MIC4452YN datasheet(11/14 Pages) MICREL

11 / 14 page

Micrel Inc.

MIC4451/4452

January 2011

M9999-011811

Transition Power Dissipation

Transition power is dissipated in the driver each time its

output changes state, because during the transition, for

a very brief interval, both the N- and P-channel

MOSFETs

the

output

totem-pole

are

simultaneously, and a current is conducted through them

from VS to ground. The transition power dissipation is

approximately:

PT = 2 f VS (A × s)

where (A

× s) is a time-current factor derived from the

typical characteristic curve “Crossover Energy vs.

Supply Voltage.” Total power (PD) then, as previously

described is:

PD = PL + PQ + PT

Definitions

CL = Load Capacitance in Farads.

D = Duty Cycle expressed as the fraction of time the

input to the driver is high.

f = Operating Frequency of the driver in Hertz

IH = Power supply current drawn by a driver when both

inputs are high and neither output is loaded.

IL = Power supply current drawn by a driver when both

inputs are low and neither output is loaded.

ID = Output current from a driver in Amps.

PD = Total power dissipated in a driver in Watts.

PL = Power dissipated in the driver due to the driver’s

load in Watts.

PQ = Power dissipated in a quiescent driver in Watts.

PT = Power dissipated in a driver when the output

changes states (“shoot-through current”) in Watts.

NOTE: The “shoot-through” current from a dual

transition (once up, once down) for both drivers is

stated in Figure 7 in ampere-nanoseconds. This

figure

must

multiplied

the

number

repetitions per second (frequency) to find Watts.

RO = Output resistance of a driver in Ohms.

VS = Power supply voltage to the IC in Volts.

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