MC33264

5

MOTOROLA ANALOG IC DEVICE DATA

Figure 7. Regulator Output Voltage Trim

Vin

Vout

3.0, 3.3 or 5.0 V

3.3

µF

0.01

N/C

N/C

R2

R1

2

3

Gnd

Adj

65

4

Base

7

Vout

Vin

1

8

On/Off

Control Input

3.3

µF

On/Off

The complete equation for the output voltage is:

Vout + Vref 1 )

R1

R2

) I

FB

R1

where Vref is the nominal 1.235 V reference voltage and IFB is

the feedback pin bias current, nominally –20 nA. The

minimum recommended load current of 1.0

µA forces an

upper limit of 1.2 M

Ω on the value of R2, if the regulator must

work with no load. IFB will produce a 2% typical error in Vout

which may be eliminated at room temperature by adjusting

R1. For better accuracy, choosing R2 = 100 K reduces this

error to 0.17% while increasing the resistor program current

to 12

µA.

Output Noise

In many applications it is desirable to reduce the noise

present at the output. Reducing the regulator bandwidth by

increasing the size of the output capacitor is the only method

for reducing noise.

Noise can be reduced fourfold by a bypass capacitor

across R1, since it reduces the high frequency gain from 4 to

unity for the MC33264D–5.0. Pick

C

BYPASS +

1

2

π R1 x 200 Hz

or about 0.01

µF. When doing this, the output capacitor must

be increased to 3.3

µF to maintain stability. These changes

reduce the output noise from 430

µV to 100 Vrms for a

100 kHz bandwidth for the 5.0 V output device. With the

bypass capacitor added, noise no longer scales with output

voltage so that improvements are more dramatic at higher

output voltages.

TYPICAL APPLICATIONS

Figure 8. Lithium Ion Battery Cell Charger

Unregulated Input

6.0 to 10 Vdc

2

3

6

4

7

1

8

5

Gnd

On/Off

Vin

Vout

Base

Adj

MC33264D–5.0

Ground

1N4001

0.22

200 k

1%

100 k

1%

50 k

Control

N/C

N/C

0.1

Lithium Ion

Rechargeable Cell

4.2 V

± 0.15 V

On/Off