MC78LC00 Series

5

MOTOROLA ANALOG IC DEVICE DATA

APPLICATIONS INFORMATION

Introduction

The MC78LC00 micropower voltage regulators are

specifically designed with high accuracy output voltage and

ultra low quiescent current by CMOS process making them

ideal for battery powered applications and hand–held

communication equipment. An input bypass capacitor is

recommended if the regulator is located an appreciable

distance (

≥ 4 inches) from the input voltage source. These

regulators require

≥ 0.1 µF capacitance between the output

terminal and ground for stability. Most types of aluminum,

tantalum or multilayer ceramic will perform adequately. Solid

tantalums or other appropriate capacitors are recommended

for operation below 25

°C. The bypass capacitors should be

mounted with the shortest possible leads or track lengths

directly across the regulator input and output terminals.

With economical electrolytic capacitors, cold temperature

operation can pose a serious stability problem. As the

electrolyte freezes, around –30

°C, the capacitance will

decrease and the equivalent series resistance (ESR) will

increase drastically, causing the circuit to oscillate. Quality

electrolytic capacitors with extended temperature ranges of

–40

° to +85°C are readily available. Solid tantalum

capacitors may be the better choice if small size is a

requirement. However, a maximum ESR limit of 3.0

Ω must

be observed over temperature to maintain stability.

In the Current Boost Circuit, shown in Figures 10 and 12,

an output current of up to 600 mA can be delivered by the

circuit. The circuit of Figure 10 has no current limit. In each

case, the external transistor must be rated for the expected

power dissipation. Figure 11 shows how a fixed output may

be programmed, using R1 and R2, to provide a higher

output voltage.

Figure 9. Typical Application

23

VO

Gnd

Vin

Gnd

1

0.1

µF

0.1

µF

MC78LC00

Figure 10. Current Boost Circuit

23

VO

Gnd

Vin

Gnd

1

0.1

µF

0.1

µF

MC78LC00

MJD32C

100

.033

µF

Figure 11. Adjustable VO

VO

Vin

ICC

C2

C1

MC78LC00

R1

Gnd

R2

23

1

Figure 12. Current Boost Circuit with

Overcurrent Limit Circuit

VO

Gnd

Vin

Gnd

0.1

µF

0.1

µF

MC78LC00

MJD32C

Q1

R1

R2

Q2

MMBT2907

ALT1

.033

µF

23

1

I

O(short circuit) [

V

BE2

R2

)

V

BE1 )

V

BE2

R1

V

O +

V

O(Reg)

1

) R2

R1

) I

CC

R2