MIC5166 datasheet(17/36 Pages) MICROCHIP

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DS20006085B-page 17

MIC5166

5.0

COMPONENT SELECTION

5.1

Input Capacitor

A 10 µF ceramic input capacitor is all that is required for

most applications if it is close to a bulk capacitance.

The input capacitor must be placed on the same side of

the board and next to the MIC5166 to minimize the

dropout voltage and voltage ringing during transient

and short-circuit conditions. It is also recommended

that each capacitor to be connected to the PGND

directly, not through vias. X7R or X5R dielectric

ceramic capacitors are recommended because of 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.

5.2

Output Capacitor

As part of the frequency compensation, the MIC5166

requires two 10 µF ceramic output capacitors for best

transient performance. To improve transient response,

any other type of capacitor can be placed in parallel as

long as the two 10 µF ceramic output capacitors are

placed next to the MIC5166.

The output capacitor type and placement criteria are

the same as the input capacitor. See the Input

Capacitor section for a detailed description.

5.3

Thermal Considerations

The MIC5166 is packaged in the 3 mm x 3 mm DFN, a

package that has excellent thermal performance. This

maximizes heat transfer from the junction to the

exposed pad (ePAD) that connects to the ground plane.

The size of the ground plane attached to the exposed

pad determines the overall thermal resistance from the

junction to the ambient air surrounding the printed

circuit board.

5.4

Thermal Design

The most complicated design parameters to consider

are thermal characteristics. Thermal design requires

the following application-speciﬁc parameters:

• Maximum ambient temperature (TA)

• Output current (IOUT)

• Output voltage (VOUT)

• Input voltage (VIN)

• Ground current (IGND)

First, calculate the power dissipation of the regulator

from these numbers and the device parameters from

this data sheet.

EQUATION 5-1:

For example, given an expected maximum ambient

temperature (TA) of 70°C with VIN = 1.2V, VBIAS = 3.3V,

VTT = 0.9V, and IOUT = 3A, first calculate the expected

PD using Equation 5-1:

EQUATION 5-2:

Next, determine the junction temperature for the

expected power dissipation above using the thermal

resistance (θJA) of the 10-pin 3 mm x 3 mm DFN (YML)

adhering to the following criteria for the PCB design

(1oz. copper and 100 mm2 copper area for the

MIC5166):

EQUATION 5-3:

To determine the maximum power dissipation allowed

that would not exceed the IC’s maximum junction

temperature (125°C) when operating at a maximum

ambient temperature of 70°C:

EQUATION 5-4:

VIN VTT

–

 I

OUT



VBIAS IGND





Where:

IOUT = Approximated by using numbers from the

Electrical Characteristics or Typical Performance

Curves.

1.2V 0.9V

–

 3A



3.3V

0.0016A



0.90528W





 T

60.7

C/W 0.90528W



 70C

124.95

C

PDMAX



TJMAX



–

 



PDMAX



125

C 70C

–

 60.7C/W





0.9061W

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