Datasheet

UCC27323-Q1, UCC27324-Q1, UCC27325-Q1

www.ti.com

SLUS678A –MARCH 2008–REVISED APRIL 2012

Figure 5.

In a power driver operating at high frequency, it is a significant challenge to get clean waveforms without much

overshoot/undershoot and ringing. The low output impedance of these drivers produces waveforms with high

Δi/Δt. This tends to induce ringing in the parasitic inductances. Utmost care must be used in the circuit layout. It

is advantageous to connect the driver as close as possible to the leads. The driver layout has ground on the

opposite side of the output, so the ground should be connected to the bypass capacitors and the load with

copper trace as wide as possible. These connections also should be made with a small enclosed loop area to

minimize the inductance.

Although quiescent V

current is very low, total supply current is higher, depending on OUTA and OUTB current

and the programmed oscillator frequency. Total V

current is the sum of quiescent V

current and the average

OUT current. Knowing the operating frequency and the MOSFET gate charge (Q

), average OUT current can be

calculated from:

OUT

= Q

× f

Where f is frequency

For the best high-speed circuit performance, two V

bypass capacitors are recommended to prevent noise

problems. The use of surface-mount components is highly recommended. A 0.1-μF ceramic capacitor should be

located closest to the V

to ground connection. In addition, a larger capacitor (such as 1-μF) with relatively low

ESR should be connected in parallel, to help deliver the high current peaks to the load. The parallel combination

of capacitors should present a low-impedance characteristic for the expected current levels in the driver

application.

Drive Current and Power Requirements

The UCC2732x drivers are capable of delivering 4 A of current to a MOSFET gate for a period of several

hundred nanoseconds. High peak current is required to quickly turn on the device. Then, to turn off the device,

the driver is required to sink a similar amount of current to ground. This repeats at the operating frequency of the

power device. A MOSFET is used in this discussion, because it is the most common type of switching device

used in high-frequency power-conversion equipment.

References 1 and 2 discuss the current required to drive a power MOSFET and other capacitive-input switching

devices. Reference 2 includes information on the previous generation of bipolar gate drivers.

When a driver is tested with a discrete capacitive load, it is a fairly simple matter to calculate the power that is

required from the bias supply. The energy that must be transferred from the bias supply to charge the capacitor

is given by:

E = ½CV

Where C is the load capacitor and V is the bias voltage feeding the driver