MIC4416 Datasheet, PDF (9/9 Pages) Micrel Semiconductor – IttyBitty™ Low-Side MOSFET Driver

MIC4416
Micrel
Power Dissipation
High-Frequency Operation
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 momen-
tarily passes from VS to GND through both internal MOSFETs.
Power dissipation is the product of supply voltage and supply
current:
1) P_D = V_S × I_S
where:
P_D = power dissipation (W)
V_S = supply voltage (V)
I_S = supply current (A) [see paragraph below]
Supply current is a function of supply voltage, switching
frequency, and load capacitance. Determine this value from
the “Typical Characteristics: Supply Current vs. Frequency”
graph or measure it in the actual application.
Although the MIC4416/7 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 MIC4416/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.
+4.5V to 18V
4.7µF
Slower rise time
observed at
MOSFET’s drain
+5V
Compare
47kΩ, 5W
to
1kΩ, 1/4W
loads
0.1µF
Logic
Input
MIC4416
3 _VS
G²
4 _{CTL GND} 1
D
G
S
Logic-Level
MOSFET
IRL3103*
* International Rectifier
14mΩ, 30V MOSFET,
logic-level, VGS = ±20V max.
Figure 5. MOSFET Capacitance Effects at High
Switching Frequency
Do not allow P_D to exceed P_{D (max)}, below.
When the MOSFET is driven off, the slower rise occurs
T_J (junction temperature) is the sum of T_A (ambient tempera-
ture) and the temperature rise across the thermal resistance
of the package. In another form:
because the MOSFET’s output capacitance recharges through
the load resistance (RC circuit). A lower load resistance
allows the output to rise faster. For the fastest driver opera-
5
tion, choose the smallest power MOSFET that will safely
2)
P_D
≤
150 − T_A
220
handle the desired voltage, current, and safety margin. The
smallest MOSFETs generally have the lowest capacitance.
where:
P_{D (max)} = maximum power dissipation (W)
150 = absolute maximum junction temperature (°C)
T_A = ambient temperature (°C) [68°F = 20°C]
220 = package thermal resistance (°C/W)
Maximum power dissipation at 20°C with the driver soldered
to a 0.25in² ground plane is approximately 600mW.
G
PCB heat sink/
ground plane
GND
VS
CTL
PCB traces
Figure 4. Heat-Sink Plane
The SOT-143 package θ_JA (junction-to-ambient thermal re-
sistance) can be improved by using a heat sink larger than the
specified 0.25in² ground plane. Significant heat transfer
occurs through the large (GND) lead. This lead is an
extension of the paddle to which the die is attached.
April 1998
5-31