Rabbit Semiconductor 101-0505 Datasheet

C.2 Power Supply

The OP6800 requires an unregulated +RAW power input of 9 V to 36 V DC, which can be supplied from the Demonstration Board through the ribbon cable connection. The OP6800 has its own switching voltage regulator.

Figure C-2 shows the distribution of the +RAW input power to the OP6800 through the

Demonstration Board. The reference grounds on the OP6800, GND, and on the Demonstration Board, 0 V, are tied together at one connection point only to avoid creating a ground loop, which could lead to considerable electromagnetic interference.

Demonstration Board

Linear

Regulator

+5 V

0 V

OP6800

Switching

Regulator

+5 V

GND

Figure C-2. Power Distribution to OP6800 and Demonstration Board

User’s Manual 63

The Demonstration Board has an onboard LM7805 linear regulator for the circuits on the

Demonstration Board only. Its major drawback is its inefficiency, which is directly proportional to the voltage drop across it. The voltage drop creates heat and wastes power.

You may wish to use a switching power supply in your applications where better efficiency is desirable. The LM2575 is an example of an easy-to-use switching voltage regulator. This part greatly reduces the heat dissipation of the regulator. The drawback in using a switching voltage regulator is its higher cost.

J5

2

1

+RAW

C1

10 mF

LINEAR POWER SUPPLY

Vcc

1

7805

U1

3

2

C2

10 mF

Figure C-3. Demonstration Board Power Supply

Capacitor C1 provides surge current protection for the voltage regulator, and allows the external power supply to be located some distance away.

Be careful to limit the current draw in any prototype circuits you build on the prototyping area of the Demonstration Board to avoid operating the linear regulator outside its recommended limits. The LEDs and buzzer together can draw up to 70 mA, which still leaves

some current capacity for your own circuits (see Table C-1) if you plan to use them with

the LEDs and the buzzer.

If you need additional current from the linear regulator beyond that specified in Table C-1,

consider adding a heat sink to the linear regulator (remember to use silicone grease between the tab and the heat sink), or use a lower voltage power supply.

64 MiniCom (OP6800)