in Figure 2 or outside the loop
as in Figure 1. This means that the LT1580 can control the
voltage at the load as long as the input-output voltage is
greater than the total of the dropout voltage of the LT1580
plus the voltage drop across RP.
5V
V
CONTROL
3.3V
SENSE
V
POWER
LT1580
ADJ
Stability
+
V
OUT
The LT1580 requires the use of an output capacitor as part
of the device frequency compensation. The device re-
quiresaminimumof 22µFtantalumor150µFofaluminum
electrolytic to ensure stability. Larger capacitor values
increase stability and improve transient performance.
R
R
P
P
LOAD
V
OUT
R1
R2
–
1580 F01
Many different types of capacitors are available and have
widely varying characteristics. These capacitors differ in
capacitor tolerance (sometimes up to±100%), equivalent
series resistance, equivalent series inductance and ca-
pacitance temperature coefficient. The LT1580 frequency
compensation optimizes frequency response with low
ESR capacitors. In general, use capacitors with an ESR of
less than 1Ω.
Figure 1. Conventional Load Sensing
5V
V
CONTROL
3.3V
SENSE
V
POWER
LT1580
ADJ
+
V
OUT
R
R
For microprocessor applications larger value capacitors
will be needed to meet the transient requirements of the
processor. Processor manufacturers require tight voltage
tolerances on the power supply. High quality bypass
capacitors must be used to limit the high frequency noise
generated by the processor. Multiple small ceramic ca-
pacitors in addition to high quality bulk tantalum capaci-
tors are typically required to limit parasitic inductance
(ESL)andresistance(ESR)inthecapacitorstoacceptable
levels. The LT1580 is stable with the type of capacitors
recommended by processor manufacturers.
P
P
LOAD
V
OUT
R1
R2
–
1580 F02
Figure 2. Remote Load Sensing
(∆I )(R )
OUT
P
V
OUT
FIGURE 1
V
OUT
Bypassing the adjust terminal on the LT1580 improves
ripple rejection and transient response. The ADJ pin is
brought out on the fixed voltage device specifically to
allow this capability.
FIGURE 2
I
OUT
TIME
1580 F03
Capacitorvaluesontheorderofseveralhundredmicrofar-
adsareusedtoensuregoodtransientresponsewithheavy
Figure 3. Remote Sensing Improves Load Regulation
8
LT1580/LT1580-2.5
U
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APPLICATIONS INFORMATION
load current changes. Output capacitance can increase
without limit and larger values of output capacitance
further improve the stability and transient response of the
LT1580.
Output Voltage
The adjustable version of the LT1580 develops a 1.25V
reference voltage between the SENSE pin and the ADJ pin
(see Figure 5). Placing a resistor R1 between these two
terminals causes a constant current to flow through R1
and down through R2 to set the overall output voltage.
Normally R1 is chosen so that this current is the specified
minimumloadcurrentof10mA.ThecurrentoutoftheADJ
pin adds to the current from R1. The ADJ pin current is
small, typically 50µA. The output voltage contribution of
the ADJ pin current is small and only needs to be consid-
ered when very precise output voltage setting is required.
Note that the top of the resistor divider should be con-
nected directly to the SENSE pin for best regulation. See
the section on grounding and Kelvin sensing above.
Modern microprocessors generate large high frequency
current transients. The load current step contains higher
order frequency components that the output coupling
network must handle until the regulator throttles to the
load current level. Capacitors are not ideal elements and
contain parasitic resistance and inductance. These para-
siticelementsdominatethechangeinoutputvoltageatthe
beginning of a transient load step change. The ESR of the
output capacitors produces an instantaneous step in out-
put voltage (∆V = ∆I)(ESR). The ESL of the output capaci-
tors produces a droop proportional to the rate of change
of the output current (V = L)(∆I/∆t). The output capaci-
tance produces a change in output voltage proportional to
the time until the regulator can respond (∆V = ∆t)(∆I/ C).
These transient effects are illustrated in Figure 4 .
V
CONTROL
+
+
V
CONTROL
V
V
V
OUT
V
OUT
POWER
POWER
+
LT1580
ADJ
ESR
EFFECTS
SENSE
ESL
V
R1
R2
REF
CAPACITANCE
EFFECTS
EFFECTS
1580 F04
I
= 50µA
V
t
∆I
C
ADJ
SLOPE,
=
POINT AT WHICH REGULATOR
TAKES CONTROL
R2
R1
V
= V
1 +
+ I
(R2)
ADJ
OUT
REF
)
(
1580 F05
Figure 4
Figure 5. Setting Output Voltage
The use of capacitors with low ESR, low ESL and good
high frequency characteristics is critical in meeting the
output voltage tolerances of these high speed micropro-
cessors. These requirements dictate a combination of
highquality, surfacemount, tantalumandceramiccapaci-
tors. The location of the decoupling network is critical to
transient performance. Place the decoupling network as
closetotheprocessorpinsaspossiblebecausetraceruns
from the decoupling capacitors to the processor pins are
inductive. The ideal location for the decoupling network is
actually inside the microprocessor socket cavity. In addi-
tion, use large power and ground plane areas to minimize
distribution drops.
Protection Diodes
In normal operation the LT1580 does not require protec-
tiondiodes.Older3-terminalregulatorsrequireprotection
diodes between the VOUT pin and the Input pin or between
the ADJ pin and the VOUT pin to prevent die overstress.
On the LT1580, internal resistors limit internal current
paths on the ADJ pin. Therefore even with bypass capaci-
tors on the ADJ pin, no protection diode is needed to
ensure device safety under short-circuit conditions. The
ADJ pin can be driven on a transient basis ±7V with
respect to the output without any device degradation.
9
LT1580/LT1580-2.5
U
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APPLICATIONS INFORMATION
A protection diode between the VOUT pin and the VPOWER
pin is usually not needed. An internal diode between the
VOUT pin and the VPOWER pin on the LT1580 can handle
microsecond surge currents of 50A to 100A. Even with
large value output capacitors it is difficult to obtain those
values of surge currents in normal operation. Only with
large values of output capacitance, such as 1000µF to
5000µF, and with the VPOWER pin instantaneously shorted
to ground can damage occur. A crowbar circuit at the
power input can generate those levels of current, and a
diode from output to power input is then recommended.
This is shown in Figure 6. Normal power supply cycling or
system “hot plugging and unplugging” will not do any
damage.
If the LT1580 is connected as a single supply device with
the VCONTROL and VPOWER input pins shorted together the
internal diode between the VOUT and the VPOWER input pin
will protect the VCONTROL input pin.
Like any other regulator exceeding the maximum input to
output differential can cause the internal transistors to
break down and none of the internal protection circuitry is
then functional.
Thermal Considerations
The LT1580 has internal current and thermal limiting
designed to protect the device under overload conditions.
Forcontinuousnormalloadconditionsmaximumjunction
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 junc-
tion-to-case, case-to-heat sink interface and heat sink
resistance itself. Thermal resistance specifications are
given in the electrical characteristics for both the Control
section and the Power section of the device. The thermal
resistance of the Control section is given as 0.65°C/W and
junction temperature of the Control section is allowed to
run at up to 125°C. The thermal resistance of the Power
section is given as 2.7°C/W and the junction temperature
of the Power section is allowed to run at up to 150°C. The
difference in thermal resistances between Control and
Power sections is due to thermal gradients between the
power transistor and the control circuitry.
V
CONTROL
+
D2*
D1*
V
CONTROL
V
V
V
OUT
V
OUT
POWER
POWER
+
+
LT1580
ADJ
SENSE
R1
*OPTIONAL DIODES: 1N4002
R2
1580 F06
Figure 6. Optional Clamp Diodes Protect Against
Input Crowbar Circuits
Virtually all of the power dissipated by the device is
dissipated in the power transistor. The temperature rise in
the power transistor will be greater than the temperature
rise in the Control section so the effective thermal resis-
tance, temperature rise per watt dissipated, will be lower
in the Control section. At power levels below 12W the
temperature gradient will be less than 25°C and the
maximum ambient temperature will be determined by the
junction temperature of the Control section. This is due to
the lower maximum junction temperature in the Control
section. At powerlevels greaterthan 12W the temperature
gradient will be greater than 25°C and the maximum
ambient temperature will be determined by the Power
section. For both cases the junction temperature is deter-
minedbythetotalpowerdissipatedinthedevice.Formost
AprotectiondiodebetweentheVOUT pinandtheVCONTROL
pin is usually not needed. An internal diode between the
VOUT pin and the VCONTROL pin on the LT1580 can handle
microsecond surge currents of 1A to 10A. This can only
occur if the VCONTROL pin is instantaneously shorted to
ground with a crowbar circuit with large value output
capacitors. SincetheVCONTROL pinisusuallyalowcurrent
supply, this condition is unlikely. A protection diode from
the VOUT pin to the VCONTROL pin is recommended if the
VCONTROL pin can be instantaneously shorted to ground.
This is shown in Figure 6. Normal power supply cycling or
system “hot plugging and unplugging” will not do any
damage.
10
LT1580/LT1580-2.5
U
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APPLICATIONS INFORMATION
lowdropoutapplicationsthepowerdissipationwillbeless
The following example illustrates how to calculate
maximum junction temperature. Using an LT1580 and
assuming:
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.
V
CONTROL (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)
The power in the drive circuit will be equal to:
P
DRIVE = (VCONTROL – VOUT)(ICONTROL
where ICONTROL is equal to between IOUT/100 (typ) and
OUT/58 (max).
)
Power dissipation under these conditions is equal to:
Total Power Dissipation = PDRIVE + POUTPUT
I
PDRIVE = (VCONTROL – VOUT) (ICONTROL
ICONTROL = IOUT/58 = 4A/58 = 69mA
)
ICONTROL is a function of output current. A curve of
ICONTROL vs IOUT can be found in the Typical Performance
Characteristics curves.
PDRIVE = (5.25V – 2.5V)(69mA) = 190mW
POUTPUT = (VPOWER – VOUT)(IOUT
The power in the output transistor is equal to:
)
POUTPUT = (VPOWER – VOUT)(IOUT
The total power is equal to:
PTOTAL = PDRIVE + POUTPUT
)
= ( 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:
Junction-to-case thermal resistance is specified from the
ICjunctiontothebottomofthecasedirectlybelowthedie.
This is the lowest resistance path for heat flow. Proper
mounting is required to ensure the best possible thermal
flowfromthisareaofthepackagetotheheatsink.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.
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
LT1580/LT1580-2.5
U
TYPICAL APPLICATION
2.5V/6A Regulator
5V
5
4
3.3V
V
V
CONT
POWER
1
SENSE
LT1580
V
OUT
= 2.5V
3
V
OUT
ADJ
2
V
CC
+
+
C3
22µF
25V
C2
R1
220µF
110Ω
10V
1%
1µF
25V
× 10
+
100µF
10V
MICROPROCESSOR
SOCKET
× 2
R2
C1
+
C4
110Ω 100µF
0.33µF
1%
10V
V
SS
RTN
1580 TA03
12
LT1580/LT1580-2.5
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
Q Package
5-Lead Plastic DD Pak
(LTC DWG # 05-08-1461)
0.060
(1.524)
TYP
0.390 – 0.415
(9.906 – 10.541)
0.060
(1.524)
0.165 – 0.180
(4.191 – 4.572)
0.256
(6.502)
0.045 – 0.055
(1.143 – 1.397)
15° TYP
+0.008
0.004
–0.004
0.060
(1.524)
0.183
(4.648)
0.059
(1.499)
TYP
0.330 – 0.370
(8.382 – 9.398)
+0.203
–0.102
0.102
(
)
0.095 – 0.115
(2.413 – 2.921)
0.075
(1.905)
0.057 – 0.077
(1.447 – 1.955)
0.050 ± 0.012
(1.270 ± 0.305)
0.300
(7.620)
0.013 – 0.023
(0.330 – 0.584)
+0.012
0.143
–0.020
0.028 – 0.038
(0.711 – 0.965)
+0.305
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
3.632
(
)
–0.508
Q(DD5) 0396
R Package
7-Lead Plastic DD Pak
(LTC DWG # 05-08-1462)
0.060
(1.524)
TYP
0.390 – 0.415
(9.906 – 10.541)
0.060
(1.524)
0.165 – 0.180
(4.191 – 4.572)
0.256
(6.502)
0.045 – 0.055
(1.143 – 1.397)
15° TYP
+0.008
0.004
–0.004
0.060
(1.524)
0.059
(1.499)
TYP
0.183
(4.648)
0.330 – 0.370
(8.382 – 9.398)
+0.203
–0.102
0.102
(
)
0.095 – 0.115
(2.413 – 2.921)
0.075
(1.905)
0.040 – 0.060
(1.016 – 1.524)
0.026 – 0.036
(0.660 – 0.914)
0.050 ± 0.012
(1.270 ± 0.305)
0.300
(7.620)
0.013 – 0.023
(0.330 – 0.584)
+0.012
0.143
–0.020
+0.305
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
3.632
(
)
–0.508
R (DD7) 0396
13
LT1580/LT1580-2.5
U
PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
T Package
5-Lead Plastic TO-220 (Standard)
(LTC DWG # 05-08-1421)
0.165 – 0.180
(4.191 – 4.572)
0.147 – 0.155
(3.734 – 3.937)
DIA
0.390 – 0.415
(9.906 – 10.541)
0.045 – 0.055
(1.143 – 1.397)
0.230 – 0.270
(5.842 – 6.858)
0.570 – 0.620
(14.478 – 15.748)
0.620
(15.75)
TYP
0.460 – 0.500
(11.684 – 12.700)
0.330 – 0.370
(8.382 – 9.398)
0.700 – 0.728
(17.78 – 18.491)
0.095 – 0.115
(2.413 – 2.921)
0.152 – 0.202
(3.861 – 5.131)
0.260 – 0.320
(6.60 – 8.13)
0.013 – 0.023
(0.330 – 0.584)
0.057 – 0.077
(1.448 – 1.956)
0.135 – 0.165
(3.429 – 4.191)
0.155 – 0.195
(3.937 – 4.953)
0.028 – 0.038
(0.711 – 0.965)
T5 (TO-220) 0398
14
LT1580/LT1580-2.5
U
PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
T7 Package
7-Lead Plastic TO-220 (Standard)
(LTC DWG # 05-08-1422)
0.165 – 0.180
(4.191 – 4.572)
0.147 – 0.155
(3.734 – 3.937)
DIA
0.390 – 0.415
(9.906 – 10.541)
0.045 – 0.055
(1.143 – 1.397)
0.230 – 0.270
(5.842 – 6.858)
0.570 – 0.620
(14.478 – 15.748)
0.620
(15.75)
TYP
0.460 – 0.500
(11.684 – 12.700)
0.330 – 0.370
(8.382 – 9.398)
0.700 – 0.728
(17.780 – 18.491)
0.095 – 0.115
(2.413 – 2.921)
0.152 – 0.202
(3.860 – 5.130)
0.260 – 0.320
(6.604 – 8.128)
0.013 – 0.023
(0.330 – 0.584)
0.040 – 0.060
(1.016 – 1.524)
0.026 – 0.036
(0.660 – 0.914)
0.135 – 0.165
(3.429 – 4.191)
0.155 – 0.195
(3.937 – 4.953)
T7 (TO-220) (FORMED) 1197
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
15
LT1580/LT1580-2.5
U
TYPICAL APPLICATION
Dual Regulators Power Pentium Processor or Upgrade CPU
R12
0.0075Ω*
I/O
SUPPLY
3.5V/3.3V
5V
V
IN
V
OUT
+
C3
220µF
10V
+
C1
220µF
10V
12V
LT1587
ADJ
R1
10k
R3
110Ω
1%
C8
0.1µF
D1
1N4148
R2
470Ω
+
LT1006
R4
C4
0.33µF
–
5V
178Ω
C6
0.01µF
1%
R10
10k
D2
1N4148
R11
10k
R14, 2Ω
1
3
4
V
SENSE
12V
CONTROL
CORE
+
C11
C10
1µF
SUPPLY
22µF
R13
LT1580
+
C7
330µF
6.3V
3.5V/2.5V
35V
0.005Ω*
5
V
V
OUT
POWER
ADJ
C9
+
+
C2
Q3
2N7002
220µF
220µF
2
10V
10V
C5
0.33µF
R7
5V
R8
Q3
107Ω
0.35%
107Ω
2N7002
0.25%
R5
R9
10k
R6
10k
Q1
ZVN4206
89.8Ω
0.5%
E3
Q2
TO CPU
2N3904
VOLTAGE
SELECT PIN
*RESISTORS ARE IMPLEMENTED AS COPPER TRACES ON PCB
IF 1 OZ COPPER, TRACE WIDTHS ARE 0.05 INCH
IF 2 OZ COPPER, TRACE WIDTHS ARE 0.025 INCH
R13 IS 0.83 INCHES LONG, R12 IS 1.24 INCHES LONG
E3 CPU TYPE
0
1
P55C
P54C
1580 TA04
RELATED PARTS
PART NUMBER
LTC®1266
LTC1267
LTC1430
LT1584
DESCRIPTION
COMMENTS
Synchronous Switching Controller
>90% Efficient High Current Microprocessor Supply
>90% Efficiency with Fixed 5V, 3.3V or Adjustable Outputs
>90% Efficient High Current Microprocessor Supply
For High Performance Microprocessors
Dual High Efficiency Synchronous Switching Regulator
High Power Synchronous Step-Down Switching Regulator
7A Low Dropout Fast Transient Response Regulator
4.6A Low Dropout Fast Transient Response Regulator
3A Low Dropout Fast Transient Response Regulator
LT1585
For High Performance Microprocessors
LT1587
For High Performance Microprocessors
158025fa LT/GP 0598 2K REV A • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1995
16 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
相关型号：
LT1580CQ#TRPBF
LT1580 - 7A, Very Low Dropout Regulator; Package: DD PAK; Pins: 5; Temperature Range: 0°C to 70°C
Linear
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