Micrel

MIC4126/27/28

July 2005

6

M9999-072605

(408) 955-1690

Application Information

Supply Bypassing

Large currents are required to charge and discharge large

capacitive loads quickly. For example, changing a 1000pF

load by 16V in 25ns requires 0.8A from the supply input.

To guarantee low supply impedance over a wide frequency

range, parallel capacitors are recommended for power

supply bypassing. Low-inductance ceramic MLC capacitors

with short lead lengths (< 0.5") should be used. A 1.0µF

film capacitor in parallel with one or two 0.1µF ceramic

MLC capacitors normally provides adequate bypassing.

Grounding

When using the inverting drivers in the MIC4126 or

MIC4128, individual ground returns for the input and output

circuits or a ground plane are recommended for optimum

switching speed. The voltage drop that occurs between the

driver’s ground and the input signal ground, during normal

high-current switching, will behave as negative feedback

and degrade switching speed.

The E-pad and MLF packages have an exposed pad under

the package. It’s important for good thermal performance

that this pad is connected to a ground plane.

Control Input

Unused driver inputs must be connected to logic high

current (< 500µA), connect unused inputs-to-ground. A

logic-high signal will cause the driver to draw up to 9mA.

The control input voltage threshold is approximately 1.5V.

and draws less than 1µA within this range.

Power Dissipation

Power dissipation should be calculated to make sure that

the driver is not operated beyond its thermal ratings.

Quiescent power dissipation is negligible. A practical value

for total power dissipation is the sum of the dissipation

Load Dissipation

Power dissipation caused by continuous load current

(when driving a resistive load) through the driver’s output

resistance is:

For capacitive loads, the dissipation in the driver is:

Transition Dissipation

In applications switching at a high frequency, transition

power dissipation can be significant. This occurs during

switching transitions when the P-channel and N-channel

output FETs are both conducting for the brief moment

when one is turning on and the other is turning off.

Charge (Q) is read from the following graph:

Crossover Energy Loss per Transition