MIC5209 datasheet(13/30 Pages) MICROCHIP

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DS20005720B-page 13

MIC5209

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 4.7 µF output

capacitance and 470 pF 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 470 pF 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 with an output less than 2.5V (fixed and

adjustable) is 0°C to +125°C.

4.8

Fixed Regulator Applications

Figure 4-1 shows a basic MIC5209-x.xYM (SOIC-8)

ﬁxed-voltage regulator circuit. See Figure 5 for a similar

conﬁguration using the more thermally-efﬁcient

MIC5209-x.xYS (SOT-223). A 1 µF minimum output

capacitor is required for basic ﬁxed-voltage

applications.

FIGURE 4-1:

Low-Noise Fixed-Voltage

Application.

Figure 4-2 includes the optional 470 pF noise bypass

capacitor between BYP and GND to reduce output

noise. Note that the minimum value of COUT must be

increased when the bypass capacitor is used.

FIGURE 4-2:

Ultra-Low-Noise

Fixed-Voltage Application.

4.9

Adjustable Regulator Applications

The MIC5209YM, MIC5209YU, and MIC5209YML can

be adjusted to a speciﬁc output voltage by using two

external resistors (Figure 4-3). The resistors set the

output voltage based on the equation:

EQUATION 4-1:

This equation is correct due to the conﬁguration of the

bandgap reference. The bandgap voltage is relative to

the output, as seen in the Functional Diagrams.

Traditional regulators normally have the reference

voltage relative to ground; therefore, their equations

are different from the equation for the MIC5209Y.

Although ADJ is a high-impedance input and, for best

performance, R2 should not exceed 470 kΩ.

FIGURE 4-3:

Low-Noise

Adjustable-Voltage Application.

Figure 4-4 includes the optional 470 pF bypass

capacitor from ADJ to GND to reduce output noise.

FIGURE 4-4:

Ultra-Low-Noise Adjustable

Application.

4.10 Slot-1 Power Supply

Intel’s Pentium II processors have a requirement for a

2.5V ±5% power supply for a clock synthesizer and its

associated loads. The current requirement for the 2.5V

supply is dependent upon the clock synthesizer used,

MIC5209-x.xYM

5 - 8

OUT

BYP

GND

OUT

1μF

MIC5209-x.xYM

5 - 8

OUT

BYP

GND

OUT

2.2μF

470pF

VOUT 1.242V 1 R2

-------











MIC5209YM

5 - 8

OUT

ADJ

GND

OUT

1μF

MIC5209YM

5 - 8

OUT

ADJ

GND

OUT

2.2μF

470pF

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