MIC23156 datasheet(16/32 Pages) MICROCHIP

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MIC23156

DS20005919A-page 16

 2017 Microchip Technology Inc.

5.0

APPLICATION INFORMATION

The MIC23156 is a high-performance, DC-to-DC

step-down regulator offering a small solution size and

supporting up to 1.5A. The device is available in a

2.8 mm x 2.5 mm QFN and a 1.81 mm x 1.71 mm

WLCSP package. Using the HyperLight Load® switch-

ing scheme, the MIC23156 is able to maintain high

efficiency and exceptional voltage accuracy throughout

the entire load range, while providing ultra-fast load tran-

sient response. Another beneficial feature is the ability to

dynamically change the output voltage in steps of

10 mV. The following subsections provide additional

device application information.

5.1

Input Capacitor

A 2.2 µF (or larger) ceramic capacitor should be placed

as close as possible to the PVIN and AVIN pins with a

short trace for good noise performance. X5R or X7R

type ceramic capacitors are recommended for better

tolerance over temperature. The Y5V and Z5U type

temperature rating ceramic capacitors are not recom-

mended due to their large reduction in capacitance

over temperature, and increased resistance at high

frequencies. These issues reduce their ability to filter

out high-frequency noise. The rated voltage of the input

capacitor should be at least 20% higher than the

maximum operating input voltage over the operating

temperature range.

5.2

Output Capacitor

Output capacitor selection is also a trade-off between

performance, size and cost. Increasing the output

capacitor will lead to an improved transient response,

however, the size and cost also increase. The

MIC23156 is designed for use with a 2.2 µF or greater

ceramic output capacitor. A low-Equivalent Series

Resistance (low-ESR) ceramic output capacitor is

recommended, based upon performance, size and

cost. Both the X7R and X5R temperature rating capac-

itors are recommended. Refer to Table 5-1 for

additional information.

5.3

Inductor Selection

Inductor selection is a balance between efficiency,

stability, cost, size and rated current. Since the

MIC23156 is compensated internally, the recommended

inductance of L is limited from 0.47 µH to 2.2 µH to

ensure system stability.

For faster transient response, a 0.47 µH inductor will

yield the best result. For lower output ripple, a 2.2 µH

inductor is recommended.

Maximum current ratings of the inductor are generally

given in two methods; permissible DC current and sat-

uration current. Permissible DC current can be rated

either for a +40°C temperature rise or a 10% to 30%

loss in inductance.

Ensure 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 does not cause the inductor to saturate. Peak

current can be calculated as noted in Equation 5-1:

EQUATION 5-1:

CALCULATING PEAK

CURRENT

As shown by Equation 5-1, the peak inductor current is

inversely proportional to the switching frequency and

the inductance. The lower the switching frequency or

the inductance, the higher the peak current. As input

voltage increases, the peak current also increases.

The size of the inductor depends upon the requirements

of the application. Refer to the “Typical Application

Schematic”

section for details.

DC Resistance (DCR) is also important. While DCR is

inversely proportional to size, it can represent a signifi-

cant efficiency loss. Refer to Section 5.6 “Efficiency

Considerations”

The transition between Continuous Conduction Mode

(CCM) to HyperLight Load mode is determined by the

inductor ripple current and the load current.

Figure 5-1 shows the signals for the High-Side Drive

(HSD) switch for tON control, the inductor current and

the Low-Side Drive (LSD) switch for tOFF control.

FIGURE 5-1:

HSD Signals for tON Control,

Inductor Current and LSD for tOFF Control.









IPEAK = IOUT + VOUT

1 – VOUT/VIN

 f  L

[]

HSD

INDUCTOR

-50 mA

LSD

HSD

INDUCTOR

LSD

OUT

LOAD

INCREASING

IN HLL MODE

ON FIXED,

OFF VARIABLE

IN CCM MODE

ON VARIABLE,

OFF FIXED

OUT

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