LT1585A/LT1585A-3.3
5A Low Dropout
Fast Response
Positive Regulators
Adjustable and Fixed
FEATURES
s
s
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DESCRIPTION
The LT
®
1585A/LT1585A-3.3 are low dropout 3-terminal
regulators with 5A output current capability. Design has
been optimized for low voltage applications where tran-
sient response and minimum input voltage are critical.
Similar to the LT1084 family, these regulators feature
lower dropout voltage and faster transient response.
These improvements make them 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 lim-
iting provides protection against any combination of over-
load that would create excessive junction temperatures.
The LT1585A/LT1585A-3.3 are available in the industry
standard 3-pin TO-220 power package.
, 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.
Fast Transient Response
Guaranteed Dropout Voltage at Multiple Currents
Load Regulation: 0.05% Typ
Trimmed Current Limit
On-Chip Thermal Limiting
Standard 3-Pin Power Package
APPLICATIONS
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Pentium
®
Processor Supplies
PowerPC
TM
Supplies
Other 2.5V to 3.6V Microprocessor Supplies
Low Voltage Logic Supplies
Battery-Powered Circuitry
Post Regulator for Switching Supply
Adjustable
3.3V Fixed
LT1585ACT
LT1585ACT-3.3
TYPICAL APPLICATION
3.3V, 5A Regulator
1.5
V
IN
≥
4.75V
LT1585A-3.3
3.3V
5A
C2*
10µF
Dropout Voltage vs Output Current
1.4
+
INPUT/OUTPUT DIFFERENTIAL (V)
C1
10µF
+
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0
OUTPUT CURRENT (A)
LT1585A TA02
* REQUIRED FOR STABILITY
1585A 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
U
U
U
I
FULL LOAD
1
LT1585A/LT1585A-3.3
ABSOLUTE
MAXIMUM
RATINGS
PRECONDITIONI G
100% Thermal Limit Functional Test
PACKAGE/ORDER INFORMATION
FRONT VIEW
3
2
1
T PACKAGE
3-LEAD PLASTIC TO-220
V
IN
V
OUT
ADJ
ORDER PART
NUMBER
LT1585ACT
FRONT VIEW
3
2
1
T PACKAGE
3-LEAD PLASTIC TO-220
θ
JA
= 50°C/W
θ
JA
= 50°C/W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Reference Voltage LT1585A
Output Voltage
Line Regulation
(Notes 1, 2)
Load Regulation
(Notes 1, 2, 3)
Dropout Voltage
LT1585A-3.3
LT1585A
LT1585A-3.3
LT1585A
LT1585A-3.3
LT1585A
LT1585A-3.3
LT1585A
LT1585A-3.3
Current Limit
(Note 3)
LT1585A
LT1585A-3.3
CONDITIONS
(V
IN
– V
OUT
) = 3V, T
J
= 25°C, I
OUT
= 10mA
1.5V
≤
(V
IN
– V
OUT
)
≤
5.75V, 10mA
≤
I
OUT
≤
5A
V
IN
= 5V, T
J
= 25°C, I
OUT
= 0mA
4.75V
≤
V
IN
≤
7V, 0mA
≤
I
OUT
≤
5A
2.75V
≤
V
IN
≤
7V, I
OUT
= 10mA
4.75V
≤
V
IN
≤
7V, I
OUT
= 0mA
q
q
q
MIN
1.238 (–1%)
1.225 (–2%)
3.267 (–1%)
3.235 (– 2%)
(V
N
– V
OUT
) = 3V, T
J
= 25°C, 10mA
≤
I
OUT
≤
I
FULL LOAD
V
IN
= 5V, T
J
= 25°C, 0mA
≤
I
OUT
≤
I
FULL LOAD
q
∆V
REF
= 1%, I
OUT
= 3A
∆V
OUT
= 1%, I
OUT
= 3A
q
∆V
REF
= 1%, I
OUT
= 5A
∆V
OUT
= 1%, I
OUT
= 5A
q
(V
IN
– V
OUT
) = 5.5V
(V
IN
– V
OUT
) = 5.5V
q
Adjust Pin Current LT1585A
Adjust Pin Current LT1585A
Change (Note 3)
Minimum
Load Current
LT1585A
1.5V
≤
(V
IN
– V
OUT
)
≤
5.75V, 10mA
≤
I
OUT
≤
I
FULL LOAD
1.5V
≤
(V
IN
– V
OUT
)
≤
5.75V
V
IN
= 5V
q
q
q
q
Quiescent Current LT1585A-3.3
2
UU
5.0
U
V
IN
............................................................................. 7V
Operating Junction Temperature Range
Control Section.................................... 0°C to 125°C
Power Transistor ................................. 0°C to 150°C
U
U
W
W W
U
W
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
V
IN
V
OUT
GND
LT1585ACT-3.3
TYP
1.250
1.250
3.300
3.300
MAX
1.262 (+1%)
1.275 (+2%)
3.333 (+1%)
3.365 (+ 2%)
UNITS
V
V
V
V
0.005
0.05
0.05
0.2
0.3
0.5
%
%
%
1.150
1.300
V
1.200
1.400
V
6.0
55
0.2
2
8
120
5
10
13
A
µA
µA
mA
mA
LT1585A/LT1585A-3.3
ELECTRICAL CHARACTERISTICS
PARAMETER
Ripple Rejection
LT1585A
LT1585A-3.3
CONDITIONS
f = 120Hz, C
OUT
= 25µF Tant., (V
IN
– V
OUT
) = 3V,
I
OUT
= 5A
f = 120Hz, C
OUT
= 25µF Tant., V
IN
= 6.3V,
I
OUT
= 5A
q
MIN
TYP
MAX
UNITS
60
72
dB
Thermal
Regulation
Temperature Stability
Long-Term Stability
RMS Output Noise
(% of V
OUT
)
Thermal Resistance
Junction to Case
LT1585A
LT1585A-3.3
T
A
= 25°C, 30ms Pulse
T
A
= 25°C, 30ms Pulse
0.004
q
0.02
1.0
%/W
%
%
%
0.5
0.03
0.003
0.7/3.0
T
A
= 125°C, 1000 Hrs.
T
A
= 25°C, 10Hz
≤
f
≤
10kHz
LT1585A
T Package: Control Circuitry/Power Transistor
°C/W
The
q
denotes specifications which apply over the specified operating
temperature range.
Note 1:
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 2:
Line and load regulation are guaranteed up to the maximum power
dissipation 28.8W for the LT1585A in T package. Power dissipation is
determined by input/output differential and the output current. Guaranteed
maximum output power will not be available over the full input/output
voltage range.
Note 3:
I
FULL LOAD
is defined as the maximum value of output load current
as a function of input-to-output voltage. I
FULL LOAD
is equal to 5A for the
LT1585A/LT1585A-3.3. The LT1585A has constant current limit with
changes in input-to-output voltage.
TYPICAL PERFORMANCE CHARACTERISTICS
LT1585A Dropout Voltage
vs Output Current
1.5
1.4
1.3
GUARANTEED
TEST POINTS
T = –5°C
OUTPUT VOLTAGE DEVIATION (%)
SHORT-CIRCUIT CURRENT (A)
DROPOUT VOLTAGE (V)
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0
1
3
4
2
OUTPUT CURRENT (A)
5
T = 25°C
T = 125°C
U W
LT1585A Short-Circuit Current
vs Temperature
6.0
LT1585A Load Regulation
vs Temperature
0.10
0.05
0
–0.05
–0.10
–0.15
–0.20
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1585A • TPC03
∆I
= 5A
5.5
5.0
4.5
4.0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1585A • TPC02
LT1585A • TPC01
3
LT1585A/LT1585A-3.3
TYPICAL PERFORMANCE CHARACTERISTICS
LT1585A Reference Voltage
vs Temperature
1.275
1.270
3.70
3.65
3.60
REFERENCE VOLTAGE (V)
1.265
1.260
1.255
1.250
1.245
1.240
1.235
1.230
1.225
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1585A • TPC04
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
LT1585A Minimum Load Current
vs Temperature
5
100
90
MINIMUM LOAD CURRENT (mA)
ADJUST PIN CURRENT (µA)
QUIESCENT CURRENT (mA)
4
3
2
1
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1585A • TPC07
LT1585A-3.3 Ripple Rejection
vs Frequency
90
80
RIPPLE REJECTION (dB)
70
60
50
40
30
20
10
0
10
LT1585A-3.3: (V
IN
– V
OUT
)
≤
3V
0.5V
≤
V
RIPPLE
≤
2V
I
OUT
= I
FULL LOAD
100
1k
10k
FREQUENCY (Hz)
100k
POWER (W)
4
U W
Output Voltage vs Temperature
Using Adjustable LT1585A
V
OUT
SET WITH 1% RESISTORS
V
OUT
= 3.6V
LT1585A-3.3 Output Voltage
vs Temperature
3.35
3.34
3.33
3.32
3.31
3.30
3.29
3.28
3.27
3.26
3.25
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1585A • TPC06
3.55
3.50
3.45
3.40
3.35
3.30
3.25
3.20
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1585A • TPC05
V
OUT
= 3.45V
V
OUT
= 3.38V
V
OUT
= 3.3V
V
OUT
= 3.3V
LT1585A Adjust Pin Current
vs Temperature
13
12
11
10
9
8
7
6
5
4
LT1585A-3.3 Quiescent Current
vs Temperature
80
70
60
50
40
30
20
10
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1585A • TPC08
3
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1585A • TPC09
LT1585A Maximum Power
Dissipation*
30
25
20
15
10
5
0
50 60 70 80 90 100 110 120 130 140 150
CASE TEMPERATURE (˚C)
LT1585A • TPC11
LT1585A • TPC10
*AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE
LT1585A/LT1585A-3.3
SI PLIFIED SCHE ATIC
V
IN
APPLICATIONS INFORMATION
General
The LT1585A/LT1585A-3.3 3-terminal regulators are
easy to use and have 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 regulators
include an adjustable and a fixed 3.3V version.
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
LT1585A/LT1585A-3.3 regulators require an output ca-
pacitor 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 re-
sponse as part of the specification. The LT1585A/
LT1585A-3.3 are specifically designed to meet the fast
current load-step requirements of these microprocessors
and save total cost by needing less output capacitance in
order to maintain regulation.
Stability
The circuit design in the LT1585A/LT1585A-3.3 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 LT1585A/
LT1585A-3.3 can use smaller value capacitors. Many
different types of capacitors are available and have widely
varying characteristics. These capacitors differ in capaci-
U
W
W
U
U
W
+
–
THERMAL
LIMIT
V
OUT
ADJ
GND
LT1585A • BD
FOR FIXED VOLTAGE DEVICE
5
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