REG101

11

SBVS026C

FIGURE 4. Block Diagram.

FIGURE 5. Output Noise versus Noise Reduction Capacitor.

ENABLE

The Enable pin is active HIGH and compatible with stan-

dard TTL-CMOS levels. Inputs below 0.5V (max) turn the

regulator off and all circuitry is disabled. Under this condi-

tion, ground pin current drops to approximately 10nA. When

is required, use values < 50k

Ω.

OUTPUT NOISE

A precision band-gap reference is used for the internal

noise source within the REG101 and it generates approxi-

mately 29

µVrms in the 10Hz to 100kHz bandwidth at the

reference output. The regulator control loop gains up the

reference noise, so that the noise voltage of the regulator is

approximately given by:

V = 29 Vrms

R+ R

R2

Vrms •

V

V

N

1

2

OUT

REF

µµ

= 29

V= 23

Vrms

V

V

N

OUT

µ

•

pin to ground, as shown in Figure 4, forms a low-pass filter for

10Hz to 100kHz bandwidth is reduced by approximately a

shown in Figure 5 and as “RMS Noise Voltage vs CNR” in the

Typical Characteristics section.

Noise can be further reduced by carefully choosing an

achieved with very low (< 0.22

µF) or very high (> 2.2µF)

Typical Characteristics section.

The REG101 utilizes an internal charge pump to develop an

internal supply voltage sufficient to drive the gate of the

ing noise (nominal switching frequency = 2MHz) is not

measurable at the output of the regulator over most values of

The REG101 adjustable version does not have the noise-

reduction pin available, however, the adjust pin is the sum-

connected from the output to the adjust pin will reduce both

the output noise and the peak error from a load transient. See

the typical characteristics for output noise performance.

Over Current

Over Temp

Protection

V

REF

(1.26V)

Low Noise

Charge Pump

DMOS

Pass

Transistor

R

1

NOTE: R

on fixed output versions.

V

OUT

Adj

(Adjustable

Versions)

R

2

NR

(fixed output

versions only)

Enable

REG101

V

IN

C

NR

(optional)

110

1k

100

10k

110

100

90

80

70

60

50

40

30

20

C

RMS NOISE VOLTAGE vs C

NR

C

10Hz < BW < 100kHz

REG101-5.0

REG101-2.5

REG101-3.3