MIC5206

Micrel

MIC5206

6

January 2000

Applications Information

Enable/Shutdown

Forcing EN (enable/shutdown) high (> 2V) enables the regu-

lator. EN is compatible with CMOS logic gates.

If the enable/shutdown feature is not required, connect EN

(enable) to IN (supply input). Refer to the text with Figures 1a

and 2.

Input Capacitor

A 1

µF capacitor should be placed from IN to GND if there is

more than 10 inches of wire between the input and the ac filter

capacitor or if a battery is used as the input.

Reference Bypass Capacitor

BYP (reference bypass) is connected to the internal voltage

reference. A 470pF capacitor (C

GND quiets this reference, providing a significant reduction in

output noise. See Figure 2. C

margin; when using C

greater are generally required to maintain stability.

The start-up speed of the MIC5206 is inversely proportional

to the size of the reference bypass capacitor. Applications

requiring a slow ramp-up of output voltage should consider

larger values of C

consider omitting C

If output noise is not a major concern, omit C

BYP open.

Output Capacitor

An output capacitor is required between OUT and GND to

prevent oscillation. The minimum size of the output capacitor

is dependent upon whether a reference bypass capacitor is

used. 1.0

µF minimum is recommended when C

used (see Figure 2). 2.2

µF minimum is recommended when

C

regulator’s transient response. The output capacitor value

may be increased without limit.

The output capacitor should have an ESR (effective series

resistance) of about 5

Ω or less and a resonant frequency

above 1MHz. Most tantalum or aluminum electrolytic capaci-

tors are adequate; film types will work, but are more expen-

sive. Since many aluminum electrolytics have electrolytes

that freeze at about –30

°C, solid tantalums are recom-

mended for operation below –25

°C.

At lower values of output current, less output capacitance is

required for output stability. The capacitor can be reduced to

0.47

µF for current below 10mA or 0.33µF for currents below

1mA.

No-Load Stability

The MIC5205 will remain stable and in regulation with no load

(other than the internal voltage divider) unlike many other

voltage regulators. This is especially important in CMOS

RAM keep-alive applications.

Error Flag Ouput

The error flag is an open-collector output and is active (low)

when an undervoltage of approximately 5% below the nomi-

nal output voltage is detected. A pullup resistor from IN to

FLAG is shown in all schematics.

If an error indication is not required, FLAG may be left open

and the pullup resistor may be omitted.

Enable Pin Ramp and the Error Flag

To prevent indeterminate behavior on the error flag during

power down of the device, ensure that the fall time of the

enable pin signal, from logic high to logic low, is faster than

100

µs.

Fixed Regulator Applications

15

2

34

1µF

MIC5206-x.xBM5

EN (pin 3) may be

connected directly

to IN (pin 1).

100k

Error Flag

Figure 1a. Low-Noise Fixed Voltage Application

EN (pin 3) is shown connected to IN (pin 1) for an application

where enable/shutdown is not required. The error flag is

shown with a 100k

Ω pullup resistor.

1

2

3

4

8

7

6

5

1µF

Flag Output

(optional)

Enable

MIC5206-x.xBMM

47k

Figure 1b. Low-Noise Fixed Voltage Application

Figure 1b is an example of a basic configuration where the

lowest-noise operation is not required. C

The error flag is shown with a 47k

Ω pullup resistor.

Ultra-Low-Noise Application

1

2

3

4

8

7

6

5

2.2µF

Flag Output

(optional)

47k

MIC5206-x.xBMM

470pF

BYP

Figure 2. Ultra-Low-Noise Fixed Voltage Application

Figure 2 includes a 470pF capacitor for low-noise operation

and shows EN (pin 7) connected to IN (pin 8) for an applica-

tion where enable/shutdown is not required. The error flag is

shown with a 47k

Ω pullup resistor.

Adjustable Regulator Applications

Figure 3 shows the MIC5206BMM adjustable output voltage

configuration. Two resistors set the output voltage. The

formula for output voltage is:

V

= 1.242V

R2

R1

1

OUT

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