Semiconductor Components Industries, LLC, 2005
April, 2005 − Rev. 6
1Publication Order Number:
MC34268/D
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
•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
Simplified Block Diagram
Input
Thermal
Limiting
Control
Circuit
Current
Limit Output
Ground
See detailed ordering and shipping information in the package
dimensions section on page 3 of this data sheet.
ORDERING INFORMATION
8
1
8
7
6
5
1
2
3
4
GND
SOIC−8
D SUFFIX
CASE 751
DPAK−3
DT SUFFIX
CASE 369A
Input
NC
NC
123
(Top View)
(Top View)
1
3
Output Output
Heatsink surface (shown as terminal 4 in
case outline drawing) is connected to Pin 2.
SOT−223
ST SUFFIX
CASE 318E
1
3
Pin 1. Ground
2. Output
3. Input
4. Output
4
MARKING
DIAGRAMS
ALYW
34268
1
8
34268
ALYWW
AYW
268ST
A = Assembly Location
L = Wafer Lot
Y = Year
W = Work Week
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MC34268
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2
MAXIMUM RATINGS
Rating Symbol Value Unit
Power Supply Input Voltage Vin 15 V
Power Dissipation and Thermal Characteristics
DT Suffix, Plastic Package, Case 369A
TA = 25°C, Derate Above TA = 25°C
Thermal Resistance, Junction−to−Case
Thermal Resistance, Junction−to−Air
D Suffix, Plastic Package, Case 751
TA = 25°C, Derate Above TA = 25°C
Thermal Resistance, Junction−to−Case
Thermal Resistance, Junction−to−Air
ST Suffix, Plastic Package, Case 318E
TA = 25°C, Derate Above TA = 25°C
Thermal Resistance, Junction−to−Case
Thermal Resistance, Junction−to−Air
PD
RqJC
RqJA
PD
RqJC
RqJA
PD
RqJC
RqJA
Internally Limited
5.0
87
Internally Limited
22
140
Internally Limited
15
245
W
°C/W
°C/W
W
°C/W
°C/W
W
°C/W
°C/W
Operating Ambient Temperature Range TA0 to +125 °C
Maximum Die Junction Temperature TJ+150 °C
Storage Temperature Tstg −55 to +150 °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
(Vin = 4.25 V, CO = 10 mF, for typical values TA = 25°C, for min/max values TA = 0°C to +125°C, unless otherwise noted.)
Characteristic Symbol Min Typ Max Unit
Output Voltage (TA = 25°C, IO = 0 mA)
Output Voltage, over Line, Load, and Temperature (Vin = 3.9 V to 15 V,
IO = 0 mA to 490 mA)
VO2.81
2.76
2.85
2.85
2.89
2.93
V
Line Regulation (Vin = 4.25 V to 15 V, IO = 0 mA, TA = 25°C) Regline − − 0.3 %
Load Regulation (IO = 0 mA to 800 mA, TA = 25°C) Regload − − 0.5 %
Dropout Voltage (IO = 490 mA) Vin −VO−0.95 1.1 V
Ripple Rejection (f = 120 Hz) RR 55 − − dB
Maximum Output Current (Vin = 5.0 V) I(max) 800 − − mA
Bias Current (Vin = 4.25 V, IO = 0 mA) IB−5.0 to 3.0 8.0 mA
Minimum Load Current to maintain Regulation (Vin = 15 V) IL(min) −−0 mA
IO, OUTPUT LOAD CURRENT (mA)
in
VO
−V
Figure 1. Dropout Voltage versus
Output Load Current
1.5
1.3
1.1
0.9
0.7
0.5 0 200 400 600 800 1000
Figure 2. Transient Load Regulation
, DR
O
P
O
UT V
O
LTA
G
E
(
V
)
TJ = 25°C
20 ms/DIV
Vin = 5.0 V
CO = 10 mF
TA = 25°C
, OUTPUT CURRENTI O
VO, OUTPUT VOLTAGE DEVIATION∆
MC34268
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3
Figure 3. Typical SCSI Application
1N5819
To SCSI Bus
MC34268
SCSI
Regulator
110W
1010
5.0V
Vin VO
GN
D
CO
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.
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.
, THERMAL RESISTANCE JUNCTION-TO-AIR ( C/W)
Figure 4. SOIC−8 Thermal Resistance versus
P.C.B. Copper Length
0 10203040
L, LENGTH OF COPPER (mm)
Figure 5. DPAK−3 Thermal Resistance
versus P.C.B. Copper Length
0 102030405060
L, LENGTH OF COPPER FLAGS (mm)
θJA °
, THERMAL RESISTANCE JUNCTION-TO-AIR ( C/W)
θJA °
70
90
80
70
60
50
40
180
160
120
80
40
0
L
L
ÉÉÉ
ÉÉÉ
ÉÉÉ
ÉÉ
ÉÉ
ÉÉ
2.0 oz
Copper
L9.0 mm
P.C. Board Heatsink Example
L
L
ÉÉÉÉÉ
ÉÉÉÉÉ
ÉÉÉÉÉ
ÉÉÉÉÉ
2.0 oz
Copper
P.C. Board Heatsink Example
ORDERING INFORMATION
Device Package Shipping Information†
MC34268D SOIC−898 Units / Rail
MC34268DG SOIC−8
(Pb−Free)
98 Units / Rail
MC34268DR2 SOIC−82500 Units / Tape & Reel
MC34268DR2G SOIC−8
(Pb−Free)
2500 Units / Tape & Reel
MC34268DT DPAK−375 Units / Rail
MC34268DTG DPAK−3
(Pb−Free)
75 Units / Rail
MC34268DTRK DPAK−32500 Units / Tape & Reel
MC34268DTRKG DPAK−3
(Pb−Free)
2500 Units / Tape & Reel
MC34268STT3 SOT−223 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.
MC34268
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4
PACKAGE DIMENSIONS
SOIC−8
D SUFFIX
CASE 751−07
ISSUE AB
SOIC−8
1.52
0.060
7.0
0.275
0.6
0.024
1.270
0.050
4.0
0.155
ǒmm
inchesǓ
SCALE 6:1
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
SOLDERING FOOTPRINT*
SEATING
PLANE
1
4
58
N
J
X 45_
K
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.
A
BS
D
H
C
0.10 (0.004)
DIM
A
MIN MAX MIN MAX
INCHES
4.80 5.00 0.189 0.197
MILLIMETERS
B3.80 4.00 0.150 0.157
C1.35 1.75 0.053 0.069
D0.33 0.51 0.013 0.020
G1.27 BSC 0.050 BSC
H0.10 0.25 0.004 0.010
J0.19 0.25 0.007 0.010
K0.40 1.27 0.016 0.050
M0 8 0 8
N0.25 0.50 0.010 0.020
S5.80 6.20 0.228 0.244
−X−
−Y−
G
M
Y
M
0.25 (0.010)
−Z−
Y
M
0.25 (0.010) Z SXS
M
____
MC34268
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5
PACKAGE DIMENSIONS
DPAK−3
DT SUFFIX
CASE 369A−13
ISSUE AB
D
A
K
B
R
V
S
F
L
G
2 PL
M
0.13 (0.005) T
E
C
U
J
H
−T−SEATING
PLANE
Z
DIM MIN MAX MIN MAX
MILLIMETERSINCHES
A0.235 0.250 5.97 6.35
B0.250 0.265 6.35 6.73
C0.086 0.094 2.19 2.38
D0.027 0.035 0.69 0.88
E0.033 0.040 0.84 1.01
F0.037 0.047 0.94 1.19
G0.180 BSC 4.58 BSC
H0.034 0.040 0.87 1.01
J0.018 0.023 0.46 0.58
K0.102 0.114 2.60 2.89
L0.090 BSC 2.29 BSC
R0.175 0.215 4.45 5.46
S0.020 0.050 0.51 1.27
U0.020 −−− 0.51 −−−
V0.030 0.050 0.77 1.27
Z0.138 −−− 3.51 −−−
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
123
4
5.80
0.228
2.58
0.101
1.6
0.063
6.20
0.244
3.0
0.118
6.172
0.243
ǒmm
inchesǓ
SCALE 3:1
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
SOLDERING FOOTPRINT*
DPAK−3
MC34268
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6
PACKAGE DIMENSIONS
SOT−223
ST SUFFIX
CASE 318E−04
ISSUE K
H
S
F
A
B
D
G
L
4
123
0.08 (0003)
C
M
K
J
DIM
A
MIN MAX MIN MAX
MILLIMETERS
0.249 0.263 6.30 6.70
INCHES
B0.130 0.145 3.30 3.70
C0.060 0.068 1.50 1.75
D0.024 0.035 0.60 0.89
F0.115 0.126 2.90 3.20
G0.087 0.094 2.20 2.40
H0.0008 0.0040 0.020 0.100
J0.009 0.014 0.24 0.35
K0.060 0.078 1.50 2.00
L0.033 0.041 0.85 1.05
M0 10 0 10
S0.264 0.287 6.70 7.30
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
____
1.5
0.059 ǒmm
inchesǓ
SCALE 6:1
3.8
0.15
2.0
0.079
6.3
0.248
2.3
0.091
2.3
0.091
2.0
0.079
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
SOLDERING FOOTPRINT*
SOT−23
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MC34268/D
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