MIC2807 datasheet(13/17 Pages) MICREL

13 / 17 page

Micrel, Inc.

MIC2807

January 2007

M9999-013007-A

Component Selection

Output Capacitor

LDO1 output requires a 2.2µF ceramic capacitor, while

the LDO2 and DC/DC regulator outputs require a 1µF

ceramic capacitor. All output capacitor values can be

increased to improve transient response, but perform-

ance has been optimized for a 2.2µF ceramic capacitor

for LDO1 and 1µF ceramic capacitors for both the

DC/DC regulator and LDO2. X7R/X5R dielectric-type

ceramic capacitors are recommended because of their

temperature performance. X5R/X7R-type capacitors

change capacitance by 15% over their operating

temperature range and are the most stable type of

ceramic capacitors. Z5U and Y5V dielectric capacitors

change value by as much as 50% to 60% respectively

over their operating temperature ranges.

Input Capacitor

For optimal bypassing a minimum 1µF ceramic, 2.2µF

recommended, should be placed as close as possible to

the VIN pin. X5R or X7R dielectrics are recommended

for the input capacitor. Y5V dielectrics lose most of their

capacitance over temperature and are therefore, not

recommended. For high frequency filtering a minimum

1µF is recommended close to the VIN and PGND pins.

Smaller case size capacitors are recommended due to

their lower ESR and ESL. Please refer to the PCB layout

section for an example of an appropriate circuit layout.

Inductor Selection

The MIC2807 is designed for use with a 4.7µH inductor.

Proper selection should ensure that the inductor can

handle the maximum average and peak currents

required by the load. Maximum current ratings of the

inductor are generally given in two methods; permissible

DC current and saturation current. Permissible DC

current can be rated either for a 40°C temperature rise

or a 10% to 20% loss in inductance. Ensure that the

inductor selected can handle the maximum operating

current. When saturation current is specified, make sure

that there is enough margin, so that the peak current will

not saturate the inductor. Peak inductor current can be

calculated as follows:

OUT

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

IPK:

Peak Inductor Current

IOUT:

Output/Load Current

VIN:

Input Voltage

VOUT:

Output Voltage

Switching Frequency of PWM Regulator

Inductor Value

MIC2807 Scheda tecnica(PDF) 13 Page - Micrel Semiconductor

MIC2807 Scheda tecnica(HTML) 13 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Scheda tecnica Scarica

Link URL