MCP16311SLASH2 datasheet(13/40 Pages) MICROCHIP

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 2013-2019 Microchip Technology Inc.

DS20005255C-page 13

MCP16311/2

4.0

DETAILED DESCRIPTION

4.1

Device Overview

The MCP16311/2 is a high input voltage step-down

regulator, capable of supplying 1A typical to a regulated

output voltage from 2.0V to 12V. Internally, the trimmed

500 kHz oscillator provides a fixed frequency, while the

peak current mode control architecture varies the duty

cycle for output voltage regulation. An internal floating

driver is used to turn the high-side integrated

N-Channel MOSFET on and off. The power for this

driver is derived from an external boost capacitor

whose energy is replenished when the low-side N-

Channel MOSFET is turned on.

4.1.1

PWM/PFM MODE OPTION

The MCP16311 selects the best operating switching

mode (PFM or PWM) for high efficiency across a wide

range of load currents. Switching to PFM mode at light-

load currents results in a low quiescent current. During

the sleep period (between two packets of switching

cycles), the MCP16311 draws 44 µA (typical) from the

supply line. The switching pulse packets represent a

small percentage of the total running cycle, and the

overall average current drawn from power line is small.

The disadvantages of PWM/PFM mode are higher

output ripple voltage and variable PFM mode frequency.

The PFM mode threshold is a function of the input

voltage, output voltage and load (see Figure 2-17).

4.1.2

PWM-ONLY MODE OPTION

In the MCP16312 devices, the PFM mode is disabled

and the part runs only in PWM over the entire load

range. During normal operation, the MCP16312

continues to operate at a constant 500 kHz switching

frequency, keeping the output ripple voltage lower than

in PFM mode. At lighter loads, the MCP16312 devices

begin to skip pulses. Figure 2-18 represents the input

voltage versus load current for the pulse skipping

threshold in PWM-only mode.

Because the MCP16312 has very low output voltage

ripple, it is recommended for noise-sensitive applications.

4.1.3

INTERNAL REFERENCE VOLTAGE

(VFB)

An integrated precise 0.8V reference combined with an

external resistor divider sets the desired converter

output voltage. The resistor divider range can vary

without affecting the control system gain. High-value

resistors consume less current, but are more

susceptible to noise. Consult typical applications for the

recommended resistors value.

4.1.4

INTERNAL BIAS REGULATOR (VCC)

An internal Low Dropout Voltage Regulator (LDO) is

used to supply 5.0V to all the internal circuits. The LDO

regulates the input voltage (VIN) and can supply

enough current (up to 50 mA) to sustain the drivers and

internal bias circuitry. The VCC pin must be decoupled

to ground with a 1 µF capacitor. In the event of a

thermal shut down, the LDO will shut down. There is a

short-circuit protection for the VCC pin, with a threshold

set at 150 mA.

In PFM switching mode, during sleep periods, the VCC

regulator enters Low Quiescent Current mode to avoid

unnecessary power dissipation.

Avoid driving any external load using the VCC pin.

4.1.5

INTERNAL COMPENSATION

All control system components necessary for stable

operation over the entire device operating range are

integrated, including the error amplifier and inductor

current slope compensation. To add the proper amount

of slope compensation, the inductor value changes

along with the output voltage (see Table 5-1).

4.1.6

EXTERNAL COMPONENTS

External components consist of:

• Input capacitor

• Output filter (inductor and capacitor)

• Boost capacitor

• Resistor divider

The selection of the external inductor, output capacitor

and input capacitor is dependent upon the output

voltage and the maximum output current.

4.1.7

ENABLE INPUT

The enable input (EN) is used to disable the device. If

disabled, the device consumes a minimum current from

the input. Once enabled, the internal soft start controls

the output voltage rate of rise, preventing high-inrush

current and output voltage overshoot.

There is no internal pull-up or pull-down resistor. To

enable the converter, the EN pin must be pulled high.

To disable the converter, the EN pin must be pulled low.

TABLE 4-1:

PART NUMBER SELECTION

Part Number

PWM/PFM

PWM

MCP16311



—

MCP16312

—



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