MIC5501 datasheet(10/22 Pages) MICROCHIP

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MIC5501/2/3/4

DS20006006B-page 10

 2019 Microchip Technology Inc.

4.0

APPLICATION INFORMATION

MIC5501/2/3/4 are low-noise 300 mA LDOs. The

MIC5502 and MIC5504 include an auto-discharge

circuit that is switched on when the regulator is

disabled through the enable (EN) pin. The MIC5503

and MIC5504 have an internal pull-down resistor on the

EN pin to ensure the output is disabled if the control

signal is tri-stated. The MIC5501/2/3/4 regulators are

fully protected from damage due to fault conditions,

offering linear current limiting and thermal shutdown.

The MIC5501/2/3/4 is not suitable for RF transmitter

systems.

4.1

Input Capacitor

The MIC5501/2/3/4 are high performance, high

bandwidth devices. An input capacitor of 1 μF is

required from the input to ground to provide stability.

Low-ESR

ceramic

capacitors

provide

optimal

performance at a minimum of space. Additional high

frequency capacitors, such as small-valued NPO

dielectric-type capacitors, help filter out high frequency

noise and are good practice in any RF-based circuit.

X5R or X7R dielectrics are recommended for the input

capacitor. Y5V dielectrics lose most of their

capacitance over temperature and are therefore, not

recommended.

4.2

Output Capacitor

The MIC5501/2/3/4 require an output capacitor of 1 μF

or greater to maintain stability. The design is optimized

for use with low-ESR ceramic chip capacitors. High

ESR capacitors are not recommended because they

may cause high frequency oscillation. The output

capacitor can be increased, but performance has been

optimized for a 1 μF ceramic output capacitor and does

not improve significantly with larger capacitance.

X7R/X5R dielectric-type ceramic capacitors are

recommended

because

their

temperature

performance. 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% and 60%, respectively, over their operating

temperature ranges. To use a ceramic chip capacitor

with Y5V dielectric, the value must be much higher than

an X7R ceramic capacitor to ensure the same

minimum capacitance over the equivalent operating

temperature range.

4.3

No-Load Stability

Unlike

many

other

voltage

regulators,

the

MIC5501/2/3/4 remain stable and in regulation with no

load. This is especially important in CMOS RAM

keep-alive applications.

4.4

Enable/Shutdown

The MIC5501/2/3/4 each come with an active-high

enable pin that allows the regulator to be disabled.

Forcing the EN pin low disables the regulator and

sends it into an off mode current state drawing virtually

zero current. When disabled, the MIC5502 and

MIC5504 switches an internal 25Ω load on the

regulator output to discharge the external capacitor.

Forcing the EN pin high enables the output voltage.

The MIC5501 and MIC5502 enable pin uses CMOS

technology and the EN pin cannot be left floating; a

floating EN pin may cause an indeterminate state on

the output. The MIC5503 and MIC5504 have an

internal pull-down resistor on the enable pin to disable

the output when the enable pin is floating.

4.5

Thermal Considerations

The MIC5501/2/3/4 are designed to provide 300 mA of

continuous current in a very small package. Maximum

ambient operating temperature can be calculated

based on the output current and the voltage drop

across the part. For example if the input voltage is 3.6V,

the output voltage is 2.8V, and the output current is

300 mA. The actual power dissipation of the regulator

circuit can be determined using Equation 4-1:

EQUATION 4-1:

V IN V OUT1

–

 I

OUT



V IN

I GND



Because this device is CMOS and the ground current

is typically <100 μA over the load range, the power

dissipation contributed by the ground current is < 1%

and can be ignored for this calculation:

EQUATION 4-2:

3.6V

2.8V

–

 300mA

0.240W



To determine the maximum ambient operating

temperature

the

package,

use

the

junction-to-ambient thermal resistance of the device

and Equation 4-3:

EQUATION 4-3:

PDMAX



T JMAX



T A

–



-----------------------------------

Where:

TJ(MAX) = 125°C, the max. junction temp. of the die.

θJA = Thermal resistance of 250°C/W for the DFN

package.

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