MIC5373 datasheet(15/19 Pages) MICREL

15 / 19 page

Micrel, Inc.

MIC5373/83

July 2010

M9999-070110

Application Information

MIC5373/83 is a triple output device with three 200mA

LDOs. The MIC5373/83 incorporates a POR function

with the capability to monitor any voltage using POR_IN.

The monitored voltage can be set to any voltage

threshold level to trigger the POR flag. A delay on the

POR flag may also be set with an external capacitor at

the DLY pin. All the LDOs have current limit and thermal

shutdown protection to prevent damage from fault

conditions. MIC5373 has active high enables while the

MIC5383 has active low enables.

Input Capacitor

The MIC5373/83 is a high performance, high bandwidth

device. An input capacitor of 1µF from the input pin to

ground is required to provide stability. Low ESR ceramic

capacitors provide optimal performance in small board

area. 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.

Output Capacitor

The MIC5373/83 requires an output capacitor of 1µF or

greater to maintain stability. The design is optimized for

use with low ESR ceramic chip capacitors. High ESR

capacitors may cause high frequency oscillation. The

output capacitor can be increased, but performance has

been optimized for a 1µF ceramic output capacitor and

does not improve significantly with larger capacitance.

X7R and X5R dielectric ceramic capacitors are

recommended

because

their

temperature

performance. X7R 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.

No Load Stability

Unlike many other voltage regulators, the MIC5373/83

will remain stable and in regulation with no load.

Thermal Considerations

The MIC5373/83 is designed to provide three outputs up

to 200mA each 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

voltages are 3.6V and the output voltages are 3.3V,

2.5V, and 1.8V each with an output current = 150mA.

The actual power dissipation of the regulator circuit can

be determined using the equation:

PD = (VINLDO1/2 – VOUT1) I OUT1 +

(VINLDO1/2 – VOUT2) I OUT2 +

(VINLDO3 – VOUT3) I OUT3 + VIN x IGND

As the MIC5373/83 is a CMOS device, the ground current

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

dissipation contributed by the ground current is < 1% and

may be ignored for this calculation.

PD ≈ (3.6V – 2.8V)150mA+(3.6V-1.8V)150mA+

(3.6V-1.2V)150mA

PD ≈ 0.75W

determine

the

maximum

ambient

operating

temperature of the package, use the junction to ambient

thermal resistance of the device and the following basic

equation:

⎟

⎠

⎞

⎜

⎝

⎛

−

J(MAX)

D(MAX)

TJ(MAX) = 125°C

θJA = 100°C/W

Substituting PD for PD(max) and solving for the ambient

operating temperature will give the maximum operating

conditions for the regulator circuit.

The maximum power dissipation must not be exceeded

for proper operation.

For example, when operating the MIC5373-MG4YMT at

an input voltage of 3.6V and 150mA load on LDO1,

LDO2 and LDO3 with a minimum layout footprint, the

maximum ambient operating temperature TA can be

determined as follows:

0.75W = (125°C – TA) / (100°C/W)

TA = 50°C

Therefore the maximum ambient operating temperature

of 50°C is allowed in a 2.5mm x 2.5mm Thin MLF

package for the voltage options specified and at the

maximum load of 150mA on each output. For a full

discussion of heat sinking and thermal effects on voltage

regulators, refer to the “Regulator Thermals” section of

Micrel’s Designing with Low-Dropout Voltage Regulators

handbook. This information can be found on Micrel's

website at:

http://www.micrel.com/_PDF/other/LDOBk_ds.pdf

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