May 2005

9

MIC4416/4417

MIC4416/4417

Micrel, Inc.

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 momen-

tarily passes from VS to GND through both internal MOSFETs.

Power dissipation is the product of supply voltage and supply

current:

1)

P

where:

P

V

I

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.

Do not allow P

T

ture) and the temperature rise across the thermal resistance

of the package. In another form:

2)

P

150

T

220

D

A

≤

−

where:

P

150 = absolute maximum junction temperature (°C)

T

220 = package thermal resistance (°C/W)

Maximum power dissipation at 20°C with the driver soldered

CTL

G

VS

GND

PCB heat sink/

ground plane

PCB traces

Figure 4. Heat-Sink Plane

sistance) can be improved by using a heat sink larger than the

occurs through the large (GND) lead.

This lead is an

extension of the paddle to which the die is attached.

High-Frequency Operation

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.

VS

CTL

G

GND

MIC4416

+4.5V to 18V

1

32

4

Logic

Input

+5V

Logic-Level

MOSFET

IRL3103*

* International Rectifier

14m

4.7µF

0.1µF

Compare

47k

Ω, 5W

to

1k

Ω, 1/4W

loads

G

D

S

Slower rise time

observed at

MOSFET’s drain

Figure 5. MOSFET Capacitance Effects at High

Switching Frequency

When the MOSFET is driven off, the slower rise occurs

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-

tion, choose the smallest power MOSFET that will safely

handle the desired voltage, current, and safety margin. The

smallest MOSFETs generally have the lowest capacitance.