MOTOROLA MC34268D, MC34268DR2, MC34268DT, MC34268DTRK Datasheet

MC34268

SCSI-2 Active Terminator
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 8–pin SOP–8 and 3–pin DPAK
and SOT–223 surface mount power packages.

Applications include active SCSI–2 terminators and post
regulation of switching power supplies.

• 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, SOT–223 and SOP–8 Surface Mount Power

Packages

Simplified Block Diagram

http://onsemi.com

Gnd

SOP–8
D SUFFIX
CASE 751

1
2

3
4

(Top View)

8

1

A = Assembly Location
L = Wafer Lot
Y = Year
W = Work Week

Output Output

Input

MARKING

DIAGRAMS

8

1

NC

8
7
6

NC

5

34268
ALYW

Input

Thermal

Limiting

Control

Circuit

Current

Limit

Ground

Output

DPAK

1

3

1

3

Heatsink surface (shown as terminal 4 in

case outline drawing) is connected to Pin 2.

DT SUFFIX

CASE 369A

SOT–223

ST SUFFIX

CASE 318E

4

123

(Top View)

Pin 1. Ground

2. Output

3. Input

4. Output

34268

ALYWW

AYW

268ST

ORDERING INFORMATION

See detailed ordering and shipping information in the package
dimensions section on page 3 of this data sheet.

 Semiconductor Components Industries, LLC, 2000

April, 2000 – Rev. 1

1 Publication Order Number:

MC34268/D

MC34268

–

,

O

O

T

OLT

G

(

)

N

MAXIMUM RATINGS

Rating Symbol Value Unit

Power Supply Input Voltage 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
Operating Junction Temperature Range T
Storage Temperature T

R
R

R
R

R
R

P

θJC
θJA

P

θJC
θJA

P

θJC
θJA

stg

in

D

D

D

J

ELECTRICAL CHARACTERISTICS

(Vin = 4.25 V, CO = 10 µF, for typical values TJ = 25°C, for min/max values TJ = 0°C to +125°C, unless otherwise noted.)

Characteristic

Output Voltage (TJ = 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)
Line Regulation (Vin = 4.25 V to 15 V, IO = 0 mA, TJ = 25°C) Reg
Load Regulation (IO = 0 mA to 800 mA, TJ = 25°C) Reg
Dropout Voltage (IO = 490 mA) Vin–V
Ripple Rejection (f = 120 Hz) RR 55 — — dB
Maximum Output Current (Vin = 5.0 V) I
Bias Current (Vin = 4.25 V, IO = 0 mA) I
Minimum Load Current to maintain Regulation (Vin = 15 V) I

15 V

Internally Limted

5.0
87

Internally Limited

22

140

Internally Limited

15

245

0 to +150 °C

– 55 to +150 °C

Symbol Min Typ Max Unit

V

O

load

(max)

B

L(min)

line

W

°C/W
°C/W

W

°C/W
°C/W

W

°C/W
°C/W

2.81

2.76

— — 0.3 %
— — 0.5 %
— 0.95 1.1 V

O

800 — — mA

— 5.0 to 3.0 8.0 mA
— — 0 mA

2.85

2.85

2.89

2.93

V

Figure 1. Dropout Voltage versus

Figure 2. Transient Load Regulation

Output Load Current

1.5

V

1.3

E
A

1.1

V
U
P

0.9

DR

O

V

0.7

in

V

0.5
0 200 400 600 800 1000

IO, OUTPUT LOAD CURRENT (mA)

TJ = 25°C

Vin = 5.0 V
CO = 10 µF

, OUTPUT VOLTAGE DEVIATIO

O

V

∆

, OUTPUT CURRENTI

O

20 ms/DIV

TA = 25°C

http://onsemi.com

2

MC34268

,

T

M

L

I

T

NC

J

NCTION

TO

I

(

C

)

Figure 3. T ypical SCSI Application

V

5.0V
1N5819

in

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.

Figure 4. SOP–8 Thermal Resistance versus

/W

°

R

-A

-

U
E

A
S

180

160

120

80

P.C.B. Copper Length

P.C. Board Heatsink Example

2.0 oz

L

Copper

9.0 mm

L

L

MC34268

SCSI

Regulator

Gnd

V

O

C

1010

O

110Ω

To SCSI Bus

The MC34268 requires an external 10 µF capacitor with

an ESR of less than 10 Ω 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.

Figure 5. DP AK Thermal Resistance

°

90

80

70

60

versus P.C.B. Copper Length

P.C. Board Heatsink Example

L

L

2.0 oz
Copper

RES

40

A
HER

0

0 102030405060

JA

θ

L, LENGTH OF COPPER FLAGS (mm)

70

50

40

, THERMAL RESISTANCE JUNCTION-TO-AIR ( C/W)

0 10203040

JA

θ

L, LENGTH OF COPPER (mm)

ORDERING INFORMATION

Device Package Shipping Information

MC34268D SO–8 98 Units / Rail
MC34268DR2 SO–8 2500 Units / Tape & Reel
MC34268DT DPAK 75 Units / Rail
MC34268DTRK DPAK 2500 Units / Tape & Reel
MC34268STT3 SOT–223 4000 Units / Tape & Reel

http://onsemi.com

3