Page 1
FEATURES
■
Low Dropout, 540mV at 7A Output Current
■
Fast Transient Response
■
Remote Sense
■
1mV Load Regulation
■
Fixed 2.5V Output and Adjustable Output
■
No Supply Sequencing Problems in
Dual Supply Mode
LT1580/LT1580-2.5
7A, Very Low
Dropout Regulator
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DESCRIPTION
The LT®1580 is a 7A low dropout regulator designed to
power the new generation of microprocessors. The dropout 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.
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APPLICATIONS
■
Microprocessor Supplies
■
Post Regulators for Switching Supplies
■
High Current Regulators
■
5V to 3.XXV for Pentium® Processors Operating
at 90MHz to 166MHz and Beyond
■
3.3V to 2.9V for Portable Pentium Processor
■
PowerPCTM Series Power Supplies
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TYPICAL APPLICATION
2.5V Microprocessor Supply
3.3V
0.2A
V
7A
+
330µF
OS-CON
5V
+
10µF
TANT
POWER
V
CONTROL
LT1580-2.5
V
OUT
SENSE
ADJGND
0.1µF
2.5V/7A
+
100µF TANT
AVX TPS
× 7
1580 TA01
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.
Dropout Voltage—
Minimum Power Voltage
1.0
INDICATES GUARANTEED TEST POINTS
≤ 125°C
0°C ≤ T
J
DATA SHEET LIMIT
0.5
TJ = 125°C
TJ = 25°C
MINIMUM POWER VOLTAGE (V)
0
0
1
3
2
OUTPUT CURRENT (A)
4
5
6
7
1580 G03
1
Page 2
LT1580/LT1580-2.5
WW
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ABSOLUTE MAXIMUM RATINGS
V
V
Storage Temperature ............................ – 65°C to 150°C
Operating Junction Temperature Range
Input Voltage ................................................ 6V
POWER
CONTROL
Input Voltage ........................................... 13V
Control Section
LT1580C ........................................... 0°C to 125°C
LT1580I........................................ – 40°C to 125°C
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W
PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
LT1580CQ
LT1580IQ
TAB
OUTPUT
IS
5-LEAD PLASTIC DD
FRONT VIEW
5
4
3
2
1
Q PACKAGE
θJA = 30°C/ W
V
POWER
V
CONTROL
V
OUT
ADJ
SENSE
Power Transistor
LT1580C ........................................... 0°C to 150°C
LT1580I........................................ – 40°C to 150°C
Lead Temperature (Soldering, 10 sec)..................300°C
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PRECONDITIONING
100% Thermal Limit Functional Test
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ORDER PART
NUMBER
LT1580CT
LT1580IT
TAB
OUTPUT
FRONT VIEW
5
IS
5-LEAD PLASTIC TO-220
4
3
2
1
T PACKAGE
θJA = 50°C/ W
V
POWER
V
CONTROL
V
OUT
ADJ
SENSE
TAB
OUTPUT
IS
FRONT VIEW
7
6
5
4
3
2
1
R PACKAGE
7-LEAD PLASTIC DD
θJA = 30°C/W
NC
V
POWER
ADJ
V
OUT
V
CONTROL
GND
SENSE
ORDER PART
NUMBER
LT1580CR-2.5
LT1580IR-2.5
TAB
OUTPUT
FRONT VIEW
7
6
IS
7-LEAD PLASTIC TO-220
5
4
3
2
1
T7 PACKAGE
θJA = 50°C/W
NC
V
POWER
ADJ
V
OUT
V
CONTROL
GND
SENSE
ORDER PART
NUMBER
LT1580CT7-2.5
LT1580IT7-2.5
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
(Note 1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage: LT1580-2.5 V
Reference Voltage: LT1580 V
(V
= 0V) V
ADJ
Line Regulation: LT1580-2.5 V
LT1580 V
V
V
I
V
I
V
I
V
I
= 5V, V
CONTROL
= 4V to 12V, V
CONTROL
= 4V to 12V, V
CONTROL
= 0mA to 7A, 0°C ≤ TJ ≤ 125°C
LOAD
= 4V to 12V, V
CONTROL
= 0mA to 6.5A, –40°C ≤ TJ < 0°C
LOAD
= 2.75V, V
CONTROL
= 2.7V to 12V, V
CONTROL
= 2.7V to 12V, V
CONTROL
= 10mA to 7A, 0°C ≤ TJ ≤ 125°C
LOAD
= 2.7V to 12V, V
CONTROL
= 10mA to 6.5A, –40°C ≤ TJ < 0°C
LOAD
= 3.65V to 12V, V
CONTROL
= 2.5V to 12V, V
CONTROL
POWER
POWER
= 3.3V, I
POWER
POWER
POWER
= 2V, I
POWER
POWER
POWER
POWER
POWER
= 0mA 2.485 2.500 2.515 V
LOAD
= 3V to 5.5V, I
= 0mA to 4A ● 2.475 2.500 2.525 V
LOAD
= 3V to 5.5V, 2.475 2.500 2.525 V
= 3V to 5.5V, 2.460 2.500 2.525 V
= 10mA 1.243 1.250 1.257 V
LOAD
= 1.75V to 5.5V, I
= 10mA to 4A ● 1.237 1.250 1.263 V
LOAD
= 2.05V to 5.5V, 1.237 1.250 1.263 V
= 2.05V to 5.5V, 1.232 1.250 1.263 V
= 3V to 5.5V, I
= 1.75V to 5.5V, I
= 10mA ● 13 mV
LOAD
= 10mA ● 13 mV
LOAD
2
Page 3
LT1580/LT1580-2.5
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Load Regulation: LT1580-2.5 V
LT1580 (V
= 0V) V
ADJ
Minimum Load Current: LT1580 V
Control Pin Current: LT1580-2.5 V
(Note 4) V
V
V
V
V
V
V
Control Pin Current: LT1580 V
(Note 4) V
V
V
V
V
V
V
Ground Pin Current: LT1580-2.5 V
ADJ Pin Current: LT1580 (V
= 0V) V
ADJ
Current Limit: LT1580-2.5 V
V
LT1580 (V
= 0V) V
ADJ
V
Ripple Rejection: LT1580-2.5 V
LT1580 VC = VP = 3.75V Avg, V
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
(V
CONTROL
– V
: LT1580-2.5 V
CONTROL
)V
OUT
V
V
V
V
V
V
Minimum V
(V
(V
– V
CONTROL
= 0V) V
ADJ
: LT1580 V
CONTROL
)V
OUT
V
V
V
V
V
V
V
= 5V, V
CONTROL
= 2.75V, V
CONTROL
= 5V, V
CONTROL
= 5V, V
CONTROL
= 5V, V
CONTROL
= 5V, V
CONTROL
= 5V, V
CONTROL
= 5V, V
CONTROL
= 5V, V
CONTROL
= 5V, V
CONTROL
= 5V, V
CONTROL
= 2.75V, V
CONTROL
= 2.75V, V
CONTROL
= 2.75V, V
CONTROL
= 2.75V, V
CONTROL
= 2.75V, V
CONTROL
= 2.75V, V
CONTROL
= 2.75V, V
CONTROL
= 2.75V, V
CONTROL
= 5V, V
CONTROL
= 2.75V, V
CONTROL
= 5V, V
CONTROL
= 5V, V
CONTROL
= 2.75V, V
CONTROL
= 2.75V, V
CONTROL
= VP = 5V Avg, V
C
= 3.3V, I
POWER
= 3.3V, I
POWER
= 3.3V, I
POWER
= 3.3V, I
POWER
= 3.3V, I
POWER
= 3.3V, I
POWER
= 3.3V, I
POWER
= 3.3V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 3.3V, I
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
POWER
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
= 2.1V, I
POWER
= 3.3V, V
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 3.3V, I
= 3V, I
= 3V, I
= 3.3V, I
= 3.3V, I
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 1.75V, I
POWER
= 1.75V, I
POWER
= 2.05V, I
POWER
= 2.05V, I
POWER
= 3.3V, I
= 2.05V, I
POWER
= 3.3V, ∆V
= 3.3V, ∆V
= 2.05V, ∆V
POWER
= 2.05V, ∆V
POWER
= 1V
RIPPLE
RIPPLE
= 100mA, 0°C ≤ TJ ≤ 125°C 1.00 1.15 V
= 100mA, –40°C ≤ TJ < 0°C 1.20 V
= 1A, 0°C ≤ TJ ≤ 125°C 1.00 1.15 V
= 1A, –40°C ≤ TJ < 0°C 1.20 V
= 4A, 0°C ≤ TJ ≤ 125°C 1.06 1.20 V
= 4A, –40°C ≤ TJ < 0°C 1.25 V
= 7A, 0°C ≤ TJ ≤ 125°C 1.15 1.30 V
= 6.5A, –40°C ≤ TJ < 0°C 1.35 V
= 100mA, 0°C ≤ TJ ≤ 125°C 1.00 1.15 V
LOAD
= 100mA, –40°C ≤ TJ < 0°C 1.20 V
LOAD
= 1A, 0°C ≤ TJ ≤ 125°C 1.00 1.15 V
LOAD
= 1A, –40°C ≤ TJ < 0°C 1.20 V
LOAD
= 2.75A, 0°C ≤ TJ ≤ 125°C 1.05 1.18 V
LOAD
= 2.75A, –40°C ≤ TJ < 0°C 1.23 V
LOAD
= 4A, 0°C ≤ TJ ≤ 125°C 1.06 1.20 V
LOAD
= 4A, –40°C ≤ TJ < 0°C 1.25 V
LOAD
= 7A, 0°C ≤ TJ ≤ 125°C 1.15 1.30 V
LOAD
= 6.5A, –40°C ≤ TJ < 0°C 1.35 V
LOAD
= 0mA to 7A ● 15mV
LOAD
= 10mA to 7A ● 15mV
LOAD
= 0V (Note 3) ● 510mA
ADJ
= 100mA, 0°C ≤ TJ ≤ 125°C610mA
LOAD
= 100mA, –40°C ≤ TJ < 0°C12mA
LOAD
= 4A, 0°C ≤ TJ ≤ 125°C3060mA
LOAD
= 4A, –40°C ≤ TJ < 0°C70mA
LOAD
= 4A, 0°C ≤ TJ ≤ 125°C3370mA
LOAD
= 4A, –40°C ≤ TJ < 0°C80mA
LOAD
= 7A, 0°C ≤ TJ ≤ 125°C 60 120 mA
LOAD
= 6.5A, –40°C ≤ TJ < 0°C 130 mA
LOAD
= 100mA, 0°C ≤ TJ ≤ 125°C610mA
LOAD
= 100mA, –40°C ≤ TJ < 0°C12mA
LOAD
= 4A, 0°C ≤ TJ ≤ 125°C3060mA
LOAD
= 4A, –40°C ≤ TJ < 0°C70mA
LOAD
= 4A, 0°C ≤ TJ ≤ 125°C3370mA
LOAD
= 4A, –40°C ≤ TJ < 0°C80mA
LOAD
= 7A, 0°C ≤ TJ ≤ 125°C 60 120 mA
LOAD
= 6.5A, –40°C ≤ TJ < 0°C 130 mA
LOAD
= 0mA ● 610mA
LOAD
= 10mA ● 50 120 µA
LOAD
= 100mV, 0°C ≤ TJ ≤ 125°C 7.1 8 A
OUT
= 100mV, –40°C ≤ TJ < 0°C 6.6 A
OUT
= 100mV, 0°C ≤ TJ ≤ 125°C 7.1 8 A
OUT
= 100mV, –40°C ≤ TJ < 0°C 6.6 A
OUT
, I
= 4A, TJ = 25°C6080dB
P-P
OUT
= 1V
, V
P-P
ADJ
= 0V, I
= 4A, TJ = 25°C6080 dB
OUT
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Page 4
LT1580/LT1580-2.5
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum V
– V
(V
POWER
Minimum V
– V
(V
POWER
(V
= 0V) V
ADJ
: LT1580-2.5 V
POWER
)V
OUT
V
V
V
V
V
: LT1580 V
POWER
)V
OUT
V
V
V
V
V
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
= 5V, I
= 5V, I
= 5V, I
= 5V, I
= 5V, I
= 5V, I
= 5V, I
= 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 ● 0.10 0.17 V
LOAD
= 1A ● 0.15 0.22 V
LOAD
= 4A, TJ = 25°C 0.34 0.40 V
LOAD
= 4A ● 0.50 V
LOAD
= 7A, TJ = 25°C 0.54 0.62 V
LOAD
= 7A, 0°C ≤ TJ ≤ 125°C 0.70 0.80 V
LOAD
= 6.5A, –40°C ≤ TJ ≤ 0°C 0.70 0.80 V
LOAD
= 100mA ● 0.10 0.17 V
LOAD
= 1A ● 0.15 0.22 V
LOAD
2.75A ● 0.26 0.38 V
LOAD
= 4A, TJ = 25°C 0.34 0.40 V
LOAD
= 4A ● 0.50 V
LOAD
= 7A, TJ = 25°C 0.54 0.62 V
LOAD
= 7A, 0°C ≤ TJ ≤ 125°C 0.70 0.80 V
LOAD
= 6.5A, –40°C ≤ TJ ≤ 0°C 0.70 0.80 V
LOAD
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: Unless otherwise specified V
adjustable device V
ADJ
= 0V.
OUT
= V
. For the LT1580
SENSE
Note 2: For the LT1580, dropout is caused by either minimum control
voltage (V
) or minimum power voltage (V
CONTROL
). Both parameters
POWER
are specified with respect to the output voltage. The specifications represent
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.
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.
the minimum input/output voltage required to maintain 1% regulation.
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TYPICAL PERFORMANCE CHARACTERISTICS
Control Pin Current
vs Output Current
140
INDICATES GUARANTEED TEST POINTS
≤ 125°C
0°C ≤ T
120
100
80
60
40
CONTROL PIN CURRENT (mA)
20
J
DATA SHEET LIMIT
TYPICAL
DEVICE
Minimum Control Voltage
2
INDICATES GUARANTEED TEST POINTS
≤ 125°C
0°C ≤ T
J
) (V)
OUT
1
– V
CONTROL
(V
MINIMUM CONTROL VOLTAGE
DATA SHEET LIMIT
TJ = 125°C
TJ = 25°C
Dropout Voltage—
Minimum Power Voltage
1.0
INDICATES GUARANTEED TEST POINTS
≤ 125°C
0°C ≤ T
J
DATA SHEET LIMIT
0.5
MINIMUM POWER VOLTAGE (V)
TJ = 125°C
TJ = 25°C
4
0
0
12
OUTPUT CURRENT (A)
467
35
1580 G01
0
0
1
3
2
OUTPUT CURRENT (A)
4
5
6
7
1580 G02
0
0
1
3
2
OUTPUT CURRENT (A)
4
5
6
7
1580 G03
Page 5
UW
TYPICAL PERFORMANCE CHARACTERISTICS
LT1580/LT1580-2.5
LT1580 Reference Voltage
vs Temperature
1.258
1.256
1.254
1.252
1.250
1.248
REFERENCE VOLTAGE (V)
1.246
1.244
1.242
–50 –25
0 25 75 125
TEMPERATURE (°C)
50
100
150
1580 G04
LT1580-2.5 Output Voltage
vs Temperature
2.508
2.506
2.504
2.502
2.500
2.498
OUTPUT VOLTAGE (V)
2.496
2.494
2.492
–50 –25
0 25 75 125
TEMPERATURE (°C)
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PIN FUNCTIONS
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):
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.
This pin is the negative side of the
(5-Lead/7-Lead)
Load Current Step Response
V
OUT
50mV/DIV
7A
LOAD
50
V
POWER
400mA
100
150
1580 G05
(Pin 5/6): This is the collector to the power device
50µs/DIV 1580 TA02
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).
V
CONTROL
(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).
V
(Pin 3/4): This is the power output of the device.
OUT
5
Page 6
LT1580/LT1580-2.5
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BLOCK DIAGRA
ADJ
V
CONTROL
SENSE
FOR FIXED
VOLTAGE
DEVICE
V
POWER
+
–
V
OUT
1580 BD
GND
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WUU
APPLICATIONS INFORMATION
The LT1580 is a low dropout regulator designed to power
the new generation of microprocessors. Low dropout
regulators have become more common in desktop computer 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. In many cases the input-output differential is very
small, effectively disqualifying many of the low dropout
regulators on the market today. The LT1580 is designed to
make use of multiple power supplies, present in most
systems, to reduce the dropout voltage. This two supply
approach maximizes efficiency.
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
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 control voltage must be at least 1V greater than the
output voltage to obtain optimum performance. The maximum voltage on the V
voltage at the V
pin is limited to 7V. GDN pin current
POWER
CONTROL
pin is 13V. The maximum
for fixed voltage devices is 6mA (typ) and is constant as a
function of load. ADJ pin current for adjustable devices is
60µA at 25°C and varies proportional to absolute tempera-
ture.
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Page 7
LT1580/LT1580-2.5
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WUU
APPLICATIONS INFORMATION
The LT1580 has improved frequency compensation which
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 microprocessors cycle load current from several hundred milliamperes 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.
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.
If the control voltage comes up first, the output current will
be limited to a few milliamperes until the power input
voltage comes up. If the power input comes up first the
output will not turn on at all until the control voltage comes
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 minimum control voltage.
The LT1580 includes several innovative features that
require additional pins over the traditional 3-terminal
regulator. Both the fixed and adjustable devices have
remote SENSE pins, permitting very accurate regulation of
output voltage at the load, where it counts, rather than at
the regulator. As a result the typical load regulation over
an output current range of 100mA to 7A with a 2.5V output
is typically less than 1mV. For the fixed voltage devices the
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 depend 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-
bined with ratiometrically accurate internal divider resistors the part can easily hold 1% output accuracy over the
full temperature range and load current range, guaranteed, 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 conversion 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
LT1580 has fast transient response that allows it to handle
the large current changes associated with today’s microprocessors. The device is fully protected against
overcurrent and overtemperature conditions. Both fixed
voltage (2.5V) and adjustable output versions are available. The device is available in a multilead TO-220 package
with five leads for the adjustable device and seven leads for
the fixed voltage device.
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
and the load which would normally degrade regulation can
be placed inside the regulation loop of the LT1580. 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 directly to the output of the device. RP represents the
parasitic resistance of the connections between the LT1580
and the load. The load is typically a microprocessor and
RP is made up of the PC traces and/or connector resistances, 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 output 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
7
Page 8
LT1580/LT1580-2.5
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WUU
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
connected inside the regulating loop of the LT1580 and the
load regulation at the load will be negligible for reasonable
5V
V
CONTROL
ADJ
R2
5V
CONTROL
LT1580
ADJ
R2
(∆I
SENSE
SENSE
OUT
V
OUT
R1
V
OUT
R1
)(RP)
LOAD
LOAD
+
V
OUT
–
1580 F01
+
V
OUT
–
1580 F02
R
P
R
P
R
P
R
P
3.3V
3.3V
V
POWER
LT1580
Figure 1. Conventional Load Sensing
V
V
POWER
Figure 2. Remote Load Sensing
V
OUT
FIGURE 1
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.
Stability
The LT1580 requires the use of an output capacitor as part
of the device frequency compensation. The device requires a minimum of 22µF tantalum or 150µF of aluminum
electrolytic to ensure stability. Larger capacitor values
increase stability and improve transient performance.
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 capacitance temperature coefficient. The LT1580 frequency
compensation optimizes frequency response with low
ESR capacitors. In general, use capacitors with an ESR of
less than 1Ω.
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 capacitors in addition to high quality bulk tantalum capacitors are typically required to limit parasitic inductance
(ESL) and resistance (ESR) in the capacitors to acceptable
levels. The LT1580 is stable with the type of capacitors
recommended by processor manufacturers.
V
OUT
FIGURE 2
I
OUT
TIME
1580 F03
Figure 3. Remote Sensing Improves Load Regulation
8
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.
Capacitor values on the order of several hundred microfarads are used to ensure good transient response with heavy
Page 9
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.
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 parasitic elements dominate the change in output voltage at the
beginning of a transient load step change. The ESR of the
output capacitors produces an instantaneous step in output voltage (∆V = ∆I)(ESR). The ESL of the output capacitors produces a droop proportional to the rate of change
of the output current (V = L)(∆I/∆t). The output capacitance 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 .
ESR
EFFECTS
ESL
EFFECTS
V
SLOPE, =
t
∆I
C
POINT AT WHICH REGULATOR
TAKES CONTROL
Figure 4
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 microprocessors. These requirements dictate a combination of
high quality, surface mount, tantalum and ceramic capacitors. The location of the decoupling network is critical to
transient performance. Place the decoupling network as
close to the processor pins as possible because trace runs
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 addition, use large power and ground plane areas to minimize
distribution drops.
CAPACITANCE
EFFECTS
1580 F04
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
minimum load current of 10mA. The current out of the ADJ
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 considered when very precise output voltage setting is required.
Note that the top of the resistor divider should be connected directly to the SENSE pin for best regulation. See
the section on grounding and Kelvin sensing above.
V
CONTROL
+
V
CONTROL
V
POWER
V
OUT
= V
V
+
REF
POWER
LT1580
SENSE
ADJ
= 50µA
I
R2
1 + + I
(
R1
ADJ
(R2)
ADJ
)
Figure 5. Setting Output Voltage
V
OUT
V
R1
REF
R2
V
+
OUT
1580 F05
Protection Diodes
In normal operation the LT1580 does not require protection diodes. Older 3-terminal regulators require protection
diodes between the V
the ADJ pin and the V
pin and the Input pin or between
OUT
pin to prevent die overstress.
OUT
On the LT1580, internal resistors limit internal current
paths on the ADJ pin. Therefore even with bypass capacitors 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
Page 10
LT1580/LT1580-2.5
U
WUU
APPLICATIONS INFORMATION
A protection diode between the V
pin is usually not needed. An internal diode between the
V
pin and the V
OUT
POWER
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 V
pin instantaneously shorted
POWER
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.
V
CONTROL
+
V
CONTROL
V
POWER
+
*OPTIONAL DIODES: 1N4002
Figure 6. Optional Clamp Diodes Protect Against
Input Crowbar Circuits
V
POWER
LT1580
ADJ
A protection diode between the V
pin is usually not needed. An internal diode between the
V
pin and the V
OUT
CONTROL
pin on the LT1580 can handle
microsecond surge currents of 1A to 10A. This can only
occur if the V
CONTROL
pin is instantaneously shorted to
ground with a crowbar circuit with large value output
capacitors. Since the V
CONTROL
supply, this condition is unlikely. A protection diode from
the V
V
CONTROL
pin to the V
OUT
CONTROL
pin is recommended if the
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.
pin and the V
OUT
V
OUT
SENSE
pin and the V
OUT
D1*
D2*
+
R1
R2
CONTROL
POWER
V
OUT
1580 F06
pin is usually a low current
If the LT1580 is connected as a single supply device with
the V
CONTROL
internal diode between the V
will protect the V
and V
CONTROL
input pins shorted together the
POWER
and the V
OUT
POWER
input pin.
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.
For continuous normal load conditions 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
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.
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 resistance, 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 power levels greater than 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 determined by the total power dissipated in the device. For most
10
Page 11
LT1580/LT1580-2.5
U
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APPLICATIONS INFORMATION
low dropout applications the power dissipation will be less
than 12W.
The power in the device is made up of two main components: 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:
P
= (V
DRIVE
where I
I
/58 (max).
OUT
I
CONTROL
I
CONTROL
CONTROL
CONTROL
is a function of output current. A curve of
vs I
OUT
Characteristics curves.
The power in the output transistor is equal to:
P
OUTPUT
= (V
The total power is equal to:
P
= P
TOTAL
DRIVE
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 electronically isolated, a thermally conductive spacer can be used
as long as the added contribution to thermal resistance is
considered. Please consult Linear Technology’s “ Mounting Considerations for Power Semiconductors,”
Linear Applications Handbook, Volume 1
RR3-20. Note that the case of the LT1580 is electrically
connected to the output.
– V
is equal to between I
OUT
)(I
CONTROL
)
/100 (typ) and
OUT
can be found in the Typical Performance
POWER
+ P
– V
OUTPUT
OUT
)(I
OUT
)
1990
, Pages RR3-1 to
The following example illustrates how to calculate
maximum junction temperature. Using an LT1580 and
assuming:
V
CONTROL
V
POWER
V
OUT
TA = 70°C, θ
θ
CASE-HEATSINK
(max continuous) = 5.25V (5V + 5%),
(max continuous) = 3.465V (3.3V + 5%),
= 2.5V, Iout = 4A,
HEATSINK
= 4°C/W,
= 1°C/W (with thermal compound)
Power dissipation under these conditions is equal to:
Total Power Dissipation = P
P
= (V
DRIVE
I
CONTROL
P
DRIVE
P
OUTPUT
CONTROL
= I
OUT
= (5.25V –␣ 2.5V)(69mA) = 190mW
= (V
– V
OUT
/58 = 4A/58 = 69mA
– V
POWER
OUT
DRIVE
) (I
CONTROL
)(I
OUT
+ P
)
OUTPUT
)
= ( 3.465V – 2.5V)(4A) = 3.9W
Total Power Dissipation = 4.05W
Junction temperature will be equal to:
TJ = TA + P
TOTAL
(θ
HEATSINK
+ θ
CASE-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 = T
for Control Section
JMAX
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 = T
for Power Section
JMAX
In both cases the junction temperature is below the
maximum rating for the respective sections, ensuring
reliable operation.
11
Page 12
LT1580/LT1580-2.5
TYPICAL APPLICATION
5V
3.3V
+
+
C3
22µF
25V
RTN
U
5
C2
220µF
10V
0.33µF
2.5V/6A Regulator
V
POWER
LT1580
ADJ
2
C4
R2
110Ω
1%
V
CONT
SENSE
V
OUT
110Ω
R1
1%
100µF
10V
4
1
= 2.5V
V
3
OUT
V
CC
+
100µF
10V
C1
+
× 2
1µF
25V
MICROPROCESSOR
× 10
SOCKET
V
SS
1580 TA03
12
Page 13
PACKAGE DESCRIPTION
LT1580/LT1580-2.5
U
Dimensions in inches (millimeters) unless otherwise noted.
Q Package
5-Lead Plastic DD Pak
(LTC DWG # 05-08-1461)
0.256
(6.502)
0.060
(1.524)
0.300
(7.620)
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
0.060
(1.524)
0.075
(1.905)
0.183
(4.648)
0.060
(1.524)
TYP
0.330 – 0.370
(8.382 – 9.398)
+0.012
0.143
–0.020
+0.305
3.632
()
–0.508
0.028 – 0.038
(0.711 – 0.965)
0.390 – 0.415
(9.906 – 10.541)
15
° TYP
0.057 – 0.077
(1.447 – 1.955)
R Package
7-Lead Plastic DD Pak
(LTC DWG # 05-08-1462)
0.165 – 0.180
(4.191 – 4.572)
0.059
(1.499)
TYP
0.013 – 0.023
(0.330 – 0.584)
0.045 – 0.055
(1.143 – 1.397)
+0.008
0.004
–0.004
+0.203
0.102
()
–0.102
0.095 – 0.115
(2.413 – 2.921)
± 0.012
0.050
(1.270 ± 0.305)
Q(DD5) 0396
0.256
(6.502)
0.060
(1.524)
0.300
(7.620)
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
0.060
(1.524)
0.075
(1.905)
0.183
(4.648)
0.060
(1.524)
TYP
0.330 – 0.370
(8.382 – 9.398)
+0.012
0.143
–0.020
+0.305
3.632
()
–0.508
0.026 – 0.036
(0.660 – 0.914)
0.390 – 0.415
(9.906 – 10.541)
15
° TYP
0.040 – 0.060
(1.016 – 1.524)
0.165 – 0.180
(4.191 – 4.572)
0.059
(1.499)
TYP
0.013 – 0.023
(0.330 – 0.584)
0.045 – 0.055
(1.143 – 1.397)
+0.008
0.004
–0.004
+0.203
0.102
()
–0.102
0.095 – 0.115
(2.413 – 2.921)
± 0.012
0.050
(1.270 ± 0.305)
R (DD7) 0396
13
Page 14
LT1580/LT1580-2.5
PACKAGE DESCRIPTION
U
Dimensions in inches (millimeters) unless otherwise noted.
T Package
5-Lead Plastic TO-220 (Standard)
(LTC DWG # 05-08-1421)
0.390 – 0.415
(9.906 – 10.541)
0.460 – 0.500
(11.684 – 12.700)
0.057 – 0.077
(1.448 – 1.956)
0.147 – 0.155
(3.734 – 3.937)
0.230 – 0.270
(5.842 – 6.858)
0.330 – 0.370
(8.382 – 9.398)
0.028 – 0.038
(0.711 – 0.965)
DIA
0.570 – 0.620
(14.478 – 15.748)
0.260 – 0.320
(6.60 – 8.13)
0.700 – 0.728
(17.78 – 18.491)
0.152 – 0.202
(3.861 – 5.131)
0.135 – 0.165
(3.429 – 4.191)
0.165 – 0.180
(4.191 – 4.572)
0.620
(15.75)
TYP
0.045 – 0.055
(1.143 – 1.397)
0.095 – 0.115
(2.413 – 2.921)
0.013 – 0.023
(0.330 – 0.584)
0.155 – 0.195
(3.937 – 4.953)
T5 (TO-220) 0398
14
Page 15
PACKAGE DESCRIPTION
LT1580/LT1580-2.5
U
Dimensions in inches (millimeters) unless otherwise noted.
T7 Package
7-Lead Plastic TO-220 (Standard)
(LTC DWG # 05-08-1422)
0.390 – 0.415
(9.906 – 10.541)
0.460 – 0.500
(11.684 – 12.700)
0.040 – 0.060
(1.016 – 1.524)
0.147 – 0.155
(3.734 – 3.937)
0.230 – 0.270
(5.842 – 6.858)
0.330 – 0.370
(8.382 – 9.398)
0.026 – 0.036
(0.660 – 0.914)
DIA
0.570 – 0.620
(14.478 – 15.748)
0.260 – 0.320
(6.604 – 8.128)
0.700 – 0.728
(17.780 – 18.491)
0.152 – 0.202
(3.860 – 5.130)
0.135 – 0.165
(3.429 – 4.191)
0.165 – 0.180
(4.191 – 4.572)
0.620
(15.75)
TYP
0.045 – 0.055
(1.143 – 1.397)
0.095 – 0.115
(2.413 – 2.921)
0.013 – 0.023
(0.330 – 0.584)
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
Page 16
LT1580/LT1580-2.5
TYPICAL APPLICATION
Dual Regulators Power Pentium Processor or Upgrade CPU
R12
0.0075Ω*
5V
R1
10k
R10
10k
12V
C11
R13
0.005Ω*
C9
220µF
10V
*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
22µF
35V
++
C2
220µF
10V
U
+
LT1006
–
+
0.33µF
12V
V
R2
470Ω
D2
1N4148
R8
107Ω
0.35%
Q1
CPU TYPE
R14, 2Ω
C10
1µF
P55C
P54C
INVOUT
LT1587
ADJ
R4
178Ω
1%
5V
R5
10k
2N3904
R3
110Ω
1%
+
R9
10k
Q2
+
C1
220µF
1N4148
SENSE
V
2
R7
107Ω
0.25%
D1
OUT
ZVN4206
10V
1
3
E3
0
1
C8
0.1µF
C6
0.01µF
4
V
CONTROL
LT1580
5
V
POWER
ADJ
C5
R6
89.8Ω
0.5%
C4
0.33µF
C7
330µF
6.3V
2N7002
+
5V
Q3
Q3
2N7002
C3
220µF
10V
R11
10k
I/O
SUPPLY
3.5V/3.3V
CORE
SUPPLY
3.5V/2.5V
E3
TO CPU
VOLTAGE
SELECT PIN
1580 TA04
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LTC®1266 Synchronous Switching Controller >90% Efficient High Current Microprocessor Supply
LTC1267 Dual High Efficiency Synchronous Switching Regulator >90% Efficiency with Fixed 5V, 3.3V or Adjustable Outputs
LTC1430 High Power Synchronous Step-Down Switching Regulator >90% Efficient High Current Microprocessor Supply
LT1584 7A Low Dropout Fast Transient Response Regulator For High Performance Microprocessors
LT1585 4.6A Low Dropout Fast Transient Response Regulator For High Performance Microprocessors
LT1587 3A Low Dropout Fast Transient Response Regulator For High Performance Microprocessors
158025fas, sn158025 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
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