MC34268
800 mA, 2.85 V, SCSI−2
Active Terminator, Low
Dropout Voltage Regulator
The MC34268 is a medium current, low dropout positive voltage
regulator specifically designed for use in SCSI−2 active termination
circuits. This device offers the circuit designer an economical
solution for precision voltage regulation, while keeping power losses
to a minimum. The regulator consists of a 1.0 V dropout composite
PNP/NPN pass transistor, current limiting, and thermal limiting.
These devices are packaged in the SOIC−8 and DPAK−3 and
SOT−223 surface mount power packages.
Applications include active SCSI−2 terminators and post
regulation of switching power supplies.
Features
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MARKING
DIAGRAMS
8
8
1
SOIC−8
D SUFFIX
CASE 751
1
A
L
Y
W
= Assembly Location
= Wafer Lot
= Year
= Work Week
1
2
8
7
6
5
(Top View)
NC
34268
ALYW
•
•
•
•
•
•
•
•
2.85 V Output Voltage for SCSI−2 Active Termination
1.0 V Dropout
Output Current in Excess of 800 mA
Thermal Protection
Short Circuit Protection
Output Trimmed to 1.4% Tolerance
No Minimum Load Required
Space Saving DPAK−3, SOT−223 and SOIC−8 Surface Mount
Power Packages
•
Pb−Free Packages are Available
GND
Output
Output
NC
3
Input
4
1
3
DPAK−3
DT SUFFIX
CASE 369A
34268
ALYWW
Simplified Block Diagram
1
Input
3
SOT−223
ST SUFFIX
CASE 318E
AYW
268ST
4
Thermal
Limiting
Control
Circuit
Current
Limit
1
2
3
Pin 1. Ground
2. Output
3. Input
4. Output
(Top View)
Output
Heatsink surface (shown as terminal 4 in
case outline drawing) is connected to Pin 2.
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 3 of this data sheet.
Ground
Semiconductor Components Industries, LLC, 2005
April, 2005
−
Rev. 6
1
Publication Order Number:
MC34268/D
MC34268
MAXIMUM RATINGS
Rating
Power Supply Input Voltage
Power Dissipation and Thermal Characteristics
DT Suffix, Plastic Package, Case 369A
T
A
= 25°C, Derate Above T
A
= 25°C
Thermal Resistance, Junction−to−Case
Thermal Resistance, Junction−to−Air
D Suffix, Plastic Package, Case 751
T
A
= 25°C, Derate Above T
A
= 25°C
Thermal Resistance, Junction−to−Case
Thermal Resistance, Junction−to−Air
ST Suffix, Plastic Package, Case 318E
T
A
= 25°C, Derate Above T
A
= 25°C
Thermal Resistance, Junction−to−Case
Thermal Resistance, Junction−to−Air
Operating Ambient Temperature Range
Maximum Die Junction Temperature
Storage Temperature
Symbol
V
in
Value
15
Unit
V
P
D
R
qJC
R
qJA
P
D
R
qJC
R
qJA
P
D
R
qJC
R
qJA
T
A
T
J
T
stg
Internally Limited
5.0
87
Internally Limited
22
140
Internally Limited
15
245
0 to +125
+150
−
55 to +150
W
°C/W
°C/W
W
°C/W
°C/W
W
°C/W
°C/W
°C
°C
°C
Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit values
(not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied, damage
may occur and reliability may be affected.
ELECTRICAL CHARACTERISTICS
(V
in
= 4.25 V, C
O
= 10
mF,
for typical values T
A
= 25°C, for min/max values T
A
= 0°C to +125°C, unless otherwise noted.)
Characteristic
Output Voltage (T
A
= 25°C, I
O
= 0 mA)
Output Voltage, over Line, Load, and Temperature (V
in
= 3.9 V to 15 V,
I
O
= 0 mA to 490 mA)
Line Regulation (V
in
= 4.25 V to 15 V, I
O
= 0 mA, T
A
= 25°C)
Load Regulation (I
O
= 0 mA to 800 mA, T
A
= 25°C)
Dropout Voltage (I
O
= 490 mA)
Ripple Rejection (f = 120 Hz)
Maximum Output Current (V
in
= 5.0 V)
Bias Current (V
in
= 4.25 V, I
O
= 0 mA)
Minimum Load Current to maintain Regulation (V
in
= 15 V)
I O, OUTPUT CURRENT
∆
VO , OUTPUT VOLTAGE DEVIATION
Symbol
V
O
Min
2.81
2.76
−
−
−
55
800
−
−
Typ
2.85
2.85
−
−
0.95
−
−
5.0 to 3.0
−
Max
2.89
2.93
0.3
0.5
1.1
−
−
8.0
0
Unit
V
Reg
line
Reg
load
V
in
−
V
O
RR
I
(max)
I
B
I
L(min)
%
%
V
dB
mA
mA
mA
1.5
V in −VO , DROPOUT VOLTAGE (V)
T
J
= 25°C
1.3
1.1
0.9
0.7
0.5
V
in
= 5.0 V
C
O
= 10
mF
T
A
= 25°C
0
200
400
600
800
1000
20 ms/DIV
I
O
, OUTPUT LOAD CURRENT (mA)
Figure 1. Dropout Voltage versus
Output Load Current
Figure 2. Transient Load Regulation
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2
MC34268
V
in
1N5819
10
MC34268
SCSI
Regulator
GN
D
V
O
C
O
10
To SCSI Bus
110W
5.0V
Figure 3. Typical SCSI Application
Figure 3 is a circuit of a typical SCSI terminator
application. The MC34268 is designed specifically to
provide 2.85 V required to drive a SCSI−2 bus. The output
current capability of the regulator is in excess of 800 mA;
enough to drive standard SCSI−2, fast SCSI−2, and some
wide SCSI−2 applications. The typical dropout voltage is
less than 1.0 V, allowing the IC to regulate to input voltages
less than 4.0 V. Internal protective features include current
and thermal limiting.
θ
JA , THERMAL RESISTANCE JUNCTION-TO-AIR
°
C/W)
(
The MC34268 requires an external 10
mF
capacitor with
an ESR of less than 10
W
for stability over temperature.
With economical electrolytic capacitors, cold temperature
operation can pose a stability problem. As temperature
decreases, the capacitance also decreases and the ESR
increases, which could cause the circuit to oscillate.
Tantalum capacitors may be a better choice if small size is
a requirement. Also, the capacitance and ESR of a tantalum
capacitor is more stable over temperature.
θ
JA , THERMAL RESISTANCE JUNCTION-TO-AIR ( C/W)
°
180
160
L
90
P.C. Board Heatsink Example
120
80
40
0
L
9.0 mm
L
70
60
50
40
0
10
20
30
40
50
L, LENGTH OF COPPER FLAGS (mm)
60
70
0
10
20
30
L, LENGTH OF COPPER (mm)
Figure 4. SOIC−8 Thermal Resistance versus
P.C.B. Copper Length
Figure 5. DPAK−3 Thermal Resistance
versus P.C.B. Copper Length
ORDERING INFORMATION
Device
MC34268D
MC34268DG
MC34268DR2
MC34268DR2G
MC34268DT
MC34268DTG
MC34268DTRK
MC34268DTRKG
MC34268STT3
Package
SOIC−8
SOIC−8
(Pb−Free)
SOIC−8
SOIC−8
(Pb−Free)
DPAK−3
DPAK−3
(Pb−Free)
DPAK−3
DPAK−3
(Pb−Free)
SOT−223
Shipping Information
†
98 Units / Rail
98 Units / Rail
2500 Units / Tape & Reel
2500 Units / Tape & Reel
75 Units / Rail
75 Units / Rail
2500 Units / Tape & Reel
2500 Units / Tape & Reel
4000 Units / Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
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3
ÉÉÉÉÉ
ÉÉÉÉÉ
ÉÉÉÉÉ
ÉÉÉÉÉ
2.0 oz
Copper
L
ÉÉÉÉÉ
ÉÉÉÉÉ
ÉÉÉÉÉ
2.0 oz
Copper
P.C. Board Heatsink Example
80
L
40
MC34268
PACKAGE DIMENSIONS
SOIC−8
D SUFFIX
CASE 751−07
ISSUE AB
−X−
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSION A AND B DO NOT INCLUDE MOLD
PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER
SIDE.
5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 (0.005) TOTAL IN
EXCESS OF THE D DIMENSION AT MAXIMUM
MATERIAL CONDITION.
6. 751−01 THRU 751−06 ARE OBSOLETE. NEW
STANDARD IS 751−07.
MILLIMETERS
MIN
MAX
4.80
5.00
3.80
4.00
1.35
1.75
0.33
0.51
1.27 BSC
0.10
0.25
0.19
0.25
0.40
1.27
0
_
8
_
0.25
0.50
5.80
6.20
INCHES
MIN
MAX
0.189
0.197
0.150
0.157
0.053
0.069
0.013
0.020
0.050 BSC
0.004
0.010
0.007
0.010
0.016
0.050
0
_
8
_
0.010
0.020
0.228
0.244
A
8
5
B
1
S
4
0.25 (0.010)
M
Y
M
−Y−
G
K
C
−Z−
H
D
0.25 (0.010)
M
SEATING
PLANE
N
X 45
_
0.10 (0.004)
M
J
Z Y
S
X
S
DIM
A
B
C
D
G
H
J
K
M
N
S
SOLDERING FOOTPRINT*
1.52
0.060
7.0
0.275
4.0
0.155
0.6
0.024
1.270
0.050
SCALE 6:1
mm
inches
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
SOIC−8
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4
MC34268
PACKAGE DIMENSIONS
DPAK−3
DT SUFFIX
CASE 369A−13
ISSUE AB
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
INCHES
MIN
MAX
0.235
0.250
0.250
0.265
0.086
0.094
0.027
0.035
0.033
0.040
0.037
0.047
0.180 BSC
0.034
0.040
0.018
0.023
0.102
0.114
0.090 BSC
0.175
0.215
0.020
0.050
0.020
−−−
0.030
0.050
0.138
−−−
MILLIMETERS
MIN
MAX
5.97
6.35
6.35
6.73
2.19
2.38
0.69
0.88
0.84
1.01
0.94
1.19
4.58 BSC
0.87
1.01
0.46
0.58
2.60
2.89
2.29 BSC
4.45
5.46
0.51
1.27
0.51
−−−
0.77
1.27
3.51
−−−
−T−
B
V
R
4
SEATING
PLANE
C
E
S
A
1
2
3
Z
U
K
F
L
D
G
2 PL
J
H
0.13 (0.005)
M
DIM
A
B
C
D
E
F
G
H
J
K
L
R
S
U
V
Z
T
SOLDERING FOOTPRINT*
6.20
0.244
2.58
0.101
5.80
0.228
1.6
0.063
6.172
0.243
3.0
0.118
SCALE 3:1
mm
inches
DPAK−3
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
http://onsemi.com
5
