MIC5166 datasheet(13/25 Pages) MICREL

13 / 25 page

Micrel, Inc.

MIC5166

June 2012

M9999-060612-A

Power Good (PG)

The power-good (PG) output provides an under and over

voltage fault flag for the VTT output. The PG output

remains high as long as VTT is within ±10% range of VREF

and goes low if the output moves beyond this range.

Figure 3. Power Good Threshold

The PG has an open-drain output. A pull-up resistor

must be connected to VIBIAS, VIN or an external source.

The external source voltage must not exceed the

maximum rating of the pin. The PG pin can be

connected to another regulator’s enable pin for

sequencing of the outputs.

VBIAS Requirement

A 1µF ceramic input capacitor is required on VBIAS pin.

To achieve the ultra-fast transient response, the

MIC5166 uses an all N-channel power output stage as

shown in the Functional Diagram. The high-side N-

channel MOSFET requires the VBIAS voltage to be 2.2V

higher than the VTT to be able to fully enhance the high-

side MOSFET.

VIN Requirement

VIN is used to supply the rail voltage for the high-side N-

channel power output stage. It is normally connected to

VDDQ, but it can be connected to a lower voltage to

reduce power dissipation. In this case, the input voltage

must be higher than the VTT voltage to ensure that the

output stage is not operating in dropout.

Component Selection

Input Capacitor

A 10µF 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.

Output Capacitor

As part of the frequency compensation, the MIC5166

requires two 10µF 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 10µF 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.

Thermal Considerations

The MIC5166 is packaged in the 3mm x 3mm MLF

®, a

package that has excellent thermal performance. This

maximizes heat transfer from the junction to the exposed

pad (ePad) which 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.

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)

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