MCP14700 datasheet(13/26 Pages) MICROCHIP

13 / 26 page

DS22201A-page 13

MCP14700

5.0

APPLICATION INFORMATION

5.1

Bootstrap Capacitor Select

The selection of the bootstrap capacitor is based upon

the total gate charge of the high-side power MOSFET

and the allowable droop in gate drive voltage while the

high-side power MOSFET is conducting.

EQUATION 5-1:

For example:

QGATE = 30 nC

ΔV

DROOP = 200 mV

CBOOT ≥ 0.15 uF

A low ESR ceramic capacitor is recommend with a

maximum voltage rating that exceeds the maximum

input voltage, VCC, plus the maximum supply voltage,

VSUPPLY. It is also recommended that the capacitance

of CBOOT does not exceed 1.2 uF.

5.2

Decoupling Capacitor

Proper

decoupling

the

MCP14700

highly

recommended to help ensure reliable operation. This

decoupling capacitor should be placed as close to the

MCP14700 as possible. The large currents required to

quickly charge the capacitive loads are provided by this

capacitor.

low

ESR

ceramic

capacitor

recommended.

5.3

Power Dissipation

The power dissipated in the MCP14700 consists of the

power loss associated with the quiescent power and

the gate charge power.

The quiescent power loss can be calculated by the

following equation and is typically negligible compared

to the gate drive power loss.

EQUATION 5-2:

The main power loss occurs from the gate charge

power loss. This power loss can be defined in terms of

both the high-side and low-side power MOSFETs.

EQUATION 5-3:

BOOT

GATE

DROOP

-----------------------------

≥

Where:

CBOOT = Bootstrap capacitor value

QGATE = Total gate charge of the high-side

MOSFET

ΔV

DROO

Allowable gate drive voltage droop

VCC

Where:

PQ = Quiescent power loss

IVCC = No Load Bias Current

VCC = Bias Voltage

GATE

HIGHDR

LOWDR

HIGHDR

HIGH

LOWDR

LOW

Where:

PGATE = Total Gate Charge Power Loss

PHIGHDR = High-Side Gate Charge Power Loss

PLOWDR = Low-Side Gate Charge Power Loss

VCC = Bias Supply Voltage

QHIGH = High-Side MOSFET Total Gate

Charge

QLOW = Low-Side MOSFET Total GAte

Charge

FSW = Switching Frequency

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