ADP151

Rev. D | Page 14 of 24

Figure 34 through Figure 38 show the typical performance of the

4 V LDO circuit.

The noise performance of the 4 V LDO circuit is only about 1 μV

worse than the same LDO used at 3.3 V because the output noise of

the circuit is almost solely determined by the LDO and not the

external components. The small difference may be attributed to the

internally generated noise in the LDO ground current working with

R2. By keeping R2 small, this noise contribution can be minimized.

The PSRR of the 4 V circuit is as much as 10 dB poorer than the

3.3 V LDO with 500 mV of headroom because the ground current

of the LDO varies slightly with input voltage. This, in turn,

increasing the headroom to 1 V, the PSRR performance is

nearly restored to the performance of the fixed output LDO.

4.04

4.03

4.02

4.01

4.00

3.99

3.98

3.97

3.96

–40

–5

25

85

125

JUNCTION TEMPERATURE (°C)

LOAD = 10mA

LOAD = 20mA

LOAD = 50mA

LOAD = 100mA

LOAD = 150mA

LOAD = 200mA

Figure 34. 4 V LDO Circuit, Typical Load Regulation over Temperature

LOAD = 10mA

LOAD = 20mA

LOAD = 50mA

LOAD = 100mA

LOAD = 150mA

LOAD = 200mA

4.040

4.035

4.030

4.025

4.020

4.015

4.010

4.005

4.000

4.4

5.2

5.4

4.8

4.6

5.0

Figure 35. 4 V LDO Circuit, Typical Line Regulation over Load Current

11

10

9

8

1

100

1k

10

LOAD CURRENT (mA)

Figure 36. 4 V LDO Circuit, Typical RMS Output Noise, 10 Hz to 100 kHz

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

10

100

1k

10k

100k

1M

10M

FREQUENCY (Hz)

200mA

100mA

50mA

10mA

Figure 37. 4 V LDO Circuit, Typical PSRR vs. Load Current, 1 V Headroom

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

10

100

1k

10k

100k

1M

10M

FREQUENCY (Hz)

200mA

100mA

50mA

10mA

Figure 38. 4 V LDO Circuit, Typical PSRR vs. Load Current, 500 mV Headroom