MIC4451_11 Datasheet, PDF (11/14 Pages) Micrel Semiconductor – 12A-Peak Low-Side MOSFET Driver

Micrel Inc.
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 in the output totem-pole are ON
simultaneously, and a current is conducted through them
from V_S to ground. The transition power dissipation is
approximately:
P_T = 2 f V_S (A × s)
where (A × s) is a time-current factor derived from the
typical characteristic curve “Crossover Energy vs.
Supply Voltage.” Total power (P_D) then, as previously
described is:
P_D = P_L + P_Q + P_T
Definitions
C_L = 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
I_H = Power supply current drawn by a driver when both
inputs are high and neither output is loaded.
I_L = Power supply current drawn by a driver when both
inputs are low and neither output is loaded.
I_D = Output current from a driver in Amps.
P_D = Total power dissipated in a driver in Watts.
P_L = Power dissipated in the driver due to the driver’s
load in Watts.
P_Q = Power dissipated in a quiescent driver in Watts.
P_T = 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 be multiplied by the number of
repetitions per second (frequency) to find Watts.
R_O = Output resistance of a driver in Ohms.
V_S = Power supply voltage to the IC in Volts.
January 2011
11
MIC4451/4452
M9999-011811