MIC5209(2000) Просмотр технического описания (PDF) - Micrel

Номер в каталоге

Компоненты Описание

Список матч

MIC5209
(Rev.:2000)

500mA Low-Noise LDO Regulator

Micrel 

MIC5209

Fixed Regulator Circuits

MIC5209-x.xBM

VIN

2

3

IN

OUT

1 EN

BYP 4

GND

5–8

VOUT

1µF

Figure 1. Low-Noise Fixed Voltage Regulator

Figure 1 shows a basic MIC5209-x.xBM (SO-8) fixed-voltage

regulator circuit. See Figure 5 for a similar configuration

using the more thermally-efficient MIC5209-x.xBS (SOT-223).

A 1µF minimum output capacitor is required for basic fixed-

voltage applications.

MIC5209-x.xBM

VIN

2

3

IN

OUT

1 EN

BYP 4

GND

5–8

470pF

VOUT

2.2µF

Figure 2. Ultra-Low-Noise Fixed Voltage Regulator

Figure 2 includes the optional 470pF 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.

Adjustable Regulator Circuits

MIC5209BM

VIN

2 IN

OUT 3

1 EN

ADJ 4 R1

GND

5–8

R2

VOUT

1µF

Figure 3. Low-Noise Adjustable Voltage Regulator

The MIC5209BM/U 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 equation:

VOUT = 1.242V 1 + RR21

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 MIC5209BM/U.

Micrel

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

mance, R2 should not exceed 470kΩ.

MIC5209BM

VIN

2

3

IN

OUT

1 EN

ADJ 4

R1

GND

5–8

R2

470pF

VOUT

2.2µF

Figure 4. Ultra-Low-Noise Adjustable Application.

Figure 4 includes the optional 470pF bypass capacitor from

ADJ to GND to reduce output noise.

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 depen-

dant upon the clock synthesizer used, the number of clock

outputs, and the type of level shifter (from core logic levels to

2.5V levels). Intel estimates a worst-case load of 320mA.

The MIC5209 was designed to provide the 2.5V power

requirement for Slot-1 applications. Its guaranteed perfor-

mance of 2.5V ±3% at 500mA allows adequate margin for all

systems, and its dropout voltage of 500mV means that it

operates from a worst-case 3.3V supply where the voltage

can be as low as 3.0V.

MIC5209-x.xBS

VIN

1 IN

OUT 3

VOUT

CIN

0.1µF

GND

2,TAB

COUT

22µF

Figure 5. Slot-1 Power Supply

A Slot-1 power supply (Figure 5) is easy to implement. Only

two capacitors are necessary, and their values are not critical.

CIN bypasses the internal circuitry and should be at least

0.1µF. COUT provides output filtering, improves transient

response, and compensates the internal regulator control

loop. Its value should be at least 22µF. CIN and COUT may be

increased as much as desired.

Slot-1 Power Supply Power Dissipation

Powered from a 3.3V supply, the Slot-1 power supply of

Figure 5 has a nominal efficiency of 75%. At the maximum

anticipated Slot 1 load (320mA), the nominal power dissipa-

tion is only 256mW.

The SOT-223 package has sufficient thermal characteristics

for wide design margins when mounted on a single layer

copper-clad printed circuit board. The power dissipation of

August 2, 2000

9

MIC5209

Share Link: