Page 12

January 1999 TOKO, Inc.

TK715xx

REVERSE BIAS PROTECTION

The internal reverse bias protection eliminates the

requirement for a reverse voltage protection diode. This

saves both cost and board space.

Another reverse bias protection technique is illustrated

below. The extra diode and extra capacitor are not

necessary with the TK715xx. The high output voltage

accuracy is maintained because the diode forward voltage

variations over temperature and load current have been

eliminated.

PARALLEL OPERATION

The series resistor R is put in the input line of the low output

voltage regulator in order to prevent overdissipation. The

voltage dropped across the resistor reduces the large

input-to-output voltage across the regulator, reducing the

power dissipation in the device.

715xxS

VOUT

VIN

GND

APPLICATION INFORMATION (CONT.)

SWITCHING OPERATION

Even though the input voltages or the output voltages are

different, the outputs of the TK715xx regulators can be

connected together, and the output voltages switched. If

two or more TK715xx regulators are turned ON

simultaneously, the highest output voltage will be present.

CURRENT BOOST OPERATION

The output current can be increased by connecting an

external PNP transistor as shown below. The output

current capability depends upon the H

transistor. Note: The TK715xx internal short circuit

protection and thermal sensor do not protect the external

transistor.

TK715xxS

VOUT

VIN

TK71550

5 V

VIN

TK71530

TK71520

3 V

2 V

R

TK715xx

VIN

VOUT

0.22 µF

150

Ω

VIN

3.3 µF

TK71530

VIN

TK71528

VIN

VOUT

3.0 OR 2.8 V