MC34268
http://onsemi.com
3
Figure 3. Typical SCSI Application
1N5819
To SCSI Bus
MC34268
SCSI
Regulator
110W
1010
5.0V
V
in
V
O
GN
D
C
O
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)
θ
JA
°
, THERMAL RESISTANCE JUNCTION-TO-AIR ( C/W)
θ
JA
°
70
90
80
70
60
50
40
180
160
120
80
40
0
L
L
2.0 oz
Copper
L9.0 mm
P.C. Board Heatsink Example
L
L
2.0 oz
Copper
P.C. Board Heatsink Example
ORDERING INFORMATION
Device Package Shipping Information
†
MC34268D SOIC−8 98 Units / Rail
MC34268DG SOIC−8
(Pb−Free)
98 Units / Rail
MC34268DR2 SOIC−8 2500 Units / Tape & Reel
MC34268DR2G SOIC−8
(Pb−Free)
2500 Units / Tape & Reel
MC34268DT DPAK−3 75 Units / Rail
MC34268DTG DPAK−3
(Pb−Free)
75 Units / Rail
MC34268DTRK DPAK−3 2500 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.