LT1580/LT1580-2.5
7A, Very Low
Dropout Regulator
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DESCRIPTION
FEATURES
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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.
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
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APPLICATIONS
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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.
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
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.
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TYPICAL APPLICATION
Dropout Voltage —
Minimum Power Voltage
2.5V Microprocessor Supply
5V
0.2A
2.5V/7A
VOUT
VPOWER
+
+
330µF
OS-CON
LT1580-2.5
VCONTROL
+
10µF
TANT
GND
100µF TANT
AVX TPS
×7
SENSE
ADJ
0.1µF
MINIMUM POWER VOLTAGE (V)
3.3V
7A
1.0
INDICATES GUARANTEED TEST POINTS
0°C ≤ TJ ≤ 125°C
DATA SHEET LIMIT
0.5
TJ = 125°C
TJ = 25°C
1580 TA01
0
0
1
3
5
4
2
OUTPUT CURRENT (A)
6
7
1580 G03
1
LT1580/LT1580-2.5
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ABSOLUTE MAXIMUM RATINGS
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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VPOWER Input Voltage ................................................ 6V
VCONTROL Input Voltage ........................................... 13V
Storage Temperature ............................ – 65°C to 150°C
Operating Junction Temperature Range
Control Section
LT1580C ........................................... 0°C to 125°C
LT1580I ........................................ – 40°C to 125°C
PRECONDITIONING
100% Thermal Limit Functional Test
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PACKAGE/ORDER INFORMATION
FRONT VIEW
TAB
IS
OUTPUT
5
VPOWER
4
VCONTROL
3
VOUT
2
ADJ
1
SENSE
ORDER PART
NUMBER
LT1580CQ
LT1580IQ
FRONT VIEW
TAB
IS
OUTPUT
5
VPOWER
4
VCONTROL
3
VOUT
2
ADJ
1
SENSE
Q PACKAGE
5-LEAD PLASTIC DD
T PACKAGE
5-LEAD PLASTIC TO-220
θJA = 30°C/ W
θJA = 50°C/ W
FRONT VIEW
7
6
5
4
3
2
1
TAB
IS
OUTPUT
NC
VPOWER
ADJ
VOUT
VCONTROL
GND
SENSE
ORDER PART
NUMBER
LT1580CR-2.5
LT1580IR-2.5
FRONT VIEW
TAB
IS
OUTPUT
NC
VPOWER
ADJ
VOUT
VCONTROL
GND
SENSE
7
6
5
4
3
2
1
R PACKAGE
7-LEAD PLASTIC DD
T7 PACKAGE
7-LEAD PLASTIC TO-220
θJA = 30°C/ W
θJA = 50°C/ W
ORDER PART
NUMBER
LT1580CT
LT1580IT
ORDER PART
NUMBER
LT1580CT7-2.5
LT1580IT7-2.5
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Output Voltage: LT1580-2.5
Reference Voltage: LT1580
(VADJ = 0V)
Line Regulation: LT1580-2.5
LT1580
2
(Note 1)
CONDITIONS
VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 0mA
VCONTROL = 4V to 12V, VPOWER = 3V to 5.5V, ILOAD = 0mA to 4A
VCONTROL = 4V to 12V, VPOWER = 3V to 5.5V,
ILOAD = 0mA to 7A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 4V to 12V, VPOWER = 3V to 5.5V,
ILOAD = 0mA to 6.5A, – 40°C ≤ TJ < 0°C
VCONTROL = 2.75V, VPOWER = 2V, ILOAD = 10mA
VCONTROL = 2.7V to 12V, VPOWER = 1.75V to 5.5V, ILOAD = 10mA to 4A
VCONTROL = 2.7V to 12V, VPOWER = 2.05V to 5.5V,
ILOAD = 10mA to 7A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 2.7V to 12V, VPOWER = 2.05V to 5.5V,
ILOAD = 10mA to 6.5A, – 40°C ≤ TJ < 0°C
VCONTROL = 3.65V to 12V, VPOWER = 3V to 5.5V, ILOAD = 10mA
VCONTROL = 2.5V to 12V, VPOWER = 1.75V to 5.5V, ILOAD = 10mA
●
●
●
●
MIN
2.485
2.475
2.475
TYP
2.500
2.500
2.500
MAX
2.515
2.525
2.525
UNITS
V
V
V
2.460
2.500
2.525
V
1.243
1.237
1.237
1.250
1.250
1.250
1.257
1.263
1.263
V
V
V
1.232
1.250
1.263
V
1
1
3
3
mV
mV
LT1580/LT1580-2.5
ELECTRICAL CHARACTERISTICS
PARAMETER
Load Regulation: LT1580-2.5
LT1580 (VADJ = 0V)
CONDITIONS
VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 0mA to 7A
VCONTROL = 2.75V, VPOWER = 2.1V, ILOAD = 10mA to 7A
●
●
TYP
1
1
MAX
5
5
Minimum Load Current: LT1580
VCONTROL = 5V, VPOWER = 3.3V, VADJ = 0V (Note 3)
●
5
10
mA
Control Pin Current: LT1580-2.5
(Note 4)
VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 100mA, 0°C ≤ TJ ≤ 125°C
VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 100mA, – 40°C ≤ TJ < 0°C
VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 4A, – 40°C ≤ TJ < 0°C
VCONTROL = 5V, VPOWER = 3V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 5V, VPOWER = 3V, ILOAD = 4A, – 40°C ≤ TJ < 0°C
VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 6.5A, – 40°C ≤ TJ < 0°C
6
10
12
60
70
70
80
120
130
mA
mA
mA
mA
mA
mA
mA
mA
10
12
60
70
70
80
120
130
mA
mA
mA
mA
mA
mA
mA
mA
6
10
mA
50
120
µA
Control Pin Current: LT1580
(Note 4)
MIN
30
33
60
VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 100mA, 0°C ≤ TJ ≤ 125°C
VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 100mA, – 40°C ≤ TJ < 0°C
VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 4A, – 40°C ≤ TJ < 0°C
VCONTROL = 2.75V, VPOWER = 1.75V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 2.75V, VPOWER = 1.75V, ILOAD = 4A, – 40°C ≤ TJ < 0°C
VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 6.5A, – 40°C ≤ TJ < 0°C
6
30
33
60
Ground Pin Current: LT1580-2.5
VCONTROL = 5V, VPOWER = 3.3V, ILOAD = 0mA
●
ADJ Pin Current: LT1580 (VADJ = 0V)
VCONTROL = 2.75V, VPOWER = 2.05V, ILOAD = 10mA
●
Current Limit: LT1580-2.5
VCONTROL = 5V, VPOWER = 3.3V, ∆VOUT = 100mV, 0°C ≤ TJ ≤ 125°C
VCONTROL = 5V, VPOWER = 3.3V, ∆VOUT = 100mV, – 40°C ≤ TJ < 0°C
VCONTROL = 2.75V, VPOWER = 2.05V, ∆VOUT = 100mV, 0°C ≤ TJ ≤ 125°C
VCONTROL = 2.75V, VPOWER = 2.05V, ∆VOUT = 100mV, – 40°C ≤ TJ < 0°C
7.1
6.6
7.1
6.6
Ripple Rejection: LT1580-2.5
LT1580
VC = VP = 5V Avg, VRIPPLE = 1VP-P, IOUT = 4A, TJ = 25°C
VC = VP = 3.75V Avg, VRIPPLE = 1VP-P, VADJ = 0V, IOUT = 4A, TJ = 25°C
60
60
Thermal Regulation
30ms Pulse
0.002
Thermal Resistance, Junction-to-Case T, T7 Packages, Control Circuitry/Power Transistor
0.65/2.70
LT1580 (VADJ = 0V)
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UNITS
mV
mV
A
A
A
A
8
80
80
dB
dB
0.020
%/W
°C/W
Dropout Voltage (Note 2)
Minimum VCONTROL: LT1580-2.5
(VCONTROL – VOUT)
Minimum VCONTROL: LT1580
(VCONTROL – VOUT)
(VADJ = 0V)
VPOWER = 3.3V, ILOAD = 100mA, 0°C ≤ TJ ≤ 125°C
VPOWER = 3.3V, ILOAD = 100mA, – 40°C ≤ TJ < 0°C
VPOWER = 3.3V, ILOAD = 1A, 0°C ≤ TJ ≤ 125°C
VPOWER = 3.3V, ILOAD = 1A, – 40°C ≤ TJ < 0°C
VPOWER = 3.3V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C
VPOWER = 3.3V, ILOAD = 4A, – 40°C ≤ TJ < 0°C
VPOWER = 3.3V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C
VPOWER = 3.3V, ILOAD = 6.5A, – 40°C ≤ TJ < 0°C
1.00
VPOWER = 2.05V, ILOAD = 100mA, 0°C ≤ TJ ≤ 125°C
VPOWER = 2.05V, ILOAD = 100mA, – 40°C ≤ TJ < 0°C
VPOWER = 2.05V, ILOAD = 1A, 0°C ≤ TJ ≤ 125°C
VPOWER = 2.05V, ILOAD = 1A, – 40°C ≤ TJ < 0°C
VPOWER = 2.05V, ILOAD = 2.75A, 0°C ≤ TJ ≤ 125°C
VPOWER = 2.05V, ILOAD = 2.75A, – 40°C ≤ TJ < 0°C
VPOWER = 2.05V, ILOAD = 4A, 0°C ≤ TJ ≤ 125°C
VPOWER = 2.05V, ILOAD = 4A, – 40°C ≤ TJ < 0°C
VPOWER = 2.05V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C
VPOWER = 2.05V, ILOAD = 6.5A, – 40°C ≤ TJ < 0°C
1.00
1.00
1.06
1.15
1.00
1.05
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
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
3
LT1580/LT1580-2.5
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum VPOWER: LT1580-2.5
(VPOWER – VOUT)
CONDITIONS
VCONTROL = 5V, ILOAD = 100mA
VCONTROL = 5V, ILOAD = 1A
VCONTROL = 5V, ILOAD = 4A, TJ = 25°C
VCONTROL = 5V, ILOAD = 4A
VCONTROL = 5V, ILOAD = 7A, TJ = 25°C
VCONTROL = 5V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 5V, ILOAD = 6.5A, – 40°C ≤ TJ ≤ 0°C
Minimum VPOWER: LT1580
(VPOWER – VOUT)
(VADJ = 0V)
MIN
●
●
●
0.54
0.70
0.70
VCONTROL = 2.75V, ILOAD = 100mA
VCONTROL = 2.75V, ILOAD = 1A
VCONTROL = 2.75V, ILOAD 2.75A
VCONTROL = 2.75V, ILOAD = 4A, TJ = 25°C
VCONTROL = 2.75V, ILOAD = 4A
VCONTROL = 2.75V, ILOAD = 7A, TJ = 25°C
VCONTROL = 2.75V, ILOAD = 7A, 0°C ≤ TJ ≤ 125°C
VCONTROL = 2.75V, ILOAD = 6.5A, – 40°C ≤ TJ ≤ 0°C
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: Unless otherwise specified VOUT = VSENSE. For the LT1580
adjustable device VADJ = 0V.
Note 2: For the LT1580, dropout is caused by either minimum control
voltage (VCONTROL) or minimum power voltage (VPOWER). Both parameters
are specified with respect to the output voltage. The specifications represent
the minimum input/output voltage required to maintain 1% regulation.
TYP
0.10
0.15
0.34
0.10
0.15
0.26
0.34
●
●
●
●
0.54
0.70
0.70
MAX
0.17
0.22
0.40
0.50
0.62
0.80
0.80
UNITS
V
V
V
V
V
V
V
0.17
0.22
0.38
0.40
0.50
0.62
0.80
0.80
V
V
V
V
V
V
V
V
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.
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TYPICAL PERFORMANCE CHARACTERISTICS
Control Pin Current
vs Output Current
140
2
100
DATA SHEET LIMIT
80
TYPICAL
DEVICE
60
40
20
0
0
1
4
3
5
2
OUTPUT CURRENT (A)
6
7
1580 G01
INDICATES GUARANTEED TEST POINTS
0°C ≤ TJ ≤ 125°C
MINIMUM POWER VOLTAGE (V)
MINIMUM CONTROL VOLTAGE
(VCONTROL – VOUT) (V)
CONTROL PIN CURRENT (mA)
1.0
INDICATES GUARANTEED TEST POINTS
0°C ≤ TJ ≤ 125°C
120
4
Dropout Voltage —
Minimum Power Voltage
Minimum Control Voltage
DATA SHEET LIMIT
1
TJ = 125°C
TJ = 25°C
0
INDICATES GUARANTEED TEST POINTS
0°C ≤ TJ ≤ 125°C
DATA SHEET LIMIT
0.5
TJ = 125°C
TJ = 25°C
0
0
1
3
5
4
2
OUTPUT CURRENT (A)
6
7
1580 G02
0
1
3
5
4
2
OUTPUT CURRENT (A)
6
7
1580 G03
LT1580/LT1580-2.5
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TYPICAL PERFORMANCE CHARACTERISTICS
LT1580-2.5 Output Voltage
vs Temperature
1.258
2.508
1.256
2.506
1.254
2.504
OUTPUT VOLTAGE (V)
REFERENCE VOLTAGE (V)
LT1580 Reference Voltage
vs Temperature
1.252
1.250
1.248
LOAD
2.498
1.244
2.494
25 50 75 100 125 150
TEMPERATURE (°C)
7A
2.500
2.496
0
VOUT
50mV/DIV
2.502
1.246
1.242
–50 –25
2.492
–50 –25
400mA
50µs/DIV
0
1580 TA02
25 50 75 100 125 150
TEMPERATURE (°C)
1580 G04
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PIN FUNCTIONS
Load Current Step Response
1580 G05
(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
LT1580/LT1580-2.5
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BLOCK DIAGRA
VCONTROL
VPOWER
+
–
SENSE
VOUT
FOR FIXED
VOLTAGE
DEVICE
1580 BD
ADJ
GND
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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
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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 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
60µA at 25°C and varies proportional to absolute temperature.
LT1580/LT1580-2.5
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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
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LT1580/LT1580-2.5
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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
connected inside the regulating loop of the LT1580 and the
load regulation at the load will be negligible for reasonable
5V
VCONTROL
3.3V
SENSE
VPOWER
LT1580
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
VOUT
ADJ
+
RP
LOAD
R1
VOUT
R2
RP
–
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.
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 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.
Figure 1. Conventional Load Sensing
5V
VCONTROL
3.3V
SENSE
VPOWER
LT1580
VOUT
ADJ
+
RP
LOAD
R1
VOUT
R2
RP
–
1580 F02
Figure 2. Remote Load Sensing
(∆IOUT)(RP)
VOUT
FIGURE 1
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.
VOUT
FIGURE 2
IOUT
TIME
1580 F03
Figure 3. Remote Sensing Improves Load Regulation
8
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.
Capacitor values on the order of several hundred microfarads are used to ensure good transient response with heavy
LT1580/LT1580-2.5
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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 .
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.
VCONTROL
+
VCONTROL
VPOWER
+
VPOWER
VOUT
+
VOUT
LT1580
ESR
EFFECTS
SENSE
ESL
EFFECTS
ADJ
CAPACITANCE
EFFECTS
VREF
R1
1580 F04
SLOPE,
V ∆I
=
t
C
POINT AT WHICH REGULATOR
TAKES CONTROL
( )
IADJ = 50µA
R2
VOUT = VREF 1 + R2 + IADJ (R2)
R1
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 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.
Protection Diodes
In normal operation the LT1580 does not require protection diodes. Older 3-terminal regulators require protection
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 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
LT1580/LT1580-2.5
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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.
VCONTROL
+
D1*
VCONTROL
VPOWER
+
VOUT
VPOWER
D2*
+
VOUT
LT1580
SENSE
ADJ
*OPTIONAL DIODES: 1N4002
R1
R2
1580 F06
Figure 6. Optional Clamp Diodes Protect Against
Input Crowbar Circuits
A protection diode between the VOUT pin and the VCONTROL
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. Since the VCONTROL pin is usually a low current
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
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.
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
LT1580/LT1580-2.5
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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:
PDRIVE = (VCONTROL – VOUT)(ICONTROL)
where ICONTROL is equal to between IOUT/100 (typ) and
IOUT/58 (max).
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
ICONTROL is a function of output current. A curve of
ICONTROL vs IOUT can be found in the Typical Performance
Characteristics curves.
PDRIVE = (VCONTROL – VOUT) (ICONTROL)
The power in the output transistor is equal to:
POUTPUT = (VPOWER – VOUT)(IOUT)
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 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,” 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.
ICONTROL = IOUT/58 = 4A/58 = 69mA
PDRIVE = (5.25V –␣ 2.5V)(69mA) = 190mW
= ( 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
LT1580/LT1580-2.5
U
TYPICAL APPLICATION
2.5V/6A Regulator
5V
5
3.3V
VPOWER
VCONT
SENSE
LT1580
ADJ
C3
22µF
25V
+
+
C2
220µF
10V
C4
0.33µF
RTN
2
VOUT
4
1
VOUT = 2.5V
3
VCC
R1
110Ω
1%
C1
R2
110Ω 100µF
10V
1%
+
100µF
10V
×2
+
1µF
25V
× 10
MICROPROCESSOR
SOCKET
VSS
1580 TA03
12
LT1580/LT1580-2.5
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PACKAGE DESCRIPTION
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)
0.060
(1.524)
TYP
0.390 – 0.415
(9.906 – 10.541)
0.165 – 0.180
(4.191 – 4.572)
0.045 – 0.055
(1.143 – 1.397)
15° TYP
0.060
(1.524)
0.183
(4.648)
0.059
(1.499)
TYP
0.330 – 0.370
(8.382 – 9.398)
(
+0.008
0.004 –0.004
+0.203
0.102 –0.102
)
0.095 – 0.115
(2.413 – 2.921)
0.075
(1.905)
0.300
(7.620)
(
+0.012
0.143 –0.020
+0.305
3.632 –0.508
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
)
0.057 – 0.077
(1.447 – 1.955)
0.028 – 0.038
(0.711 – 0.965)
0.050 ± 0.012
(1.270 ± 0.305)
0.013 – 0.023
(0.330 – 0.584)
Q(DD5) 0396
R Package
7-Lead Plastic DD Pak
(LTC DWG # 05-08-1462)
0.256
(6.502)
0.060
(1.524)
0.060
(1.524)
TYP
0.390 – 0.415
(9.906 – 10.541)
0.165 – 0.180
(4.191 – 4.572)
15° TYP
0.060
(1.524)
0.183
(4.648)
0.059
(1.499)
TYP
0.330 – 0.370
(8.382 – 9.398)
BOTTOM VIEW OF DD PAK
HATCHED AREA IS SOLDER PLATED
COPPER HEAT SINK
(
+0.008
0.004 –0.004
+0.203
0.102 –0.102
)
0.095 – 0.115
(2.413 – 2.921)
0.075
(1.905)
0.300
(7.620)
0.045 – 0.055
(1.143 – 1.397)
(
+0.012
0.143 –0.020
+0.305
3.632 –0.508
)
0.040 – 0.060
(1.016 – 1.524)
0.026 – 0.036
(0.660 – 0.914)
0.013 – 0.023
(0.330 – 0.584)
0.050 ± 0.012
(1.270 ± 0.305)
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)
0.390 – 0.415
(9.906 – 10.541)
0.165 – 0.180
(4.191 – 4.572)
0.147 – 0.155
(3.734 – 3.937)
DIA
0.045 – 0.055
(1.143 – 1.397)
0.230 – 0.270
(5.842 – 6.858)
0.460 – 0.500
(11.684 – 12.700)
0.570 – 0.620
(14.478 – 15.748)
0.330 – 0.370
(8.382 – 9.398)
0.620
(15.75)
TYP
0.700 – 0.728
(17.78 – 18.491)
0.152 – 0.202
0.260 – 0.320 (3.861 – 5.131)
(6.60 – 8.13)
0.095 – 0.115
(2.413 – 2.921)
0.013 – 0.023
(0.330 – 0.584)
0.057 – 0.077
(1.448 – 1.956)
0.028 – 0.038
(0.711 – 0.965)
0.135 – 0.165
(3.429 – 4.191)
0.155 – 0.195
(3.937 – 4.953)
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)
0.390 – 0.415
(9.906 – 10.541)
0.165 – 0.180
(4.191 – 4.572)
0.147 – 0.155
(3.734 – 3.937)
DIA
0.045 – 0.055
(1.143 – 1.397)
0.230 – 0.270
(5.842 – 6.858)
0.460 – 0.500
(11.684 – 12.700)
0.570 – 0.620
(14.478 – 15.748)
0.330 – 0.370
(8.382 – 9.398)
0.620
(15.75)
TYP
0.700 – 0.728
(17.780 – 18.491)
0.152 – 0.202
0.260 – 0.320 (3.860 – 5.130)
(6.604 – 8.128)
0.040 – 0.060
(1.016 – 1.524)
0.095 – 0.115
(2.413 – 2.921)
0.013 – 0.023
(0.330 – 0.584)
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LT1580/LT1580-2.5
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TYPICAL APPLICATION
Dual Regulators Power Pentium Processor or Upgrade CPU
R12
0.0075Ω*
5V
+
12V
R1
10k
C8
0.1µF
VIN
C1
220µF
10V
VOUT
D1
1N4148
R2
470Ω
LT1006
R10
10k
+
C9
220µF
10V
+
C4
0.33µF
D2
1N4148
12V
R13
0.005Ω*
R4
178Ω
1%
C6
0.01µF
C11
22µF
35V
C2
220µF
10V
4
+
VCONTROL SENSE
R11
10k
C10
1µF
VPOWER
VOUT
ADJ
+
3
C7
330µF
6.3V
R7
107Ω
0.25%
R6
89.8Ω
0.5%
R8
107Ω
0.35%
5V
Q1
ZVN4206
Q3
2N7002
R5
10k
R9
10k
E3
TO CPU
VOLTAGE
SELECT PIN
Q2
2N3904
*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
CORE
SUPPLY
3.5V/2.5V
Q3
2N7002
2
C5
0.33µF
5V
R14, 2Ω
1
LT1580
5
C3
220µF
10V
R3
110Ω
1%
ADJ
+
–
+
LT1587
I/O
SUPPLY
3.5V/3.3V
E3 CPU TYPE
0
P55C
1
P54C
1580 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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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
®
16
Linear Technology Corporation
158025fas, sn158025 LT/GP 0598 2K REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
LINEAR TECHNOLOGY CORPORATION 1995
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