MIC4102 datasheet(17/28 Pages) MICROCHIP

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 2016 Microchip Technology Inc.

DS20005575A-page 17

MIC4102

The same energy is dissipated by ROFF, RG, and

RG_FET when the driver IC turns the MOSFET off.

EQUATION 6-10:

and

EQUATION 6-11:

The power dissipated inside the MIC4102 equals the

ratio of RON and ROFF to the external resistive losses in

RG and RG_FET. The power dissipated in the MIC4102

due to driving the external MOSFET is:

EQUATION 6-12:

6.5

Supply Current Power Dissipation

Power is dissipated in the MIC4102 even if there is

nothing being driven. The supply current is drawn by

the bias for the internal circuitry, the level shifting

circuitry, and shoot-through current in the output

drivers. The supply current is proportional to operating

frequency and the VDD and VHB voltages. The typical

characteristic graphs show how supply current varies

with switching frequency and supply voltage.

The power dissipated by the MIC4102 due to supply

current is:

EQUATION 6-13:

6.6

Total Power Dissipation and

Thermal Considerations

Total power dissipation in the MIC4102 equals the

power dissipation caused by driving the external

MOSFETs, the supply current, and the internal

bootstrap diode.

EQUATION 6-14:

The die temperature may be calculated once the total

power dissipation is known.

EQUATION 6-15:

6.7

Anti-Shoot-Through, Propagation

Delay, and Other Timing

Considerations

The block diagram on page two illustrates how the

MIC4102 drives the power stage of a synchronous

buck converter. It is important that only one of the two

MOSFETs is on at any given time. If both MOSFETs are

simultaneously on, they will short VIN to ground,

causing high current from the VIN supply to “shoot

through” the MOSFETs and into ground. Excessive

shoot-through causes higher power dissipation in the

MOSFETs, voltage spikes, and ringing in the circuit.

The high current and voltage ringing generate

conducted and radiated EMI.

Minimizing shoot-through can be done passively,

actively, or though a combination of both. Passive

shoot-through protection uses delays between the high

and low gate drivers to prevent both MOSFETs from

being on at the same time. These delays can be

adjusted for different applications. Although simple, the

driver

---



Where:

Edriver

Energy Dissipated during Turn-On

or Turn-Off

driver

---



Where:

Pdriver

Power Dissipated during Turn-On

or Turn-Off

Total Gate Charge at VGS

VGS

Gate-to-Source Voltage on the

MOSFET

Switching Frequency of the Gate

Drive Circuit

Pdiss

drive

driver

G_FET

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

driver

OFF

G_FET

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



Pdiss

supply



Pdiss

total

Pdiss

supply

Pdiss

drive

Pdiode

total

Pdiss

total





Where:

Junction Temperature

Maximum Ambient Temperature

Pdisstotal

Power Dissipation of the MIC4102

θJA

Thermal Resistance from Junction

to Ambient Air

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