Datasheet

LM5114

SNVS790E –JANUARY 2012–REVISED MARCH 2013

www.ti.com

Power Dissipation

It is important to keep the power consumption of the driver below the maximum power dissipation limit of the

package at the operating temperature. The total power dissipation of the LM5114 is the sum of the gate charge

losses and the losses in the driver due to the internal CMOS stages used to buffer the output as well as the

power losses associated with the quiescent current.

The gate charge losses can be calculated with the total input gate charge as follows.

(1)

(2)

Where F

is switching frequency.

The power dissipation associated with the internal circuit operation of the driver can be estimated with the

characterization curves of the LM5114. For a given ambient temperature, the maximum allowable power loss of

the IC can be defined as

(3)

Where P is the total power dissipation of the driver.

Layout Considerations

Attention must be given to board layout when using LM5114. Some important considerations include:

1. The first priority in designing the layout of the driver is to confine the high peak currents that charge and

discharge the FETs gate into a minimal physical area. This will decrease the loop inductance and minimize

noise issues on the gate.

2. To reduce the loop inductance, the driver should be placed as close as possible to the FETs. The gate trace

to and from the FETs are recommended to be placed closely side by side, or directly on top of one another.

3. A low ESR/ESL ceramic capacitor must be connected close to the IC, between VDD and VSS pins to

support the high peak current being drawn from VDD during turn-on of the FETs. It is most desirable to place

the VDD decoupling capacitor on the same side of the PC board as the driver. The inductance of via holes

can impose excessive ringing on the IC pins.

4. The parasitic source inductance, along with the gate capacitor and the driver pull-down path, can form a LCR

resonant tank, resulting in gate voltage oscillations. An optional resistor or ferrite bead can be used to damp

the ringing.

Product Folder Links: LM5114