LT1584/LT1585/LT1587
7A, 4.6A, 3A Low Dropout
Fast Response
Positive Regulators
Adjustable and Fixed
U
DESCRIPTIO
FEATURES
■
■
■
■
■
■
Fast Transient Response
Guaranteed Dropout Voltage at Multiple Currents
Load Regulation: 0.05% Typical
Trimmed Current Limit
On-Chip Thermal Limiting
Standard 3-Pin Power Package
U
APPLICATIO S
■
■
■
■
■
■
PentiumTM Processor Supplies
PowerPCTM Supplies
Other 2.5V to 3.6V Microprocessor Supplies
Low Voltage Logic Supplies
Battery-Powered Circuitry
Post Regulator for Switching Supply
The LT ®1584/LT1585/LT1587 are low dropout threeterminal regulators with 7A, 4.6A and 3A output current
capability, respectively. Design has been optimized for low
voltage applications where transient response and minimum input voltage are critical. Similar to the LT1083/4/5
family, it has lower dropout voltage and faster transient
response. These improvements make it ideal for low voltage microprocessor applications requiring a regulated
2.5V to 3.6V output with an input supply below 7V.
Current limit is trimmed to ensure specified output current
and controlled short-circuit current. On-chip thermal limiting provides protection against any combination of overload that would create excessive junction temperatures.
LT1585/7CM, LT1584/5/7CT
Adjustable
LT1585/7CM-3.3, LT1584/5/7CT-3.3
3.3V Fixed
LT1585CM-3.38, LT1584/5CT-3.38
3.38V Fixed
LT1585/7CM-3.45, LT1584/5/7CT-3.45
3.45V Fixed
LT1585/7CM-3.6, LT1584/5/7CT-3.6
3.6V Fixed
The LT1585/LT1587 are available in both the through-hole
and surface mount versions of the industry standard 3-pin
TO-220 power package. The LT1584 is available in the
through-hole 3-pin TO-220 power package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Pentium is a trademark of Intel Corporation. PowerPC is a trademark of IBM Corporation.
U
TYPICAL APPLICATIO
Dropout Voltage vs Output Current
1.5
3.3V, 7A, 4.6A, 3A Regulator
VIN ≥ 4.75V
+
C1
10µF
* REQUIRED FOR STABILITY
LT1584: C2 = 22µF,
LT1585/LT1587: C2 = 10µF
+
3.3V
7A, 4.6A, 3A
C2*
SOLID
TANTALUM
1585 TA01
NOTE: MICROPROCESSOR APPLICATIONS WITH LOAD TRANSIENTS OF 3.8A REQUIRE
OUTPUT DECOUPLING CAPACITANCE > 1300µF ON FIXED VOLTAGE PARTS TO ACHIEVE
< 50mV OF DEVIATION FROM NOMINAL OUTPUT. CONSULT FACTORY FOR DETAILS
INPUT/OUTPUT DIFFERENTIAL (V)
LT1584-3.3
LT1585-3.3
LT1587-3.3
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0
IFULL LOAD
OUTPUT CURRENT (A)
1585 TA02
158457a
1
LT1584/LT1585/LT1587
U
W W
W
ABSOLUTE
AXI U RATI GS
(Note 1)
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
UU
U
VIN ............................................................................. 7V
Operating Junction Temperature Range
C-Grade
Control Section ................................... 0°C to 125°C
Power Transistor ................................. 0°C to 150°C
I-Grade
Control Section ............................... –40°C to 125°C
Power Transistor ............................. –40°C to 150°C
PRECONDITIONI G
100% Thermal Limit Functional Test
U
W
U
PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
ORDER PART
NUMBER
FRONT VIEW
TAB
IS
OUTPUT
3
VIN
2
VOUT
1
ADJ
TAB
IS
OUTPUT
3
VIN
2
VOUT
1
ADJ
M PACKAGE
3-LEAD PLASTIC DD
T PACKAGE
3-LEAD PLASTIC TO-220
θJA = 30°C/W*
θJA = 50°C/W
FRONT VIEW
TAB
IS
OUTPUT
FRONT VIEW
LT1585CM
LT1587CM
3
VIN
2
VOUT
1
GND
LT1585CM-3.3
LT1585CM-3.38
LT1585CM-3.45
LT1585CM-3.6
LT1587CM-3.3
LT1587CM-3.45
LT1587CM-3.6
FRONT VIEW
TAB
IS
OUTPUT
3
VIN
2
VOUT
1
GND
M PACKAGE
3-LEAD PLASTIC DD
T PACKAGE
3-LEAD PLASTIC TO-220
θJA = 30°C/W*
θJA = 50°C/W
* With package soldered to 0.5 square inch copper area over backside
ground plane or internal power plane. θJA can vary from 20°C/W to
> 40°C/W with other mounting techniques.
LT1584CT
LT1585CT
LT1587CT
LT1584CT-3.3
LT1584IT-3.3
LT1585CT-3.3
LT1587CT-3.3
LT1584CT-3.38
LT1585CT-3.38
LT1584CT-3.45
LT1585CT-3.45
LT1587CT-3.45
LT1584CT-3.6
LT1585CT-3.6
LT1587CT-3.6
Consult LTC Marketing for parts specified with wider operating temperature ranges.
158457a
2
LT1584/LT1585/LT1587
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
Reference Voltage LT1584
LT1585
Output Voltage
Line Regulation
(Notes 2, 3)
Load Regulation
(Notes 2, 3, 4)
Dropout Voltage
LT1587
LT1584-3.3
LT1585-3.3
LT1587-3.3
LT1584-3.38
LT1585-3.38
LT1584-3.45
LT1585-3.45
LT1587-3.45
LT1584-3.6
LT1584-3.6
LT1584-3.6
LT1584-3.6
LT1585/7-3.6
LT1585/7-3.6
LT1585-3.6
LT1585-3.6
LT1584/5/7
LT1584/5/7-3.3
LT1584/5-3.38
LT1584/5/7-3.45
LT1584/5/7-3.6
LT1584/5/7
LT1584/5/7-3.3
LT1584/5-3.38
LT1584/5/7-3.45
LT1584/5/7-3.6
LT1585/7
LT1585/7-3.3
LT1585-3.38
LT1585/7-3.45
LT1585/7-3.6
LT1585
LT1585-3.3
LT1585-3.38
LT1585-3.45
LT1585-3.6
LT1584
LT1584-3.3
LT1584-3.38
LT1584-3.45
LT1584-3.6
LT1584IT-3.3
CONDITIONS
1.5V ≤ (VIN – VOUT) ≤ 3V, 10mA ≤ IOUT ≤ 7A
1.5V ≤ (VIN – VOUT) ≤ 5.75V, 10mA ≤ IOUT ≤ 4.6A, TJ ≥ 25°C
1.5V ≤ (VIN – VOUT) ≤ 5.75V, 10mA ≤ IOUT ≤ 4A, TJ < 25°C
1.5V ≤ (VIN – VOUT) ≤ 5.75V, 10mA ≤ IOUT ≤ 3A
4.75V ≤ VIN ≤ 6.3V, 0mA ≤ IOUT ≤ 7A
4.75V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 4.6A, TJ ≥ 25°C
4.75V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 4A, TJ < 25°C
4.75V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 3A
4.75V ≤ VIN ≤ 6.38V, 0mA ≤ IOUT ≤ 7A
4.75V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 4A
4.75V ≤ VIN ≤ 6.45V, 0mA ≤ IOUT ≤ 7A
4.75V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 4A
4.75V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 3A
4.75V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 6A
4.80V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 6A
4.80V ≤ VIN ≤ 6.6V, 0mA ≤ IOUT ≤ 7A
4.85V ≤ VIN ≤ 6.6V, 0mA ≤ IOUT ≤ 7A
4.75V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 3A
4.80V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 3A
4.80V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 4A
4.85V ≤ VIN ≤ 7V, 0mA ≤ IOUT ≤ 4A
2.75V ≤ VIN ≤ 7V, IOUT = 10mA
4.75V ≤ VIN ≤ 7V, IOUT = 0mA
4.75V ≤ VIN ≤ 7V, IOUT = 0mA
4.75V ≤ VIN ≤ 7V, IOUT = 0mA
4.75V ≤ VIN ≤ 7V, IOUT = 0mA
(VN – VOUT) = 3V, TJ = 25°C, 10mA ≤ IOUT ≤ IFULL LOAD
VIN = 5V, TJ = 25°C, 0mA ≤ IOUT ≤ IFULL LOAD
VIN = 5V, TJ = 25°C, 0mA ≤ IOUT ≤ IFULL LOAD
VIN = 5V, TJ = 25°C, 0mA ≤ IOUT ≤ IFULL LOAD
VIN = 5.25V, TJ = 25°C, 0mA ≤ IOUT ≤ IFULL LOAD
∆VREF = 1%, IOUT = 3A
∆VOUT = 1%, IOUT = 3A
∆VOUT = 1%, IOUT = 3A
∆VOUT = 1%, IOUT = 3A
∆VOUT = 1%, IOUT = 3A
∆VREF = 1%, IOUT = 4.6A, TJ ≥ 25°C
∆VREF = 1%, IOUT = 4A, TJ < 25°C
∆VOUT = 1%, IOUT = 4.6A, TJ ≥ 25°C
∆VOUT = 1%, IOUT = 4A, TJ < 25°C
∆VOUT = 1%, IOUT = 4A
∆VOUT = 1%, IOUT = 4A
∆VOUT = 1%, IOUT = 4A
∆VREF = 1%, IOUT = 6A
∆VOUT = 1%, IOUT = 6A
∆VOUT = 1%, IOUT = 6A
∆VOUT = 1%, IOUT = 6A
∆VOUT = 1%, IOUT = 6A
TJ ≥ 25°C
TJ < 25°C
TJ < 25°C
MIN
TYP
MAX
●
1.225 (– 2%)
1.250
1.275 (+ 2%)
V
●
3.235 (– 2%)
3.300
3.365 (+ 2%)
V
●
3.313 (– 2%)
3.380 3.465 (+ 2.5%)
V
●
3.381 (– 2%)
3.400 (– 5.5%)
3.450 (– 4%)
3.431 (– 4.7%)
3.481 (– 3.3%)
3.474 (– 3.5%)
3.528 (– 2%)
3.450 (– 4%)
3.492 (– 3%)
3.450
3.600
3.600
3.600
3.600
3.600
3.600
3.600
3.600
3.519 (+ 2%)
3.672 (+ 2%)
3.672 (+ 2%)
3.672 (+ 2%)
3.672 (+ 2%)
3.672 (+ 2%)
3.672 (+ 2%)
3.672 (+ 2%)
3.672 (+ 2%)
V
V
V
V
V
V
V
V
V
●
0.005
0.2
%
●
0.05
0.05
0.3
0.5
%
%
●
1.150
1.300
V
●
1.200
1.400
V
●
●
●
1.200
1.200
1.200
1.300
1.350
1.450
V
V
V
●
●
●
●
●
●
●
●
UNITS
158457a
3
LT1584/LT1585/LT1587
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
Dropout Voltage
Current Limit
(Note 4)
LT1584
LT1584-3.3
LT1584-3.38
LT1584-3.45
LT1584-3.6
LT1584IT-3.3
CONDITIONS
∆VREF = 1%, IOUT = 7A
∆VOUT = 1%, IOUT = 7A
∆VOUT = 1%, IOUT = 7A
∆VOUT = 1%, IOUT = 7A
∆VOUT = 1%, IOUT = 7A
TJ < 25°C
●
●
LT1584
LT1584-3.3
LT1584-3.38
LT1584-3.45
LT1584-3.6
(VIN – VOUT) = 3V
(VIN – VOUT) = 3V
(VIN – VOUT) = 3V
(VIN – VOUT) = 3V
(VIN – VOUT) = 3V
●
7.100
8.250
A
LT1585
LT1585-3.3
(VIN – VOUT) = 5.5V
(VIN – VOUT) = 5.5V
TJ ≥ 25°C
TJ < 25°C
●
●
4.600
4.100
5.25
5.25
A
A
LT1585-3.38
LT1585-3.45
LT1585-3.6
(VIN – VOUT) = 5.5V
(VIN – VOUT) = 5.5V
(VIN – VOUT) = 5.5V
●
4.100
4.750
A
LT1587
LT1587-3.3
LT1587-3.45
LT1587-3.6
(VIN – VOUT) = 5.5V
(VIN – VOUT) = 5.5V
(VIN – VOUT) = 5.5V
(VIN – VOUT) = 5.5V
●
3.100
3.750
A
Adjust Pin Current LT1584/5/7
MIN
TYP
MAX
UNITS
1.250
1.250
1.400
1.500
V
V
55
1.5V ≤ (VIN – VOUT) ≤ 3V, 10mA ≤ IOUT ≤ IFULL LOAD
1.5V ≤ (VIN – VOUT) ≤ 5.75V, 10mA ≤ IOUT ≤ IFULL LOAD
●
0.2
5
µA
Minimum
Load Current
1.5V ≤ (VIN – VOUT) ≤ 5.75V
●
2
10
mA
Quiescent Current LT1584/5/7-3.3
LT1584/5-3.38
LT1584/5/7-3.45
LT1584/5/7-3.6
LT1584IT-3.3
VIN = 5V
VIN = 5V
VIN = 5V
VIN = 5V
VIN = 5V
●
●
8
8
13
15
mA
mA
Ripple Rejection
f = 120Hz, COUT = 25µF Tant., (VIN – VOUT) = 2.5V, IOUT = 7A
f = 120Hz, COUT = 25µF Tant., VIN = 5.8V, IOUT = 7A
f = 120Hz, COUT = 25µF Tant., VIN = 5.88V, IOUT = 7A
f = 120Hz, COUT = 25µF Tant., VIN = 5.95V, IOUT = 7A
f = 120Hz, COUT = 25µF Tant., VIN = 6.1V, IOUT = 7A
f = 120Hz, COUT = 25µF Tant., (VIN – VOUT) = 3V,
IOUT = 4.6A, TJ ≥ 25°C
f = 120Hz, COUT = 25µF Tant., (VIN – VOUT) = 3V,
IOUT = 4A, TJ < 25°C
f = 120Hz, COUT = 25µF Tant., VIN = 6.3V,
IOUT = 4.6A, TJ ≥ 25°C
f = 120Hz, COUT = 25µF Tant., VIN = 6.3V,
IOUT = 4A, TJ < 25°C
f = 120Hz, COUT = 25µF Tant., VIN = 6.38V, IOUT = 4A
f = 120Hz, COUT = 25µF Tant., VIN = 6.45V, IOUT = 4A
f = 120Hz, COUT = 25µF Tant., VIN = 6.6V, IOUT = 4A
f = 120Hz, COUT = 25µF Tant., (VIN – VOUT) = 3V, IOUT = 3A
f = 120Hz, COUT = 25µF Tant., VIN = 6.3V, IOUT = 3A
f = 120Hz, COUT = 25µF Tant., VIN = 6.45V, IOUT = 3A
f = 120Hz, COUT = 25µF Tant., VIN = 6.6V, IOUT = 3A
●
LT1584/5/7
LT1584
LT1584-3.3
LT1584-3.38
LT1584-3.45
LT1584-3.6
LT1585
LT1585-3.3
LT1585-3.38
LT1585-3.45
LT1585-3.6
LT1587
LT1587-3.3
LT1587-3.45
LT1587-3.6
60
72
120
µA
●
Adjust Pin Current LT1584
Change (Note 4)
LT1585/7
dB
158457a
4
LT1584/LT1585/LT1587
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
Thermal Regulation
CONDITIONS
LT1584/5/7
LT1584/5/7-3.3
LT1584/5-3.38
LT1584/5/7-3.45
LT1584/5/7-3.6
MIN
TA = 25°C, 30ms pulse
TA = 25°C, 30ms pulse
TA = 25°C, 30ms pulse
TA = 25°C, 30ms pulse
TA = 25°C, 30ms pulse
Temperature Stability
●
TYP
MAX
UNITS
0.004
0.02
%/W
1.0
%
0.5
Long-Term Stability
TA = 125°C, 1000 Hrs.
0.03
RMS Output Noise
(% of VOUT)
TA = 25°C, 10Hz ≤ f ≤ 10kHz
0.003
Thermal Resistance
Junction to Case
LT1584
LT1585
LT1585
LT1587
LT1587
T Package: Control Circuitry/Power Transistor
T Package: Control Circuitry/Power Transistor
M Package: Control Circuitry/Power Transistor
T Package: Control Circuitry/Power Transistor
M Package: Control Circuitry/Power Transistor
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: See thermal regulation specifications for changes in output voltage
due to heating effects. Load and line regulation are measured at a constant
junction temperature by low duty cycle pulse testing.
Note 3: Line and load regulation are guaranteed up to the maximum power
dissipation (25W for the LT1584 in T package, 26.5W for the LT1585 in T
package, 18W for the LT1587 in T package). Power dissipation is
determined by input/output differential and the output current. Guaranteed
%
%
0.65/2.7
0.7/3.0
0.7/3.0
0.7/3.0
0.7/3.0
°C/W
°C/W
°C/W
°C/W
°C/W
maximum output power will not be available over the full input/output
voltage range.
Note 4: IFULL LOAD is defined as the maximum value of output load current
as a function of input-to-output voltage. IFULL LOAD is equal to 7A for the
LT1584, 4.6A at TJ ≥ 25°C and 4A at TJ < 25°C for the LT1585/LT1585-3.3
and 3A for the LT1587. The remaining LT1585 fixed voltage versions are
4A. The LT1585 and LT1587 have constant current limit with changes in
input-to-output voltage. The LT1584 has variable current limit which
decreases about 4A as input-to-output voltage increases from 3V to 7V.
158457a
5
LT1584/LT1585/LT1587
U W
TYPICAL PERFORMANCE CHARACTERISTICS
LT1584 Short-Circuit Current
vs Input/Output Differential
LT1584 Dropout Voltage
vs Output Current
10
1.5
0.10
1.3
T = –5°C
1.2
1.1
1.0
T = 125°C
T = 25°C
0.9
0.8
0.7
OUTPUT VOLTAGE DEVIATION (%)
SHORT-CIRCUIT CURRENT (A)
GUARANTEED
TEST POINTS
1.4
DROPOUT VOLTAGE (V)
LT1584 Load Regulation
vs Temperature
8
6
T = 125°C
T = 25°C
T = –5°C
4
MINIMUM
2
∆I = 7A
0.05
0
–0.05
–0.10
–0.15
0.6
0
0.5
0
4
3
2
5
OUTPUT CURRENT (A)
1
6
0
7
–0.20
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
7
LT1584 • TPC02
LTC1584 • TPC01
LT1584 • TPC03
LT1585 Short-Circuit Current
vs Temperature
LT1585 Dropout Voltage
vs Output Current
LT1585 Load Regulation
vs Temperature
6.0
1.5
0.10
T = –5°C
1.2
1.1
T = 125°C
1.0
T = 25°C
0.9
0.8
0.7
OUTPUT VOLTAGE DEVIATION (%)
1.3
SHORT-CIRCUIT CURRENT (A)
GUARANTEED
TEST POINTS
1.4
DROPOUT VOLTAGE (V)
4
3
2
5
6
1
INPUT/OUTPUT DIFFERENTIAL (V)
5.5
5.0
4.5
∆I = 4.6A
0.05
0
–0.05
–0.10
–0.15
0.6
0
1
3
4
2
OUTPUT CURRENT (A)
LT1584 • TPC03
LT1584 • TPC05
LT1585 • TPC04
LT1587 Dropout Voltage
vs Output Current
LT1587 Short-Circuit Current
vs Temperature
LT1587 Load Regulation
vs Temperature
5.0
1.5
0.10
SHORT-CIRCUIT CURRENT (A)
GUARANTEED
TEST POINTS
1.4
1.3
DROPOUT VOLTAGE (V)
–0.20
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
4.0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
5
1.2
T = –5°C
1.1
1.0
T = 25°C
0.9
T = 125°C
0.8
0.7
OUTPUT VOLTAGE DEVIATION (%)
0.5
4.5
4.0
3.5
∆I = 3A
0.05
0
–0.05
–0.10
–0.15
0.6
0.5
0
0.5
1.5
2.0
1.0
OUTPUT CURRENT (A)
2.5
3.0
LT1584 • TPC07
3.0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1584 • TPC05
–0.20
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1584 • TPC09
158457a
6
LT1584/LT1585/LT1587
U W
TYPICAL PERFORMANCE CHARACTERISTICS
1.270
3.65
1.265
3.60
1.260
1.255
1.250
1.245
1.240
3.70
VOUT SET WITH 1% RESISTORS
3.65
VOUT = 3.6V
3.60
OUTPUT VOLTAGE (V)
3.70
OUTPUT VOLTAGE (V)
REFERENCE VOLTAGE (V)
1.275
3.55
3.50
VOUT = 3.45V
3.45
VOUT = 3.38V
3.40
3.35
VOUT = 3.3V
3.30
1.235
3.50
3.45
3.40
VOUT = 3.45V
VOUT = 3.38V
3.35
VOUT = 3.3V
1.230
3.25
3.25
1.255
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
3.20
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
3.20
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1584 • TPC11
LT1584 • TPC12
LT1584/5/7 Adjust Pin Current
vs Temperature
LT1584/5/7 Minimum Load
Current vs Temperature
ADJUST PIN CURRENT (µA)
4
3
2
1
LT1584/5/7-3.XX Quiescent
Current vs Temperature
100
13
90
12
80
QUIESCENT CURRENT (mA)
5
70
60
50
40
30
20
10
11
10
9
8
7
6
5
4
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1584 • TPC13
3
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1584 • TPC14
LT1584 • TPC15
LT1585/7 Maximum Power
Dissipation*
LT1584/5/7 Ripple Rejection
vs Frequency
90
LT1584 Maximum Power
Dissipation*
30
30
LT1585
80
25
25
70
20
50
40
30
LT1584: (VIN – VOUT) ≤ 2.5V
LT1585/87: (VIN – VOUT) ≤ 3V
0.5V ≤ VRIPPLE ≤ 2V
IOUT = IFULL LOAD
20
10
0
20
LT1587
POWER (W)
60
POWER (W)
RIPPLE REJECTION (dB)
VOUT = 3.6V
3.55
3.30
LT1584 • TPC10
MINIMUM LOAD CURRENT (mA)
LT1584/5/7-3.XX Output Voltage
vs Temperature
Output Voltage vs Temperature
Using Adjustable LT1584/5/7
LT1584/5/7 Reference Voltage
vs Temperature
15
10
10
5
5
0
10
100
1k
10k
FREQUENCY (Hz)
100k
LT1584 • TPC16
15
0
50 60 70 80 90 100 110 120 130 140 150
CASE TEMPERATURE (˚C)
LT1584 • TPC17
*AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
50 60 70 80 90 100 110 120 130 140 150
CASE TEMPERATURE (°C)
LT1584 • TPC18
*AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
158457a
7
LT1584/LT1585/LT1587
W
W
SI PLIFIED SCHE ATIC
VIN
+
–
THERMAL
LIMIT
VOUT
ADJ
GND
LT1584 • BD
FOR FIXED VOLTAGE DEVICE
158457a
8
LT1584/LT1585/LT1587
U
W
U
U
APPLICATIONS INFORMATION
General
The LT1584/LT1585/LT1587 family of three-terminal
regulators is easy to use and has all the protection features
expected in high performance linear regulators. The devices are short-circuit protected, safe-area protected, and
provide thermal shutdown to turn off the regulators
should the junction temperature exceed about 150°C. The
LT1584/LT1585/LT1587 family includes adjustable and
fixed voltage versions.
These ICs are pin compatible with the LT1083/LT1084/
LT1085 family of linear regulators but offer lower dropout
voltage and faster transient response. The trade-off for this
improved performance is a 7V maximum supply voltage.
Similar to the LT1083/LT1084/LT1085 family, the LT1584/
LT1585/LT1587 regulators require an output capacitor for
stability. However, the improved frequency compensation
permits the use of capacitors with much lower ESR while still
maintaining stability. This is critical in addressing the needs
of modern, low voltage, high speed microprocessors.
Current generation microprocessors cycle load current
from almost zero to amps in tens of nanoseconds. Output
voltage tolerances are tighter and include transient response as part of the specification. The LT1584/LT1585/
LT1587 family is specifically designed to meet the fast
current load-step requirements of these microprocessors
and saves total cost by needing less output capacitance in
order to maintain regulation.
Stability
The circuit design in the LT1584/LT1585/LT1587 family
requires the use of an output capacitor as part of the
frequency compensation. For all operating conditions, the
addition of a 22µF solid tantalum or a 100µF aluminum
electrolytic on the output ensures stability. Normally, the
LT1584/LT1585/LT1587 can use smaller value capacitors.
Many different types of capacitors are available and have
widely varying characteristics. These capacitors differ in
capacitor tolerance (sometimes ranging up to ±100%),
equivalent series resistance, equivalent series inductance,
and capacitance temperature coefficient. The LT1584/
LT1585/LT1587 frequency compensation optimizes frequency response with low ESR capacitors. In general, use
capacitors with an ESR of less than 1Ω.
On the adjustable LT1584/LT1585/LT1587, bypassing the
adjust terminal improves ripple rejection and transient
response. Bypassing the adjust pin increases the required
output capacitor value. The value of 22µF tantalum or
100µF aluminum covers all cases of bypassing the adjust
terminal. With no adjust pin bypassing, smaller values of
capacitors provide equally good results.
Normally, capacitor values on the order of several hundred
microfarads are used on the output of the regulators to
ensure good transient response with heavy load current
changes. Output capacitance can increase without limit
and larger values of output capacitance further improve the
stability and transient response of the LT1584/LT1585/
LT1587 family.
Large load current changes are exactly the situation presented by modern microprocessors. The load current step
contains higher order frequency components that the
output decoupling 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 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 1.
ESR
EFFECTS
ESL
EFFECTS
CAPACITANCE
EFFECTS
LT1584 • F01
SLOPE,
V ∆I
=
t
C
POINT AT WHICH REGULATOR
TAKES CONTROL
Figure 1
158457a
9
LT1584/LT1585/LT1587
U
W
U U
APPLICATIONS INFORMATION
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 capacitors and ceramic capacitors. The location of the decoupling network is critical to
transient response performance. Place the decoupling
network as close as possible to the processor pins 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.
A possible stability problem that occurs in monolithic linear
regulators is current limit oscillations. The LT1585/LT1587
essentially have a flat current limit over the range of input
supply voltage. The lower current limit rating and 7V
maximum supply voltage rating for these devices permit
this characteristic. Current limit oscillations are typically
nonexistent, unless the input and output decoupling capacitors for the regulators are mounted several inches
from the terminals. The LT1584 differs from the LT1585/
LT1587 and provides current limit foldback as input-tooutput differential voltage increases. This safe-area characteristic exhibits a negative impedance because increasing voltage causes output current to decrease. Negative
resistance during current limit is not unique to the LT1584
devices and is present on many power IC regulators. The
value of the negative resistance is a function of how fast the
current limit is folded back as input-to-output voltage
increases. This negative resistance can react with capacitors and inductors on the input and output to cause
oscillation during current limit. Depending on the values of
series resistances, the overall system may end up unstable.
However, the oscillation causes no problem and the IC
remains protected. In general, if this problem occurs and is
unacceptable, increasing the amount of output capacitance
helps dampen the system.
put pin and the input pin or between the adjust pin and the
output pin to prevent die overstress.
On the adjustable LT1584/LT1585/LT1587, internal resistors limit internal current paths on the adjust pin. Therefore, even with bypass capacitors on the adjust pin, no
protection diode is needed to ensure device safety under
short-circuit conditions.
A protection diode between the input and output pins is
usually not needed. An internal diode between the input and
output pins on the LT1584/LT1585/LT1587 family 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 input pin instantaneously shorted to
ground can damage occur. A crowbar circuit at the input of
the LT1584/LT1585/LT1587 can generate those levels of
current, and a diode from output to input is then recommended. This is shown in Figure 2. Usually, normal power
supply cycling or system “hot plugging and unplugging”
will not generate current large enough to do any damage.
The adjust pin can be driven on a transient basis ±7V with
respect to the output, without any device degradation. As
with any IC regulator, exceeding the maximum input-tooutput voltage differential causes the internal transistors to
break down and none of the protection circuitry is then
functional.
D1
1N4002
(OPTIONAL)
VIN
+
IN
C1
10µF
LT1584-3.3
OUT
GND
+
VOUT
C2
22µF
D1
1N4002
(OPTIONAL)
LT1584
Protection Diodes
In normal operation, the LT1584/LT1585/LT1587 family
does not require any protection diodes. Older three-terminal regulators require protection diodes between the out-
VIN
+
IN
C1
10µF
OUT
ADJ
R1
+
VOUT
C2
22µF
+
CADJ
R2
LT1584 • F02
Figure 2
158457a
10
LT1584/LT1585/LT1587
U
W
U U
APPLICATIONS INFORMATION
Overload Recovery
The LT1584 devices have safe-area protection similar to
the LT1083/LT1084/LT1085. The safe-area protection decreases current limit as input-to-output voltage increases.
This behavior keeps the power transistor inside a safe
operating region for all values of input-to-output voltage.
The LT1584 protection circuitry provides some output
current at all values of input-to-output voltage up to the 7V
maximum supply voltage. When power is first applied, the
input voltage rises and the output voltage follows the input.
The input-to-output voltage remains small and the regulator can supply large output currents. This action permits
the regulator to start-up into very heavy loads.
With higher input voltages, a problem can occur where the
removal of an output short does not permit the output
voltage to recover. This problem is not unique to the
LT1584 devices and is present on the LT1083/LT1084/
LT1085 family and older generation linear regulators. The
problem occurs with a heavy output load, a high input
voltage, and a low output voltage. An example is immediately after the removal of a short circuit. The load line of
such a load may intersect the output current curve at two
points. If this happens, two stable output operating points
exist for the regulator. With this double intersection, the
power supply may require cycling down to zero and back up
again to make the output recover. This situation does not
occur with the LT1585/LT1587 because no foldback circuitry is required to provide safe-area protection.
Ripple Rejection
The typical curve for ripple rejection reflects values for the
LT1584/LT1585/LT1587 fixed output voltage parts between 3.3V and 3.6V. In applications that require improved
ripple rejection, use the adjustable devices. A bypass
capacitor from the adjust pin to ground reduces the output
ripple by the ratio of VOUT/1.25V. The impedance of the
adjust pin capacitor at the ripple frequency should be less
than the value of R1 (typically in the range of 100Ω to
120Ω) in the feedback divider network in Figure 2. Therefore, the value of the required adjust pin capacitor is a
function of the input ripple frequency. For example, if R1
equals 100Ω and the ripple frequency equals 120Hz, the
adjust pin capacitor should be 22µF. At 10kHz, only 0.22µF
is needed.
Output Voltage
The LT1584/LT1585/LT1587 adjustable regulators develop
a 1.25V reference voltage between the output pin and the
adjust pin (see Figure 3). 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, this current is the specified minimum
load current of 10mA. The current out of the adjust pin adds
to the current from R1 and is typically 55µA. Its output
voltage contribution is small and only needs consideration
when very precise output voltage setting is required.
LT1584
VIN
+
IN
C1
10µF
OUT
ADJ
+
VREF
R1
VOUT
C2
22µF
IADJ
55µA
VOUT = VREF (1 + R2/R1) + IADJ (R2)
R2
LT1585 • F03
Figure 3. Basic Adjustable Regulator
Load Regulation
It is not possible to provide true remote load sensing
because the LT1584/LT1585/LT1587 are three-terminal
devices. Load regulation is limited by the resistance of the
wire connecting the regulators to the load. Load regulation
per the data sheet specification is measured at the bottom
of the package.
For fixed voltage devices, negative side sensing is a true
Kelvin connection with the ground pin of the device returned to the negative side of the load. This is illustrated in
Figure 4.
VIN
IN
LT1584-3.3
OUT
RP
PARASITIC
LINE RESISTANCE
GND
RL
LT1585 • F04
Figure 4. Connection for Best Load Regulation
158457a
11
LT1584/LT1585/LT1587
U
W
U U
APPLICATIONS INFORMATION
For adjustable voltage devices, negative side sensing is a
true Kelvin connection with the bottom of the output divider
returned to the negative side of the load. The best load
regulation is obtained when the top of resistor divider R1
connects directly to the regulator output and not to the
load. Figure 5 illustrates this point. If R1 connects to the
load, the effective resistance between the regulator and the
load is:
RP × (1 + R2/R1), RP = Parasitic Line Resistance
The connection shown in Figure 5 does not multiply RP by
the divider ratio. As an example, RP is about four milliohms
per foot with 16-gauge wire. This translates to 4mV per foot
at 1A load current. At higher load currents, this drop
represents a significant percentage of the overall regulation. It is important to keep the positive lead between the
regulator and the load as short as possible and to use large
wire or PC board traces.
RP
PARASITIC
LINE RESISTANCE
LT1584
VIN
IN
OUT
ADJ
R1*
RL
R2*
*CONNECT R1 TO CASE
CONNECT R2 TO LOAD
LT1584 • F05
Figure 5. Connection for Best Load Regulation
Thermal Considerations
The LT1584/LT1585/LT1587 family protects the device
under overload conditions with internal power and thermal
limiting circuitry. However, for normal continuous load
conditions, do not exceed maximum junction temperature
ratings. It is important to consider all sources of thermal
resistance from junction-to-ambient. These sources include the junction-to-case resistance, the case-to-heat
sink interface resistance, and the heat sink resistance.
Thermal resistance specifications have been developed to
more accurately reflect device temperature and ensure safe
operating temperatures. The electrical characteristics section provides a separate thermal resistance and maximum
junction temperature for both the control circuitry and the
power transistor. Older regulators, with a single junctionto-case thermal resistance specification, use an average of
the two values provided here and allow excessive junction
temperatures under certain conditions of ambient temperature and heat sink resistance. Calculate the maximum
junction temperature for both sections to ensure that both
thermal limits are met.
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 ensures the best thermal flow from this area of
the package to the heat sink. Linear Technology strongly
recommends thermal compound at the case-to-heat sink
interface. Use a thermally conductive spacer if the case of
the device must be electrically isolated and include its
158457a
12
LT1584/LT1585/LT1587
U
U U
W
APPLICATIONS INFORMATION
contribution to the total thermal resistance. Please consult
“Mounting Considerations for Power Semiconductors”
1990 Linear Applications Handbook, Volume I, Pages
RR3-1 to RR3-20. The output connects to the case of all
devices in the LT1584/LT1585/LT1587 series.
Junction temperature will be equal to:
TJ = TA + PD(θHEAT SINK + θCASE-TO-HEAT SINK + θJC)
For the Control Section:
TJ = 70°C + 9W (4°C/W + 1°C/W + 0.7°C/W) = 121.3°C
121.3°C < 125°C = TJMAX (Control Section Commercial
range)
For example, using an LT1585CT-3.3 (TO-220, commercial) and assuming:
VIN(Max Continuous) = 5.25V (5V + 5%), VOUT = 3.3V,
IOUT = 4.6A
For the Power Transistor:
TJ = 70°C + 9W (4°C/W + 1°C/W + 3°C/W) = 142°C
142°C < 150°C = TJMAX (Power Transistor Commercial
Range)
TA = 70°C, θHEAT SINK = 4°C/W
θCASE-TO-HEAT SINK = 1°C/W (with Thermal Compound)
In both cases the junction temperature is below the maximum rating for the respective sections, ensuring reliable
operation.
Power dissipation under these conditions is equal to:
PD = (VIN – VOUT)(IOUT) = (5.25 – 3.3)(4.6) = 9W
U
TYPICAL APPLICATIONS N
Recommended LT1587-3.45 Circuit for the Intel 486TM DX4TM Overdrive Microprocessor
PLACE AT MICROPROCESSOR SOCKET VCC PINS
VIN ≥ 4.75V
OUT
IN
+
C1
10µF
10V
LT1587-3.45
+
C2
22µF
10V
+
C3 TO C6
47µF
10V
GND
C7 TO C15
0.1µF
ESR OF THE 47µF IS
工商网监
湘ICP备2023018690号
