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GM6155
7
This equation is correct due to the configuration of the bandgap reference. The bandgap voltage is relative to
the output, as seen in the block diagram. Traditional regulators normally have the reference voltage relative to
ground and have a different V
equation.
OUT
Resistor values ate not critical because ADJ(adjust) has a high input impedance, but for best results use
resistors of 470kW or less. A capacitor from ADJ to ground provides greatly improved noise performance.
Figure 5. Ultra-Low- Noise Adjustable Voltage Application
Figure 5 includes the optional 470pF noise bypass capacitor from ADJ to GND to reduce output noise.
Dual-Supply Operation
When used in dual supply systems where the regulator load is returned to a negative supply, the output voltage
must be diode clamped to ground.
VIN
R1
R2
1
2
3
4
5
VOUT
2.2µF
470pF
Typical Characteristics
0
-20
-40
-60
-80
-100
10
100
1k
10k
100k
1M
10M
Figure 6. Power Supply Rejection Ratio
FREQUENCY(Hz)
V
= 6V
IN
V
= 5V
OUT
I
=100mA
OUT
C
= 1µF
OUT
0
-20
-40
-60
-80
-100
10
100
1k
10k
100k
1M
10M
Figure 7. Power Supply Rejection Ratio
FREQUENCY(Hz)
V
= 6V
IN
V
= 5V
OUT
I
=100mA
OUT
C
= 2.2µF
OUT
C
= 0.01µF
BYP
320
280
240
200
160
120
80
40
0
0
40
80
120
160
Figure 8. Dropout Voltage vs.
Output Current
OUTPUT CURRENT (mA)
125°C
25°C
-40°C
Figure 9. Noise Performance
FREQUENCY(Hz)
10
1
0.1
0.01
0.001
0.0001
10
100
1k
10k
100k
1M
10M
100mA
10mA
1mA
V
=5V
OUT
C
=10µF
OUT
electrolytic
C
=10nF
BYP