www.fairchildsemi.com
Pentium is a registered trademark of Intel Corporation.
REV. 1.1.4 10/8/02
Features
Fast transient response
Low dropout voltage at up to 5A
Load regulation: 0.05% typical
Trimmed current limit
On-chip thermal limiting
Standard TO-220, TO-263, TO-263 center cut and TO-252
packages
Applications
Pentium
class GTL+ bus supply
Low voltage logic supply
Post regulator for switching supply
Description
The RC1585 and RC1585-1.5 are low dropout three-terminal
regulators with 5A output current capability. These devices
have been optimized for low voltage applications including
V
TT
bus termination, where transient response and mini-
mum input voltage are critical. The RC1585 is ideal for low
voltage microprocessor applications requiring a regulated
output from 1.5V to 3.6V with an input supply of 5V or less.
The RC1585-1.5 offers fixed 1.5V with 5A current capabili-
ties for GTL+ bus V
TT
termination.
Current limit is trimmed to ensure specified output current
and controlled short-circuit current. On-chip thermal limit-
ing provides protection against any combination of overload
and ambient temperature that would create excessive junc-
tion temperatures.
The RC1585 series regulators are available in the industry-
standard TO-220, TO-263, TO-263 center cut and TO-252
power packages.
Typical Applications
V
IN = 3.3V
10
F
10
F
22
F
22
F
1.5V at 5A
124
24.9
+
+
V
IN
ADJ
V
OUT
RC1585
V
IN = 3.3V
1.5V at 5A
+
+
V
IN
GND
V
OUT
RC1585-1.5
65-1585-01a
RC1585
5A Adjustable/Fixed Low Dropout Linear Regulator
RC1585
PRODUCT SPECIFICATION
2
REV. 1.1.4 10/8/02
Pin Assignments
Absolute Maximum Ratings
Parameter
Min.
Max.
Unit
V
IN
7
V
Operating Junction Temperature Range
0
125
C
Storage Temperature Range
-65
150
C
Lead Temperature (Soldering, 10 sec.)
300
C
ADJ
*
JA
can vary from 20
C/W to >40C/W with various mounting techniques.
OUT
FRONT VIEW
3-Lead Plastic TO-220
JC
= 3
C/W
IN
ADJ
FRONT VIEW
3-Lead Plastic TO-263
JC
= 3
C/W*
IN
1
2
3
1
2
3
GND OUT
OUT
OUT
FRONT VIEW
IN
1
2
3
GND
FRONT VIEW
RC1585M
RC1585M-1.5
RC1585T-1.5
RC1585T
IN
1
2
3
ADJ
FRONT VIEW
3-Lead Plastic TO-263 Center Cut
JC
= 3
C/W*
IN
Tab is Out.
1
2
3
GND
FRONT VIEW
RC1585MC
RC1585MC-1.5
IN
1
2
3
ADJ
FRONT VIEW
3-Lead Plastic TO-252
JC
= 3
C/W*
IN
Tab is Out.
1
2
3
GND
FRONT VIEW
RC1585D
RC1585D-1.5
IN
1
2
3
65-1585-02
PRODUCT SPECIFICATION
RC1585
REV. 1.1.4 10/8/02
3
Electrical Characteristics
Tj = 25C unless otherwise specified.
The
denotes specifications which apply over the specified operating temperature range.
Notes:
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.
2. Line and load regulation are guaranteed up to the maximum power dissipation (18W). Power dissipation is determined by
input/output differential and the output currrent. Guaranteed maximum output power will not be available over the full input/
output voltage range.
3. RC1585 only.
4. RC1585-1.5 only.
Parameter
Conditions
Min.
Typ.
Max
Units
Reference Voltage
3
1.5V
(V
IN
V
OUT
)
5.75V,
10mA
I
OUT
5A
1.225
(-2%)
1.250
1.275
(+2%)
V
Output Voltage
4
3V
V
IN
7V
10mA
I
OUT
5A
1.47
1.5
1.53
V
Line Regulation
1, 2
(V
OUT
+ 1.5V)
V
IN
7V,
I
OUT
= 10mA
0.005
0.2
%
Load Regulation
1, 2, 3
(V
IN
V
OUT
) = 3V,
10mA
I
OUT
5A
0.05
0.5
%
Dropout Voltage
V
REF
= 1%, I
OUT
= 5A
1.150
1.300
V
Current Limit
(V
IN
V
OUT
) = 2V
5.1
5.5
A
Adjust Pin Current
3
35
120
A
Adjust Pin Current Change
3
1.5V
(V
IN
V
OUT
)
5.75V,
10mA
I
OUT
5A
0.2
5
A
Minimum Load Current
1.5V
(V
IN
V
OUT
)
5.75V
10
mA
Quiescent Current
V
IN
= 5V
4
13
mA
Ripple Rejection
f = 120Hz, C
OUT
= 22
F Tantalum,
(V
IN
V
OUT
) = 3V, I
OUT
= 5A
60
72
dB
Thermal Regulation
T
A
= 25
C, 30ms pulse
0.004
0.02
%/W
Temperature Stability
0.5
%
Long-Term Stability
T
A
= 125
C, 1000 hrs.
0.03
1.0
%
RMS Output Noise
(% of V
OUT
)
T
A
= 25
C, 10Hz f 10kHz
0.003
%
Thermal Resistance,
Junction to Case
TO-220
3
C/W
TO-263, TO-252
3
C/W
Thermal Shutdown
150
C
RC1585
PRODUCT SPECIFICATION
4
REV. 1.1.4 10/8/02
Typical Performance Characteristics
Figure 1. Dropout Voltage vs. Output Current
Figure 2. Load Regulation vs. Temperature
Figure 3. Reference Voltage vs. Temperature
Figure 4. Output Voltage vs. Temperature
Figure 5. Minimum Load Current vs. Temperature
Figure 6. Adjust Pin Current vs. Temperature
1
2
3
OUTPUT CURRENT (A)
DROPOUT VOLTAGE (V)
4
5
0
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
T=25
C
T=0
C
T=125
C
65-1585-03
JUNCTION TEMPERATURE (
C)
OUTPUT VOLTAGE DEVIATION (%)
-75 -50 -25
0
25
50
75 100 125 150 175
0.10
0.05
0
-0.05
-0.10
-0.15
-0.20
I = 5A
65-1585-04
JUNCTION TEMPERATURE (
C)
REFERENCE VOLTAGE (V)
-75 -50 -25
0
25
50
75 100 125 150 175
3.70
3.65
3.60
3.55
3.50
3.45
3.40
3.35
3.30
3.25
3.20
V
OUT
SET WITH 1% RESISTORS
V
OUT
= 3.6V
1
V
OUT
= 3.3V
1
Note:
1. RC1585 Only
65-1585-06
JUNCTION TEMPERATURE (
C)
REFERENCE VOLTAGE (V)
-75 -50 -25
0
25
50
75 100 125 150 175
1.275
1.270
1.265
1.260
1.255
1.250
1.245
1.240
1.235
1.230
1.225
65-1585-05
JUNCTION TEMPERATURE (
C)
MINIMUM LOAD CURRENT (mA)
-75 -50 -25
0
25
50
75 100 125 150 175
5
4
3
2
1
0
65-1585-07
JUNCTION TEMPERATURE (
C)
ADJUST PIN CURRENT (
A)
-75 -50 -25
0
25
50
75 100 125 150 175
100
90
80
70
60
50
40
30
20
10
0
65-1585-08
Note:
1. RC1585 Only
PRODUCT SPECIFICATION
RC1585
REV. 1.1.4 10/8/02
5
Typical Performance Characteristics
(continued)
Figure 7. Short-Circuit Current vs. Temperature
Figure 8. Ripple Rejection vs. Frequency
Figure 9. Maximum Power Dissipation
JUNCTION TEMPERATURE (
C)
SHORT-CIRCUIT CURRENT (A)
-75 -50 -25
0
25
50
75 100 125 150 175
8.0
7.0
6.0
5.0
4.0
65-1585-09
FREQUENCY (Hz)
RIPPLE REJECTIONS (dB)
10
100
1K
10K
100K
90
80
70
60
50
40
30
20
10
0
65-1585-10
(V
IN
V
OUT
)
3V
0.5V
V
RIPPLE
2V
I
OUT
= 5A
CASE TEMPERATURE (
C)
POWER (W)
50
60
70
80
90 100 110 120 130 140 150
20
15
10
5
0
65-1585-11
RC1585
PRODUCT SPECIFICATION
6
REV. 1.1.4 10/8/02
Applications Information
General
The RC1585 and RC1585-1.5 are three-terminal regulators
optimized for GTL+ V
TT
termination and logic applica-
tions. These devices are short-circuit protected and offer
thermal shutdown to turn off the regulator when the junction
temperature exceeds about 150C. The RC1585 series pro-
vides low dropout voltage and fast transient response. Fre-
quency compensation uses capacitors with low ESR while
still maintaining stability. This is critical in addressing the
needs of low voltage high speed microprocessor buses like
GTL+.
Stability
The RC1585 series requires an output capacitor as a part of
the frequency compensation. It is recommended to use a
22F solid tantalum or a 100 F aluminum electrolytic on
the output to ensure stability. The frequency compensation of
these devices optimizes the frequency response with low
ESR capacitors. In general, it is suggested to use capacitors
with an ESR of <300m
. It is also recommended to use
bypass capacitors such as a 22F tantalum or a 100F alumi-
num on the adjust pin of the RC1585 for low ripple and fast
transient response. When these bypassing capacitors are not
used at the adjust pin, larger values of output capacitors pro-
vide equally good results.
Protection Diodes
In normal operation, the RC1585 series does not require any
protection diodes. For the RC1585, 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 condi-
tions.
A protection diode between the input and output pins is
usually not needed. An internal diode between the input and
the output pins on the RC1585 series can handle micro-
second 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 1000F to 5000F, and with the
input pin instantaneously shorted to ground can damage
occur. A crowbar circuit at the input can generate those
levels of current; a diode from output to input is then recom-
mended, as shown in Figure 10. Usually, normal power sup-
ply 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-to-
output voltage differential causes the internal transistors to
break down and none of the protection circuitry is then
functional.
Figure 10. Optional Protection
Ripple Rejection
In applications that require improved ripple rejection, a
bypass capacitor from the adjust pin of the RC1585 to
ground reduces the output ripple by the ratio of V
OUT
/1.25V.
The impedance of the adjust pin capacitor at the ripple fre-
quency should be less than the value of R1 (typically in the
range of 100
to 120) in the feedback divider network in
Figure 10. Therefore, the value of the required adjust pin
capacitor is a function of the input ripple frequency. For
example, if R1 equals 100
and the ripple frequency equals
120Hz, the adjust pin capacitor should be 22F. At 10kHz,
only 0.22F is needed.
Output Voltage
The RC1585 regulator develops a 1.25V reference voltage
between the output pin and the adjust pin (see Figure 11).
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 35A. Its output voltage contribution is
small and only needs consideration when a very precise out-
put voltage setting is required.
RC1585
ADJ
C
ADJ
R2
R1
65-1585-12
+
C2
22
F
V
OUT
+
C1
10
F
+
IN
OUT
D1
1N4002
(OPTIONAL)
V
IN
RC1585-1.5
GND
C2
22
F
V
OUT
C1
10
F
+
+
IN
OUT
D1
1N4002
(OPTIONAL)
V
IN
PRODUCT SPECIFICATION
RC1585
REV. 1.1.4 10/8/02
7
Figure 11. Basic Regulator Circuit
Load Regulation
It is not possible to provide true remote load sensing because
the RC1585 series are three-terminal devices. Load regula-
tion 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 12.
Figure 12. Connection for Best Load Regulation
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 regu-
lation is obtained when the top of the resistor divider R1 con-
nects directly to the regulator output and not to the load.
Figure 13 illustrates this point.
If R1 connects to the load, then the effective resistance
between the regulator and the load would be:
R
P
x (1 + R2/R1), R
P
= Parasitic Line Resistance
The connection shown in Figure 13 does not multiply R
P
by
the divider ratio. As an example, R
P
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 repre-
sents 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.
Figure 13. Connection for Best Load Regulation
Thermal Considerations
The RC1585 series protect themselves under overload condi-
tions with internal power and thermal limiting circuitry.
However, for normal continuous load conditions, do not
exceed maximum junction temperature ratings. It is impor-
tant to consider all sources of thermal resistance from junc-
tion-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 tempera-
ture and ensure safe operating temperatures.
For example, look at using an RC1585T to generate 5A @
1.5V 2% from a 3.3V source (3.2V to 3.6V).
Assumptions:
V
IN
= 3.6V worst case
V
OUT
= 1.46V worst case
I
OUT
= 5A continuous
T
A
= 60
C
Case-to-Ambient
= 3
C/W (assuming both a heatsink and
a thermally conductive material)
The power dissipation in this application is:
P
D
= (V
IN
V
OUT
) * (I
OUT
) = (3.6 1.46) * (5) = 10.7W
From the specification table:
T
J
= T
A
+ (P
D
) * (
Case-to-Ambient
+
JC
)
= 60 + (10.7) * (3 + 3) = 120
C
The junction temperature is below the maximum rating.
RC1585
ADJ
I
ADJ
35
A
R2
R1
C2
22
F
V
OUT
V
REF
+
C1
10
F
+
65-1585-13
IN
V
OUT
= V
REF
(1 + R2/R1) + I
ADJ
(R2)
OUT
V
IN
RC1585-1.5
GND
R
L
65-1585-14
R
P
PARASITIC
LINE RESISTANCE
IN
OUT
V
IN
RC1585
ADJ
R2*
CONNECT R1 TO CASE
CONNECT R2 TO LOAD
*
R1*
R
L
65-1585-15
R
P
PARASITIC
LINE RESISTANCE
IN
OUT
V
IN
RC1585
PRODUCT SPECIFICATION
8
REV. 1.1.4 10/8/02
Figure 14. Application Circuit (RC1585)
Table 1. Bill of Materials for Application Circuit for the RC1585
Figure 15. Application Circuit (RC1585-1.5)
Table 2. Bill of Materials for Application Circuit for the RC1585-1.5
Item
Quantity
Manufacturer
Part Number
Description
C1
1
Xicon
L10V10
10F, 10V Aluminum
C2, C3
2
Xicon
L10V100
100F, 10V Aluminum
R1
1
Generic
124
, 1%
R2
1
Generic
24.9
, 1%
U1
1
Fairchild
RC1585T
5A Regulator
Item
Quantity
Manufacturer
Part Number
Description
C1
1
Xicon
L10V10
10F, 10V Aluminum
C3
1
Xicon
L10V100
100F, 10V Aluminum
U1
1
Fairchild
RC1585T-1.5
5A Regulator
RC1585
U1
ADJ
C2
100
F
R2
24.9
R1
124
65-1586-16
+
C3
100
F
V
OUT
1.5V
+
C1
10
F
+
V
IN
V
OUT
V
IN
3.3V
RC1585-1.5
U1
GND
65-1585-17
C3
100
F
V
OUT
1.5V
+
C1
10
F
+
V
IN
V
OUT
V
IN
3.3V
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. Use of a thermally conductive material at the
case-to-heat sink interface is recommended. Use a thermally
conductive spacer if the case of the device must be electri-
cally isolated and include its contribution to the total thermal
resistance. The cases of the RC1585 series are directly con-
nected to the output of the device.
PRODUCT SPECIFICATION
RC1585
REV. 1.1.4 10/8/02
9
Mechanical Dimensions
3-Lead TO-263 Package
A
.160
.190
4.06
4.83
Symbol
Inches
Min.
Max.
Min.
Max.
Millimeters
Notes
b
.020
.036
0.51
0.91
b2
.049
.051
1.25
1.30
c2
.045
.055
1.14
1.40
D
.340
.380
8.64
9.65
.380
.405
9.65
10.29
.100 BSC
E
e
L
.575
.625
14.61
15.88
.090
.110
2.29
2.79
L1
L2
--
.055
--
1.40
.017
.019
0.43
0.78
R
0
8
0
8
Notes:
1. Dimensions are exclusive of mold flash and metal burrs.
2. Standoff-height is measured from lead tip with ref. to Datum -B-.
3. Foot length is measured with ref. to Datum -A- with lead surface
(at inner R).
4. Dimensiuon exclusive of dambar protrusion or intrusion.
5. Formed leads to be planar with respect to one another at seating
place -C-.
2.54 BSC
E
@PKG/
@HEATSINK
D
L2
A
-C-
L
c2
L1
R (2 PLCS)
-A-
-B-
E-PIN
b2
b
e
RC1585
PRODUCT SPECIFICATION
10
REV. 1.1.4 10/8/02
Mechanical Dimensions
(continued)
3-Lead TO-263 Center Cut Package
A
.160
.190
4.06
4.83
Symbol
Inches
Min.
Max.
Min.
Max.
Millimeters
Notes
b
.020
.036
0.51
0.91
b2
.049
.051
1.25
1.30
c2
.045
.055
1.14
1.40
D
.340
.380
8.64
9.65
.380
.405
9.65
10.29
.100 BSC
E
e
L
.575
.625
14.61
15.88
.090
.110
2.29
2.79
.050
.070
1.27
1.78
L1
L2
L3
--
.055
--
1.40
.017
.019
0.43
0.78
R
0
8
0
8
Notes:
1. Dimensions are exclusive of mold flash and metal burrs.
2. Standoff-height is measured from lead tip with ref. to Datum -B-.
3. Foot length is measured with ref. to Datum -A- with lead surface
(at inner R).
4. Dimensiuon exclusive of dambar protrusion or intrusion.
5. Formed leads to be planar with respect to one another at seating
place -C-.
2.54 BSC
E
@PKG/
@HEATSINK
D
L2
L3
A
-C-
L
c2
L1
R (2 PLCS)
-A-
-B-
E-PIN
b2
b
e
PRODUCT SPECIFICATION
RC1585
REV. 1.1.4 10/8/02
11
Mechanical Dimensions
(continued)
3-Lead TO-220 Package
A
.140
.190
3.56
4.83
Symbol
Inches
Min.
Max.
Min.
Max.
Millimeters
Notes
b
.015
.040
.38
1.02
.070
1.78
b1
.045
1.14
c1
.014
.022
.36
.56
P
.139
.161
3.53
4.09
D
.560
.650
14.22
16.51
.380
.420
9.65
10.67
.090
.110
2.29
2.79
E
e
e1
.190
.210
4.83
5.33
.045
--
1.14
--
.020
.055
.51
1.40
e3
F
H1
.230
.270
5.94
6.87
.060
.115
2.04
2.92
.500
.580
12.70
14.73
J1
L
6.35 BSC
.250 BSC
L1
.100
.135
2.54
3.43
3
7
3
7
Q
b1
b
e3
L1
L
H1
Q
E
e
e1
E-PIN
P
c1
J1
D
F
A
(5X)
Notes:
1. Dimension c1 apply for lead finish.
RC1585
PRODUCT SPECIFICATION
12
REV. 1.1.4 10/8/02
Mechanical Dimensions
(continued)
3-Lead TO-252 Package
D
D1
GAGE PLANE
NOTES: UNLESS OTHERWISE SPECIFIED
A)
ALL DIMENSIONS ARE IN MILLIMETERS.
B)
THIS PACKAGE CONFORMS TO JEDEC, TO-252,
ISSUE C. VARIATION AA & AB, DATED NOV. 1999.
C)
DIMENSIONING AND TOLERANCING PER
ASME Y14.51994.
D)
HEAT SINK TOP EDGE COULD BE IN CHAMFERED
CORNERS OR EDGE PROTRUSION.
E)
DIMENSIONS L3, D, E1 & D1 TABLE:
OPTION AA OPTION AB
0.89 1.27
1.52 2.03
5.97 6.22
5.33 5.59
4.32 MIN
3.81 MIN
5.21 MIN
L3
D
E1
D1
4.57 MIN
0.51
SEATING PLANE
DETAIL A
(1.54)
1.78
1.40
0.61
0.48
10
0
0.127 MAX
(ROTATED 90
SCALE 12X
E1
L3
1
1
2
3
1
2
3
4
3
4
6.73
6.35
1.02
0.84
6.25
6.00 MIN
6.50 MIN
4.80
2.38
2.18
0.58
0.48
0.10
B
10.41
9.40
SEE
DETAIL A
3.00 MIN
1.40 MIN
LAND PATTERN RECOMMENDATION
1.14
0.78
0.89
0.54
SEE
NOTE D
(0.59)
2.29
5.46
5.21
4.57
0.25
A
C
M
M
2.90
2.30
C
A
B
RC1585
PRODUCT SPECIFICATION
10/8/02 0.0m 002Stock#DS30001585
2000 Fairchild Semiconductor Corporation
DISCLAIMER
FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY
PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY
LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER
DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
LIFE SUPPORT POLICY
FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, or (c) whose failure to perform
when properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to
result in significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
www.fairchildsemi.com
Ordering Information
Product Number
Package
RC1585M
TO-263
RC1585MC
TO-263 Center Cut
RC1585T
TO-220
RC1585D
TO-252
RC1585M-1.5
TO-263
RC1585MC-1.5
TO-263 Center Cut
RC1585T-1.5
TO-220
RC1585D-1.5
TO-252
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