MIC4414 Datasheet, PDF (10/14 Pages) Micrel Semiconductor – 1.5A, 4.5V to 18V Low-Side MOSFET Driver

Micrel, Inc.
At low voltages, the MIC4414/15’s internal P- and N-
channel MOSFET’s on-resistance will increase and slow
the output rise time. Refer to “Typical Characteristics”
graphs.
Inductive Loads
Switching off an inductive load in a low-side application
forces the MOSFET drain higher than the supply voltage
(as the inductor resists changes to current). To prevent
exceeding the MOSFET’s drain-to-gate and drain-to-
source ratings, a Schottky diode should be connected
across the inductive load.
MIC4414/MIC4415
frequency, and load capacitance. Determine this value
from the “Typical Characteristics: Supply Current vs.
Frequency” graph or measure it in the actual application.
Do not allow P_D to exceed P_D (MAX), as shown in the Eq 2.
T_J (junction temperature) is the sum of T_A (ambient
temperature) and the temperature rise across the
thermal resistance of the package. In another form:
125  T
P (MAX) 
A
D
140
Equation 2
where:
P_D (MAX) = maximum power dissipation (W)
125 = Operating maximum junction temperature (˚C)
T_A = ambient temperature (˚C)
140 = package thermal resistance (˚C/W)
Figure 3. Switching an Inductive Load
Power Dissipation
The maximum power dissipation must not be exceeded
to prevent die meltdown or deterioration. Power
dissipation in on/off switch applications is negligible.
Fast repetitive switching applications, such as SMPS
(switch mode power supplies), cause a significant
increase in power dissipation with frequency. Power is
dissipated each time current passes through the internal
output MOSFETs when charging or discharging the
external MOSFET. Power is also dissipated during each
transition when some current momentarily passes from
VDD to GND through both internal MOSFETs. Power
dissipation is the product of supply voltage and supply
current:
High-Frequency Operation
Although the MIC4414/15 driver will operate at
frequencies greater than 1MHz, the MOSFET’s
capacitance and the load will affect the output waveform
(at the MOSFET’s drain). For example, an
MIC4414/IRL3103 test circuit using a 47Ω, 5W load
resistor will produce an output waveform that closely
matches the input signal shape up to about 500kHz. The
same test circuit with a 1kΩ load resistor operates only
up to about 25kHz before the MOSFET source
waveform shows significant change.
P_D  V_DD  I_DD
Equation 1
where:
P_D = Power dissipation (W)
V_DD = Supply voltage (V)
I_DD = Supply current (A)
Supply current is a function of supply voltage, switching
Figure 4. MOSFET Capacitance Effects at High
Switching Frequency
August 2012
10
M9999-080112-A