MC33264D-2.8 データシートの表示（PDF） - Motorola => Freescale
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MC33264D-2.8 Datasheet PDF : 8 Pages
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MC33264
Figure 7. Regulator Output Voltage Trim
Vin
3.3 µF
1
2
Vin
Control Input On/Off
8
Vout
7
Base N/C
3 On/Off
4
R1
N/C
0.01
Gnd
Adj
6
5
Vout
3.0, 3.3 or 5.0 V
3.3 µF
R2
+ ǒ ) Ǔ ) The complete equation for the output voltage is:
Vout
Vref 1
R1
R2
IFB 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 MΩ 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
+ CBYPASS
1
2π 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.
Unregulated Input
6.0 to 10 Vdc
0.1
Ground
TYPICAL APPLICATIONS
Figure 8. Lithium Ion Battery Cell Charger
1
2
Vin
Control On/Off
8
Vout
7
Base N/C
MC33264D–5.0
3
On/Off
4
N/C
Gnd Adj
6
5
1N4001
200 k
1%
100 k
1%
0.22
50 k
4.2 V ± 0.15 V
Lithium Ion
Rechargeable Cell
MOTOROLA ANALOG IC DEVICE DATA
5
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