LP2950 LP2951
error to 0.17% while increasing the resistor program current
to 12 µA. Since the LP2951 typically draws 75 µA at no load
with Pin 2 open circuited, the extra 12 µA of current drawn is
often a worthwhile tradeoff for eliminating the need to set
output voltage in test.
Figure 17. 1.0 A Regulator with 1.2 V Dropout
Unregulated
Input
MTB23P06E
1.0 µF
10 k
0.01 µF
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 on the 3 lead LP2950. However,
increasing the capacitor from 1.0 µF to 220 µF only
decreases the noise from 430 µV to 160 µVrms for a 100 kHz
bandwidth at the 5.0 V output.
Noise can be reduced fourfold by a bypass capacitor
across R1, since it reduces the high frequency gain from 4 to
unity. Pick
V
out
5.0 V
0 to 1.0 A
±
1.0%
8
V
in
1
2
5
3
Error
Output
V
Error
out
SNS
LP2951CN
6
Shutdown
Input
SD
V
T
O
220 µF
Gnd
4
FB
7
1
C
Bypass
0.002
1.0 M
µF
2 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 126 µVrms
for a 100 kHz bandwidth at 5.0 V output. With bypass
capacitor added, noise no longer scales with output voltage
so that improvements are more dramatic at higher output
voltages.
2.0 k
9
MOTOROLA ANALOG IC DEVICE DATA
MOTOROLA [ MOTOROLA ]
