MIC5207

Micrel

MIC5207

8

January 2000

(see “Block Diagram”). Selecting larger output and bypass

capacitors allows additional time for the error amplifier and

reference to turn on and prevent overshoot.

To ensure that no overshoot is present when starting up into

a light load (100

µA), use a 4.7µF output capacitance and

470pF bypass capacitance. This slows the turn-on enough to

allow the regulator to react and keep the output voltage from

exceeding its nominal value. At heavier loads, use a 10

µF

output capacitance and 470pF bypass capacitance. Lower

values of output and bypass capacitance can be used,

depending on the sensitivity of the system.

Applications that can withstand some overshoot on the

output of the regulator can reduce the output capacitor and/

or reduce or eliminate the bypass capacitor. Applications that

are not sensitive to overshoot due to power-on reset delays

can use normal output and bypass capacitor configurations.

Please note the junction temperature range of the regulator

at 1.8V output (fixed and adjustable) is 0˚C to +125˚C.

Fixed Regulator Applications

15

2

3

4

2.2µF

470pF

MIC5207-x.xBM5

Figure 1. Ultra-Low-Noise Fixed Voltage Regulator

Figure 1 includes a 470pF capacitor for ultra-low-noise op-

eration and shows EN (pin 3) connected to IN (pin 1) for an

application where enable/shutdown is not required. C

2.2

µF minimum.

15

2

34

1.0µF

Enable

Shutdown

EN

MIC5207-x.xBM5

Figure 2. Low-Noise Fixed Voltage Regulator

Figure 2 is an example of a basic low-noise configuration.

C

Adjustable Regulator Applications

The MIC5207BM5 can be adjusted to a specific output

voltage by using two external resistors (figure 3). The resis-

tors set the output voltage based on the following equation:

VV

1

R2

R1

, V

1.242V

OUT

REF

REF

=+









=

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;

therefore, their equations are different from the equation for

the MIC5207BM5.

Resistor values are not critical because ADJ (adjust) has a

high input impedance, but for best results use resistors of

470k

Ω or less. A capacitor from ADJ to ground provides

greatly improved noise performance.

15

2

3

4

2.2µF

470pF

MIC5207BM5

R1

R2

Figure 3. Ultra-Low-Noise

Adjustable Voltage Regulator

Figure 3 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.

USB Application

Figure 4 shows the MIC5207-3.3BZ (3-terminal, TO-92) in a

USB application. Since the V

10 inches from the regulator, a 1

µF input capacitor is in-

cluded.

D+

D–

GND

USB

Port

Data

EN

OUT

FLG

IN

ON/OFF

OVERCURRENT

MIC2525

USB Controller

GND

OUT

IN

5.0V

0.1µF

10k

MIC5207-3.3BZ

IN

OUT

GND

Upstream

100mA max.

Ferrite

Beads

150µF

D+

D–

GND

Data

1µF

1µF

Figure 4. Single-Port Self-Powered Hub